- Catalytic consequences of hydroxyl group location on the kinetics of n-hexane hydroisomerization over acidic zeolites
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The measured kinetics of n-C6H14 hydroisomerization reactions is consistent with a bifunctional mechanism involving the facile dehydrogenation of n-hexane on the metal catalyst and a kinetically relevant step involving isomerization of n-hexene on zeolitic acidic sites. The measured activation entropy in small 8-MR pockets of MOR (-35 J mol-1 K -1) is similar to that in larger 12-MR channels of MOR (-37 J mol-1 K-1) and BEA (-33 J mol-1 K-1) but higher than that in medium pore FER (-86 J mol-1 K -1), suggesting that partial confinement of C6 olefinic reactants results in lower free energy for the isomerization reaction in 8-MR pockets of MOR. The hypothesis that a cyclopropane-like cationic transition state is not completely contained within the 8-MR pockets of MOR is consistent with the observed selectivity to 2-methylpentane and 3-methylpentane in the 8-MR pockets being identical to that measured in larger 12-MR channels of MOR and BEA. The lower activation energy measured in 8-MR pockets compared to larger 12-MR channels of MOR may arise due to greater electrostatic stabilization of the positively charged transition state by framework oxygen atoms located on the pore mouth of the smaller 8-MR pockets of MOR or due to the larger heat of adsorption caused by confinement in smaller 8-MR pockets. The lower activation energy in 8-MR channels and comparable loss in entropy mediated by partial confinement results in the rate per proton in 8-MR pockets being five times larger than the rate in 12-MR channels of MOR. These results provide another conceptual consideration for rigorous and quantitative understanding of local environment effects of zeolite channel size and connectivity on the rate and selectivity of acid-catalyzed reactions.
- Chiang, Hsu,Bhan, Aditya
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- Comparative studies on enzyme activity of immobilized horseradish peroxidase in silica nanomaterials with three different shapes and methoxychlor degradation of vesicle-like mesoporous SiO2 as carrier
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In the present work, three differently shaped mesoporous silica nanoparticles, spherical nano-SiO2, tubular mesoporous SiO2 and vesicle-like mesoporous SiO2 (VSL), were prepared and used to immobilize Horse radish peroxida
- Yang, Yuxiang,Zhao, Min,Yao, Pingping,Huang, Yan,Dai, Zuocheng,Yuan, Hongming,Ni, Chaoying
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- Spectroscopic characterization-catalytic activity correlation of molybdena based catalysts
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Titania-supported molybdena catalyst was prepared by calcination at 773 K of ammonium heptamolybdate-impregnated TiO2 pellets with the equivalent of 5 monolayers of MoO3. Then, potassium-modified versions of the catalyst were prepared at 0.5-5 wt%-K. The modified and unmodified catalysts were characterized, before and after H2-reduction at 673 K, by means of ISS, XPS, UPS and FT-IR spectroscopy techniques. Results obtained enabled revealing the presence of density of states (DOS) at the Fermi level and, hence, metallic properties related to the deformed rutile structure of MoO2. On the other hand, Br?nsted (MoOH) acidic function was found to form on the surface of the MoO2 structure, thereby producing a metal-acid (bifunctional) MoO2-x(OH)y catalyst. The presence of Br?nsted acid MoOH groups was evidenced by in situ IR spectra of adsorbed pyridine molecules. On the other hand, the K-modification was found to enhance the molybdena dispersity and reducibility, but to suppress the surface acidity by transforming the bifunctional MoO2-x(OH) y species into the monofunctional MoO2-x(OK)y species. Subsequent catalytic measurements employing hydrotreating reactions of 1-hexene and n-hexane could confirm the exposure of bifunctional or monofunctional sites on the catalysts tested. The combination of research methods adopted in the present investigation has shown competency in unravelling the nature of active sites on heterogeneous catalysts.
- Al-Kandari,Mohamed,Al-Kandari,Al-Kharafi,Mekhemer,Zaki,Katrib
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- Effective n-octane isomerization under exceptionally mild conditions using a novel class of superacidic ionic liquids
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Superacidic chloroaluminate ionic liquids of the general formula [cation]Cl/AlCl3[X(AlCl3) > 0.5] + H2SO 4 effectively isomerize n-octane to form branched liquid hydrocarbon isomers. Due to the highly acidic character of the ionic liquid the reaction proceeds under extremely mild conditions in a liquid-liquid biphasic reaction mode leading to a minimum of undesired cracking side-reactions.
- Meyer, Carolin,Wasserscheid, Peter
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- Ionic Hydrogenations using Transition Metal Hydrides. Rapid Hydrogenation of Hindered Alkenes at Low Temperature
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Tetra-substituted, tri-substituted, and 1,1-disubstituted alkenes can be rapidly hydrogenated in high yield at -75 deg C using CF3SO3H/HMo(CO)3(C5H5) or CF3SO3H/HSiEt3
- Bullock, R. Morris,Rappoli, Brian J.
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- OSMIUM LIQUID-PHASE CATALYSTS FOR HYDROGENOLYSIS OF SATURATED HYDROCARBONS AND HYDROGENATION OF ARENES
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Reduction of OsO4 by molecular hydrogen in alkane (cycloalkane) or benzene (toluene) solution produces small-lagand clusters of osmium of composition Os1.5-2.5CH0-2 with a particle size 10-40 Angstroem and a specific surface area of 34-46 m2/g.Hydrogenation of dry catalyst produces methane.The small-ligand osmium clusters obtained effectively catalyze hydrogenolysis of alkanes and cycloalkanes at 100-150 deg C and PH2 = 5 MPa and hydrogenation of benzene at 20 deg C and PH2 = 0.1 MPa.
- Akhrem, I. S.,Reznichenko, S. V.,Grushin, V. V.,Simonova, O. Yu.,Christovalova, N. M.,Vol'pin, M. E.
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- ETUDE DE L'ISOMERISATION DU METHYL-4 PENTENE-1 PAR L'HYDRIDO DIAZOTE TRIS(TRIPHENYLPHOSPHINE)COBALT(I): CoHN2(PPh3)3
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At 25 deg C, and under 1 to 7 bar nitrogen pressure, the isomerization of 4-methyl-1-pentene catalyzed in benzene by CoHN2(PPh3)3 involves two active species: HCoN2(S1)(PPh3)2 and HCo(S1)(PPh3)3, respectively, in greater quantities at higher (P(N2) > 7 bars) and small quantities at P(N2) - O nitrogen pressures. The kinetic study shows that the rate of the reaction is always ruled by the equation:
- Petit, F.,Arzouyan, C.,Peiffer, G.,Gaydou, E.
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- High yield of renewable hexanes by direct hydrolysis-hydrodeoxygenation of cellulose in an aqueous phase catalytic system
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In aqueous phosphoric acid, cellulose was efficiently converted into hexanes using a Ru/C catalyst combined with layered compounds or silica-alumina materials. In this process, the direct production of hexanes from cellulose can be improved by suppressing the formation of isosorbide, which makes it difficult to yield hexanes by further hydrodeoxygenation. As the co-catalyst, layered compounds showed a significant inhibition effect on the formation of isosorbide from sorbitol due to the steric restrictions of sorbitol dehydration within the interlayers of layered compounds. Typically, layered LiNbMoO6 played a great role in promoting the production of hexanes directly from cellulose and a promising yield (72% carbon mol) of hexanes was obtained. In addition, the protonic acid, H3PO4, offered efficient catalysis for the hydrolysis of cellulose and the dehydration of the sorbitol hydroxyl moiety.
- Liu, Yong,Chen, Lungang,Wang, Tiejun,Zhang, Xinghua,Long, Jinxing,Zhang, Qi,Ma, Longlong
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- Transformations of n-Hexane over EUROPT-1: Fragments and C6 Products on Fresh and Partially Deactivated Catalyst
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The reactions of n-hexane have been studied on 6.3percent Pt/SiO2 (EUROPT-1) at different hydrogen and n-hexane pressures, and at 543-633 K, over fresh catalyst and over catalysts deactivated by long runs.Turnover numbers are compared with literature data: the differences are attributed to hydrogen pressure effects.Deactivation influences first of all, selectivity.In addition, the 'depth' and 'pattern' of hydrogenolysis have been determined.At low temperature multiple splitting seems to be favoured.Isomerization gives predominantly 3-methylpentane.At medium temperatures, isomerization, C5-cyclization and internal splitting prevall; their ratio is controlled by the hydrogen pressure.The ratio of 2-methylpentane to 3-methylpentane is related to the ratio of internal to terminal rupture.Terminal splitting prevails at highest temperature.Aromatization increases with temperature but seems to be independent of the other reactions.The results are interpreted in terms of three different surface states.These correspond to Pt-H, Pt-C-H and Pt-C under increasing severity of conditions.
- Paal, Zoltan,Groeneweg, Helga,Paal-Lukacs, Julia
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- Optimization of manganese content by high-throughput experimentation of Pt/WOx-ZrO2-Mn catalysts
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A library of Pt/WOx-ZrO2-Mn catalysts was developed in order to optimize the manganese content in this catalytic system for the isomerization of n-hexane. The catalysts were synthesized, characterized and screened using high-throughput experimentation (HTE) techniques. The catalysts were prepared by surfactant-assisted coprecipitation whereas the characterization was done by X-ray diffraction (XRD), Raman and UV-vis spectroscopy. For this second screening, several catalysts with different manganese contents were prepared; it was found that the incorporation of Mn modifies the anchorage of tungsten on the zirconia surface, thus improving its catalytic properties, in terms of the n-hexane conversion and selectivity, depending on the catalyst composition. These results suggest that this methodology allows the optimization of manganese and tungsten contents on these solid catalysts.
- Hernandez-Pichardo,Fuente, J.A. Montoya de la,Angel, P. del,Vargas,Hernández,González-Brambila
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- Cyclohexane transformations over metal oxide catalysts 2. Selective cyclohexane ring opening to form n-hexane over mono- and bimetallic rhodium catalysts
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The activity of monometallic Rh and Pt catalysts and bimetallic Pt-Rh catalysts on oxide supports in cyclohexane ring opening to form n-hexane was studied. The Rh-containing catalysts are highly active and selective in this reaction. Cyclohexane dehydroge
- Vasina, T. V.,Masloboishchikova, O. V.,Khelkovskaya-Sergeeva, E. G.,Kustov, L. M.,Zeuthen, P.
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- Molecular sieving carbon catalysts for liquid phase reactions: Study of alkene hydrogenation using platinum embedded nanoporous carbon
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We present a simple method to synthesize shape selective carbon catalysts for large alkene hydrogenation reactions by tailoring porosity of platinum embedded in polyfurfuryl alcohol derived carbons. A small amount of mesoporosity, in addition to the intrinsic microporous nature of the carbon, shortens the diffusion length for the reactant molecule, enabling these materials to be used for catalysis in the liquid phase. A systematic study of hydrogenation reactions of liquid phase alkenes is reported. The molecular sieving effect of the catalyst was examined by varying molecular length, size, double bond position, stereoregularity and the number of double bonds in the alkenes.
- Holbrook, Billy Paul M.,Rajagopalan, Ramakrishnan,Dronvajjala, Krishna,Choudhary, Yogesh Kumar,Foley, Henry C.
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- ACID CATALYSIS BY DEALUMINATED ZEOLITE Y. 2. THE ROLES OF ALUMINUM
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Hexane cracking activity was determined for a series of dealuminated zeolites which were prepared both by treatment with SiCl4 and by reaction with steam.Over a range of Si/Al ratios from 4.7 to 255 the cracking activity increased in a linear manner with respect to the number of lattice Al ions per unit cell.Thus, a constant turnover frequency is obtained, which is taken as evidence that the acid strenght does not vary over this range of Si/Al ratios.By contrast, a zeolite prepared by deamination of NH4-Y was very much less active than expected on the basis of the number of protonic sites.The acidity of the protons in this material is clearly less than in the dealuminated zeolite.These results support a model of strong Broensted acidity in which a structural aluminum atom has no next-nearest aluminum neighbors in a common 4-ring of the zeolite.
- Sohn, Jong Rack,DeCanio, Stephen J.,Fritz, Paul O.,Lunsford, Jack H.
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- Ir/KLTL zeolites: Structural characterization and catalysis of n-hexane reforming
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Ir/KLTL zeolite catalysts were prepared by incipient wetness impregnation of LTL zeolites with [Ir(NH3)5Cl]Cl2. The catalysts were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy, infrared spectroscopy, and H2 chemisorption. EXAFS data show that the average Ir cluster size (after treatment at 300°C in H2) increased from about 7 to 20 A as the zeolite K : Al atomic ratio increased from 0.34 to 1.56. Infrared spectra of adsorbed CO show that the electron donation to the Ir increased as the K : Al ratio increased. In contrast to the performance reported for Pt/KLTL zeolites with metal clusters as small as those observed in the present experiments, the Ir/KLTL catalyst has a low selectivity for dehydrocyclization of n-hexane at 440-480°C and 1 atm with a H2 : n-hexane feed molar ratio of 6. Instead, the catalysts are selective for hydrogenolysis. The selectivity is insensitive to the K : Al ratio, but the activity for dehydrocyclization is a maximum at a K : Al atomic ratio of about 1. The results show that even the smallest Ir clusters to which electron donation is significant still behave essentially like metallic Ir in the catalytic reactions.
- Triantafillou,Deutsch,Alexeev,Miller,Gates
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- Investigation of active metal species formation in Pd-promoted sulfated zirconia isomerization catalyst
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The state of palladium in Pd/SO42--ZrO2 (Pd/SZ) isomerization catalyst was investigated by the temperature-programmed reduction (TPR), chemisorption technique, infrared spectroscopy of adsorbed carbon monoxide (FTIRS), X-ray photoelectron spectroscopy (XPS), diffuse-reflectance UV-vis spectroscopy (UV-vis DRS), and benzene hydrogenation as a test reaction. It has been stated that reduction temperature has a great impact on the metal function of Pd-promoted sulfated zirconia catalyst. Metal centers are formed at about 30-70 °C and characterized by high palladium dispersion and activity in benzene hydrogenation. At temperatures above 200 °C, intensive sulfate decomposition occurs and products of sulfate reduction poison the metal function of the catalyst. According to XPS and FTIRS study, palladium particles in the poisoned samples are only partly oxidized, but the main part is presented by metallic phase without large amount of PdS. Reduction of Pd-containing catalyst at 150 °C (instead of 250 °C) leads to higher conversion and 2,2-dimethylbutane yield in acid-catalyzed reaction of n-hexane isomerization. Higher isomerization activity in this case is provided by prevention of active sulfate species decomposition due to the capability of palladium metallic particles formation at low reduction temperatures.
- Belskaya, Olga B.,Danilova, Irina G.,Kazakov, Maxim O.,Gulyaeva, Tatyana I.,Kibis, Lidiya S.,Boronin, Andrey I.,Lavrenov, Alexander V.,Likholobov, Vladimir A.
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- Hydroisomerization of saturated hydrocarbons with novel MCM-41 immobilized Re(V) complex catalysts
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The hetero-functionalized phosphines HPN2, H2PNO and HPN-Pip containing tricarbonyl Re(V) complexes, i.e. [Re(CO)3(κ 3-PN2)] (I), [Re(CO)3Br(κ2- H2PNO)] (II) and [Re(CO)3Br(κ2-HPN-Pip)] (III) were covalently bonded to modified and MCM-41 to obtain novel supported hybrid catalysts. Remarkable high catalytic effects were observed with these catalysts in the hydroisomerization of n-alkanes at low temperature. The catalyst II/MCM-41 provided the highest TONs 3.32 × 103 with 37% yield for n-hexane and 3.18 × 103 with 30% yield for n-heptane. Under optimized condition, good selectivities for n-hexane (85%) and for n-heptane (91%) were obtained. The TGA was used to evaluate the stability of catalysts and reusable for several cycles. A possible carbenium-based mechanism been used to explain product formation.
- Mishra, Gopal S.,Kumar, Anil
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- Hydrogenation of methyl isobutyl ketone over bifunctional Pt-zeolite catalyst
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Methyl isobutyl ketone (MIBK) can be viewed as a key intermediate for the conversion of biomass-derived acetone - the by-product of biobutanol production - to transportation fuel. Zeolite H-ZSM-5 doped with Pt nanoparticles was found to be a highly efficient catalyst for gas-phase hydrogenation of MIBK to methylpentanes with >99% yield at 200 °C. The reaction proceeds via bifunctional metal-acid catalysed pathway involving MIBK hydrogenation to 4-methyl-2-pentanol (MP-ol) on metal sites followed by MP-ol dehydration on acid sites to form olefin and finally olefin hydrogenation to 2-methylpentane (2MP) on metal sites, with all three steps occurring on a single catalyst bed. 2MP thus obtained underwent isomerisation over bifunctional Pt/H-ZSM-5 catalyst to give a mixture of 2- and 3-methylpentanes in a ratio of 83:17. The catalyst did not show any deactivation for at least 16 h on stream.
- Alotaibi, Mshari A.,Kozhevnikova, Elena F.,Kozhevnikov, Ivan V.
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- Influence of chlorine on the catalytic properties of supported rhodium, iridium and platinum in ring opening of naphthenes
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Pt, Ir and Rh were deposited on SiO2 or Al2O 3 using chlorinated precursors and various amounts of HCl in the impregnation medium. The Br?nsted and Lewis acidities increased with the chlorine content of the alumina supported catalysts. The silica-supported catalysts only presented Lewis acid sites. The catalysts were evaluated in methylcyclopentane (MCP) and methylcyclohexane (MCH) ring-opening (RO) under pressure (2.85 and 3.95 MPa, respectively), from 200 to 425 C. For MCP conversion, the acidity of the alumina support had no sensitive effect on the activity and selectivity to RO products, and few effects on the distribution of RO products. No isomerization or hydrocracking products were observed, confirming that these reactions occurred mainly on the metal function, which was not modified by the presence of chlorine. The nature of the support, SiO 2 or Al2O3, had a strong effect on both the activity (1.9 against 0.5 mol h-1 g-1metal for Ir/Al2O3 and Ir/SiO2, respectively at 225 C) and selectivity to RO products (99.6% against 97.5% for Ir/Al2O 3 and Ir/SiO2, respectively, at 80% of MCP conversion) for Ir catalysts only. Interestingly, the Rh/SiO2 exhibited a high selectivity for converting MCP to RO products, similar to Ir/Al 2O3, i.e. 99.6% at 80% of conversion. Depending on the metal and the supports, three types of behavior were observed for MCH ring-opening: (i) a direct ring-opening on the metal function whatever the support for Ir, (ii) a first step of isomerization, and then a need of a sufficiently acidic support, for Pt and (iii) an intermediate behavior for Rh, which was able to either directly convert MCH in absence of acidic support or favor a bifunctional mechanism on chlorinated alumina.
- Samoila,Epron,Marécot,Especel
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- Iridium Clusters in KLTL Zeolite: Structure and Catalytic Selectivity for n-Hexane Aromatization
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Catalysts consisting of Ir clusters in zeolite KLTL were prepared by reduction of Cl2 in the zeolite with H2 at temperatures 300 or 500 deg C.The catalysts were tested for reactions of n-hexane and H2 at 400, 440, and 480 deg C and were characterized by temperature-programmed reduction, hydrogen chemisorption, transmission electron microscopy, infrared spectroscopy of adsorbed CO, and extended X-ray absorption fine structure spectroscopy.The cluster consist of 4 to 6 IR atoms on average and are sufficiently small to reside within the pores of the zeolite.The infrared spectra characteristic of terminal CO suggest that the support environment is slightly basic and that the Ir clusters are electron rich relative to the bulk metal.Notwithstanding the small cluster size, the support basicity, and the confining geometry of the LTL zeolite pore structure, the catalytic performance is similar to those of other Ir catalysts, with a poor selectivity for aromatization and a high selectivity for hydrogenolysis.These results are consistent with the inference that the principal requirements for selective naphtha aromatization catalysts are both a nonacidic support and a metal with a low hydrogenolysis activity, i.e., Pt.
- Triantafillou, N. D.,Miller, J. T.,Gates, B. C.
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- Catalytic application of zeolites in the methanol conversion to hydrocarbons
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The product compositions in the methanol conversion to hydrocarbons over several zeolites are compared and discussed. Although a great number of different compounds are present, small alkanes, such as isobutane and isopentane, and polymethylbenzenes are the major compounds over zeolites beta, mordenite and faujasite. However, zeolite ferrierite is quite selective for alkenes. Also, zeolite beta can transform acetone into hydrocarbons.
- Aramendia, Maria A.,Borau, Victoriano,Jimenez, Cesar,Marinas, Jose M.,Roldan, Rafael,Romero, Francisco J.,Urbano, Francisco J.
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- The Influence of Reaction Temperature on the Cracking Mechanism of 2-Methylhexane
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The cracking of 2-methylhexane on USHY has been studied in the temperature range 400-500 deg C.It was found that this reaction leads to the formation of hydrogen, paraffins, olefins, and aromatics ranging from C1 to C10.Of these only hydrogen, C1-C7 compounds, and coke were found to be primary products.Mechanistic considerations indicate that two main processses take place during 2-methylhexane conversion on USHY: (1) initiation by protolysis on pristine Broensted sites; (2) chain processes involving isomerization, hydrogen transfer, and disproportionation.At low temperatures, cpnversion of 2-methylhexane proceeds to a significant extent via both mechanisms, while at higher temperatures protolytic cracking is the dominant process by far.We find that protolysis accounts for 67, 83, and 94percent of total conversion of 2-methylhexane at 400, 450, and 500 deg C, respectively.The average activation energy for protolytic cracking of 2-methylhexane on USHY was found to be 159 kJ/mol.The unexpectedly low activation energy for protolysis vis-a-vis the comparable value in 2-methylpentane cracking (246 kJ/mol) is discussed in terms of temperature effects on active densities and in terms of the compensation effect in protolysis.Hydride abstraction from gas phase 2-methylhexane by C6H13+ and C7H15+ ions leads to the formation of the paraffinic C6 and C7 skeletal isomers found in the primary products.In addition to hydride transfer, the set of active bimolecular chain reactions involves some but not all possible disproportionations between feed molecules and carbenium ions in the range C2H5+ and C5H1111.The reasons for this specifificity in disproportionation are discussed.The probability of initial coke formation was found to decrease with increasing temperature, suggesting a diminished rate of bimolecular reaction between adjacent carbenium ions at higher temperatures.We explain this as being the result of lower surface coverage by carbenium ions at elevated temperatures.
- Bamwenda, G. R.,Zhao, Y. X.,Wojciechowski, B. W.
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- Mechanism for isomerization of n-hexane over sulfated zirconia: Role of hydrogen
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The complex influence of hydrogen on n-hexane isomerization over sulfated zirconia enriched with platinum has been kinetically modelled with a simple three parameter rate equation derived from a mechanism involving Lewis sites and hydride species.
- Duchet, Jean-Claude,Guillaume, Denis,Monnier, Agnes,Van Gestel, Jacob,Szabo, Georges,Nascimento, Pedro,Decker, Sebastien
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- Isomerisation of n-hexane over bifunctional Pt-heteropoly acid catalyst: Enhancing effect of gold
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Isomerisation of n-hexane was studied in the presence of acid and bifunctional metal-acid catalysts based on Keggin-type heteropoly acids (HPA), in particular focusing on Cs2.5H0.5PW12O40 (CsPW) and Pt/CsPW as the catalysts, using a fixed-bed microreactor under differential conditions (n-hexane conversion ≤ 10%) at 180–220 °C, ambient pressure and a ratio of n-hexane and H2 partial pressures of 0.06–0.24. The turnover rate of HPA-catalysed isomerisation was found to correlate with the acid strength of HPA (initial enthalpy of ammonia adsorption). Bifunctional Pt-HPA catalysts were more efficient than monofunctional HPA catalysts. In the isomerisation over Pt/CsPW bifunctional catalyst, n-hexane dehydrogenation step was found to equilibrate at a molar ratio of Pt and H+ surface sites Pts/H+ ≥ 0.8, corresponding to a Pt loading ≥6%. Bimetallic PtAu/CsPW catalyst showed higher activity in n-hexane isomerisation than Pt/CsPW, although the Au alone without Pt was inert. In the presence of Au, the turnover rate at Pt sites increased more than twofold. The effect of Au is attributed to PtAu alloying. Scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM-EDX) and X-ray diffraction (XRD) analyses of PtAu/CsPW indicated the presence of bimetallic PtAu nanoparticles with a wide range of Pt/Au atomic ratios.
- Alazman, Abdulrahman,Belic, Domagoj,Kozhevnikova, Elena F.,Kozhevnikov, Ivan V.
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- Catalysis with Palladium Deposited on Rare Earth Oxides: Influence of the Support on Reforming and Syngas Activity and Selectivity
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The influence of the support has been tested on the reactivity of Pd/rare earth oxides catalysts (La2O3, CeO2, Pr6O11, Nd2O3, Tb4O7).According to BET surface area, chemisorption, temperature-programmed reduction (TPR) and oxidation (TPO), X-ray diffraction (XRD) and X-ray photoemission (XPS) characterizations, these catalysts have been classified into threeclasses according to their ability to create anion vacancies: (i) oxides of the type Re2O3 which are unreducible, (ii) CeO2 where anion vacancies can be created extrinsically by the reduction process, and (iii) Pr6O11 and Tb4O7 where anion vacancies exist due to the nonstoichiometric nature of these oxides.We emphasize also the role of chlorine, coming from the palladium precursor salt, which reacts with the support to form a stable oxychloride phase surrounding the metallic particle and interacting with it.Concerning the catalytic activity, (i) the active site is purely metallic in methylcyclopentane hydrogenolysis, with small selectivity changes on fluorite oxides as compared to Pd/Al2O3 catalysts due to some electronic interaction with the support, but (ii) the mechanism is found to be partly bifunctional in 3-methylhexane aromatization with a large increase in aromatization on Pr6O11 and Tb4O7 supports, and (iii) in syngas conversion, production of high alcohols occurs at the metal-support interface and is favored by the presence of intrinsic anion vacancies on Pr6O11 and Tb4O7 supports.A correlation is found between the density of anion vacancies on these supports and the chain growth probability deduced from the Anderson-Schulz-Flory plot.
- Normand, F. Le,Barrault, J.,Breault, R.,Hilaire, L.,Kiennemann, A.
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- Skeletal Reactions of n-Hexane over Pt-NaY, Pt/SiO2,HY, and Mixed Pt/SiO2 + HY Catalysts
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The activity and selectivity of three samples of 8percent Pt-NaY calcined at 633, 723, and 823 K, respectively, have been probed with n-hexane as the model reactant at 603 K and subatmospheric pressures in a glass closed-loop reactor.These catalysts were
- Paal, Zoltan,Zhan, Zhaoqi,Manninger, Istvan,Sachtler, W.M.H.
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- The pathway to total isomer selectivity: N-hexane conversion (reforming) on platinum nanoparticles supported on aluminum modified mesoporous silica (MCF-17)
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When pure mesoporous silica (MCF-17) was modified with aluminum (Al modified MCF-17), Lewis acid sites were created, but this material was inactive for the catalytic conversion (reforming) of n-hexane to isomers. When colloidally synthesized platinum nanoparticles were loaded onto traditional MCF-17, the catalyst showed very low activity toward isomer production. However, when Pt nanoparticles were loaded onto Al modified MCF-17, isomerization became the dominant catalytic pathway, with extremely high activity and selectivity (>90%), even at high temperatures (240-360 °C). This highly efficient catalytic chemistry was credited to the tandem effect between the acidic Al modified MCF-17 and the Pt metal.
- Musselwhite, Nathan,Na, Kyungsu,Alayoglu, Selim,Somorjai, Gabor A.
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- Designed catalysts from Pt nanoparticles supported on macroporous oxides for selective isomerization of n-hexane
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Selective isomerization toward branched hydrocarbons is an important catalytic process in oil refining to obtain high-octane gasoline with minimal content of aromatic compounds. Colloidal Pt nanoparticles with controlled sizes of 1.7, 2.7, and 5.5 nm were deposited onto ordered macroporous oxides of SiO2, Al2O3, TiO2, Nb 2O5, Ta2O5, and ZrO2 to investigate Pt size-and support-dependent catalytic selectivity in n-hexane isomerization. Among the macroporous oxides, Nb2O5 and Ta2O5 exhibited the highest product selectivity, yielding predominantly branched C6 isomers, including 2-or 3-methylpentane, as desired products of n-hexane isomerization (140 Torr n-hexane and 620 Torr H2 at 360 °C). In situ characterizations including X-ray diffraction and ambient-pressure X-ray photoelectron spectroscopy showed that the crystal structures of the oxides in Pt/oxide catalysts were not changed during the reaction and oxidation states of Nb2O5 were maintained under both H2 and O2 conditions. Fourier transform infrared spectra of pyridine adsorbed on the oxides showed that Lewis sites were the dominant acidic site of the oxides. Macroporous Nb 2O5 and Ta2O5 were identified to play key roles in the selective isomerization by charge transfer at Pt-oxide interfaces. The selectivity was revealed to be Pt size-dependent, with improved isomer production as Pt sizes increased from 1.7 to 5.5 nm. When 5.5 nm Pt nanoparticles were supported on Nb2O5 or Ta 2O5, the selectivity toward branched C6 isomers was further increased, reaching ca. 97% with a minimum content of benzene, due to the combined effects of the Pt size and the strong metal-support interaction.
- An, Kwangjin,Alayoglu, Selim,Musselwhite, Nathan,Na, Kyungsu,Somorjai, Gabor A.
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- Solid Superacids: The Alumina/ZrCl4 System
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The physico-chemical and catalytic properties of alumina exposed to ZrCl4 vapour have been studied.It was found that ZrCl4 reacts with both basic surface OH groups and exposed O2- ions forming Lewis superacid centres as well as Broensted acid sites.The mechanism of n-pentane low-temperature isomerization involving H- abstraction from the alkane has been postulated.
- Juszczyk, Wojciech,Marczewski, Marek
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- Ring opening of methylcyclopentane on alumina-supported Rh catalysts of different metal loadings
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The hydrogenolytic ring opening of methylcyclopentane (MCP) was studied on Rh/Al2O3 catalysts (prepared by the incipient wetness process) with varied metal loadings (0.3, 3, and 10%) and altered reduction temperatures, i.e., low-temperature range (573 K, LTR) and high-temperature range (973 K, HTR). The catalysts exhibited a ″selective″ ring-opening mechanism for MCP. Strong dependence was observed in the distribution of ring-opening products as a function of hydrogen pressure and temperature with 10Rh and 3RhHTR. However, 0.3Rh, 3RhLTR catalysts showed random fragment production from each ring-opening surface species. The selectivity depended on the reaction temperature, hydrogen pressure, and catalyst preparation. Changes in metal loading and pretreatment can cause interconversion between the two forms of Rh. Since the changes in TPR and catalytic behavior with metal loading and pretreatment were parallel, the changes in product distribution were ascribed to different morphologies of Rh particles. The results agreed well with earlier assumptions that selective ring opening involves an associative flat-lying intermediate that can be a common surface intermediate for single and multiple C-C bond cleavage.
- Teschner,Matusek,Paal
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Read Online
- LOW TEMPERATURE ISOMERIZATION OF PARAFFINS OVER ALUMINA TREATED WITH CF3Cl
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Paraffins such as butane, pentane, and hexane were isomerized, at temperatures as low as 0 deg C, over Al2O3 treated with CF3Cl.The isomerizations were promoted by strong acid sites having H0 values of -13.75 >= H0 > -14.52, which were formed on the treated surface.
- Kurosaki, Akito,Okazaki, Susumu
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- 1-Hexene Oligomerization in Liquid, Vapor, and Supercritical Phases over Beidellite and Ultrastable Y Zeolite Catalysts
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1-Hexene was oligomerized at 200°C and a pressure of 5 MPa in a down-flow fixed-bed tubular reactor filled with beidellite or ultrastable Y zeolite catalysts. Vapor, liquid, and supercritical states of the reacting hydrocarbons in the reactor tube were established by using propane, pentane, octane, and dodecane as solvents. The initial activity, stability with operation time, and selectivity are very dependent on the physical state of the hydrocarbons. Highest activity and stability are reached in the liquid phase using octane and dodecane solvent. The chain length of the solvent has a strong influence on the deactivation of the catalyst, on the oligomerization selectivity and on the formation of C6 saturates and cracked products.
- Pater, Jerome P. G.,Jacobs, Pierre A.,Martens, Johan A.
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- Iridium-catalyzed hydrosilylative reduction of glucose to hexane(s)
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In light of diminishing petroleum feedstocks, there is significant interest in developing carbohydrate defunctionalization reactions. In this context we have examined the use of iridium pincer catalysts for the hydrosilylative reduction of sugars, and we report herein complete reduction of silyl-protected glucose to a mixture of hexane isomers.
- McLaughlin, Matthew P.,Adduci, Laura L.,Becker, Jennifer J.,Gagné, Michel R.
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Read Online
- Influence of Nitrate and Phosphate on Silica Fibrous Beta Zeolite Framework for Enhanced Cyclic and Noncyclic Alkane Isomerization
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Phosphate and nitrate were loaded on silica BEA (P/HSi?BEA and N/HSi?BEA), which is fibrously protonated by the impregnation method for n-hexane and cyclohexane isomerization. The characterization analysis specified the removal of tetrahedral aluminum atoms in the framework, which was triggered by the existence of phosphate and nitrate groups in the catalyst. The exchanged role of Si(OH)Al to P-OH as active acidic sites in the P/HSi?BEA catalyst reduced its acidic strength, which was confirmed by the FTIR results. Lewis acidic sites of P/HSi?BEA performance are a significant part in the generation of high protonic acid sites, as proven by the in situ ESR study. However, FTIR evacuation and 27Al NMR revealed that the reduction in the amount of extraframework Al (EFAl) is due to its interaction with the nitrate group on the outside of the catalyst surface. The N/HSi?BEA catalyst exhibited high acidic strength because of the existence of more Si(OH)Al, which was initiated during the nitrate-incorporation process. Of significance is that the catalytic performance of n-hexane isomerization in the presence of hydrogen reached 50.3% product isomer yield at 250 °C, which might be ascribed to the presence of P-OH active sites that are responsible for accepting electrons, forming active protonic acid sites. NO3-EFAl interaction induced the formation of Br?nsted acid sites, and higher mesopore volume favors the production of cyclohexane isomers up to 48.4% at 250 °C. This fundamental study exhibits that significant interactions given by such phosphate and nitrate groups with the unique silica fibrous BEA support could enhance isomerization, which contributes to the high quality of fuel.
- Hitam, Che Ku Nor Liana Che Ku,Izan, Siti Maryam,Jalil, Aishah Abdul,Nabgan, Walid
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p. 1723 - 1735
(2020/02/28)
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- Preparation and catalytic performance of a novel organometallic CoH/Hβ catalyst for: n -hexane isomerization
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As a novel alkane isomerization catalyst, namely CoH/Hβ, was prepared by the reduction of CoH(P(OPh)3)4, which was pre-impregnated on Hβ as support. The as-prepared CoH/Hβ catalyst was structurally compared with CoH(P(OPh)3)4, CoH(P(OPh)3)4/Hβ via FT-IR, TPR, SEM, XRD and other techniques. The results show that the new organometallic hydride catalyst was synthesized successfully and exhibited excellent catalytic performance for the isomerization of n-hexane. For the best performance of the CoH/Hβ catalyst, the optimal catalytic reaction temperature, pressure, space velocity, and hydrogen/oil molar ratio were 300 °C, 2.0 MPa, 1.0 h-1, and 4.0, respectively, in the isomerization process of n-hexane. Under the optimal reaction conditions, the conversion of n-hexane, the yield of isomerization, and the selectivity towards iso-paraffins were 80.2%, 63.0%, and 78.6%, respectively. This performance is mainly attributed to the new structure of Co-H hydride in the CoH/Hβ catalyst, which has strong hydrogenation/dehydrogenation activity in the isomerization of n-hexane. This journal is
- Zhang, Mei,Wang, Congcong,Zhang, Chao,Cai, Tingting,Zhu, Lijun,Xia, Daohong
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p. 15646 - 15653
(2020/10/22)
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- Metal and acid sites instantaneously prepared over Ni/SAPO-11 bifunctional catalyst
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The Ni/SAPO-11 bifunctional catalyst for hydroisomerization of n-hexane was prepared via a novel synthesis method. It involved grinding of nickel source with amorphous precursors used for SAPO-11 followed by crystallization at 473 K for 24 h, thus avoiding the use of extra solvents in the synthesis. The highly dispersed nickel species and acid sites in the Ni/SAPO-11 bifunctional catalyst were instantaneously formed. The Ni/SAPO-11 catalyst contains framework nickel, nickel monoxide (NiO) and nickel aluminate spinel. The nickel monoxide with a size of 2–4 nm provides (de)hydrogenation function after reduction, while the framework nickel supplies more acid sites leading to an enhanced isomerization activity. The Ni/SAPO-11 catalyst shows a great synergetic effect between the metallic nickel and acid sites with a high metal-to-acid sites ratio (CNi/CA) and close proximity. A single metallic nickel site is able to balance ca. 5 acid sites (CNi/CA ≈ 0.19) over the Ni/SAPO-11 catalyst in n-hexane hydroisomerization. The high dispersion of nickel over the catalyst provides relatively excessive metal sites (CNi/CA > 0.19), leaving the rate limiting reaction to occur on the acid sites. The Ni/SAPO-11 catalyst exhibits comparable n-hexane conversion (71.2%) and iso-hexane yield (66.7%) to the classical Pt/SAPO-11 catalyst. With enhancing acidity, the Ni/SAPO-11 catalyst exhibits one of the highest iso-hexane yields reported in the n-hexane hydroisomerization, which render the new material as a promising candidate for the hydroisomerization catalysts.
- Lyu, Yuchao,Yu, Zhumo,Yang, Ye,Liu, Yuxiang,Zhao, Xinxin,Liu, Xinmei,Mintova, Svetlana,Yan, Zifeng,Zhao, Guofeng
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p. 208 - 216
(2019/05/14)
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- Physicochemical and Catalytic Properties of Ni,H/ZSM-5 and Ni,H/ZSM-5–Binder Catalysts Prepared in the Absence and in the Presence of Binder
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Physicochemical and catalytic properties of H/ZSM-5 and Ni,H/ZSM-5 along with Ni,H/ZSM-5–Al2O3 (1 : 1) systems were examined. The systems with a binder were prepared by two different methods of mixing zeolite with aluminum hydroxide. The samples were characterized by N2 sorption (at 77 K), X-ray diffraction, 27Al magic-angle spinning (MAS) NMR spectroscopy, temperature-programmed desorption of ammonia and adsorption of pyridine. Preparation of the zeolite catalyst with aluminium hydroxide was made by two methods: (1) mixing of powders and (2) combining appropriate pastes. Regardless of the method used for mixing there was no blocking of zeolite channels by aluminum oxide. The method of mixing zeolite with aluminium hydroxide powders promotes migration of aluminum from aluminum hydroxide/oxide to the zeolite framework. The results of n-hexane conversion showed that with Ni,H/ZSM-5 a slightly lower conversion than with H/ZSM-5 catalyst was observed that can be explained by a reduced yield of cracking products. Ni,H/ZSM-5–Al2O3 (1 : 1) catalytic systems were insignificantly less efficient in n-hexane transformation than alumina free samples but at the same time they were less selective towards hydrocarbons with boiling temperatures higher than this of n-hexane, precursors of carbonaceous deposits.
- Grzechowiak, J. R.,Jaroszewska, K.,Masalska, A.
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p. 851 - 861
(2020/02/21)
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- Mechanistic Insight into Synergistic Catalysis of Olefin Hydrogenation by a Hetero-Dinuclear RuII-CoII Complex with Adjacent Reaction Sites
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We have designed and synthesized a hetero-dinuclear RuII-CoII complex with a dinucleating ligand inspired by hetero-dinuclear active sites of metalloenzymes. A synergistic effect between the adjacent RuII and CoII sites has been confirmed in catalytic olefin hydrogenation by the complex, exhibiting a much higher turnover number than those of mononuclear RuII or CoII complexes as the components. A RuII-hydrido species was detected by 1H NMR and electrospray ionization (ESI)-time-of-flight (TOF)-MS measurements as an intermediate to react with olefins, and CoII-bound methanol was suggested to act as a proton source.
- Hong, Dachao,Ohgomori, Yuji,Shimoyama, Yoshihiro,Kotani, Hiroaki,Ishizuka, Tomoya,Kon, Yoshihiro,Kojima, Takahiko
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supporting information
p. 11284 - 11288
(2019/09/03)
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- High-Quality Gasoline Directly from Syngas by Dual Metal Oxide–Zeolite (OX-ZEO) Catalysis
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Despite significant efforts towards the direct conversion of syngas into liquid fuels, the selectivity remains a challenge, particularly with regard to high-quality gasoline with a high octane number and a low content of aromatic compounds. Herein, we show that zeolites with 1D ten-membered-ring (10-MR) channel structures such as SAPO-11 and ZSM-22 in combination with zinc- and manganese-based metal oxides (ZnaMnbOx) enable the selective synthesis of gasoline-range hydrocarbons C5–C11 directly from syngas. The gasoline selectivity reached 76.7 % among hydrocarbons, with only 2.3 % CH4 at 20.3 % CO conversion. The ratio of isoparaffins to n-paraffins was as high as 15, and the research octane number was estimated to be 92. Furthermore, the content of aromatic compounds in the gasoline was as low as 16 %. The composition and structure of ZnaMnbOx play an important role in determining the overall activity. This process constitutes a potential technology for the one-step synthesis of environmentally friendly gasoline with a high octane number from a variety of carbon resources via syngas.
- Li, Na,Jiao, Feng,Pan, Xiulian,Chen, Yuxiang,Feng, Jingyao,Li, Gen,Bao, Xinhe
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supporting information
p. 7400 - 7404
(2019/05/10)
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- Tailoring the structure and acid site accessibility of mordenite zeolite for hydroisomerisation of n-hexane
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Mordenite zeolites with diffusion-restricted access to the acid sites located in mono-dimensional 12-ring channels and 8-ring side pockets have found broad applications as catalysts for hydroisomerisation of linear C5 and C6 alkanes and other highly relevant acid-catalysed processes. The accessibility of the porous structure of mordenite (MOR) zeolite is traditionally enhanced by dealumination, but this is invariably connected with a dramatic reduction in the aluminium content and corresponding concentration of the acid sites in the zeolites. Here we describe the preparation of MOR zeolite with high micropore volume, three-dimensional supermicropores (d ～ 7.5 ?) and good acid site accessibility by concurrent extraction of Si and Al using postsynthesis fluorination-alkaline-acid treatment. The concurrent extraction of Si and Al enables formation of more developed supermicroporous structure and preservation of the molecular Si/Al. The procedure yields MOR with a crystalline structure in which the Si/Al ratio and the micropore volume can be tailored (Si/Al from ～ 6, VMI up to 0.25 cm3.g?1) by the chemical conditions of the treatment. The Al-rich 3D supermicroporous structure with accessible Br?nsted and Lewis active sites provides strongly enhanced activity, selectivity and long-term catalytic stability in the transformation of n-hexane into the corresponding branched isomers.
- Pastvova, Jana,Pilar, Radim,Moravkova, Jaroslava,Kaucky, Dalibor,Rathousky, Jiri,Sklenak, Stepan,Sazama, Petr
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p. 159 - 172
(2018/06/14)
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- Superior activity of non-interacting close acidic protons in Al-rich Pt/H-*BEA zeolite in isomerization of n-hexane
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Skeletal isomerization of linear alkanes, an essential reaction for the production of gasoline, relies on environmentally questionable chlorinated catalysts, whose activity exceeds that of alternative zeolite catalysts. This work describes an attempt to understand relations between the local arrangement of active sites and skeletal isomerization of n-hexane in order to adapt the structure of zeolite catalysts to increase the reaction rates. For this purpose, we used a combination of synthesis of zeolites of*BEA structural topology with unique density and distribution of strongly acid sites, analysis of the nature of the acid sites by1H MAS NMR spectroscopy and FTIR spectroscopy of the OH groups and adsorbed d3-acetonitrile, UV–vis-NIR spectroscopy of carbocations formed by protonization, and kinetic analysis. We demonstrate that the high density of non-interacting but close and strongly acidic structural hydroxyl groups significantly lower the activation barrier in the isomerization reaction compared to far-distant acid sites. The organotemplate-free synthesized Al-rich Pt/H-*BEA zeolite (Si/Al 4.2) with an unparalleled high concentration of the non-interacting close H+ions balancing the charge of the Al-Si-Al sequences forming a wall between the two channels yields 6 times higher reaction rates compared to state-of-the-art Si-rich Pt/H-zeolite catalysts.
- Sazama, Petr,Kaucky, Dalibor,Moravkova, Jaroslava,Pilar, Radim,Klein, Petr,Pastvova, Jana,Tabor, Edyta,Sklenak, Stepan,Jakubec, Ivo,Mokrzycki, Lukasz
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- Divalent Silicon-Assisted Activation of Dihydrogen in a Bis(N-heterocyclic silylene)xanthene Nickel(0) Complex for Efficient Catalytic Hydrogenation of Olefins
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The first chelating bis(N-heterocyclic silylene)xanthene ligand [SiII(Xant)SiII] as well as its Ni complexes [SiII(Xant)SiII]Ni(η2-1,3-cod) and [SiII(Xant)SiII]Ni(PMe3)2 were synthesized and fully characterized. Exposing [SiII(Xant)SiII]Ni(η2-1,3-cod) to 1 bar H2 at room temperature quantitatively generated an unexpected dinuclear hydrido Ni complex with a four-membered planar Ni2Si2 core. Exchange of the 1,3-COD ligand by PMe3 led to [SiII(Xant)SiII]Ni(PMe3)2, which could activate H2 reversibly to afford the first SiII-stabilized mononuclear dihydrido Ni complex characterized by multinuclear NMR and single-crystal X-ray diffraction analysis. [SiII(Xant)SiII]Ni(η2-1,3-cod) is a strikingly efficient precatalyst for homogeneous hydrogenation of olefins with a wide substrate scope under 1 bar H2 pressure at room temperature. DFT calculations reveal a novel mode of H2 activation, in which the SiII atoms of the [SiII(Xant)SiII] ligand are involved in the key step of H2 cleavage and hydrogen transfer to the olefin.
- Wang, Yuwen,Kostenko, Arseni,Yao, Shenglai,Driess, Matthias
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supporting information
p. 13499 - 13506
(2017/10/05)
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- Direct Synthesis of Renewable Dodecanol and Dodecane with Methyl Isobutyl Ketone over Dual-Bed Catalyst Systems
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For the first time, we demonstrated two integrated processes for the direct synthesis of dodecanol or 2,4,8-trimethylnonane (a jet fuel range C12-branched alkane) using methyl isobutyl ketone (MIBK) that can be derived from lignocellulose. The reactions were carried out in dual-bed continuous flow reactors. In the first bed, MIBK was selectively converted to a mixture of C12 alcohol and ketone. Over the Pd-modified magnesium– aluminium hydrotalcite (Pd-MgAl-HT) catalyst, a high total carbon yield (73.0 %) of C12 oxygenates can be achieved under mild conditions. In the second bed, the C12 oxygenates generated in the first bed were hydrogenated to dodecanol over a Ru/C catalyst or hydrodeoxygenated to 2,4,8-trimethylnonane over a Cu/SiO2 catalyst. The as-obtained dodecanol can be used as feedstock in the production of sodium dodecylsulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS), which are widely used as surfactants or detergents. The asobtained 2,4,8-trimethylnonane can be blended into conventional jet fuel without hydroisomerization.
- Sheng, Xueru,Li, Ning,Li, Guangyi,Wang, Wentao,Wang, Aiqin,Cong, Yu,Wang, Xiaodong,Zhang, Tao
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p. 825 - 829
(2017/03/17)
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- GAS-TO-LIQUID REACTOR AND METHOD OF USING
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A device and a process to propagate molecular growth of hydrocarbons, either straight or branched chain structures, that naturally occur in the gas phase to a molecular size sufficient to shift the natural occurring phase to a liquid or solid state is provided. According to one embodiment, the device includes a grounded reactor vessel having a gas inlet, a liquid outlet, and an electrode within the vessel; a power supply coupled to the electrode for creating an elecirostatic field within the vessel for converting the gas to a liquid and or solid state.
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Paragraph 0140-0142
(2019/08/15)
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- Use of steric encumbrance to develop conjugated nanoporous polymers for metal-free catalytic hydrogenation
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The design and synthesis of metal-free heterogeneous catalysts for efficient hydrogenation remains a great challenge. Here we report a novel approach to create conjugated nanoporous polymers with efficient hydrogenation activities toward unsaturated ketones by leveraging the innate steric encumbrance. The steric bulk of the framework as well as the local sterics of the Lewis basic sites within the polymeric skeleton result in the generation of the putative catalyst. This approach opens up new possibilities for the development of innovative metal-free heterogeneous catalysts.
- Tian, Chengcheng,Zhu, Xiang,Abney, Carter W.,Tian, Ziqi,Jiang, De-En,Han, Kee Sung,Mahurin, Shannon M.,Washton, Nancy M.,Dai, Sheng
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supporting information
p. 11919 - 11922
(2016/10/11)
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- Selective ring opening of methylcyclopentane over surface-decorated Ir-Co bimetallic catalysts synthesized by galvanic replacement reaction
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Surface-decorated Ir-Co bimetallic catalysts were synthesized by a modified galvanic replacement reaction and evaluated by the selective ring opening (SRO) of methylcyclopentane (MCP). Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was utilized to characterize the catalyst synthesis process, and H2-temperature-programmed reduction (H2-TPR) was performed to characterize the reduction behavior of the calcined catalysts and oxidation resistance of the reduced catalysts. Transmission electron microscopy (TEM) analysis was used to characterize metallic particle size distribution. The reactor evaluation results show quite different behaviors in conversion and product selectivity of the surface-decorated Ir-Co/SiO2 and monometallic Ir/SiO2. At optimized Ir content, MCP conversion and mass-specific rate of SRO are significantly higher when catalyzed by surface-decorated Ir-Co/SiO2 than by monometallic Ir/SiO2. Moreover, compared with Ir/SiO2, Ir-Co/SiO2 has decreased 2-methylpentane selectivity but improved n-hexane selectivity. These catalytic behaviors were found to correlate with the surface-decorated bimetallic structure consisting of Co/SiO2 decorated with surface Ir atoms.
- Wang, Zhen,Zheng, Aiguo,Zheng, Renyang,Li, Mingfeng,Li, Huifeng,Xu, Guangtong,Xia, Guofu
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p. 105063 - 105069
(2016/11/18)
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- Isomerization of n-hexane on binder-free shaped platinum-containing mordenite
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A catalyst has been prepared as binder-free shaped MOR-type zeolite in the H form promoted with 0.5 wt % platinum, and n-hexane conversion over this catalyst has been studied. It has been found that the selectivity for C4-C6 isoparaffins on the new catalyst is about 90% at 300°C, a feed space velocity of 1.5 h-1, and a hydrogen pressure of 3 MPa, with the hexane conversion being 80.0-83.0 wt % and the selectivity for isohexane making 83.0-86.0%. It has been shown that the new catalyst is stable for 50 h on-stream under these conditions.
- Travkina,Kuvatova,Pavlova,Ramadan, Ahmed Kanaan,Akhmetov,Kutepov
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- Facile Synthesis, Characterization, and Catalytic Behavior of a Large-Pore Zeolite with the IWV Framework
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Large-pore microporous materials are of great interest to process bulky hydrocarbon and biomass-derived molecules. ITQ-27 (IWV) has a two-dimensional pore system bounded by 12-membered rings (MRS) that lead to internal cross-sections containing 14MRS. Investigations into the catalytic behavior of aluminosilicate (zeolite) materials with this framework structure have been limited until now due to barriers in synthesis. The facile synthesis of aluminosilicate IWV in both hydroxide and fluoride media is reported herein using simple, diquaternary organic structure-directing agents (OSDAs) that are based on tetramethylimidazole. In hydroxide media, a zeolite product with Si/Al=14.8-23.2 is obtained, while in fluoride media an aluminosilicate product with Si/Al up to 82 is synthesized. The material produced in hydroxide media is tested for the hydroisomerization of n-hexane, and results from this test reaction suggest that the effective pore size of zeolites with the IWV framework structure is similar to but slightly larger than that of ZSM-12 (MTW), in fairly good agreement with crystallographic data. Microporous materials: Synthesis of aluminosilicate IWV under industrially relevant conditions has been demonstrated, and the material can be produced in both fluoride and hydroxide media across a wide composition range. The zeolite demonstrates catalytic activity in the hydroisomerization of n-hexane (see figure).
- Schmidt, Joel E.,Chen, Cong-Yan,Brand, Stephen K.,Zones, Stacey I.,Davis, Mark E.
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p. 4022 - 4029
(2016/03/16)
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- Isomerization of n-hexane over Pt‐H3PW12O40/SBA-15 bifunctional catalysts: Effect of the preparation method on catalytic performance
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Pt-H3PW12O40 based bifunctional catalysts immobilized on SBA-15 were prepared either by mechanically mixing of acidic (HPW/SBA-15 or HPW@SBA-15) and metallic (Pt/SBA-15) monofunctional materials or by incorporation of the two active phases within the same composite using dual encapsulation (Pt@HPW@SBA-15) and encapsulation/impregnation (Pt/HPW@SBA-15) methodologies. The phase structure, chemical composition and surface physico-chemical properties were characterized in details by XRD, FT-IR, 31P MAS NMR, N2 adsorption‐desorption and HRTEM, STEM and EDX microscopy techniques. All hybrid materials showed highly ordered mesostructuration of the SBA-15 matrix with homogeneous dispersion of both metallic and HPW phases. In the case of the monophase bifunctional catalysts, Pt/HPW@SBA-15 and Pt@HPW@SBA-15, both functions were found to coexist in close vicinity, with the HPW crystallites mainly located in the silica walls whereas Pt was found either in the channels or as part of the walls depending on the preparation route. Their catalytic performance was then evaluated in the isomerization of n-hexane. The catalysts prepared by mechanical mixing exhibited higher activity than those where the Pt and HPW were integrated within a single solid. These results were interpreted by assuming that the carbocations in the latter case were hydrogenated faster on the Pt particles thus decreasing their preponderance at the steady-state compared to the mechanical mixture.
- Pinto, Teresa,Arquillière, Philippe,Dufaud, Véronique,Lefebvre, Frédéric
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- Understanding reaction processes for n-heptane over 10Mo2C/SZ catalyst
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Supported carbided molybdena catalysts was prepared by treating MoO3/sulfated zirconia in methane/hydrogen (1:4 volumetric ratio) at 923?K. Characterisation shows the oxide to be different from the carbide phase. Carburisation did not induce phase change of the support with the tetragonal phase remaining dominant but did results in some changes to the textural properties. Lewis acid site density was constant in transforming from oxide to carbide forms while Br?nsted acidity site densities was diminished by ca 10% to give a Br?nsted/Lewis density ratio 2.46 in the carbide form. The ratio of hydrogenation sites to (Br?nsted) acid sites on the carbidic form of the catalyst was 0.12. Increasing temperature and decreasing WHSV augmented heptane conversion but leads to multiple cracking. Analysis of the product distribution as a function of conversion or as a function of temperature implied that the reaction did not simply proceed via a single consecutive reaction pathway Conversion increased the research octane number (RON) due to of the increased fraction of pentane isomers.
- Oloye,McCue,Anderson
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p. 246 - 256
(2016/10/05)
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- Catalytic conversion of sorbitol to gasoline-ranged products without external hydrogen over Pt-modified Ir-ReOx/SiO2
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Deoxygenation of sorbitol was carried out over a Pt-modified Ir-ReOx/SiO2 catalyst in biphasic solvent system (n-decane + H2O) without external hydrogen. Good yield of gasoline-ranged products was obtained including C5-C6 alkanes and C2-C6 mono-functionalized compounds such as ketones, alcohols, cyclic ethers and carboxylic acids. The Pt(3 wt%)-Ir-ReOx/SiO2 catalyst showed the best performance in the production of gasoline-ranged products. The maximum yield of gasoline-ranged products was 42%. The distribution of the products can be tuned by the addition of HZSM-5. The main products were C5-C6 alkanes with addition of HZSM-5 while the main products were C2-C6 mono-functionalized compounds without addition of HZSM-5. Characterizations such as TPR, XRD, TEM, XANES, EXAFS, CO adsorption were performed. The results demonstrated that the Pt-Ir-ReOx/SiO2 catalyst showed the structure of Pt-Ir alloy particles partially covered with ReOx species. The number of surface Pt atoms in Pt(3)-Ir-ReOx/SiO2 was larger than that of Pt/SiO2 or Pt-ReOx/SiO2 because of the small size of Pt-Ir alloy particles. The large number of surface Pt atoms and the synergetic effect of Pt, Ir and ReOx species make the catalyst efficiently generate hydrogen by aqueous phase reforming of sorbitol, and the generated hydrogen is consumed in the hydrogenolysis C-O bonds.
- Liu, Sibao,Okuyama, Yasuyo,Tamura, Masazumi,Nakagawa, Yoshinao,Imai, Akio,Tomishige, Keiichi
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p. 122 - 131
(2016/05/11)
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- En Route to a Practical Primary Alcohol Deoxygenation
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A long-standing scientific challenge in the field of alcohol deoxygenation has been direct catalytic sp3 C-O defunctionalization with high selectivity and efficiency, in the presence of other functionalities, such as free hydroxyl groups and amines widely present in biological molecules. Previously, the selectivity issue had been only addressed by classic multistep deoxygenation strategies with stoichiometric reagents. Herein, we propose a catalytic late-transition-metal-catalyzed redox design, on the basis of dehydrogenation/Wolff-Kishner (WK) reduction, to simultaneously tackle the challenges regarding step economy and selectivity. The early development of our hypothesis focuses on an iridium-catalyzed process efficient mainly with activated alcohols, which dictates harsh reaction conditions and thus limits its synthetic utility. Later, a significant advancement has been made on aliphatic primary alcohol deoxygenation by employing a ruthenium complex, with good functional group tolerance and exclusive selectivity under practical reaction conditions. Its synthetic utility is further illustrated by excellent efficiency as well as complete chemo- and regio-selectivity in both simple and complex molecular settings. Mechanistic discussion is also included with experimental supports. Overall, our current method successfully addresses the aforementioned challenges in the pertinent field, providing a practical redox-based approach to the direct sp3 C-O defunctionalization of aliphatic primary alcohols.
- Dai, Xi-Jie,Li, Chao-Jun
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supporting information
p. 5433 - 5440
(2016/05/19)
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- INTEGRATED PROCESS FOR GASOLINE PRODUCTION
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An integrated process for gasoline production is described. The process includes introducing a feed comprising n-C5 hydrocarbons into a disproportionation reaction zone in the presence of a disproportionation catalyst to form a disproportionation mixture comprising iso-C4 and C6+ disproportionation products and unreacted n-C5 hydrocarbons. An iso-C4 hydrocarbon stream and an olefin feed are introduced into an alkylation reaction zone in the presence of an alkylation catalyst to produce an alkylation mixture comprising alkylate and unreacted iso-C4 paraffins. The disproportionation mixture and the alkylation mixture are combined, and the combined mixture is separated into at least a stream comprising the alkylate product, an iso-C4 stream, and an unreacted n-C5 hydrocarbon stream. The iso-C4 stream is recycled to the alkylation reaction zone, and the unreacted n-C5 hydrocarbon stream is recycled to the disproportionation reaction zone. The stream comprising the alkylate product is recovered.
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Paragraph 0081
(2016/07/05)
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- SSZ-87: A borosilicate zeolite with unusually flexible 10-ring pore openings
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The structure of the as-synthesized borosilicate zeolite SSZ-87 has been solved by combining high-resolution X-ray powder diffraction (XPD) and rotation electron diffraction (RED) techniques. The unit cell and space group symmetry were found from the XPD data, and were essential for the initial analysis of the RED data. Although the RED data were only 15% complete, this proved to be enough for structure solution with the program Focus. The framework topology is the same as that of ITQ-52 (IFW), but for SSZ-87 the locations of the structure directing agent (SDA) and the B atoms could also be determined. SSZ-87 has large cages interconnected by 8- and 10-rings. However, results of hydroisomerization and Al insertion experiments are much more in line with those found for 12-ring zeolites. This prompted the structure analyses of SSZ-87 after calcination, and Al insertion. During calcination, the material is also partially deboronated, and the location of the resulting vacancies is consistent with those of the B atoms in the as-synthesized material. After Al insertion, SSZ-87 was found to contain almost no B and to be defect free. In its calcined and deboronated form, the pore system of SSZ-87 is more flexible than those of other 10-ring zeolites. This can be explained by the fact that the large cages in SSZ-87 are connected via single rather than double 10-ring windows and that there are vacancies in some of these 10-rings.
- Smeets, Stef,McCusker, Lynne B.,Baerlocher, Christian,Xie, Dan,Chen, Cong-Yan,Zones, Stacey I.
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p. 2015 - 2020
(2015/03/04)
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- The comparison of two classes of bifunctional SBA-15 supported platinum-heteropolyacid catalysts for the isomerization of n-hexane
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Mono- and bifunctional catalysts composed of silicotungstic acid (H4SiW12O40) and/or platinum nanoparticles supported on SBA-15 mesostructured silica were comparatively tested for the isomerization of n-hexane. Monofunctional catalysts were produced by impregnating the SBA-15 support with either H4SiW12O40 or the platinum particle precursor, H2PtCl6. In the bifunctional catalysts, both metallic and acidic functions were combined either by mechanically mixing the monofunctional solids yielding a multiphase bifunctional material (HSiW/SBA-15 + Pt/SBA-15), or by dual impregnation of H4SiW12O40 and Pt within a single material leading to the monophasic bifunctional catalyst, HSiW/Pt/SBA-15. These hybrid materials, with the exception of the monofunctional platinum catalyst, were all active for the gas-phase isomerization of n-hexane. The two bifunctional catalyst systems showed high activity and selectivity for branched isomers with no catalyst degradation over 3 days of reaction.
- Pinto, Teresa,Arquillière, Philippe,Niccolai, Gerald P.,Lefebvre, Frédéric,Dufaud, Véronique
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p. 5300 - 5308
(2015/07/07)
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- Hydrogenation of ketones over bifunctional Pt-heteropoly acid catalyst in the gas phase
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Gas-phase hydrogenation of a wide range of ketones to alkanes, including hydrogenation of aliphatic ketones and acetophenone, was investigated using bifunctional metal-acid catalysis. The catalysts were comprised of a metal (Pt, Ru, Ni, and Cu) supported on acidic caesium salt of tungstophosphoric heteropoly acid Cs2.5H0.5PW12O40 (CsPW). The reaction occurred via a sequence of steps involving hydrogenation of ketone to alcohol on metal sites followed by dehydration of alcohol to alkene on acid sites and finally hydrogenation of alkene to alkane on metal sites. Catalyst activity decreased in the order: Pt > Ru >> Ni > Cu. Pt/CsPW showed the highest catalytic activity, giving almost 100% alkane yield at 100 °C and 1 bar pressure. Evidence is provided that the reaction with Pt/CsPW at 100 °C is limited by ketone-to-alcohol hydrogenation, whereas at lower temperatures (≤60 °C) by alcohol dehydration yielding alcohol as themain product. The catalyst comprised of a physical mixture of Pt/C + CsPW was found to be highly efficientas well, which indicates that the reaction is not limited by migration of intermediates between metal andacid sites in the bifunctional catalyst.
- Alharbi,Kozhevnikova,Kozhevnikov
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p. 457 - 462
(2015/10/05)
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- 3D ordered mesoporous Fe-KIT-6 catalysts for methylcyclopentane (MCP) conversion and carbon dioxide (CO2) hydrogenation for energy and environmental applications
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The direct hydrothermal synthesis of Fe-KIT-6 mesoporous materials with Ia3d symmetry and high iron loadings is reported for the first time. The Fe-KIT-6 mesoporous materials were characterized by XRD, N2 adsorption/desorption isotherms, SEM, FT-IR, XPS and EPR spectroscopy. The physico-chemical characterization results show that all of the samples have well-ordered cubic mesostructures and that the structural integrity is preserved for nSi/nFe ratios as high as 10. It was found that most of the iron ions exist as isolated framework species, but for Fe-KIT-6 with an nSi/nFe ratio of 10, the presence of extra-framework species/small iron oxide clusters cannot be excluded. The catalytic performances of these materials were tested for carbon dioxide (CO2) hydrogenation and methylcyclopentane (MCP) conversion. The catalytic results show that their catalytic activity increases significantly with increasing iron content. For the MCP conversion, the ring-opening selectivity can be improved by increasing the density of isolated iron atom sites at low reaction temperatures. For the CO2 hydrogenation, the methanation selectivity can be improved by increasing the iron active site density and employing a high reaction temperature. Specifically, the high density of iron sites at high catalyst loadings promotes the methanation reaction at the expense of the RWGS (reverse water gas shift) reaction. Thus, the Fe-KIT-6 materials appear to be suitable catalysts for MCP conversion at low temperatures and CO2 hydrogenation at high temperatures.
- Merkache,Fechete,Maamache,Bernard,Turek,Al-Dalama,Garin
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p. 672 - 681
(2015/10/05)
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- Effect of the doping agent nature on the characteristic and catalytic properties of aerogel zirconia catalysts doped with sulfate groups or heteropolytungstic acid
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Zirconia catalysts doped with sulfates or heteropolytungstic acid (HPW) prepared by sol-gel method and dried in supercritical conditions of solvent have been evaluated in n-hexane isomerization in the temperature range 150-220°C. Using HPW as dopant, the obtained catalyst is active at 220°C and selective towards isomers having higher Individual Octane Number, i.e., 2,2-DMB and 2,3-DMB compared with using sulfates as dopant. Based on N2-physisorption, XRD, SEM and TEM analyses, low specific area, particular morphology of grains and the lack of tetragonal ZrO2 particles reduce the adsorption of n-hexane reactant and led to inefficient catalyst throughout the temperature range 150-200°C. The catalyst doped with sulfur deactivates at T > 200°C since agglomerates of zirconia particles (TEM and SEM results) favor the coke formation. Using HPW, agglomerates of W oxide as well as phosphate groups (revealed by TGA, FTIR, EDX and UV/visible DRS) favor the formation of more valuable isomers at 220°C.
- Chakhari, Samir,Younes, Mohamed Kadri,Rives, Alain,Ghorbel, Abdelhamid
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- Catalytic Ketone Hydrodeoxygenation Mediated by Highly Electrophilic Phosphonium Cations
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Ketones are efficiently deoxygenated in the presence of silane using highly electrophilic phosphonium cation (EPC) salts as catalysts, thus affording the corresponding alkane and siloxane. The influence of distinct substitution patterns on the catalytic effectiveness of several EPCs was evaluated. The deoxygenation mechanism was probed by DFT methods.
- Mehta, Meera,Holthausen, Michael H.,Mallov, Ian,Pérez, Manuel,Qu, Zheng-Wang,Grimme, Stefan,Stephan, Douglas W.
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supporting information
p. 8250 - 8254
(2015/07/07)
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- A novel route for the synthesis of alkanes from glycerol in a two step process using a Pd/SBA-15 catalyst
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Glycerol is produced as a valuable by-product in the transesterification of fatty acids, but it cannot be used directly as a fuel additive. In this study, we developed a systematic conversion for glycerol, which proceeds via synthesizing the key intermediate, 1,2,3-tribromopropane and using the Suzuki coupling reaction to introduce the alkyl group. A series of Pd/SBA-15 catalysts with different wt% of Pd (10%, 15% and 20%) was prepared by a one step sol-gel method. The structure and composition of the catalysts were characterized by X-ray diffraction analysis (XRD), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM) and inductively coupled plasma optical emission spectrometry (ICP-OES). The metallic state of dispersed palladium in SBA-15 is confirmed with X-ray photoelectron spectroscopy (XPS). Pd/SBA-15 with a Pd loading of 20 wt% shows good catalytic activity at 90 °C with methylboronic acid, allowing the complete conversion of 1,2,3-tribromopropane and 64% selectivity of 3-methylpentane. The optimized catalysts were also employed in coupling reactions between various alkylhalides and methylboronic acid, which obtained the desired product with an excellent selectivity. The catalyst can be successfully recycled five times. After the first cycle, we observed a drop in activity with 20% Pd/SBA-15, which was due to the leaching of palladium but in the later cycles, there was no significant decrease in activity.
- Udayakumar,Pandurangan
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p. 78719 - 78727
(2015/10/05)
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- PROCESS FOR SELECTIVE RING OPENING OF CYCLIC HYDROCARBONS
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PURPOSE: A process for ring opening is provided to obtain improved conversion ratio and selectivity in comparison with the case of using hydrogen as a reducing agent. CONSTITUTION: A cyclic hydrocarbon and a reducing agent are provided as supplying materials. The supplying materials are transferred into a reactor (5) and reacted under the presence of a catalyst. A product is separated from the effusion of reaction zone. The catalyst is a heterogeneous catalyst having both acid site and metallic component. The product is obtained by evaporating and heating a mixture containing 100 parts by weight of porous molecular sieve and 0.01-20 parts by weight of water soluble metallic salt. The cyclic hydrocarbon is a naphthene group cyclic hydrocarbon which is pentagonal or hexagonal compound, or an alkyl derivative thereof selected from cyclopentane and cyclohexane. The alkyl derivative is methyl, ethyl, profile, butyl, isopropyl or an isobutyl derivative.
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Paragraph 0069-0076; 0087-0094
(2020/04/29)
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- Influence of Na content on the catalytic properties of Pt-Ir/Al 2O3 catalysts for selective ring opening of decalin
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The influence of the Na addition on Pt-Ir/Al2O3 on the reaction of selective ring opening of decalin and methyl cyclopentane was studied. The catalysts were evaluated by means of TPR, pyridine TPD, TEM, FTIR-CO and by the reaction tests of cyclohexane dehydrogenation, hydrogenolysis of cyclopentane, selective ring opening of decalin and methyl cyclopentane. It was found that Na strongly decreases the acidity and influences the metal properties of Pt-Ir/Al2O3 catalysts. The interaction between Pt and Ir is increased by the presence of Na, with larger metal crystals being obtained on the support modified by Na. As a consequence, the catalytic properties are also modified and the CP/CH ratio (parameter of demanding/not demanding reaction) is increased with sodium concentration. In the case of MCP reaction, Na strongly decreases the aromatic and n-C6 formation and favors the selective reaction mechanism, thus favoring the formation of 2MP and 3MP. For the decalin reaction, it was found that the yield to the dehydrogenated product of the catalysts supported on Al2O3-Na is lower than that of the free Na-alumina supported catalyst, whereas the opposite occurs with the yield to C1 due to the higher hydrogenolytic and lower dehydrogenation activity of the catalysts with Na. The yield to ring contraction (RC) products is higher on the catalyst without Na due to the higher acidity which favors the ring contraction reaction and the lower metallic activity; thus, the transformation of the RC product to ring opening products is decreased.
- Vicerich, María A.,Oportus, Marcelo,Benitez, Viviana M.,Reyes, Patricio,Pieck, Carlos L.
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- Dramatic promotion of copper-alumina catalysts by sodium for acetone trimerisation
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Na-promoted Cu-Al materials are efficient multifunctional catalysts for the direct conversion of gas phase acetone to diisobutyl ketone (DIBK) with unprecedented yields (up to 31%). The Na content is a major parameter determining the stability and the catalytic performance of these materials.
- Ligner, Emanuelle,Meunier, Frederic,Travert, Arnaud,Maury, Sylvie,Cadran, Nicolas
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p. 2480 - 2483
(2014/07/22)
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- Metal nanocrystals embedded in single nanocrystals of MOFs give unusual selectivity as heterogeneous catalysts
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The growth of nanocrystalline metal-organic frameworks (nMOFs) around metal nanocrystals (NCs) is useful in controlling the chemistry and metric of metal NCs. In this Letter, we show rare examples of nMOFs grown in monocrystalline form around metal NCs. Specifically, Pt NCs were subjected to reactions yielding Zr(IV) nMOFs [Zr6O4(OH)4(fumarate)6, MOF-801; Zr6O4(OH)4(BDC)6 (BDC = 1,4-benzenedicarboxylate), UiO-66; Zr6O4(OH)4(BPDC)6 (BPDC = 4,4′-biphenyldicarboxylate), UiO-67] as a single crystal within which the Pt NCs are embedded. These constructs (Pt?nMOF)nanocrystal are found to be active in gas-phase hydrogenative conversion of methylcyclopentane (MCP) and give unusual product selectivity. The Pt?nUiO-66 shows selectivity to C6-cyclic hydrocarbons such as cyclohexane and benzene that takes place with 100 °C lower temperature than the standard reaction (Pt-on-SiO2). We observe a pore size effect in the nMOF series where the small pore of Pt?nMOF-801 does not produce the same products, while the larger pore Pt?nUiO-67 catalyst provides the same products but with different selectivity. The (Pt?nMOF)nanocrystal spent catalyst is found to maintain the original crystallinity, and be recyclable without any byproduct residues.
- Na, Kyungsu,Choi, Kyung Min,Yaghi, Omar M.,Somorjai, Gabor A.
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p. 5979 - 5983
(2015/02/19)
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- Metal-free deoxygenation of carbohydrates
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The conversion of readily available cellulosic biomass to valuable feedstocks and fuels is an attrative goal but a challenging transformation that requires the cleavage of multiple nonactivated C-O bonds. Herein, the Lewis acid trispentafluorophenylborane (B(C6F5)3) is shown to catalyze the metal-free hydrosilylative reduction of monosaccharides and polysaccharides to give hydrocarbons with reduced oxygen content. The choice of the silane reductant influences the degree of deoxygenation, with diethylsilane effecting the complete reduction to produce hexanes while tertiary silanes give partially deoxygenated tetraol and triol products. A spoonful of sugar: The Lewis acid B(C6F5)3 catalyzes the complete deoxygenation of carbohydrates to give a mixture of hexane and hexene isomers, with diethylsilane (Et2SiH2) providing the hydride equivalent. A variety of carbohydrates including methyl cellulose can be deoxygenated by this metal-free method, and the system can be tuned for selective deoxygenation at certain sites. Copyright
- Adduci, Laura L.,McLaughlin, Matthew P.,Bender, Trandon A.,Becker, Jennifer J.,Gagne, Michel R.
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supporting information
p. 1646 - 1649
(2014/03/21)
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- Effect of acidic properties of mesoporous zeolites supporting Pt nanoparticles on hydrogenative conversion of methylcyclopentane
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The effect of acidic properties of mesoporous zeolites on the control of product selectivity during the hydrogenative isomerization of methylcyclopentane has been investigated. A series of mesoporous zeolites with controlled acidic properties were prepared by postdealumination process with hydrochloric acid under hydrothermal conditions, and the resultant zeolites used for supporting colloidal Pt nanoparticles (NPs) with a mean size of 2.5 nm (±0.6 nm). As compared to the pure Pt NPs supported on catalytically inert mesoporous silica (MCF-17) as the reference catalyst that can produce isomers most selectively (～80%), the Pt NPs supported on mesoporous zeolites produced C6-cyclic hydrocarbons (i.e., cyclohexane and benzene) most dominantly. The type and strength of the Br?nsted (B) and Lewis (L) acid sites of those zeolites with a controlled Al amount are analyzed by using FT-IR after the adsorption of pyridine and NH3 temperature-programmed desorption measurements, and they are correlated with the selectivity change between cyclohexane and benzene. From this investigation, we found a linear relationship between the number of Br?nsted acid sites and the formation rate for cyclohexane. In addition, we revealed that more Lewis acidic zeolite having relatively smaller B/L ratio is effective for the cyclohexane formation, whereas more Br?nsted acidic zeolite having relatively larger B/L ratio is effective for the benzene formation.
- Na, Kyungsu,Alayoglu, Selim,Ye, Rong,Somorjai, Gabor A.
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supporting information
p. 17207 - 17212
(2015/02/19)
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- Influence of iridium content on the behavior of Pt-Ir/Al2O 3 and Pt-Ir/TiO2 catalysts for selective ring opening of naphthenes
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The influence of Ir content on the properties of Pt-Ir/Al2O 3 and Pt-Ir/TiO2 catalysts for selective ring opening of naphthenes was studied. It was found that these catalysts display a strong Pt-Ir interaction but only a weak metal-support interaction. Catalyst acidities depend on the metal loading, but opposite effects were observed on alumina (decrease) or titania (increase) as the metal loading increased. The results obtained from test reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis) showed that titania supported catalysts were less active than their alumina supported counterparts. This behavior could be due to the partial blockage of metallic sites by migrated TiOx species and the sinterization of metallic phase during the reduction step. The methylcyclopentane ring opening reaction was found to occur through a partially selective mechanism, and an increase in activity as the Ir loading increased was observed. The selective mechanism was favored by higher total metal loadings, possibly due to an increase in the size of metallic aggregates. Alumina supported catalysts present higher ring opening selectivities. The activity for decalin ring opening increased both with metal loading and reaction temperature level.
- Vicerich, María A.,Benitez, Viviana M.,Especel, Catherine,Epron, Florence,Pieck, Carlos L.
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p. 167 - 174
(2013/03/29)
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- Effects of calcination temperature and water-washing treatment on n-hexane hydroisomerization behavior of Pt-promoted sulfated zirconia based catalysts
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Synthesis of Pt-promoted sulfated zirconia catalyst Pt/SO4 2-/ZrO2 (designated as PSZ), Pt/SO4 2-/ZrO2-Al2O3 (designated as PSZA), and Pt/SO42-/ZrO2-Al2O 3-Y2O3 (designated as PSZAY) was reported. These catalysts were characterized by N2 adsorption-desorption, thermal gravimetric (TG) analysis, NH3-temperature programmed desorption (NH3-TPD), and H2-temperature programmed reduction (H2-TPR) techniques. Effects of calcination temperature of the catalysts on the n-hexane hydroisomerization behavior were investigated in details. The experiment results revealed that the addition of Al and Y or Al promoter alone could improve the thermal stability of the catalysts. PSZA and PSZAY exhibited higher isomerization activity than unmodified PSZ as the calcination temperature of sulfated Zr(OH)4 was relatively high, for example, between 650 C and 750 C. For the first time, it was found that water-washing treatment of PSZA and PSZAY at different preparation stages had considerably different impacts on their catalytic activity. Water-washing after calcination of the sulfated Zr(OH)4, the catalytic activity of PSZA and PSZAY was high, as indicated by approximately 80% of n-hexane conversion. However, water-washing before calcination of sulfated Zr(OH)4 led to a significant decrease in the catalytic activity of PSZA and PSZAY, that is, the n-hexane conversion diminished to around 35%. It was proposed that the presence of excessive sulfur species over sample was favorable for keeping the active sulfur species in the catalyst surface.
- Song, Yueqin,Tian, Jing,Ye, Yurong,Jin, Yaqing,Zhou, Xiaolong,Wang, Jin-An,Xu, Longya
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p. 108 - 114
(2013/07/26)
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- C5-C7 linear alkane hydroisomerization over MoO 3-ZrO2 and Pt/MoO3-ZrO2 catalysts
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The catalytic activity of MoO3-ZrO2 and Pt/MoO 3-ZrO2 has been assessed based on the C5-C 7 linear alkane hydroisomerization in a microcatalytic pulse reactor at 323-623 K. The introduction of Pt altered the crystallinity and acidity of MoO3-ZrO2. The catalytic activity of Pt/MoO 3-ZrO2 was inferior than that of MoO3-ZrO 2, although the Pt/MoO3-ZrO2 performed higher hydrogen uptake capacity. IR and ESR studies confirmed the heating of MoO 3-ZrO2 in the presence of hydrogen formed active protonic acid sites and electrons which led to change in the Mo oxidation state. Similar phenomenon was observed for Pt/MoO3-ZrO2 at ≤323 K. Contrarily, heating of Pt/MoO3-ZrO2 in the presence of hydrogen at higher temperature did not form protonic acid sites but intensified Lewis acidic sites. It is suggested that Pt facilitates in the interaction of spiltover hydrogen atom and MoO3 to form MoO2 or Mo 2O5 over ZrO2 support which may be intensified the Lewis acidic sites.
- Triwahyono,Jalil,Ruslan,Setiabudi,Kamarudin
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- Isomerization of n-Hexane Catalyzed by Supported Monodisperse PtRh Bimetallic Nanoparticles
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Composition and size of Pt x Rh1-x bimetallic nanoparticles were varied in order to study the effects in the catalytic reforming of n-hexane. Hexane isomerization, an analogue to the important industrial process of hydrocarbon reforming is a reaction in which we aim to investigate the molecular level details of catalysis. It is known, that in hydrocarbon isomerization, Pt atoms act to isomerize the reactants, while small amounts of promoter metal atoms (such as Rh, Ir, Re and Sn) provide C-C and C-H bond breaking activity. Herein, we report on the effect of composition and size in model bimetallic Pt x Rh1-x nanoparticle catalysts utilized in n-hexane reforming. Both nanoparticle composition and size were shown to influence catalytic turnover frequency and product selectivity. It was found, through ambient pressure X-ray photoelectron spectroscopy, that the surface of these nanoparticles is both dynamic, and Rh rich under relevant reaction conditions. The findings suggest that an ensemble effect exists, in which the highest isomer production occurs when Rh atoms are surrounded by Pt atoms on the metal surface. Graphical Abstract: [Figure not available: see fulltext.]
- Musselwhite, Nathan,Alayoglu, Selim,Melaet, Gerome,Pushkarev, Vladimir V.,Lindeman, Avery E.,An, Kwangjin,Somorjai, Gabor A.
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p. 907 - 911
(2013/10/08)
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- A novel monolith catalyst of plate-type anodic alumina for the hydrolysis of dimethyl ether
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A novel monolith catalyst of plate-type anodic alumina was applied in the dimethyl ether (DME) hydrolysis reaction system. The reactivity of the anodic alumina with hydration treatments in DME hydrolysis reaction was investigated. The preferred hydration-treated temperature was found to be 80 C and the anodic Al2O3/Al monolith exhibited higher activity than the commercial Al2O3 in DME hydrolysis reaction. Meanwhile, the anodic Al2O3/Al monolith was proven to have higher MeOH effluent mole percentage with less unfavorable side reactions than the ZSM-5 catalyst. The anodic γ-Al2O3/Al monolith had just 0.85% coking while the ZSM-5 catalyst had 8.81% after 100 h of continuous experiments.
- Zhang, Qi,Sun, Dongmei,Fan, Feiyue,Zhang, Qinghui,Zhu, Zibin
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- PROCESS FOR PREPARING JET FUEL FROM MOLECULES DERIVED FROM BIOMASS
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The invention relates to a process for preparing jet fuel or jet fuel precursors which comprises the treatment of a charge derived from biomass, the said charge comprising at least one compound chosen from terpenes of formula [CH2=C(CH3)CH=CH2]n, in which n is an integer of from 2 to 12, the carbon chain of which is linear, cyclic or branched, or cyclic or branched terpenes as defined previously, which have been chemically modified by oxidation and/or rearrangement of the carbon backbone, the said process comprising a cycloaddition step (i) followed by a cracking and hydrogenation step (ii).
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Page/Page column 16; 17
(2013/04/25)
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- Identification of carbonaceous deposits formed on H-mordenite during alkane isomerization
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To identify hydrocarbon surface species accumulating during alkane isomerization, a strategy involving in situ UV-vis and FTIR spectroscopies, reaction of formed species with various bases, adsorption of reference compounds, and extraction of spent catalysts was applied. During conversion of n-butane or n-pentane on H-mordenite at reaction temperatures below ≈550 K, species characterized by an intense absorption band at a wavelength of 292-296 nm were observed by in situ diffuse reflectance UV-vis spectroscopy. Species with a comparable electronic signature formed after adsorption of 1-butene, 1-pentene, or 1-hexene, indicating that olefins are intermediates in the formation of carbonaceous deposits from alkanes. The chromophore was largely invariant to the carbon chain length and the species were identified as alkyl-substituted cyclopentenyl cations. Carbonaceous deposits formed at temperatures higher than ≈550 K consisted of methyl-substituted naphthalenes, anthracenes, and tetracenes; these species also existed as stable cations on the zeolite during catalysis, producing a broad absorption at 350-500 nm. The polycyclic aromatic species were neutralized by water vapor, whereas the alkyl-substituted cyclopentenyl cations required a stronger base, such as ammonia.
- Wulfers, Matthew J.,Jentoft, Friederike C.
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p. 204 - 213
(2013/09/23)
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- Efficient hydrodeoxygenation of biomass-derived ketones over bifunctional Pt-polyoxometalate catalyst
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Acidic heteropoly salt Cs2.5H0.5PW12O 40 doped with Pt nanoparticles is a highly active and selective catalyst for one-step hydrogenation of methyl isobutyl and diisobutyl ketones to the corresponding alkanes in the gas phase at 100 °C with 97-99% yield via metal-acid bifunctional catalysis.
- Alotaibi, Mshari A.,Kozhevnikova, Elena F.,Kozhevnikov, Ivan V.
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supporting information; experimental part
p. 7194 - 7196
(2012/08/13)
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