- Influence of the preparation method on the morphological and composition properties of Pd-Au/ZrO2 catalysts and their effect on the direct synthesis of hydrogen peroxide from hydrogen and oxygen
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Bimetallic Pd-Au samples supported on zirconia were prepared by different methods and tested for the direct synthesis of hydrogen peroxide under very mild conditions (room temperature and atmospheric pressure), outside the explosion range and without halides addition. Further catalytic tests were performed at higher pressure using solvents expanded with CO2. Samples were characterized by N2 physisorption, metal content analysis, XRD, HRTEM combined with X-ray EDS, TPR, and FTIR. The effect of the addition of gold to Pd in enhancing the yield of H2O2 is sensitive to the preparation method: the best catalytic results were obtained by depositing gold by deposition-precipitation (DP) and by introducing in a second step Pd by incipient wetness impregnation. The origin of the differences between samples is discussed. The role of Au in the catalytic reaction seems to be a complex one, changing the chemical composition of the metallic particles, their morphology, and charge of the exposed Pd sites.
- Menegazzo, Federica,Signoretto, Michela,Manzoli, Maela,Boccuzzi, Flora,Cruciani, Giuseppe,Pinna, Francesco,Strukul, Giorgio
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- On the effect of the strength of acid sites in heterogeneous catalysts on the activity in the skeletal isomerization of n-butane
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The catalytic activity of three groups of acid catalysts different in the nature and strength of acid sites in the skeletal isomerization of n-butane was studied. It was found that the strength of the sites did not correlate with the rate of the reaction.
- Shmachkova,Kotsarenko,Paukshtis
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- Synthesis of lead zirconate titanate from an amorphous precursor by mechanical activation
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Many of the chemistry-based processing routes for functional ceramics inevitably involve calcining the chemical-derived precursors at an intermediate/high temperature, in order to form the designed ceramic phase. This is very undesirable, although widely used, as the calcination can result in an extensive degree of crystal growth and particle coarsening at the calcination temperature and therefore ruins almost all the advantages offered by the chemistry-based processing routes, such as an ultrafine particle size and high sintering-reactivity. Using a specifically designed PZT precursor prepared by co-precipitation, it is demonstrated that the precursor-to-ceramic conversion can alternatively be realized by mechanical activation. In this connection, a single phase, nanocrystalline perovskite PZT powder has been successfully derived from an amorphous hydroxide precursor by mechanical activation. The resulting PZT powder was well dispersed, and the particle size was in the range of 30-50 nm, as observed using the scanning electron microscopy and transmission electron microscopy. This is in contrast to the poor particle characteristics, represented by very coarse and irregular particle and agglomerate sizes, for the powder derived from calcination at 750 °C. The activation-triggered PZT powder was sintered to a density of 97.6% theoretical density at 1150 °C for 1 h. Sintered PZT ceramic exhibits a dielectric constant of 927 at room temperature and a peak dielectric constant of approximately 9100 at the Curie point of 380 °C when measured at the frequency of 1 kHz.
- Junmin, Xue,Wang, John,Weiseng, Toh
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- Thermoanalytical investigations on hydrous zirconia
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The variations in the thermoanalytical curves for three differently produced powders of hydrous zirconia are discussed in connection with X-ray measurements and powder-metallurgical characterization. They were shown to characterize ZrO2-H2O bonding and the thermal treatment for the calcination of hydrous zirconia. They allowed selection of the product with the most favorable microstructure for a high sinter activity, an explanation of the phase formation and phase transformations, and estimations of energy content of the amorphous material and the thermal stability of the tetragonal phase. It was shown that thermal analysis is an appropriate method for the optimizing of ZrO2-powder production.
- Schuster, G.,Braun, G.,Henkel, K.,Querner, G.
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- FT-IR and laser Raman spectroscopic investigation of the formation and stability of low temperature t-ZrO2
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The influence of the preparation chemistry on the formation and the stability of metastable t-ZrO2 was studied. γ-Irradiation has very small (if any) influence on the t-ZrO2 → m-ZrO2 transition, while increased temperature and pressure caused gradual transition of pure t-ZrO2 to m-ZrO2. Metastable t-ZrO2 containing SO4/2- impurities proved to be more stable, and its transition was not uniform. The mentioned effects were monitored by FT-IR and laser Raman spectroscopy. X-ray diffraction was used as a complementary technique.
- Stefanic,Music,Popovic,Sekulic
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- Thermodynamic complexity of sulfated zirconia catalysts
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A series of sulfated zirconia (SZ) catalysts were synthesized by immersion of amorphous zirconium hydroxide in sulfuric acid of various concentrations (1–5?N). These samples were fully characterized by X-ray diffraction (XRD), thermogravimetric analysis and mass spectrometry (TGA-MS), and aqueous sulfuric acid immersion and high temperature oxide melt solution calorimetry. We investigated the enthalpies of the complex interactions between sulfur species and the zirconia surface (ΔHSZ) for the sulfated zirconia precursor (SZP), ranging from ?109.46?±?7.33 (1?N) to ?42.50?±?0.89 (4?N) kJ/mol S. ΔHSZ appears to be a roughly exponential function of sulfuric acid concentration. On the other hand, the enthalpy of SZ formation (ΔHf), becomes more exothermic linearly as sulfur surface coverage increases, from ?147.90?±?4.16 (2.14?nm?2) to ?317.03?±?4.20 (2.29?nm?2) kJ/mol S, indicating formation of energetically more stable polysulfate ?species.
- Liu, Naiwang,Guo, Xiaofeng,Navrotsky, Alexandra,Shi, Li,Wu, Di
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- Influence of precipitation chemistry and ball-milling on the thermal behavior of zirconium hydroxide
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Zirconium hydroxide precipitates, obtained by rapid precipitation at pH 2.5, 7.5, and 10.5, were ball-milled for up to 60 h and then heated inside a differential scanning calorimeter (DSC) at temperatures of up to 600°C. Crystal phases produced after heating were analyzed by FTIR and laser Raman spectroscopy. It was found that without regard to the precipitation pH the first stage of ball-milling caused an increase of the crystallization temperature that resulted in the formation of pure t-ZrO2. The second stage of ball-milling caused a decrease of the crystallization temperature resulting in the formation of m-ZrO2. The ball-milling process also influenced the dependence of the crystallization enthalpy of zirconium hydroxide on the precipitation pH. In the case of zirconium hydroxide precipitated at pH 2.5, the ball-milling caused dehydration and an increase in its hygroscopy. The nature of these effects was discussed. The extension of FTIR spectra to the far infrared region made it possible to distinguish between t-ZrO2 and m-ZrO2 polymorphs by this technique. Also, the influence of laser power on the identification of ZrO2 polymorphs by Raman spectroscopy was elaborated.
- Stefanic,Music,Sekulic
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- CO oxidation by oxygen of the catalyst and by gas-phase oxygen(0.5–15)%CoO/ZrO2
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CO adsorption on (0.5–15)%CoO/ZrО2 catalysts has been investigated by temperature-programmed desorption and IR spectroscopy. At 20°С, carbon monoxide forms carbonyl and monodentate carbonate complexes on Com2+On2- clusters located on the surface of crystallites of tetragonal ZrO2. With an increasing CoO content of the clusters, the amount of these complexes increases and the temperature of carbonate decomposition, accompanied by CO2 desorption, decreases from 400 to 304°С. On the 5%CoO/ZrО2 sample, the carbonyls formed on the Со2+ and Со+ cations and Со0 atoms decompose at 20, 90, and 200–220°С, respectively, releasing CO. At 20°С, they are oxidized by oxygen to monodentate carbonates, which decompose at 180°С. Adsorbed oxygen decreases the temperature of their decomposition on oxidation sites by ~40°C, and the sample remains in an oxidized state ensuring the possibility of subsequent CO adsorption and oxidation. The rate of the oxidation of 5%CoO/ZrО2 containing adsorbed CO by oxygen is higher than the rate of the oxidation of the same sample reduced by carbon monoxide, because the latter reaction is an activated one. In view of the properties of the complexes, it can be concluded that the carbonates decomposing at 180°С are involved in CO oxidation by oxygen from the gas phase in the presence of hydrogen, a process occurring at 50–200°С. The rate-limiting step of this process the decomposition of the carbonates, which is characterized by an activation energy of 77–94 kJ/mol.
- Il’ichev,Fattakhova,Shashkin,Matyshak,Korchak
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- Modified zirconia solid acid catalysts for organic synthesis and transformations
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The sulfate, molybdate and tungstate promoted ZrO2 catalysts were investigated by X-ray diffraction, NH3-TPD, and Raman spectroscopy and were evaluated for various organic synthesis and transformation reactions. All catalysts exhibit good catalytic activity for synthesis of diphenylureas, coumarines and 1,5-benzodiazepines, acylation of alcohols, phenols and amines, and protection of carbonyl compounds. A series of sulfate, molybdate and tungstate promoted ZrO2 catalysts were prepared by wet impregnation method. To incorporate these promoters to Zr(OH)4, sulfuric acid, ammonium heptamolybdate, and ammonium metatungstate were used as precursors, respectively. Further, a Pt promoted Mo-ZrO2 catalyst was also prepared separately by impregnating with hexachloroplatinic acid. The surface and bulk properties of various promoted ZrO2 catalysts were investigated by means of X-ray powder diffraction, BET surface area, ammonia-TPD, and Raman spectroscopy techniques. The unpromoted ZrO2 when calcined at 873 K exists in the crystalline form with monoclinic phase dominating over the tetragonal phase. Incorporation of various promoters into Zr(OH)4 shows a strong influence on the bulk and the surface properties. Addition of promoters enhanced the tetragonal zirconia phase and the surface acidity. In the case of Pt/Mo-ZrO2 catalyst, a complete tetragonal ZrO2 phase is observed. The ammonia-TPD results indicate that the impregnated sulfate ions show a strong influence on the acidity of ZrO2, which is followed by molybdate. The prepared catalysts were evaluated for various organic synthesis and transformation reactions in the liquid phase. All catalysts exhibit good catalytic activity for synthesis of diphenylureas, coumarines and 1,5-benzodiazepines, acylation of alcohols, phenols and amines, and protection of carbonyl compounds. In particular, the sulfate and molybdate promoted catalysts exhibited excellent catalytic activity.
- Reddy, Benjaram M.,Sreekanth, Pavani M.,Reddy, Vangala R.
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- Evolution of the Catalytic Activity in Pt/Sulfated Zirconia Catalysts: Structure, Composition, and Catalytic Properties of the Catalyst Precursor and the Calcined Catalyst
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A 3% Pt/sulfated zirconia catalyst was prepared and characterized before and after calcination at 900 K by XRD, XPS, EM, and in the catalytic hydroisomerization of n-hexane. The fresh sample exhibited small but definite catalytic properties. Calcination brought about a dramatic increase of the activity with practically constant high (90-100%) selectivity for hydroisomerization versus cracking. This increased activity was accompanied by the transformation of the predominantly amorphous support to predominantly tetragonal crystals and the wrapping up of most parts of surface Pt atoms into the bulk, as shown by the physical characterization methods. Hence metallic Pt particles exhibited mainly Pt-O rather than Pt-S interactions. S was present as sulfate. Pt-sulfated zirconia was different from traditional bifunctional metal catalysts on acidic supports. We attributed its higher catalytic activity and favorable isomerization selectivity to a few but very active centers, formed by interaction of Pt sites with sulfate groups on the high Miller-index surfaces of ZrO2. Calcination must be essential to create these active sites. H2 dissociating on Pt sites would provide the hydride species that are necessary for isomerization occurring on the acidic (sulfate-zirconia) part of that ensemble. We proposed the name compressed bifunctional sites for these centers of acid-metal cooperation. The assumption of such active sites, the maximum activity as a function of the hydrogen pressure, can also be explained in a consistent way.
- Manoli, Jean-Marie,Potvin, Claude,Muhler, Martin,Wild, Ute,Resofszki, Gabor,Buchholz, Thomas,Paal, Zoltan
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- Efficient microwave synthesis of novel aromatic esters catalyzed by zirconia and its modified forms: A kinetic study
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A series of solid acids such as ZrO2, 5%Mo(vi)/ZrO2, 10%Mo(vi)/ZrO2, 20%Mo(vi)/ZrO2 and SO42-/ZrO2 were prepared. These solid acids were characterized by BET, NH3-TPD/n-butylamine back titration, powder-XRD, FT-IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ICP-OES techniques. The catalytic performance of these solid acids was evaluated in the synthesis of novel aromatic esters by the assistance of microwave irradiation and the catalytic activity of these solid acids was compared with pTsOH. The results clearly indicated that the zirconia based solid acids are efficient green catalysts for esterification reactions, which gave a maximum yield of the ester in a shorter reaction time and comparable catalytic activity of the pTsOH Br?nsted acid. Kinetic studies were carried out to calculate the temperature coefficients (1.66 and 1.56) and energy of activation (66.82 kJ mol-1 and 58.93 kJ mol-1) for SO42-/ZrO2 and pTsOH respectively. Pre-adsorption studies revealed that the reaction follows the Langmuir-Hinshelwood mechanism. The SO42-/ZrO2 solid acid catalyst was found to be reactivable and reusable.
- Thimmaraju,Mohamed Shamshuddin,Pratap,Raja
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- Heterogeneous Liquid-Phase Oxidation of Alcohols with Solid Oxidizing Reagents of Vanadium(V) Oxide and Chromium(VI) Oxide Supported on Zirconium(IV) Oxide
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The oxidizing reagents in a heterogeneous system were obtained by impregnating Zr(OH)4 with NH4VO3 and (NH4)2CrO4 followed by calcination in air at 773 K.These materials (V2O5/ZrO2 and CrO3/ZrO2) converted alcohols into their corresponding aldehydes or ketones at moderate temperatures in a solvent with very high selectivity.Changes in the oxidation states of vanadium and chromium were investigated by a temperature-programmed reduction method (TPR).A linear relation was found between the yield of cyclohexanone formed from cyclohexanol and the amount of reduced vanadium or chromium, determined by TPR.It was confirmed that the active species of V(V) and Cr(VI) were reduced to V(II) and Cr(IV), respectively, in the oxidation process.
- Nakamura, Hideo,Matsuhashi, Hiromi
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- Development of a novel mesoporous catalyst UDCaT-6: Kinetics of synthesis of tert-amyl methyl ether (TAME) from tert-amyl alcohol and methanol
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UDCaT-6, a novel active mesoporous and stable catalyst, was synthesized by generating in situ nanosized acidic centers of chlorosulfonic acid treated zirconia in the pores of highly ordered hexagonal mesoporous silica (HMS). For the first time, we have used chlorosulfonic acid as a source of sulfating agent to treat zirconia in pores of the HMS. The catalyst is characterized by XRD, FTIR, EDAX, SEM, and BET surface area and pore size analysis, and probe reactions. The structural integrity of HMS is maintained in UDCaT-6. The activity and stability of UDCaT-6 was tested in liquid phase alkylation of toluene with benzyl chloride and vapor phase synthesis of tert-amyl methyl ether (TAME) from ferf-amyl alcohol (TAA) and methanol where corrosive acid HCl and water are generated as biproducts. A complete theoretical and experimental analysis is presented and kinetics are evaluated. The model explains the experimental data very well.
- Yadav, Ganapati D.,Murkute, Ambareesh D.
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- Synthesis of solid superacid catalyst with acid strength of H0 ≤ -16.04 1
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A solid superacid catalyst with an acid strength of H0 ≤ -16.04, which was active for reactions of propane and butane, was obtained by exposing Zr(OH)4, prepared by the hydrolyses of ZrOCl2 and ZrO(NO3)2, to 1 N H2SO4 and then calcining in air at 575-650°C.
- Hino, Makoto,Arata, Kazushi
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- Synthesis and characterization of mesoporous and nano-crystalline phosphate zirconium oxides
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In this work the preparation and characterization of the materials such as zirconia (ZrO2) and zirconia promoted with phosphate ion (ZrO2-PO43-) is presented. Pure zirconium hydroxide [Zr(OH)4] was synthesized by the sol-gel method using precursors such as zirconium n-butoxide and 1-butanol maintaining a pH 8 during the synthesis. Zr(OH)4 was impregnated with 15 wt.% of the acid agent. Both were calcined in a dynamic air atmosphere for 3 h at 400, 500 and 600 °C. The supports were characterized by thermal analysis, X-ray diffraction, nitrogen physisorption as well as infrared spectroscopy. The results showed a positive effect on the physicochemical properties of the catalytic supports after Zr(OH)4 impregnation with the dopping agent (H3PO4). Phosphate zirconium oxides remained thermically stable after calcination. It was observed that the dopping agent remained firmly attached to the zirconium oxide surface, inhibiting the particle growth and delaying the syntherization of the material and the apparition of the monoclinic phase, obtaining mesoporous and nano-crystalline materials (crystallite size 1.0-6.5 nm) with high surface areas (210-329 m2/g) and tetragonal structure defined for the calcination temperature of 600 °C.
- Hernández Enríquez,Cortez Lajas,García Alamilla,Castillo Mares,Sandoval Robles,García Serrano
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- Influence of the preparation and of the activation treatments on the catalytic activity of mechanical mixtures of sulfated zirconia and Pt/Al2O3
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Zirconium hydroxides with specific surface areas in the range of 60 to 300 m2/g were obtained by varying between 6 and 12 the final pH of precipitation of the gels and the nature of the precursor salt. These compounds were sulfated by impregnation with 15 and 35 ml of aqueous 0.5 MH2SO4. Their sulfur content was 3 to 5 wt%. Sulfation increases the thermal stabilities of the zirconias by nearly 200 K. The solids remain amorphous up to at least 673 K and then crystallize in the tetragonal and monoclinic phases. The properties of mechanical mixtures of the sulfated zirconias and a Pt/alumina catalyst were evaluated for the isomerization of n-hexane. The study of the conditions of activation show that the highest performances of these catalysts result from a pretreatment under hydrogen at 573 and 623 K when the amounts of H2SO4 added are, respectively, of 35 and 15 ml/g of zirconium hydroxide, whatever their specific surface areas. A close correlation is found between the activities of the catalysts and their specific surface areas. This suggests that the active sites are located at the low coordination sites of zirconia and that their efficiency increases with their dispersion. The acidity determined by IR spectroscopy of NH3 adsorption is essentially of Lewis type after evacuation at 573 K. However, Bronsted acidity results from a reversible redox equilibrium between hydrogen and zirconia. The isomerization of n-hexane is considered to follow a classical bifunctional mechanism.
- Tichit,El Alami,Figueras
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- Improvement of energy storage density with trace amounts of ZrO2 additives fabricated by wet-chemical method
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Lead-free (1-x)[0.6SrTiO3-0.4Na0.5Bi0.5TiO3]-xZrO2 ceramics (STNBT-xZr) were synthesized in single perovskite phase. The average grain size decreased from 3.2 μm (x = 0.1 mol%) to 1.6 μm (x = 0.6 mol%) related to the addition of ZrO2 powders prepared by microwave hydrothermal method. With the increasing of ZrO2 content, the permittivity decreased gradually, and the breakdown strength (Eb) was remarkably improved due to composition induced disturbing of long range ferroelectric order. The increase of Eb led to the improvement of the recoverable energy storage density (Wre) from 1.80 J/cm3 (x = 0.1 mol%) to 2.84 J/cm3 (x = 0.5 mol%). However, when Zr4+ content was more than 0.5 mol%, the Wre decreased from 2.84 J/cm3 to 2.26 J/cm3 (x = 0.6 mol%) due to the reduction of the maximum polarization. The best energy storage properties were achieved in STNBT-xZr ceramic with Zr4+ content of x = 0.5 mol%, which exhibited the Wre of 2.77–2.84 J/cm3 in the range of 4–40 Hz, revealing an excellent frequency stability. All these results demonstrate the STNBT-xZr (x = 0.5 mol%) ceramics are quite promising for frequency-stable energy storage applications.
- Cui, Chenwei,Pu, Yongping
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- Metal-reinforced sulfonic-acid-modified zirconia for the removal of trace olefins from aromatics
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Metal-reinforced sulfonic-acid-modified zirconia catalysts were successfully prepared and used to remove trace olefins from aromatics in a fixed-bed reactor. Catalysts were characterized by ICP-OES, N2 adsorption–desorption, X-ray diffraction, thermogravimetric analysis (TGA), and pyridine-FTIR spectroscopy. Different metals and calcination temperatures had great influence on the catalytic activity. Alumina-reinforced sulfated zirconia exhibited outstanding catalytic performance, stable regeneration activity, and giant surface area, and are promising in industrial catalysis. TGA showed that the decomposition of methyl could be attributed to Br?nsted acid sites, and pyridine-FTIR spectroscopy proved the weak Br?nsted sites on these synthesized metal-reinforced sulfated zirconia. Also, a relation between the reaction rate and weak Br?nsted acid density is proposed.
- Kong, Decun,Peng, Qian,Shi, Li,Wang, Xin,Meng, Xuan,Hu, Xiude,Liu, Naiwang
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- A new solid superacid catalyst prepared by doping ZrO2 with Ce and modifying with sulfate simultaneously
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A new solid superacid catalyst, Ce-ZrO2/SO4 2-, having high surface area and thermal stability even after calcination at temperatures of 650-700 °C, is prepared simply by doping ZrO2 with Ce and modifying with sulfate simultaneously. The role of Ce is to form a thermally stable solid solution with zirconia and consequently to give high surface area of the sample.
- Jong, Rack Sohn,Jun, Seob Lim,Si, Hoon Lee
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- Hydrogen effect on n-butane isomerization over sulfated zirconia-based catalysts
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Iron- and manganese-promoted sulfated zirconia (SFMZ) has been tested as an n-butane isomerization catalyst in the temperature range of 35 to 180°C. The catalytic activity exhibits an induction period whose length is dependent on the reaction conditions. The presence of H2 in the feed stream strongly suppresses n-butane conversion over unpromoted sulfated zirconia (SZ) and over Pt-containing SFMZ (PtSFMZ). However, hydrogen had no effect on n-butane isomerization over SFMZ. These findings were interpreted on the basis of a bimolecular mechanism where unsaturated intermediates (carbenium ions and/or butene) are formed during the break-in period. The role of promoters (Fe and Mn) is not only facilitating the formation of hydrogen-deficient intermediates and their accumulation on the catalyst surface, but also enhancing their stability. The negative effect of hydrogen over PtSFMZ is attributed to the occurrence of atomic hydrogen via the dissociative adsorption of H2 on Pt.
- Sayari, Abdelhamid,Yang, Yong,Song, Xuemin
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- Synthesis and characterization of triflic acid-functionalized mesoporous Zr-TMS catalysts: Heterogenization of CF3SO3H over Zr-TMS and its catalytic activity
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Triflic acid-functionalized Zr-TMS (zirconium oxide with a mesostructured framework; TMS, transition metal oxide mesoporous molecular sieves) catalysts have been synthesized by functionalizing triflic acid onto the walls of Zr-TMS via post synthesis method. The synthesized materials were characterized by powder XRD, N2-sorption, FT-IR spectroscopy, elemental analysis, solid-state 13C CP and DD/MAS NMR spectroscopy, FT-Raman analysis, NH3-TPD, SEM, TEM, TG-DTA, and DTG techniques. All these results revealed that an ordered Zr-TMS material was synthesized and triflic acid was anchored on the walls of the Zr-TMS. Typical XRD patterns of the Zr-TMS and functionalized Zr-TMS (f-Zr-TMS) showed ordered structures. Synthesized materials showed type IV isotherms. The chemical shift observed (≈119 ppm) and 13C-19F coupling (JC-F≈310 Hz) by 13C DD/MAS NMR showed that the triflic acid was intact on the catalyst framework. According to Raman spectral analysis, triflate was adsorbed on the zirconia surface at all loadings as a tridentate ligand through three equivalent S-O bonds (local C3v symmetry). Ammonia TPD measurements revealed an increase in number of acid sites with an increase in loading of triflic acid. Functionalized amorphous ≡Zr-O-SO2-CF 3 catalysts were also synthesized by an in situ method and SO 42-/ZrO2 was obtained for comparison. The catalytic activity of the materials was tested in the acetalization of ethylacetoacetate and in the benzoylation of biphenyl in a batch reactor at 100 and 150°C, respectively. Recycling was performed in the acetalization of ethylacetoacetate using f-Zr-TMS-30 three times and no major deactivation of the catalyst was observed.
- Chidambaram,Curulla-Ferre,Singh,Anderson
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- Zirconia supported phosphotungstic acid as an efficient catalyst for resorcinol tert-butylation and n-heptane hydroisomerization
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The alkylation of resorcinol with tert-butanol was carried out using zirconia supported phosphotungstic acid (PTA) as catalyst in liquid phase conditions. Among the different PTA loaded catalysts, the 15% PTA/ZrO2 calcined at 750 °C was found t
- Devassy, Biju M.,Halligudi,Elangovan,Ernst,Hartmann,Lefebvre
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- Nanocrystalline yttria-stabilized zirconia fibers from plant fibers and their polymer composites
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Nanocrystalline zirconia-8-mol% yttria (yttria-stabilized zirconia (YSZ): ZrO2-8-m% Y2O3) fibers have been prepared from aqueous poly vinyl alcohol (PVA)-zirconium oxy nitrate solution and jute (plant fiber). Soluble Zr and Y ions in PVA solution formed a uniform coating on the surface of jute once it dried completely. Slow hydrolysis of zirconium ion with ammonium hydroxide deposited zirconium hydroxide on the jute surface. Decomposition of the dried zirconium hydroxide-coated jute at high temperature (1200°C/2 h) resulted in the formation of single-phase, nanocrystalline cubic-YSZ with the corresponding average X-ray crystallite size 30-35 nm. Heat-treated fibers have been characterized by X-ray diffraction and scanning electron microscopy. We also prepared polymer composites by incorporating chopped, ground YSZ fibers into epoxy matrix and investigated polymer/fiber interface by transmission electron microscopy analysis.
- Das, Rabindra N.,Nad, Sanjukta,Pramanik, Panchanan
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- Effect of ZnO additives and acid treatment on catalytic performance of Pt/WO3/ZrO2 for n-C7 hydroisomerization
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The effect of WO3 (5-50 wt%) and ZnO (0.7-22 wt%) on the catalytic properties of Pt/WO3/(ZnO)-ZrO2 for n-heptane (n-C7) hydroisomerization was investigated. The optimized WO3 and ZnO contents are 20 wt% and 3.4 wt%, respectively. The catalytic performance is achieved at 81% n-C7 conversion and 89% C7 isomer selectivity at 250 °C, which is reproducible and can be kept constant over 82 h under reaction conditions. Both WO3 and ZnO can stabilize the tetragonal phase of ZrO2. The Bronsted acid-to-Lewis acid ratio should be optimized to achieve high catalytic performance. The activity for Pt/WO3/ZrO2 using Zr(OH)4 as the catalyst support (n-C7 conversion, 88% at 250 °C) is much higher than that for Pt/WO3/ZrO2 with ZrO2 as the support (n-C7 conversion, 9% at 250 °C) with the same Pt and WO3 loadings. BET, SEM-EDX, and pyridine-FTIR analyses show that acid treatment can successfully enhance the surface area (from 73 to 91 m2/g), increase the number of Bronsted acid sites, and lower the surface Zn:Zr ratio (from 0.43 to 0.15) for ZnO-ZrO2 with 22 wt% ZnO. The yield of C7 isomers is increased from nil to 47% at 300 °C on Pt/WO3/ZnO-ZrO2 catalyst after acid treatment. It is suggested that n-heptane hydroisomerization activity is related to acidity, surface area, and crystalline phase of ZrO2.
- Liu, Yan,Guan, Yejun,Li, Can,Lian, Juan,Gan, Geok Joo,Lim, Eng Chew,Kooli, Fethi
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- Catalytic transfer hydrogenation of furfural to furfuryl alcohol using easy-to-separate core-shell magnetic zirconium hydroxide
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A hollow core-shell magnetic zirconium hydroxide catalyst was synthesized and employed for the catalytic transfer hydrogenation (CTH) ofnumerous biomass-derived platform molecules (furfural and other carbonyl compounds). 93.9% conversion of furfural and 97.3% selectivity of furfuryl alcohol was achieved under mild reaction conditions (160 °C, 4 h, 0.1 g catalyst) with 2-propanol as the H-donor. After 7 times of reaction cycles, the catalyst retained excellent conversion (91.1%) and selectivity (97.8%) and no structural damage was found. Furthermore, a scale-up experiment was carried out, and the results proved that the catalyst has a prospect for industrial applications in the CTH reaction.
- Hou, Pan,Ma, Mingwei,Zhang, Peng,Cao, Jingjie,Liu, Hui,Xu, Xingliang,Yue, Huijuan,Tian, Ge,Feng, Shouhua
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- Catalytic and surface properties of ZrO2 modified with sulfur compounds
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A series of ZrO2 catalysts modified with sulfur compounds were prepared by treating Zr(OH)4 with sulfate ion and by treating ZrO2 with H2S, CS2, and SO2 followed by oxidation. The redoxidized sulfur species on ZrO2 and the oxidation state of sulfur were investigated by infrared and X-ray photoelectron spectroscopies. It was found that the SO42- species in the highest oxidation state was responsible for enhancing the acidity and catalytic activity of the catalyst. There was a close relationship between the oxidation state of sulfur and the catalytic activity, when 1-butene isomerization was carried out as a test reaction. The surface properties of ZrO2/SO42-, such as specific surface area, phase transition temperture, crystalline structure, acidity and acid strength, were very different from those of ZrO2 not modified with sulfur compounds.
- Sohn, Jong Rack,Kim, Hae Won
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- Structural Properties and State of a Zirconium Dioxide Surface Layer Modified with Mе3+ Cations
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Abstract: The effect Ме3+ (Al, Y, Sc, Fe, and Mn) cations on the structural properties and state of a zirconium dioxide surface layer is investigated. The thermal stability of the Ме3+ solid solutions based on a metastable zirconium dioxide modification is established via X-ray diffraction analysis. It is shown using X?ray photoelectron spectroscopy that the distribution of surface–volume cationic modifier is determined by the type of cation. In Al-, Fe-, and Mn-ZrO2 systems, modifiers are mainly distributed over a surface; in Y and Sc-ZrО2, modifiers are distributed uniformly. The nature of the cation distribution affects the thermal stability of the solid solutions formed.
- Kuznetsova,Obukhova,Bondarenko,Fetisova, O. Yu.,Mikhlin, Yu. L.,Kirik,Kuznetsov
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- Preparation of a novel catalyst UDCaT-5: Enhancement in activity of acid-treated zirconia - Effect of treatment with chlorosulfonic acid vis-a-vis sulfuric acid
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UDCaT-5, a zirconia-based catalyst, with high sulfur content (9% w/w) but preservation of the tetragonal phase of zirconia was synthesized for the first time, by using chlorosulfonic acid as a new source for sulfate ions. UDCaT-5 was characterized by using elemental analysis, FTIR, ammonia-TPD, XRD, and BET surface area. Its catalytic activity and stability were evaluated and compared with S-ZrO2 in three different reactions. The characterization and reaction studies show that UDCaT-5 exhibits more superacidity vis-a-vis conventional sulfated zirconia prepared by using sulfuric acid.
- Yadav, Ganapati D.,Murkute, Ambareesh D.
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- Probing the low temperature initiation sites in Fe-, Mn-promoted sulfated zirconia via CO and H2 adsorption
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Exposing freshly activated Fe-, Mn-promoted sulfated zirconia to CO at ≤ 50°C induced permanent loss of activity, while adding CO after butane isomerization had a reversible effect, regardless of whether the butane flow was interrupted or not. Similar experiments using dissociated hydrogen instead of CO led to irreversible poisoning in all cases. These findings were analyzed, based on the occurrence of initiation sites that are consumed stoichiometrically and very rapidly on exposure to butane, such initiation sites which are also consumed by CO or dissociated hydrogen, CO which competes effectively for adsorption sites without affecting accumulated reaction intermediates, and such intermediates that are removed in the presence of dissociated hydrogen.
- Sayari, Abdelhamid,Yang, Yong
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- Isomerization of Caryophyllene Oxide Catalyzed by Solid Acids and Bases
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The reaction of caryophyllene oxide over eleven catalysts of solid acids and bases gave 4,5-dihydrocaryophyllen-5-one (III), (1R, 5S, 8R, 9R)-4,4,8-trimethyltricyclo1,5>dodeca-2-en-9-ol (IV), (2S, 5R, 9R)-caryophylla-1(12),8(15)-dien-9-ol (V), (2S, 5R, 9R)-caryophylla-1(12),7-dien-9-ol (VI), and (2S, 5R, 9S)-caryophylla-1(12)-7-dien-9-ol (VII).A large amount of III was formed together with IV over FeSO4 and Zr(SO4)2.Allylic alcohols (V, VI, and VII) were preferentially given by Al2O3-II and TiO2-ZrO2 in >74percent selectivity: 96percent on TiO2-ZrO2.Other catalysts formed three to five species of the products uniformly.
- Arata, Kazushi,Hayano, Kiyoharu,Shirahama, Haruhisa
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- Thiolation of dimethyl sulfide to methanethiol over WO3/ZrO 2 catalysts
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The thiolation of dimethyl sulfide with H2S over a variety of tungsten-zirconia (WO3/ZrO2) catalysts with different contents of WO3 was studied. The maximum yield of methanethiol was obtained at the reaction temperature of 633 K in the presence of 10 wt.%WO 3/ZrO2 catalyst. XRD, BET and TPD characterization results reveal that supporting WO3 species on ZrO2 gives rise to the improvement of both in structure stability and surface acidity. The MT yield increased first and then decreased with the increase of reaction temperature for all of the catalysts due to the decomposition of methanethiol and dimethyl sulfide. The optimum loading of WO3 was found to be 5-10 wt.% (with a surface density of 3.5-4.5 w-atom nm-2). Furthermore, the WO 3/ZrO2 catalyst exhibits high resistance to water.
- Chen, Shiping,Wang, Weiming,Zhang, Yuanhua,Wei, Yucai,Fang, Weiping,Yang, Yiquan
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- A discussion of a mechanism for isomerization of n-butane on sulfated zirconia
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The mechanism of n-butane isomerization, considering experimental and theoretical works, was studied. MM2 and density functional theory simple calculations were conducted to clarify the nature of the supported active species in sulfated zirconia. A penta-coordinated species, monomeric or even dimeric, would be responsible for forming the most active sites at reaction conditions of n-butane isomerization. No superacidity was present before contact with n-butane. The sites formed at reaction conditions allowed the n-butane dehdyrogenation and its isomerization. At low reaction temperatures, not more than 250°C, additon of hydrogen as carrier gas decreased the conversion comparing it with N2 as carrier gas. At higher temperatures, it increased the activity.
- Garcia,Volpe,Ferreira,Rueda
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- Transesterification of diethyl malonate with benzyl alcohol catalyzed by modified zirconia: Kinetic study
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Zirconia and its modified forms such as 10%Mo(VI)/ZrO2, 10%V(V)/ZrO2, 10%W(VI)/ZrO2 and SO4 2-/ZrO2 were prepared and characterized for their physico-chemical properties such as BET for surface area, NH3-TPD and n-butylamine back titration method for total surface acidity, PXRD technique for crystallinity and ICP-OES technique for elemental analysis. These materials were used as catalysts in liquid phase transesterification reaction of diethyl malonate (DEM) with benzyl alcohol (BA). Optimization of reaction conditions such as reaction time, reaction temperature, weight of the catalyst and molar ratio of reactants were carried out to obtain highest possible transester yield. Dibenzyl malonate (DBM) and benzyl ethyl malonate (BEM) were obtained as major products. Highest total transester yield of (88%) was obtained in the presence of 0.75 g of SZ catalyst at a molar ratio of DEM: BA = 1:3, reaction temperature of 393 K and reaction time 5 h. Kinetic studies were carried out to find out the rate of the reaction and energy of activation values for zirconia catalysts, in order to identify a facile catalyst system for this reaction. A possible reaction mechanism was proposed based on the kinetic data and it was observed that Eley-Rideal mechanism fits well for this reaction. Reactivation and reusability studies of the catalysts were also taken up.
- Thimmaraju,Mohamed Shamshuddin,Pratap,Venkatesh
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- Effects of dispersion states of Pb, Ti and Zr ions upon the formation of PbTiO3 and PbZrO3
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Kinetic studies on the formations of PbTiO3 and PbZrO3 were made using the mixtures of PbO/TiO2 and PbO/ZrO2 with different dispersion states of the constituents. Although the rates of both formations were accel
- Takahashi,Kakuta,Ueno
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- Blend formed by oxygen deficient MoO3-δ oxides as lithium-insertion compounds
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Oxygen deficient MoxOy 200 nm-thick particles were synthesized by a citrate sol-gel method using ammonium heptamolybdate tetrahydrate as a source of Mo and heat treated with a small fraction of zirconia under reducing atmosphere. The samples were investigated by X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscope (SEM) and Raman spectroscopy (RS). The structural analyses show that the composite is a blend formed by layered α-MoO3, orthorhombic oxygen deficient phases MoO3-δ with δ = 0.25 (γ-Mo4O11) and α-ZrMo2O8. The insertion of lithium into the lattice was performed by electrochemical method. Redox peaks were observed for the MoO3-δ composite attributed to distinct Li+ ion insertion/extraction reactions in the MoO3 and Mo4O11 hosts. The cyclic performance revealed improved reversibility, rate capability, and electrochemical stability of the ZrMo2O8-decorated composite with respect to the bare molybdenum oxides. At C/10 rate, the composite delivered a stable reversible capacity of 135 mAh g-1 after the 50th cycle. At a rate of 2C the reversible capacity is maintained at 118 mAh g-1, approximately twice the capacity observed for the MoO3 particles alone.
- Hashem,Abbas,Abdel-Ghany,Eid,Abdel-Khalek,Indris,Ehrenberg,Mauger,Julien
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- Silicotungstic acid supported zirconia: An effective catalyst for esterification reaction
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A series of solid acid catalysts were synthesized by incipient wetness impregnation method by varying the wt% of silicotungstic acid on hydrous zirconia (ZSTA). The prepared catalysts were characterized by PXRD, FTIR, UV-vis DRS, EPMA, BET surface area, acid sites, etc. FTIR and UV-vis DRS studies indicate that the material retain the Keggin-type structure of silicotungstic acid up to 500 °C. The suitability of the materials was studied for acid catalysed esterification reactions using formic, acetic, propionic, n-butyric acid and n-butyl alcohol (NBA), isobutyl alcohol (IBA) and sec-butyl alcohol (SBA). Material with 15 wt% STA on hydrous zirconia having high surface area and acid sites acts as better catalyst for esterification reactions. The esterification of acids with NBA was found to be higher than IBA and SBA. In all the cases, the selectivity for the corresponding esters is nearly100%. The straight-line plot of -ln(1 - conversion) versus reaction time for the reactions carried out at 98 °C supports that the esterification reaction obeys first order kinetics with respect to acid concentration. The reusability study justifies that the catalyst is stable and active.
- Parida,Mallick, Sujata
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- Properties of nanocrystalline ZrO2-Y2O 3-CeO2-CoO-Al2O3 powders
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We have studied the properties of nanocrystalline ZrO2-Y 2O3-CeO2-CoO-Al2O3 powders prepared via hydrothermal treatment of a mixture of coprecipitated hydroxides at 210°C. A number of general trends are identified in the variation of the properties of the synthesized powders during heat treatment at temperatures from 500 to 1200°C. Our results demonstrate that the addition of 0.3 mol % CoO to nanocrystalline ZrO2-based powders containing 1 to 5 mol % Al2O3 allows one to obtain composites with good sinterability at a reduced temperature (1200°C).
- Dudnik,Tsukrenko,Shevchenko,Ruban,Lopato
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- Hydrated surface structure and its impacts on the stabilization of t-ZrO2
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We first optimized the preparation conditions to 3.6-6.0 nm ZrO2 in a pure tetragonal structure (t-phase). All samples were characterized by X-ray diffraction, high-resolution transmission electron microscope, thermal analysis, Raman spectra, and infrared spectra. It is found that the surfaces of t-ZrO2 nanostructures were terminated by an amorphous hydration layer co-existing with small amounts of carbonate molecules. With the removal of hydrated surface layers under hydrothermal conditions at T>150 °C, t-ZrO2 nanostructures became thermodynamically unstable, which partially transformed into monoclinic ZrO2 (m-phase). Such a transformation occurs initially at surface regions and then develops into the bulk. High-temperature annealing in air could also remove the hydrated surface layers, which is however followed by a gradual transformation of t-ZrO2 into m-ZrO2 in both bulk and surface regions. These observations are explained in terms of the difference in surface free energies of m-ZrO2 and t-ZrO2 upon H2O adsorption.
- Wang, Hui,Li, Guangshe,Xue, Yanfeng,Li, Liping
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- Skeletal isomerization of n-pentane over Pt-promoted cesium hydrogen salts of 12-tungstophosphoric acid
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Two kinds of Pt-promoted Cs2.5H0.5PW12O40 (Cs2.5H0.5PW12O40 will be denoted by Cs2.5), Pt directly impregnated on Cs2.5 (Pt/Cs2.5) and a physical mixture of Cs2.5 and Pt/Al2O3 (Pt + Cs2.5), were used to catalyze the isomerization of n- pentane in the presence of hydrogen at 453-573 K. Cs2.5 showed a high initial activity but deactivated rapidly. Addition of Pt greatly suppressed the deactivation and increased the selectivity to isopentane. High stationary conversion (34.8%) and selectivity (96.9%) were obtained by using Pt + Cs2.5 at a relatively low temperature (453 K) and a low hydrogen pressure (0.05 atm, hydrogen/pentane = 1). Under these reaction conditions, the stationary activity and selectivity of Pt + Cs2.5 were significantly higher than those of Pt-promoted H-ZSM-5 or SO4/2-/ZrO2. It was deduced that the remarkable effect of Pt in suppressing the catalyst deactivation was brought about by activated hydrogen, which were formed on Pt, transferred to Cs2.5, and utilized to remove carbonaceous deposits or their precursors. Increase in the hydrogen pressure decreased the initial activity probably due to a decrease in the concentration of pentenes or pentyl carbenium ion.
- Liu, Yanyong,Na, Kyutae,Misono, Makoto
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- Synthesis of Solid Superacid of Tungsten Oxide supported on Zirconia and its Catalytic Action for Reactions of Butane and Pentane
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A solid superacid catalyst with an acid strength of H0 =/ -14.52 was obtained by impregnating Zr(OH)4 or amorphous ZrO2 with aqueous ammonium metatungstate followed by calcining in air at 800-850 deg C (13 wt.percent W); this catalyst was active for the isomerisations butane to isobutane at 50 deg C, and pentane to isopentane at 30 deg C.
- Hino, Makoto,Arata, Kazushi
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- Regioselective side-chain as well as nuclear monobromination of aromatic substrates with N-bromosuccinimide using phosphotungstic acid supported on zirconia as a heterogeneous catalyst
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Regioselective monobromination of aromatic substrates with N-bromosuccinimide has been achieved in excellent isolated yields (84-98%) using phosphotungstic acid supported on zirconia as a novel heterogeneous catalyst. The catalyst has been characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area and acidity measurements. Remarkably, the new catalyst system described brought about the side-chain bromination of aromatics to afford bromomethyl arenes in excellent yields (86-98%) without the need for a radical initiator. Recovery and recylability of the catalyst have been well established.
- Rajagopal,Siddiqui,Daniel, Thomas,Lahoti,Srinivasan
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- Estimation of oxyhydroxide specific surface area using the amounts of OH groups adsorbed
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A procedure for pH-metric determination of the limiting adsorption of OH groups (AOH) by FeIII, ZrIV, CrIII, and InIII oxyhydroxide hydrogels from 0.1 and 1.0 M solutions of NaCl is described. Data on the molecular area occupied by a single OH group on the hydrogel surface (SOH) and the Sspec values, which were calculated from AOH and SOH. are presented. The Sspec value does not depend on the pH of hydrogel precipitation: the true Sspec value can be determined only from sorption of the OH groups at the actual point of zero charge of the hydrogel. The AOH values for hydrogels were found to change only slightly during aging of hydrogels in electrolyte solutions.
- Pechenyuk,Matveenko,Semushin
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- Solubility of Zr(OH)4(am) and the Formation of Zr(IV) Carbonate Complexes in Carbonate Solutions Containing 0.1–5.0?mol·dm?3 NaNO3
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The solubility of amorphous zirconium hydroxide [Zr(OH)4(am)] was investigated in carbonate solutions containing various concentrations of sodium nitrate. The observed dependences of Zr(IV) solubility on the hydrogen ion concentration (pHc
- Kobayashi, Taishi,Sasaki, Takayuki
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- Methanol Synthesis from CO2 and H2 over CuO-ZnO Catalysts Combined with Metal Oxides under 13 atm Pressure
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The synthesis of methanol from CO2 and H2 in a flow reactor was studied over CuO-ZnO catalysts combined with ZrO2, MgO, Al2O3, or Cr2O3 under a pressure of 13 atm.CuO-ZnO-Al2O3, CuO-ZnO-ZrO2, and CuO-ZnO-MgO showed higher activity and higher selectivity for methanol than did CuO-ZnO.The selectivity for methanol formation became higher as the reaction temperature was lower, or any of the H2/CO2 ratio, the pressure and the space velocity were higher.On the basis of analyses by XRD, XPS and ultraviolet diffused reflectance spectroscopy, the active centers of CuO-ZnO-ZrO2 seem to be a Cu+-ZnO species stabilized by ZrO2.
- Xu, Zheng,Qian, Zaihu,Mao, Liqun,Tanabe, Kozo,Hattori, Hideshi
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- Zirconia-supported 12-tungstophosphoric acid as a solid catalyst for the synthesis of linear alkyl benzenes
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The liquid-phase alkylation of benzene with 1-octene and 1-dodecene was investigated with zirconia-supported 12-tungstophosphoric acid (TPA) as catalysts. We prepared the catalysts, with different TPA loading (5-20 wt% calcined at 750°C) and calcination temperatures (15 wt% calcined from 650 to 850°C), by suspending hydrous zirconia in a methanol solution of TPA, followed by drying and calcination. These catalysts were characterized by X-ray diffraction, DTG-DTA, FTIR pyridine adsorption, NH3-TPD, and 31P MAS NMR spectroscopy measurements. The catalyst with optimum TPA loading (15%) and calcination temperature (750°C) was prepared in different solvents and characterized by 31P MAS NMR spectroscopy. The XRD results indicate that TPA stabilizes the tetragonal phase of zirconia. The catalysts show both Bronsted and Lewis acidity, and 15% TPA on zirconia calcined at 750°C shows the highest acidity. 31P MAS NMR spectra show two types of phosphorous species: one is the Keggin unit and the other is the decomposition product of TPA. The relative amount of each depends on TPA loading, calcination temperature, and the solvent used for the catalyst preparation. Under reaction conditions of 84°C and a benzene/1-olefin molar ratio of 10 (time 1 h), the most active catalyst, 15% TPA, calcined at 750°C, gave more than 98% olefin conversion with selectivity for 2-phenyl octane (53.5%) and 2-phenyl dodecane (47%).
- Devassy, Biju M.,Lefebvre,Halligudi
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- Catalytic dehydration of fructose to 5-hydroxymethylfurfural over a mesoscopically assembled sulfated zirconia nanoparticle catalyst in organic solvent
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The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in DMSO was performed over a sequence of mesoscopically assembled sulfated zirconium nanostructures (MASZN) derived from zirconyl chloride with a template as a fastening agent. The materials were characterized by X-ray diffraction, FTIR spectroscopy, NH3 temperature-programmed desorption, pyridine FTIR spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and N2 sorption. The heterogeneous catalyst MASZN with Lewis-Bronsted acid sites had a superior performance in the dehydration of fructose to HMF. With MASZN-3 as catalyst, a HMF yield of 91.9% with a 98.5% fructose conversion was obtained at 110°C for 120 min in DMSO. Finally, the catalyst MASZN-3 was recycled in four consecutive cycles with scarcely any loss of activity. The excellent catalytic properties together with its easy synthesis, low cost, and nontoxic nature make this MASZN a promising catalyst for the development of new and efficient processes for biomass-based chemicals.
- Wang, Ningning,Yao, Yuan,Li, Wei,Yang, Yan,Song, Zhanxin,Liu, Wentao,Wang, Haijun,Xia, Xiao-Feng,Gao, Haiyan
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- Oxidative esterification of renewable furfural on gold-based catalysts: Which is the best support?
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Gold-based catalysts over different supports were investigated in the oxidative esterification of furfural by employing an efficient and sustainable process. The catalytic performances follow the trend: Zirconia-Au > Ceria-Au a‰
- Menegazzo, Federica,Signoretto, Michela,Pinna, Francesco,Manzoli, Maela,Aina, Valentina,Cerrato, Giuseppina,Boccuzzi, Flora
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- Fluorite-like hydrolyzed hexanuclear coordination clusters of Zr(IV) and Hf(IV) with syn-syn bridging N,N,N-trimethylglycine in soft crystal structures exhibiting cold-crystallization
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Tetravalent metal ions are hydrolyzed under presence of N,N,N-trimethylglycine hydrochloride (betaine hydrochloride, [Hbet]Cl) in aqueous solutions to afford [M6(μ3-O)4(μ3-OH)4(μ-bet)8(κ-bet)4(H2O)4]12+ (M4+ = Zr4+ (1), Hf4+ (2)) as hydrated perchlorate salts. These compounds were characterized by single crystal X-ray diffraction, elemental analysis and IR spectroscopy. As a result, we have found that fluorite-like [M6O8] coordination clusters are formed through octahedral arrangement of six M4+ linked by μ3-O atoms. Additionally, each pair of neighboring M4+ are connected by the μ-bet ligand through a syn-syn bridging coordination of its carboxylate moiety. This interaction seems to prevent further growth of the fluorite structure leading to formation of MO2. It was difficult to directly distinguish each μ3-O atom to be μ3-OH? or μ3-O2? due to its strongly anisotropic thermal displacement in the obtained structures. Bond valence sum analysis suggested that four μ3-OH? and four μ3-O2? are alternately arranged in the [M6O8] core motifs. Indeed, such a symmetric structure of [M6(μ3-O)4(μ3-OH)4] was confirmed in another phase of 1 at 296 K, where 1 transforms to a monoclinic structure (1′). The number of ClO4? counteranions found in the structure determination is not enough to compensate + 12 charge of [M6(μ3-O)4(μ3-OH)4(μ-bet)8(κ-bet)4(H2O)4]12+ in any unit cells of 1, 1′ and 2. Instead, large solvent/ion accessible voids have been actually observed in their crystal structures, indicating that the missing ClO4? are located therein and are significantly disordered to make them invisible in the crystallography. DSC analysis revealed that ClO4? and H2O/H3O+ in the crystal lattice of 1 undergo unique structure relaxation and rearrangements pronounced by cold-crystallization to induce the phase transition from 1 to 1′ with elevating temperature.
- Matsuoka, Moe,Takao, Koichiro,Tsushima, Satoru
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- Transfer hydrogenation of furfural to furfuryl alcohol over modified Zr-based catalysts using primary alcohols as H-donors
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Catalytic transfer hydrogenation is gaining increasing attention as a promising alternative to conventional hydrogenation with H2. In present work, a series of modified Zr-based catalysts were synthesized and tested for furfural catalytic transfer hydrogenation into furfuryl alcohol (FA). The results indicated that more than 13 % of furfural conversion and furfuryl alcohol yield could be achieved with modified zirconium hydroxide (mZrH) at 140 °C when compared with zirconium hydroxide (ZrH) using ethanol as H-donor and solvent in continuous flow regime, and the activity could be further enhanced by increasing the reaction temperature or Ru loading on the catalyst. The best result of 92 % furfural conversion with ~99 % FA selectivity was obtained at 150 °C with 6% Ru/mZrH as catalyst, and the productivity of FA is 5.5 mmol g?1 h?1 which is 2 times higher than that reported with ZrH in batch. Moreover, long-term stability study of the catalysts indicated that 6% Ru/mZrH not only performs a better activity, but also a better stability than 6% Ru/ZrH. Characterizations of the catalysts by BET, XRD, EA, IR, SEM-EDS, XPS and CO2 adsorption indicated that zirconium hydroxide (ZrH) was successfully modified with hydroxylamine, leading to significantly change of its morphology and basic sites. And the deactivation of the catalysts was due to both the leaching of Ru and the deposition of side-products on its surface.
- Wang, Yantao,Zhao, Deyang,Liang, Rui,Triantafyllidis, Konstantinos S.,Yang, Weiran,Len, Christophe
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- Tuning the Lewis acidity of ZrO2for efficient conversion of CH4and CO2into acetic acid
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The conversion of CH4 and CO2 into acetic acid is a dream reaction, but it remains a great challenge owing to the inertness of both CH4 and CO2. The formation of acetic acid requires efficient activation of CH4 and CO2. In this work, we demonstrated that enhanced acetic acid production from CH4 and CO2 is achieved via improving the Lewis acidity of ZrO2-containing catalysts. Definitely, the best catalyst (SZ-3) exhibits about 14 times higher activity for acetic acid formation than that of pure ZrO2, owing to its strongest Lewis acidity that facilitates the activation of both CH4 and CO2. The mechanism of acetic acid formation is revealed via DFT calculations. CH4 is activated at Lewis acid sites to form Zr-CH3 and O-H species, and subsequently, the O-H species could readily hydrogenate CO3 species formed from CO2 activation at Lewis acid sites to give HCO3, followed by facile coupling with Zr-CH3 yielding acetic acid with a lower energy barrier.
- Li, Yufeng,Liu, Bing,Liu, Jie,Wang, Ting,Shen, Yu,Zheng, Ke,Jiang, Feng,Xu, Yuebing,Liu, Xiaohao
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p. 8978 - 8985
(2021/06/02)
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- The selective reductive amination of aliphatic aldehydes and cycloaliphatic ketones with tetragonal zirconium dioxide as the heterogeneous catalyst
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A selective reductive amination of aliphatic aldehydes and cycloaliphatic ketones is achieved with tetragonal zirconium dioxide (t-ZrO2) as the catalyst. With N, N-dimethyl formamide (DMF) as the solvent, low-molecular-weight amine source and reductant, a more than 99 percent yield of N, N-dimethylpentan-1-amine or N, N-dimethyl cyclohexanamine was obtained when n-pentanal or cyclohexanone was used as the substrate. Particularly, the crystallographic structures exhibit a significant effect on catalytic performance where the tetragonal crystalline was preferable to monoclinic one during the reductive amination reaction. In addition, the recycling experiments of catalysts indicate that t-ZrO2 still kept a high catalytic activity even after being reused five times. From the result of DFT calculations, it is concluded that the crystalline of zirconium dioxide is closely related to the charge transferring rate between the catalyst and the adsorbed reactant. Finally, based on the experiment phenomena and simulation result, a possible reaction mechanism is proposed for the reductive amination of cyclohexanone.
- Bai, Peng,Li, Jiacong,Tong, Xinli,Wang, Shun,Zhang, Haigang,Zhang, Ming
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- Cu/Ni-doped sulfated zirconium oxide immobilized on CdFe2O4 NPs: a cheap, sustainable and magnetically recyclable inorgano-catalyst for the efficient preparation of α-aminonitriles in aqueous media
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Abstract: A new multifunctional bimetallic nanocatalyst was prepared by immobilization of Cu/Ni-doped sulfated zirconium oxide on magnetic cadmium ferrite (CdFe2O4@SiO2@ZrO2/SO42?/Cu/Ni) and used as an efficient recyclable catalyst for one-pot as well as stepwise preparation of α-aminonitriles under mild conditions. The magnetic nanocatalyst was characterized by FTIR, TGA, VSM, XRD, EDX, FE-SEM, and TEM analyses. Also, the surface acidity of the catalyst was measured by pyridine adsorption assay. The catalyst possesses various active sites which could catalyst a variety of aromatic and aliphatic aldehydes to the corresponding α-amionitriles under moderate to high yields in the presence of aniline. Furthermore, transformation of ketones to the desired α-amionitriles and some bis-aminonitriles was also performed by this method. The catalyst could be readily recovered from the reaction mixture and reused for several times without significant loss of activity. Graphic abstract: A general and efficient method has been developed for transformation of a variety of aliphatic, aromatic aldehydes and ketones to the corresponding α-aminonitriles using a multifunctional recyclable CdFe2O4@SiO2@ZrO2/SO42?/Cu/Ni nanocatalyst.[Figure not available: see fulltext.]
- Nasseri, Mohammad Ali,Ramezani-Moghadam, Simin,Kazemnejadi, Milad,Allahresani, Ali
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p. 4233 - 4256
(2020/07/08)
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- The CuFe2O4@SiO2@ZrO2/SO42-/Cu nanoparticles: An efficient magnetically recyclable multifunctional Lewis/Br?nsted acid nanocatalyst for the ligand- and Pd-free Sonogashira cross-coupling reaction in water
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Herein, the synthesis and application of copper-incorporated sulfated zirconium oxide supported on CuFe2O4 NPs (CuFe2O4@SiO2@ZrO2/SO42-/Cu NPs) as a novel Lewis/Br?nsted acid nanocatalyst were studied for the Sonogashira C-C cross-coupling reaction. The fabricated CuFe2O4@SiO2@ZrO2/SO42-/Cu catalyst exhibited efficient activity for a large variety of aryl iodides/bromides and, most importantly, aryl chlorides in water and in the presence of NaOH as a base in short reaction times. The catalyst was fully characterized by FTIR, TG-DTG, VSM, XRD, EDX, FE-SEM and TEM analyses. A synergetic effect could be considered to have arisen from the various Lewis acid and Br?nsted acid sites present in the catalyst. The efficient incorporation of copper into zirconia provided a robust highly stable hybrid, which prevented any metal leaching, whether from the magnetite moiety and/or Cu sites in the reaction mixture. Moreover, the catalyst was successfully recovered from the mixture by a simple external magnet and reused for at least 9 consecutive runs. Zero metal leaching, stability, consistency with a variety of substrates, fast performance, cost-effectiveness, environmental friendliness, and preparation with accessible and cheap materials are some of the advantages and highlights of the current protocol.
- Nasseri, Mohammad Ali,Alavi, Seyyedeh Ameneh,Kazemnejadi, Milad,Allahresani, Ali
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p. 20749 - 20759
(2019/07/12)
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- Thermochemical study of tetravalent metal sulfate tetrahydrates: A4+(SO4)2(H2O)4 (A4+?=?Zr, Ce, U)
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The syntheses, characterization, and calorimetric measurements of enthalpies of formation of four tetravalent metal sulfate tetrahydrates (A4+(SO4)2(H2O)4 (A4+ = Zr, Ce, U): α-Zr(SO4)2(H2O)4, α-Ce(SO4)2(H2O)4, β-Ce(SO4)2(H2O)4, and β-U(SO4)2(H2O)4)are reported. Direct calorimetric measurements showed that the formation enthalpies of these compounds from the corresponding oxides correlate with the eightfold coordination radius of the tetravalent cations. An energetic slope change is observed between the α- (Fddd)and β- (Pnma)forms and is consistent with previously reported studies.
- Zhang, Lei,Lobeck, Haylie L.,Dzik, Ewa A.,Sigmon, Ginger E.,Burns, Peter C.
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- Preparation and catalytic property of Pb-Zr mixed oxides for methyl phenyl carbonate disproportionation to synthesize diphenyl carbonate
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Pb-Zr mixed oxides with 15.2 wt% PbO loading were prepared by four different preparation processes, and their catalytic performances for the disproportionation of methyl phenyl carbonate (MPC) to synthesize diphenyl carbonate (DPC) were evaluated. Physicochemical characterizations including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), BET surface area measurement, H2-temperature programmed reduction (H2-TPR), ammonia temperature programmed desorption (NH3-TPD) and infrared spectroscopy of pyridine adsorption (Py-IR), as well as catalytic tests of MPC disproportionation reaction showed that catalyst preparation process exerted significant influence on the composition, structural property, catalytic performance of obtained catalysts, and the catalyst prepared by co-precipitation method (PbZr-CP) demonstrated better dispersion of active phase, larger specific surface area and more Lewis acid sites on the surface due to the strong interaction of Pb and Zr, and thus exhibited higher catalytic activity than those prepared by other processes.
- Wang, Songlin,Niu, Hongying,Wang, Jianji,Chen, Tong,Wang, Gongying
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- Esterification of Tertiary Amides by Alcohols Through C?N Bond Cleavage over CeO2
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CeO2 has been found to promote ester forming alcoholysis reactions of tertiary amides. The present catalytic system is operationally simple, recyclable, and it does not require additives. The esterification process displays a wide substrate scope (>45 examples; up to 93 % isolated yield). Results of a density functional theory (DFT) study combined with in situ FT-IR observations indicate that the process proceeds through rate limiting addition of a CeO2 lattice oxygen to the carbonyl group of the adsorbed acetamide species with energy barrier of 17.0 kcal/mol. This value matches well with experimental value (17.9 kcal/mol) obtained from analysis of the Arrhenius plot. Further studies by in situ FT-IR and temperature programmed desorption using probe molecules demonstrate that both acidic and basic properties are important, and consequently, CeO2 showed the best performance for the C?N bond cleavage reaction.
- Toyao, Takashi,Nurnobi Rashed, Md.,Morita, Yoshitsugu,Kamachi, Takashi,Hakim Siddiki,Ali, Md. A.,Touchy,Kon, Kenichi,Maeno, Zen,Yoshizawa, Kazunari,Shimizu, Ken-ichi
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p. 449 - 456
(2018/09/11)
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- Effect of zirconia polymorph on the synthesis of diphenyl carbonate over supported lead catalysts
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Zirconia supported Pb-based catalysts with purely tetragonal/monoclinic crystals were prepared and analyzed well by XRD, TEM-EDS, XPS, H2-TPR, BET, Py-IR and NH3-TPD techniques. The results indicate that zirconia polymorph has great effect on their structure and catalytic property for the synthesis of diphenyl carbonate (DPC) through methyl phenyl carbonate (MPC) disproportionation due to the differences of surface chemical properties, and tetragonal zirconia supported lead catalyst (TZ-Pb) shows bigger dispersion degree of PbO, higher surface area and Lewis acid amounts and thereby exhibits higher catalytic activity and selectivity compared to monoclinic zirconia supported catalyst (MZ-Pb). Furthermore, TZ-Pb shows better reusability due to strong metal-support interaction and may be readily recycled for at least four times without remarkable reactivity loss. This work provides a prospective reference for the facile and efficient synthesis of zirconia polymorph materials in various catalysis applications.
- Wang, Songlin,Niu, Hongying,Guo, Mengjun,Wang, Jianji,Chen, Tong,Wang, Gongying
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p. 117 - 124
(2019/03/05)
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- Catalytic synthesis of benzimidazole derivatives over modified forms of zirconia
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The solid acid catalysts, ZrO2, Mo(VI)/ZrO2 and Pt-SO42-/ZrO2 have been prepared and characterized for their surface area by BET, total surface acidity by NH3-TPD/ n-butyl amine back titration and crystallinity by powder XRD methods. These solid acid catalysts have been used in the synthesis of various benzimidazole derivatives. The results have been interpreted based on the variation of acidic properties and powder XRD phases of zirconia on incorporation of Mo(VI) or Pt-SO42– ions. Mo(VI)/ZrO2 is found to be an efficient solid acid catalyst for the synthesis of benzimidazoles with up to ~98% yield. These solid acids were found to be reusable up to at least 5 reaction cycles. Plausible mechanism for the formation of benzimidazoles over protonic acid sites of the solid acid catalysts is proposed.
- Kumar, T.E. Mohan,Shamshuddin, S.Z. Mohamed,Venkatesh,Saritha, S. Reena
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p. 1465 - 1470
(2017/08/04)
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- Iridium catalysts for C-C and C-O hydrogenolysis: Catalytic consequences of iridium sites
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The support effect on the properties of iridium catalysts for C-C and C-O hydrogenolysis was investigated. Cyclohexane conversion and glycerol hydrogenolysis were used to compare the behavior of iridium catalysts in terms of C-C and C-O cleavage. The nature of the support influenced the catalyst performance in both cyclohexane conversion and glycerol hydrogenolysis. This effect was more evident on the product selectivity. Ir/SiO2 catalyst presented the highest cyclohexane hydrogenolysis activity and the highest selectivity to minor hydrocarbons formed from hexane re-adsorption. For glycerol hydrogenolysis, all catalysts displayed a higher selectivity to products formed by C-O cleavage, mainly 1,2-propanediol (1,2-PDO). Ir/ZrO2 catalyst presented the highest activity in all reaction conditions and the lowest selectivity to minor alcohols produced by C-C cleavage like methanol, ethanol and ethylene glycol. The results were explained in terms of the requirements and the structure of the catalytic sites. Printed in Brazil -
- Pamphile-Adrián, Aracelis J.,Florez-Rodriguez, Pedro P.,Passos, Fabio B.
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p. 958 - 966
(2016/06/06)
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- Characterization of an alkaline earth metal-doped solid superacid and its activity for the esterification of oleic acid with methanol
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The leaching of grafted sulfate groups is one of the major issues for the solid acid catalysts with sulfate modification. A detailed study of sulfated alkaline earth metal-ferric composite oxides was carried out to suppress the leaching of sulfate groups as well as maintain high reactivity during the esterification of oleic acid. The acid properties and quantities of the active sites present on the catalysts were studied with pyridine-adsorption, FT-IR, TGA, and titration methods. The following order of acidic strength was observed: SO42-/Sr-Fe oxide > SO42-/Ca-Fe oxide > SO42-/Mg-Fe oxide. After sulfate modification, sulfate ions are linked to the composite oxides in a bridged bidentate form. SO42-/Sr-Fe oxide exhibits superacidic nature due to the high induction effect of the sulfated ion grafted on the Sr cation. TGA and FT-IR spectroscopic analyses provide new insights into the function of the iron cations implanted on the catalyst surface for enhancing the turnover frequency (TOF) of the active sites on SO42-/Sr-Fe oxide in the esterification. It was verified that the active energy of SO42-/Sr-Fe oxide for the esterification of oleic acid with methanol was as low as 28.53 ± 0.72 kJ mol-1. In the reusability study, SO42-/Sr-Fe oxide exhibited high reusability in the esterification, due to the high stability of the sulfate ion grafted on SO42-/Sr-Fe oxide.
- Huang, Chien-Chang,Yang, Chieh-Ju,Gao, Pei-Jyuan,Wang, Nai-Ci,Chen, Ching-Lung,Chang, Jo-Shu
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p. 3609 - 3620
(2015/06/25)
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- Sulfated zirconia as a novel and recyclable catalyst for removal of olefins from aromatics
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A novel sulfated zirconia (ZrO2/SO42 -) catalyst was prepared and the catalytic property of this catalyst was compared with active clay and zeolite (USY) in removing olefins from aromatics. Pyridine-FTIR indicated that the abundance of Lewis acid centers on sulfated zirconia is a vital factor for its excellent catalytic activity. N2 adsorption analysis shows that sulfated zirconia is a promising mesopore catalyst material. The superior catalytic performance as well as efficient reusability demonstrated that sulfated zirconia possesses bright application prospects in industry.
- Yao, Jiajia,Liu, Naiwang,Shi, Li,Wang, Xin
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p. 126 - 129
(2015/04/14)
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- Acceptorless dehydrogenative synthesis of benzothiazoles and benzimidazoles from alcohols or aldehydes by heterogeneous Pt catalysts under neutral conditions
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Abstract Pt/Al2O3 and Pt/TiO2 were effective catalysts for the synthesis of 2-substituted benzothiazoles and benzimidazoles from 2-aminothiophenol and 1,2-phenylenediamine with alcohols or aldehydes under acceptor-free and additive-free conditions.
- Chaudhari, Chandan,Siddiki, S.M.A. Hakim,Shimizu, Ken-Ichi
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p. 4885 - 4888
(2015/07/28)
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- Bimetallic Ni-Cu Catalysts for the Low-Temperature Ethanol Steam Reforming: Importance of Metal-Support Interactions
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The activity of bimetallic Ni-Cu catalysts in ethanol steam reforming was evaluated and compared to the activity of the corresponding monometallic Ni catalyst. Copper addition positively affected the catalytic activity only if the proper metal-support int
- Nichele, Valentina,Signoretto, Michela,Pinna, Francesco,Ghedini, Elena,Compagnoni, Matteo,Rossetti, Ilenia,Cruciani, Giuseppe,Di Michele, Alessandro
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p. 549 - 558
(2015/08/04)
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- One-step synthesis of nitriles by the dehydrogenation-amination of fatty primary alcohols over Cu/m-ZrO2
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An effective method for one-step synthesis of nitriles employing C2-C8 fatty primary alcohols and ammonia over 5%Cu/m-ZrO2 has been found. The conversion of alcohols and selectivity of nitriles obtained are > 96 and > 87 wt.%, respectively, and are obviously influenced by the C2-substitution rather than the chain length of fatty primary alcohols. Cu/m-ZrO2 was characterized by XRD, H2-TPR, CO2-TPD and NH3-TPD. It is revealed that a substantial amount of Cu species over m-ZrO2 is in highly dispersed CuO. A plausible mechanism is proposed and supported by different experiments, and aldehyde generation is an important step in the reaction mechanism.
- Hu, Yunfeng,Jin, Shuhan,Zhang, Zhichao,Zhang, Likun,Deng, Jun,Zhang, Hongsheng
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- Characterization and reactivity of 11-molybdo-1-vanadophosphoric acid catalyst supported on zirconia for dehydration of glycerol to acrolein
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A series of vanadium-substituted phosphomolybdic acid (HPA) catalysts supported on zirconia were prepared by impregnation method with varying the HPA active phase content from 10 to 50 wt% on the support. The calcined catalysts were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed desorption of NH3, FT-IR spectra of pyridine adsorption and surface area measurements. XRD results suggest that the active phase of heteropolyacid is present in a highly dispersed state at lower loadings and as a crystalline phase at higher HPA loadings and these findings are well-supported by the results of FT-IR and Raman spectra. Calcination of the samples did not affect the Keggin ion structure of HPA. The ammonia TPD results suggest that acidity of the catalysts was found to increase with increase of HPA loading up to 40 wt% and decreases at higher loadings. FT-IR spectra of pyridine adsorption show that the Bronsted acidic sites increase with increase of HPA loadings up to 40 wt% catalyst. However, Lewis acid sites decrease with increase of HPA loading. Catalytic properties were evaluated during vapour phase dehydration of glycerol to acrolein. The catalyst with 40 wt% HPA has exhibited excellent selectivity towards acrolein formation with complete conversion of glycerol at 225°C under atmospheric pressure. Catalytic performances during dehydration of glycerol are well-correlated with acidity of the catalysts.
- Viswanadham, Balaga,Srikanth, Amirineni,Chary, Komandur V. R.
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p. 445 - 454
(2014/06/09)
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- Zirconium phosphate combined with Ru/C as a highly efficient catalyst for the direct transformation of cellulose to C6 alditols
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The selective transformation of cellulose to C6 alditols provides a feasible route towards the sustainable synthesis of chemicals and fuels. Herein, the catalytic performance of amorphous zirconium phosphate (ZPA) combined with 5 wt% Ru/C was evaluated in the direct conversion of cellulose to C6 alditols (sorbitol and mannitol) under hydrothermal conditions. The yield of C6 alditols reached 63.5% and 85.5% with microcrystalline cellulose and ball-milled cellulose as the feedstock, respectively. This hybrid catalyst was developed to convert concentrated cellulose to obtain C6 alditols with a high concentration of 68.8 mg mL-1 in the final products. The high yield of C6 alditols from cellulose was ascribed to the fact that ZPA favoured the adsorption of cellulose and promoted its depolymerization to cellobiose and glucose, which was hydrogenated immediately to C6 alditols over Ru/C. The weak adsorption of C6 alditols over ZPA inhibited the dehydration of C6 alditols to sorbitan. Furthermore, ZPA exhibited excellent hydrothermal stability and could be reused for several runs. This journal is the Partner Organisations 2014.
- Liao, Yuhe,Liu, Qiying,Wang, Tiejun,Long, Jinxing,Ma, Longlong,Zhang, Qi
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p. 3305 - 3312
(2014/06/10)
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- Greener iodination of arenes using sulphated ceria-zirconia catalysts in polyethylene glycol
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An environmentally benign method for the selective monoiodination of diverse aromatic compounds has been developed using reusable sulphated ceria-zirconia under mild conditions. The protocol provides moderate to good yields and selectively introduces iodine at the para/ortho position in monosubstituted arenes. SO42-/Ce0.07Zr 0.93O2 was found to be the best choice for the synthesis of aryl iodides in high yield, presumably due to the maximum number of acid sites (4.23 mmol g-1) among the various compositions of the catalyst system.
- Kahandal, Sandeep S.,Kale, Sandip R.,Gawande, Manoj B.,Zboril, Radek,Varma, Rajender S.,Jayaram, Radha V.
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p. 6267 - 6274
(2014/01/23)
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- PROCESS FOR TRANSFORMATION OF LIGNOCELLULOSIC BIOMASS OR CELLULOSE BY TUNGSTEN-OXIDE-BASED SOLID LEWIS ACID CATALYSTS AND A METAL THAT IS SELECTED FROM GROUPS 8 TO 11
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The invention relates to a process for transformation of lignoceliulosic biomass or cellulose that uses tungsten-oxide-based heterogeneous catalysts that are dispersed on an oxide-based substrate, preferably with a base of oxide(s) of aluminum and/or zirconium and/or titanium and/or niobium and containing an element in the particular metallic state. The use of these catalysts makes it possible to obtain directly upgradable products containing three carbon atoms, in particular hydroxyacetone and propylene glycol with high selectivity.
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Paragraph 0088
(2013/07/25)
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- Heterogeneous cobalt catalysts for the acceptorless dehydrogenation of alcohols
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A series of transition metal(M)-loaded TiO2 catalysts (M/TiO2) and Co-loaded catalysts on various support materials were prepared by an impregnation method, followed by in situ H2-reduction at 400 °C, and tested for the acceptor-free oxidation of cyclododecanol in the liquid phase. Among the catalysts including noble metal catalysts, Co/TiO2 showed the highest activity. In the presence of Co/TiO 2 (0.1-3 mol%) the dehydrogenation of various aliphatic secondary alcohols proceeded to afford the corresponding ketones. The catalyst was recoverable and was reused after the H2-reduction treatment. Based on the spectroscopic characterization of the catalyst combined with the studies on the effect of the Co oxidation states on the catalytic activity, it is clarified that the surface metallic Co sites with electron deficiency are the catalytically active species.
- Shimizu, Ken-Ichi,Kon, Kenichi,Seto, Mayumi,Shimura, Katsuya,Yamazaki, Hiroshi,Kondo, Junko N.
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p. 418 - 424
(2013/03/29)
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- PROCESS FOR TRANSFORMATION OF LIGNOCELLULOSIC BIOMASS OR CELLULOSE BY TUNGSTEN-BASED SOLID LEWIS ACIDS
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The invention relates to a process for transformation of lignocellulosic biomass or cellulose that uses tungsten-based heterogeneous catalysts that are dispersed on an oxide-based substrate, preferably with a base of oxide(s) of aluminum and/or zirconium and/or titanium and/or niobium. The use of these catalysts makes it possible to obtain directly lactic acid with high selectivity while limiting the production of oligosaccharides and soluble polymers.
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Paragraph 0061; 0062; 0063
(2013/03/26)
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- Multiphase reaction kinetics of epoxidation of polyisobutene
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The kinetics of epoxidation of polyisobutene by peracetic acid generated in situ from hydrogen peroxide and acetic acid in the presence of solid acid WO3/ZrO2 were studied. The effect of several reaction parameters such as stirring speed, acetic acid-to- double bond molar ratio, temperature and content of catalyst were examined. Dynamic parameters were estimated using nonlinear regression method from the experimental data. A multiphase kinetic model of the epoxidation reaction was developed. There was good agreement between experimental and predicted data and simulation was performed to validate the model.
- Li, Mei,Xiao, Guomin,Chen, Zhiming
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p. 8493 - 8497
(2013/11/06)
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- Zr-La doped sulfated titania with a by far better catalytic activity and stability than pure sulfated titania in the esterification of acetic acid and n-butanol
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A novel solid superacid catalyst TiO2-Zr-La/SO4 2- was prepared by doping Zr and La to the bulk of TiO2. The modified TiO2-Zr-La/SO4 2- and the unmodified TiO2/SO4 2- were used to catalyze the esterification of acetic acid and n-butanol, in which these two catalysts were systematically compared in a lost of aspects such as catalytic activity and stability and so on. When a small amount of Zr and La were co-doped into the bulk of TiO2, the modified catalyst obtained a by far better catalytic activity and stability than the unmodified, showing that the modified is more resistive to deactivation than the unmodified. Under the set reaction conditions, the average conversion (of acetic acid) and the 20th-cycle conversion (of acetic acid) are 88.83 and 77.35 % for the modified, 80.83 and 46.15 % for the unmodified, respectively. The two catalysts were characterized by means of FTIR, XRD, BET, SEM, TG, and NH3-TPD methods to find the possible reasons for the superiority of the modified catalyst to the unmodified one. The characteristic results indicated that the incorporation of a small amount of Zr and La into the catalyst was beneficial to the modified catalyst: (1) improving its water-tolerance; (2) increasing its surface sulfate group content; (3) decreasing its crystallinity after calcination by retarding its crystallization from amorphous TiO2 to anatase TiO2; (4) increasing its specific surface area; (5) increasing its acidity including the concentration and acid strength of the surface acidic sites of it. All the above advantageous effects arisen from the two-element-doping are to be responsible for the substantially-improved catalytic performances of the modified catalyst.
- Shi, Wenping
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p. 732 - 738
(2013/07/26)
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- Reaction of iodine with metal oxides
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The reaction of iodine with various metal oxides has been studied in both vapour phase (373-873 K) and in solution in cyclohexane, under anhydrous conditions. The course of the reaction has been revised in accordance with literature and experimental data. Apart from adsorbed iodine molecules ([I 2] -1), the presence of I - ions ([I-] -1) has been noted. IOn- ions have been observed only when both water and strong basic sites, such as those on MgO or La2O 3, are present. It has been found that the strength of interaction of iodine with metal oxide increases with basicity of the oxide.
- Glinski, Marek,Ulkowska, Urszula
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p. 1370 - 1374
(2011/12/13)
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- ISOMERIZATION OF WET HEXANES
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A method to isomerize one or more wet hexanes in the presence of a catalyst comprising tungsten, zirconium and a Group VIII metal is provided.
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Page/Page column 2
(2010/08/22)
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- Nano- and microagglomeration processes in the thermolysis of titanium and zirconium oxyhydrates
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Titanium and zirconium oxyhydrates have been prepared using various additives and synthesis procedures, and the heating kinetics of polyacids and the mechanism of nanoparticle agglomeration during the thermolysis process have been studied. The resultant m
- Shveikin,Nikolaenko
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p. 510 - 516
(2010/09/17)
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- CO-free hydrogen production via dehydrogenation of a Jet A hydrocarbon mixture
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The dehydrogenation of a Jet A hydrocarbon mixture was investigated for the production of hydrogen for fuel cell applications. This process differs from steam/partial oxidation reforming of hydrocarbons in that the hydrogen produced is free of CO, and therefore can be used in low temperature fuel cells without further purification. Because of their relative importance with respect to the spectrum of hydrocarbons in the mixture, cyclohexane and decalin were investigated independently. A hybrid catalyst, Pt/γ-Al2O3-ZrO2/SO2-4, was designed to enhance the hydrogen production yields.
- Wang, Bo,Froment, Gilbert F.,Goodman, D. Wayne
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p. 239 - 243
(2008/09/16)
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- Method for conversion of beta-hydroxy carbonyl compounds
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A process is disclosed for conversion of salts of β-hydroxy carbonyl compounds forming useful conversion products including, e.g., α,β-unsaturated carbonyl compounds and/or salts of α,β-unsaturated carbonyl compounds. Conversion products find use, e.g., as feedstock and/or end-use chemicals.
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Page/Page column 10
(2008/06/13)
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- METHOD FOR PRODUCING OLEFINS
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A process of producing olefins by a metathesis reaction in a practical low temperature range by improving the reactivity of the catalyst is provided. The process of producing olefins according to the present invention allows a metathesis reaction of olefins, which uses a catalyst containing metal elements such as tungsten, molybdenum, rhenium or the like, to proceed at an industrially sufficient reaction rate in a practical low temperature range, by using a compound containing at least one metal element selected from the metals of Group Ia (alkali metals), Group IIa (alkaline earth metals), Group IIb and Group IIIa as co-catalyst and allowing hydrogen gas to co-exist with the reaction raw material.
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Page/Page column 11
(2008/06/13)
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