13987-01-4Relevant articles and documents
Definitive Proof for the Operation of Isotopically Sensitive Branching ('Metabolic Switching') in FeI-Mediated C-H Bond Activation in the Gas Phase
Seemeyer, Katrin,Pruesse, Tilmann,Schwarz, Helmut
, p. 1632 - 1635 (1993)
Rigorous regio- and stereospecific labeling experiments are performed to demonstrate the operation of the previously suggested operation of 'isotopically sensitive branching' in FeI-mediated C-H bond activation.For the hexane-1,6-diol/Fe(1+)-complex, it is shown that dehydrogenation involves specifically the central C(3)/C(4) position, and the study of the stereospecifically labeled D,L- and meso--isotopomers 1e and 1f demonstrates that dehydrogenation proceeds via two competing pathways (i.e. 'anti'-vs. 'syn'-route).The contribution of these routes to the product formation is-due to a kinetic isotope effect-controlled by the relative configuration at the labeled positions C(3)/C(4).For the D,L-form 1e, we estimate a ratio of 49:1 in favor of the 'anti'-route; due to an isotope effect, this ratio drops to 4.3:1 for the meso-form 1f.
Highly stable boron-modified hierarchical nanocrystalline ZSM-5 zeolite for the methanol to propylene reaction
Hu, Zhijie,Zhang, Hongbin,Wang, Lei,Zhang, Hongxia,Zhang, Yahong,Xu, Hualong,Shen, Wei,Tang, Yi
, p. 2891 - 2895 (2014)
A highly stable MTP (methanol to propylene) catalyst, boron-modified hierarchical nanocrystalline ZSM-5 zeolite, has been constructed by a facile salt-aided seed-induced route. The cooperative effect of its hierarchical structure and modified acidity gives rise to a significantly stable activity (725 h) even at a high WHSV (weight hourly space velocity) of 4.0 h -1. the Partner Organisations 2014.
Omium Ylide Chemistry. 1. Bifunctional Acid-Base-Catalyzed Conversion of Heterosubstituted Methanes into Ethylene and Derived Hydrocarbons. The Onium Ylide Mechanism of the C1 -> C2 Conversion
Olah, George A.,Doggweiler, Hans,Felberg, Jeff D.,Frohlich, Stephan,Grdina, Mary Jo,et al.
, p. 2143 - 2149 (1984)
The conversion of heterosubstituted methanes, such as methyl alcohol, dimethyl ether, methyl mercaptan, dimethyl sulfide, methylamines, and methyl halides, to ethylene and hydrocarbons derived thereof takes place over bifunctional acidic-basic-supported transition-metal oxide or oxyhalide catalysts, such as tungsten oxide supported on alumina, between 300 and 350 deg C.The conversion of methyl alcohol starts with bimolecular dehydration to dimethyl ether followed by acid-catalyzed transmethylation giving trimethyloxonium ion (or related catalyst-bound methyloxonium ion).The trimethyloxonium ion then undergoes base-induced deprotonation forming a catalyst surface-bound methylenedimethyloxonium ylide.Intermolecular methylation of the ylide, indicated by experiments using singly 13C-labeled dimethyl ether, gives methylethyloxonium ion thus providing the crucial first C-C bond.No intramolecular Steven's-type rearrangement takes place, and methyl ethyl ether is not a significant intermediate as also shown in experiments comparing the products formed from reacting CD3OCH2CH3 under similar conditions.The ethyloxonium ion readily undergoes β-elimination forming ethylene.Initially formed ethylene subsequently can undergo further reaction with the ylide giving via cyclopropane propylene or it can undergo more complex alkylation/oligomerization/cracking reactions giving a mixture of alkenes, alkanes and via cyclization-dehydrogenation aromatics.The complexity of these processes was shown by reacting ethylene itself, as well as 13CH3OH and ethylene, under conditions of the condensation reaction.It is also necessary to differentiate initally formed ethylene via direct C1 -> C2 conversion from that formed in secondary processes together with higher condensation products.The conversion of methyl mercaptan (dimethyl sulfide), methyl halides, and methylamines to ethylene follows similar onium ylide pathways.
Mesoporogen-Free Synthesis of Hierarchical SAPO-34 with Low Template Consumption and Excellent Methanol-to-Olefin Conversion
Sun, Qiming,Wang, Ning,Bai, Risheng,Chen, Guangrui,Shi, Zhiqiang,Zou, Yongcun,Yu, Jihong
, p. 3812 - 3820 (2018)
Significant interest has emerged in the development of nanometer-sized and hierarchical silicoaluminophosphate zeolites (SAPO-34) because of their enhanced accessibility and improved catalytic activity for methanol-to-olefin (MTO) conversion. A series of nanometer-sized SAPO-34 catalysts with tunable hierarchical structures was synthesized in a Al2O3/H3PO4/SiO2/triethylamine(TEA)/H2O system by using a mesoporogen-free nanoseed-assisted method. The nanometer-sized hierarchical SH-3.0 catalyst (TEA/Al2O3=3.0) possessed the highest crystallinity, highest abundance of intracrystalline meso-/macropores, and the most suitable acidity among all obtained catalysts, showing the highest ethylene and propylene selectivity of 85.4 %. This is the highest reported selectivity for MTO reactions under similar conditions. Detailed analysis of the coke produced during the reaction revealed that the small-sized methyl-substituted benzene and bulky methyl-substituted pyrene were mainly located inside the crystals instead of on the surface of the crystals, which provided further insight into understanding the deactivation of the SAPO-34 catalyst during MTO reaction. Significantly, the simple and cost-effective synthetic process and superb catalytic performance of the nanometer-sized hierarchical SAPO-34 is promising for their practical large-scale application for MTO conversion.
Enhanced (photo)catalytic activity of Wells-Dawson (H6P2W18O62) in comparison to Keggin (H3PW12O40) heteropolyacids for 2-propanol dehydration in gas-solid regime
Marcì, Giuseppe,García-López, Elisa I.,Pomilla, Francesca Rita,Liotta, Leonarda F.,Palmisano, Leonardo
, p. 113 - 122 (2016)
Catalytic and photocatalytic 2-propanol dehydration to propene at atmospheric pressure and a temperature range of 60–120?°C were carried out in gas-solid regime by using bare and supported Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O62 (P2W18) heteropolyacids (HPAs). Binary materials were prepared by impregnation of the HPAs on commercial SiO2 and TiO2. The Wells-Dawson was in any case more active than the Keggin heteropolyacid and the differences were enhanced when the supported samples were used. In particular, Wells-Dawson HPA supported on TiO2 and under irradiation showed the highest activity. The HPA species played the key role both in the catalytic and photo-assisted reactions. The acidity of the cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction. The estimated apparent activation energy resulted always lower for the photocatalytic process than for the catalytic one.
Synthesis of SAPO-34 Zeolite from Laponite and Its Application in the MTO Reaction
Chen, Xueshuai,Jiang, Rongli,Wang, Xingwen,Zhou, Zihan
, (2020)
In this work, SAPO-34 zeolite with high catalytic activity was successfully synthesized by hydrothermal method from laponite as the single Si source. Compared with the traditional method of synthesizing zeolites from clay, the laponite after swelling can be directly used in the synthesis process of zeolite. The crystallization behavior of SAPO-34 synthesized from laponite was investigated by XRD, FTIR, N2 adsorption–desorption, SEM-EDX, ICP-MS, and DR-UV/Vis. The process can be summarized as follows: the Si and Mg elements were produced by the depolymerization of laponite, then the primary building units of SAPO-34 zeolite were formed under hydrothermal conditions; finally, the crystal nucleus began to form, and crystallization was triggered. Compared with the conventional SAPO-34 synthesized from TEOS, the SAPO-34 synthesized from laponite exhibited higher selectivity to light olefins and longer lifetime, which can be attributed to the suitable strength of acidity. This work points to a straightforward route to the synthesis of SAPO-34 from laponite.
Characteristics of Iron Phosphate as a Catalyst for Partial Oxidation
Ai, Mamoru,Muneyama, Etsuhiro,Kunishige, Atsuhiro,Ohdan, Kyoji
, p. 551 - 556 (1994)
The catalytic performances of iron phosphate were compared with those obtained from the phosphates of vanadium and molybdenum in the partial oxidation of various compounds, such as 1-butene, crotonaldehyde, methacrylaldehyde, propinaldehyde, butyraldehyde, isobutyraldehyde, propionic acid, butyric acid, and isobutyric acid.Iron phosphate showed excellent performance for only the oxidative dehydrogenation of isobutyraldehyde and isobutyric acid to form methacrylaldehyde and methacrylic acid, respectively.
Controlling Reaction Selectivity through the Surface Termination of Perovskite Catalysts
Polo-Garzon, Felipe,Yang, Shi-Ze,Fung, Victor,Foo, Guo Shiou,Bickel, Elizabeth E.,Chisholm, Matthew F.,Jiang, De-En,Wu, Zili
, p. 9820 - 9824 (2017)
Although perovskites have been widely used in catalysis, tuning of their surface termination to control reaction selectivity has not been well established. In this study, we employed multiple surface-sensitive techniques to characterize the surface termination (one aspect of surface reconstruction) of SrTiO3 (STO) after thermal pretreatment (Sr enrichment) and chemical etching (Ti enrichment). We show, by using the conversion of 2-propanol as a probe reaction, that the surface termination of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivity over a wide range, which is not possible with single-metal oxides, either SrO or TiO2. Density functional theory (DFT) calculations explain well the selectivity tuning and reaction mechanism on STO with different surface termination. Similar catalytic tunability was also observed on BaZrO3, thus highlighting the generality of the findings of this study.
Influence of rhenium additives on the activity of Cu/sibunite catalyst in transformations of isopropyl alcohol
Ryashentseva
, p. 1768 - 1770 (2002)
The dehydrogenating and dehydrating properties of the Cu(2%)/sibunite catalyst with rhenium additives were studied in the transformations of isopropyl alcohol at 200-270°C. The catalyst containing 0.25% Re was found to possess the maximum dehydrogenating activity at 200°C.
Embryonic zeolite-assisted synthesis of SSZ-13 with superior efficiency and their excellent catalytic performance
Cui, Wenhao,Fan, Dong,Han, Jingfeng,Li, Bing,Liu, Zhongmin,Tian, Peng,Wang, Juan,Wang, Linying,Zhu, Dali
, p. 15238 - 15245 (2021)
An X-ray amorphous material with a CHA-like structure, named embryonic CHA zeolite, has been designed and employed for the synthesis of SSZ-13, which leads to ultra-fast crystallization (1.5-12 h), wide product SiO2/Al2O3ratio (SAR = 22-100) and high yield (82.8-92.9%). The usage ofN,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) for the synthesis can be controlled at unprecedentedly low amounts (TMAdaOH/SiO2= 0.035-0.050). Characterization results reveal that the embryonic zeolite has a small particle size of 10-20 nm, large micro/mesopore volume and abundant double 6-ring units (subunits of the CHA structure). It provides ample active surface and subunits for the formation of the CHA structure and promotes the fast synthesis of SSZ-13 with a wide phase region. The resultant material (SAR = 23.2), after Cu2+exchange, exhibits superior NH3-SCR activity and extraordinary hydrothermal stability (steaming at 800 °C for 16 h), implying its promising application for NOxremoval. In addition, high-silica SSZ-13 shows good catalytic performance for the MTO reaction. It is anticipated that the embryonic zeolite-assisted strategy will benefit the synthesis of more industrially important zeolites.
Olefin Synthesis from Dimethyl Ether in the Presence of a Hydrothermally Treated Mg–HZSM-5/Al2O3 Catalyst: Effect of Reaction Conditions on the Product Composition and Ratio
Magomedova,Peresypkina,Davydov,Khadzhiev
, p. 1043 - 1051 (2017)
Systematic studies of olefin synthesis from dimethyl ether (DME) in the presence of a hydrothermally treated HZSM-5 zeolite catalyst modified with magnesium have been conducted. Dependences of DME conversion, product yield and selectivity, and lower olefin ratio on space time in the temperature range of 320–360°C have been analyzed. The type of the resulting products has been determined, and assumptions about the reaction chemistry have been made to reveal the role of methylation and hydrogen-transfer reactions in the products formation.
Reaction of Hydrogen Atoms with Cyclopropane in the Temperature Range from 628 to 779 K
Marshall, Roger M.,Purnell, Howard,Satchell, Paul W.
, p. 2395 - 2404 (1984)
The reaction between cyclopropane and hydrogen atoms has been investigated in the temperature range from 628 to 779 K at a total argon pressure between 5.3 and 13.2 Torr using a discharge-flow system with gas-chromatographic product analysis.The measured products, methane, ethane, ethene, propane and propene, are shown to be consistent with a mechamism .Measurement of kw permits evaluation of the rate constant for the abstraction process log(k1/cm3 mol-1s-1) = (13.6+/-1.0)-(48.5 +/-13.0 kJ mol-1/2.3RT) which is similar to that for the corresponding reaction of methane on account of the almost identical C-H bond strengths in the molecules.A composite function of the rate constants for addition to the two positions in propene is evaluated.It is shown that the flow rate of hydrogen atoms as measured by our previously described ethene titration technique gives values which are consistently only 80 percent of those evaluated by summation of the products of reaction cyclopropane.
Transformation of methane to propylene: A two-step reaction route catalyzed by modified CeO2 nanocrystals and zeolites
He, Jieli,Xu, Ting,Wang, Zhihui,Zhang, Qinghong,Deng, Weiping,Wang, Ye
, p. 2438 - 2442 (2012)
Propylene from methane: The transformation of methane to propylene has been realized in a two-step route via CH3Cl or CH3Br. CeO 2 serves as an efficient and stable catalyst for the oxidative chlorination and bromination of methane to CH3Cl and CH 3Br. In the second step, a modified zeolite is highly a selective and stable catalyst for the conversion of CH3Cl or CH3Br into propylene. Copyright
A route to form initial hydrocarbon pool species in methanol conversion to olefins over zeolites
Li, Junfen,Wei, Zhihong,Chen, Yanyan,Jing, Buqin,He, Yue,Dong, Mei,Jiao, Haijun,Li, Xuekuan,Qin, Zhangfeng,Wang, Jianguo,Fan, Weibin
, p. 277 - 283 (2014)
The formation mechanism of the original C-C bond in methanol conversion to hydrocarbons over zeolite catalysts remains a grand challenge, although many researchers have done a lot of work and made significant progress. Here, a convincing route for formation of initial hydrocarbon pool (HCP) species involving original C-C bonds from dimethyl ether (DME) and/or methanol is illustrated by combining coincident experimental and theoretically calculated results. Elaborate experimental results gave strong evidence for predominant direct mechanism in the initial methanol-to-olefins process catalyzed by SAPO-34. A critical intermediate of the methoxymethyl cation was detected and theoretically verified through the reaction of the methoxy group and DME. This intermediate species subsequently reacted with DME or methanol to produce C-C bond-containing compounds 1,2-dimethoxyethane or 2-methoxyethanol. Further formation of oxonium cations led to generation of ethers or alcohols, and further to propene as the primary alkene product that induced the occurrence of the HCP mechanism.2014 Elsevier Inc. All rights reserved.
Epitaxial and Strong Support Interactions between Pt and LaFeO3Films Stabilize Pt Dispersion
Fornasiero, Paolo,Foucher, Alexandre C.,Gorte, Raymond J.,Mao, Xinyu,Montini, Tiziano,Stach, Eric A.
, p. 10373 - 10382 (2020)
The ability to stabilize very small Pt crystallites in supported-metal catalysts following harsh treatments is an important industrial problem. Here, we demonstrate that Pt particles can be maintained in the 1-to 2-nm range following multiple oxidation and reduction cycles at 1073 K when the particles are supported on 0.5-nm LaFeO3 films that have been deposited onto MgAl2O4 using atomic layer deposition. Characterization by scanning transmission electron microscopy suggests that when the catalyst is oxidized at 1073 K, the Pt crystallites are oriented with respect to the underlying LaFeO3. X-ray absorption spectroscopy also shows evidence of changes in the Pt environment. CO-oxidation rates for the reduced catalyst remain unchanged after five redox cycles at 1073 K. Epitaxial growth of Pt clusters and the consequent strong metal-support interaction between Pt and LaFeO3 are suggested to be the main reasons for the enhanced catalytic performances.
In situ UV-visible assessment of extent of reduction during oxidation reactions on oxide catalysts
Argyle, Morris D.,Chen, Kaidong,Resini, Carlo,Krebs, Catherine,Bell, Alexis T.,Iglesia, Enrique
, p. 2082 - 2083 (2003)
The extent of reduction of active centers during oxidative alkane dehydrogenation on VOx/Al2O3 was measured from pre-edge UV-visible spectral features and found to increase with increasing VOx domain size and propane/O2 ratio.
Role of the Structure and Electronic Properties of Fe2O3-MoO3 Catalyst on the Dehydration of Isopropyl Alcohol
Said, Abdel-Aziz Ahmed
, p. 3450 - 3454 (1992)
Molybdenum oxide catalysts doped or mixed with (1-50) molpercent Fe3+ ions were prepared.The structure of the original samples and calcined at 400 deg C were characterized using DTA, X-ray diffraction, and IR spectra.The measurements of the electrical conductivity of calcined samples with and without isopropyl alcohol revealed that the conductance increases on the increasing the content of Fe3+ ions up to 50 molpercent.The activation energies of charge carriers were determined in presence and absence of alcohol.The catalytic dehydration of isopropyl alcohol was carried out at 250 deg C using flow system.The results obtained showed that the doped or mixed catalysts are active and selective towards propene formation.However, the catalyst containing 40 molpercent Fe3+ ions exhibited the highest activity and selectivity.Correlations were attempted between the catalyst composition and their electronic and catalytic properties.Probable mechanism for the dehydration process is proposed in terms of surface active sites.
Operando spectroscopic investigation of supported metal oxide catalysts by combined time-resolved UV-VIS/Raman/on-line mass spectrometry
Nijhuis,Tinnemans, Stan J.,Visser, Tom,Weckhuysen, Bert M.
, p. 4361 - 4365 (2003)
A new experimental set-up for characterizing supported metal oxide catalysts under working conditions was been developed. The set-up combines product analysis using on-line MS with catalyst characterization by time-resolved operando UV-visible and Raman spectroscopy. The potentials of this approach were illustrated by the propane dehydrogenation over a chromium oxide on alumina catalyst. Different states of the active metal oxide phase can be observed, as well as information on coke formation on the catalyst. These spectroscopic techniques gave valuable complimentary information on the changing catalyst performance during successive propane dehydrogenation operating cycles. They also provide complimentary pieces of information, which agreed well with each other.
The Mechanism of Formaldehyde Loss from the Oxonium Ions CH3CH2CH2CH=O+CH3 and CH3CH2CH2CH2+O=CH2
Bowen, Richard D.,Colburn, Alex W.,Derrick, Peter J.
, p. 1274 - 1276 (1989)
In contrast to CH3CH2(CH3)C=O+CH3 and (CH3)2CHCH=O+CH3, which in slow dissociations lose mainly CH3OH, metastable CH3CH2CH2CH=O+CH3 expels predominantly CH2O by isomerising to CH3CH2CH2CH2+O=CH2, probably via two 1,2-H shifts and a subsequent 1,5-H shift; CH3CH2CH2CH2+O=CH2 undergoes limited interconversion with CH3+CHCH2CH2OCH3, prior to CH2O elimination, via a 1,5-H shift.
DEHYDROMERIZATION OF METHANE ON METAL SULFIDES
Kushch, S. D.,Sachenko, V. I.
, p. 883 - 884 (1989)
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CONVERSION OF METHANOL INTO HYDROCARBONS OVER METAL SALTS OF HETEROPOLYACIDS.
BABA,SAKAI,ONO
, p. 2657 - 2658 (1982)
METAL SALTS OF HETEROPOLYACIDS ARE ACTIVE CATALYSTS FOR THECONVERSION OF METHANOL INTO HYDROCARBONS. THOUGH THE ACTIVITY DEPENDS ON THE KIND OF METAL SALT, THE REACTION MECHANISMFOR THE CONVERSION IS COMMON TO MOST OF THE METAL SALTS, AND THE ACTIVE CENTERS ARE PROBABLY BRONSTED ACID CENTERS.
Altering C2H4/C3H6 yield in methanol to light olefins over HZSM-5, SAPO-34 and SAPO-34/HZSM-5 nanostructured catalysts: Influence of Si/Al ratio and composite formation
Mohammadkhani, Bahman,Haghighi, Mohammad,Sadeghpour, Parisa
, p. 25460 - 25471 (2016)
A series of nanostructured catalysts composed of HZSM-5 zeolite with various ratios of Si/Al (120, 140, 180 and 220) was successfully synthesized by a hydrothermal method. The HZSM-5 sample with optimum ratio of Si/Al = 180 was then added into SAPO-34 synthetic gel to synthesize SAPO-34/HZSM-5 composite. The physicochemical properties and catalytic performance of SAPO-34/HZSM-5 composite were then compared to HZSM-5 (Si/Al = 180) and SAPO-34 catalysts. The nanostructured catalysts were characterized by XRD, FESEM, EDX, BET and FTIR techniques. The XRD patterns indicated that the extent of crystallization and crystallite size were dependent on the Si/Al ratio and type of structure phase (CHA and/or MFI). The EDX images show high distribution of Si for the SAPO-34/HZSM-5 composite. The highest BET surface area (388 m2 g-1) was obtained for HZSM-5 zeolite catalyst with Si/Al ratio of 220. For the MTO reaction, comparing to the HZSM-5 synthesized with different Si/Al ratios, the HZSM-5 (Si/Al = 180) sample possesses highest crystallinity and therefore exhibits the highest selectivity to ethylene. The SAPO-34/HZSM-5 composite is an active catalyst with high selectivity toward light olefins of around 80%.
Mononuclear, Trinuclear, and Metallic Rhenium Catalysts Supported on MgO: Effects of Structure on Catalyst Performance
Kirlin, P. S.,Knoezinger, H.,Gates, B. C.
, p. 8451 - 8456 (1990)
MgO-supported Re catalysts were prepared from and to give isolated Re subcarbonyls and ensembles of three subcarbonyls, respectively.The latter sample was reduced in H2 to give Re metal crystallites on the support.The reactivities of the various surface species were characterized by temperature-programmed reduction, temperature-programmed desorption and wet chemical experiments.The samples were probed as catalysts for the structure-insensitive propene hydrogenation and the structure-sensitive cyclopropane isomerization/hydrogenolysis.The supported Re complexes formed from and MgO catalyze the alkene hydrogenation but not the C-C bond rupture.The ensembles of these complexes formed from catalyze both, in this respect resembling supported crystallites of Re metal partially poisoned with CO.It is inferred that neighboring metal centers are required for the C-C bond rupture, whereas isolated metal centers are active for the hydrogenation.The catalyst containing Re metal is also active for both of these conversion and is the only one of these samples that is active for the isomerization of cyclopropane to give propene.
Photodissociation of Trimethylene Sulfoxide. Energy Partitioning and the Possible Formation of SO(1Δ)
Dorer, F. H.,Salomon, K. E.
, p. 3024 - 3028 (1980)
On direct photolysis or Hg(3P1) sensitized decomposition trimethylene sulfoxide (I) undergoes fragmentation in the gas phase to yield ethylene, propylene, and cyclopropane.There is a nonrandom distribution of the available energy in the cyclopropane-forming reaction which is interpreted to indicate that, in order to conserve spin angular momentum, this reaction channel may be driven to produce SO(1Δ) during direct photolysis, and SO(3Σ) during Hg(3P1) sensitized decomposition.There is a comparison of some aspects of the photochemistry of trimethylene sulfoxide to cyclobutanone photochemistry.
Mesoporous niobiosilicate NbMCF modified with alkali metals in the synthesis of chromene derivatives
Smuszkiewicz, Agata,Lopez-Sanz, Jesús,Sobczak, Izabela,Ziolek, Maria,Martín-Aranda, Rosa M.,Soriano, Elena,Pérez-Mayoral, Elena
, p. 133 - 142 (2016)
We report the synthesis, characterization and activity of new series of catalysts based on Niobium Mesoporous Cellular Foams (NbMCF), modified with alkaline metal elements. These materials exhibit very different acid-base properties attributed to the Nb source for the preparation of the catalysts and the presence and loading of different alkaline metals. The Me/NbMCF materials (where Me are alkaline metals) were tested in the reaction of 2-hydroxybenzaldehyde and ethyl cyanoacetate, under solvent-free conditions, at room temperature, leading to mixtures of the corresponding chromenes 4 and 5, as mixtures of diastereomers erythro/threo, in a 2:1 ratio, respectively, with good to excellent yields. Our experimental results indicate that the metal loading on the catalysts and the acid-base character, and the texture parameters are probably determining factors in the reactivity and the observed diastereoselectivity. The computational study suggests that the presence of alkaline oxides on Me/NbMCF catalyst, exhibiting strong basicity, activates the formation of the nucleophile species, the corresponding enolate, and initiates the reaction. However, the cation size has a deep impact on the stability of the reactant complex so that the effective aldolization could be obstructed by the presence of the bulkier centers.
A ZEOLITE CATALYST AND USE THEREOF FOR THE DEHYDROGENATION OF ALKANES
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Page/Page column 29-31, (2022/02/05)
The present invention relates to a zeolite catalyst, wherein the zeolite catalyst comprises a zeolitic material, wherein the framework of the zeolitic material comprises Y02 and X203, wherein Y is a tetravalent element and X is a trivalent element, wherein the Y : X molar ratio of Y and X contained in the framework of the zeolitic material is comprised in the range of from 500 to 10,000, and wherein the zeolite catalyst further comprises Pt which is supported on the zeolitic material. Furthermore, the present invention relates to a molding comprising the zeolite catalyst, as well as to processes for the preparation of the molding. The present invention also relates to a process for the dehydrogenation of alkanes using the inventive zeolite catalyst or molding, as well as to their respective use. In particular, the catalyst can be Pt/ZSM-5, Pt-Zn/ZSM-5, Pt-K/ZSM-5 or Pt-Zn-K / ZSM-5, with the zeolite exhibiting a Si/A I molar ratio of 850.
TfO-···H-O-H Interaction-Assisted Generation of a Silicon Cation from Allylsilanes: Access to Phenylallyl Ferrier Glycosides from Glycals
Addanki, Rupa Bai,Halder, Suvendu,Kancharla, Pavan K.
supporting information, p. 1465 - 1470 (2022/02/23)
We demonstrate here that the strained and bulky protonated 2,4,6-tri-tert-butylpyridine (TTBPy) triflate salt serves as a mild and efficient organocatalyst for the diastereoselective C-Ferrier glycosylation of various glycals. The importance of the role of the 1/2 H2O molecule trapped in the catalyst has been disclosed. The mechanism of action involves unique anionic triflate and H2O hydrogen-bond interactions that assist the activation of allylsilanes, providing unprecedented access to diastereoselective phenylallyl Ferrier glycosides.
Impact of composition and structural parameters on the catalytic activity of MFI type titanosilicalites
Bruk, Lev,Chernyshev, Vladimir,Khramov, Evgeny,Kravchenko, Galina,Kustov, Aleksander,Kustov, Leonid,Kuz'Micheva, Galina,Markova, Ekaterina,Pastukhova, Zhanna,Pirutko, Larisa
, p. 3439 - 3451 (2022/03/14)
Titanosilicalite of the MFI type was obtained via a hydrothermal method. Its initial and annealed at 75 °C (TS-1P(75)) and 500 °C (TS-1P(500)) forms were studied by X-ray powder diffraction (PXRD), X-ray absorption spectroscopy (XAS-method), Fourier-transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), temperature-programmed ammonia desorption (TPD NH3), and pyridine adsorption (Py). The full-profile Rietveld method allowed us to observe the presence of the organic template tetrapropylammonium hydroxide (TPAOH) in the framework voids, as well as to determine the silicate module (Si/Ti = 73.5) and the distribution of Ti4+ ions over the MFI-type structure sites (Ti atoms replace Si ones in two positions: T1 and T6). The coordination numbers of titanium (CNTi = 4.6 for TS-1P and TS-1P(75), CNTi = 3.8 for TS-1P(500)) were established by the XAS-method. The catalytic activity of titanosilicalites was found in the reactions of nitrous oxide decomposition (the maximal decomposition rate is demonstrated for the TS-1P(75) sample), allyl chloride epoxidation to epichlorohydrin (the best combination of all indicators was exhibited for the TS-1P sample) and propane conversion (maximum propane conversion, and butadiene and propylene selectivity were observed in both TS-1P(75) and TS-1P(500) samples). Mechanisms for the catalytic processes are proposed. The relationship between the catalytic properties and the composition (Si/Ti), Ti4+ ion distribution over the MFI-type structure sites, the local environment of titanium ions, and the number of acid sites in the titanosilicalites are discussed.
