Effect of Acid–Base Characteristics of Zeolite Catalysts on Oxidative Dehydrogenation of Propane with Carbon Dioxide

Theoretical and Experimental Chemistry - The peculiarities of propane dehydrogenation with carbon dioxide over zeolite catalysts of different structural types, in particular, BEA with incorporated...     

Effect of Addition of Base on Ceria and Reactivity of CuO/CeO2 Catalysts for Low-Temperature CO Oxidation

In this work, we have reported the influence of the addition of base (KOH) on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction by H2 (H2-TPR). The catalytic properties of the CuO/CeO2 catalysts for low-temperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials.     

Effect of Citric Acid Solution Treatment on Textural Properties and Alkylation Activity of Zeolite Beta Catalyst

Zeolitebetaisalarge porecrystallinealuminosil icate,whichwasfirstsynthesizedbyWadlingeretal[1] in 196 7.Duetoitspeculiarframeworktopologyandsuitableacidity ,zeolitebetahasreceivedincreas ingindustrialinterestforsomeimportantreactionssuchasalkylationofbenzenewithlightolefins[2 ] andalkylationofisobutanewithbutene[3] .Manylitera turepapershavereportedmethodstomodifytheacid ityofzeolitebeta ,whichincludeion exchange ,hy drothermaltreatment ,andacidtreatment .Forexam ple ,Xieetal[4 ] investigated…     

Effect of the Conditions of Solution Combustion Synthesis on the Properties of Monolithic Pt–MnOx Catalysts for Deep Oxidation of Hydrocarbons

Kinetics and Catalysis - Catalysts based on manganese oxides, doped with Pt, and supported on ceramic monoliths with a honeycomb structure were produced by impregnation and solution combustion...     

Effect of the State of a Surface Layer on the Properties of Pd–P Catalysts in the Hydrogenation of Alkylanthraquinones

Kinetics and Catalysis - X-ray photoelectron spectroscopy (XPS) was used to study the state of the surface layer of a Pd–P catalyst, which exhibits high selectivity in the hydrogenation of...     

Acid–Base Properties of Polyhalogenated Tetraphenylporphyrins

Russian Journal of Organic Chemistry - [2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]zinc(II) and...     

The Effect of Preliminary Treatment on the Catalytic Activity of Cobalt–Silica Gel Catalysts in the Complete Oxidation of Methane

The effect of temperature in multiple oxidative–reductive treatments on the activity of cobalt–silica gel catalysts in the complete oxidation of methane is studied. A decrease in the temperature of oxidative–reductive treatments from 500°C to 300°C results in an irreversible decrease in the activity of samples prepared by the impregnation of SiO₂with cobalt nitrate. A sample prepared from cobalt acetate and calcined at 500°C shows a lower activity, which was close to the activity of samples prepared from nitrates and calcined at 300°C.     

Effect of Support on Catalytic Properties of Platinum-Containing Catalysts in Hydrogenation of a Biphenyl–Diphenylmethane Eutectic Mixture

Russian Journal of Applied Chemistry - Pt/Sup catalysts with SiO2, MCM-48, and Al2O3 supports (Sup) were prepared. The catalysts were studied by methods of low-temperature nitrogen adsorption,...     

Doping Effect of CuO on CeO_2 for CO Oxidation

CeO2withfluoritestfuctureisnoticeableasacata1yticactivematerialinredoxreactions,duetoitshighoxygenstoragecapacity(OSC)andoxygenvacancieswitheasyreducibilityandhighmobility.Fluorite-typecomplexoxides,dopedwithtransitionmetalion,canbeimprovedfurtherandhavehighercatalyticactivity.Forthisreason,ithasstimulatedmuchresearcheffortintheuseandthestudyofCeO2-containingcatalystsystem,especiallysincel99Os'-3.Amongthecatalysts,theCu-Ce-Osystemseemstobethemostpromising,inwhichtheroleofcopperhasbeenexten…     

Effect of Chemical Modification of the Tetrapyrrole Macrocycle Structure on the Spectral,Acid–Base,and Complexing Properties of tert-Butyl-Substituted Porphyrazines

Russian Journal of Organic Chemistry - The effect of chemical modification of the tetrapyrrole macrocycle structure on the spectral, acid–base, and complexing properties of...     

Participation of Water in the Secondary Transformations of Hydrocarbons on Cobalt–Zeolite Catalysts for the Fischer–Tropsch Synthesis

This review is dedicated to the effect of water as the main by-product of the Fischer–Tropsch synthesis on the process. The reasons for the negative effect of water are analyzed and the possible versions of the control of its participation in the process are considered. As an optimal solution to the problem, the use of zeolites in the H form as the constituents of cobalt catalysts for the Fischer–Tropsch synthesis is proposed. Bibliography: 148 references.     

Acid–Base Properties of Macroporous Weak Base Anionite Based on Aminated Acrylonitrile/Divinylbenzene Copolymer

Potentiometric titration of weak base anionite (the degree of crosslinking was 12–16%) was performed within the pH range of 2–12 and NaCl concentration range of 0.1–1.0 mol/L. The maximum ionexchange ability against HCl does not depend on the solution ionic strength and is 6.50 ± 0.12 mmol/g of dry solid matter. It was shown that the process of acid–base equilibrium can be adequately described by the Gregor equation within the studied stock electrolyte concentration and pH ranges. Two type of groups were discovered in anionite. The ionization constants of these groups differ by three orders of magnitude. The existence of amino groups of different nature was proved by the data obtained by functional analysis; it was estimated that the acidity of these groups decreases as NaCl concentration increases.     

Effect of Alkali Treatment on the Structure and Catalytic Properties of ZSM-5 Zeolite

Catalytic properties of ZSM-5 zeolite samples pretreated with NaOH solution have been investigated. The samples are characterized by XRD, SEM, chemical analysis, and N2 adsorption.The results indicate that mesopores are created in ZSM-5 crystals under alkali treatment without change the microporous structure and acidic strength of the zeolite, but the crystallinity is greatly decreased under severe treatment. IR indicates that the concentration of silanol is greatly enriched by alkali treatment. The etherification activities of ZSM-5 zeolites are greatly increased byalkali-treatment. The noticeably improved catalytic activity of treated samples is ascribed to the formation of mesopores and greatly enriched silanol group.     

Activity Enhancement of Vanadium Catalysts with Ultrasonic Preparation Process for the Oxidation of Sulfur Dioxide

The effect of ultrasonic cavitations on the activity of vanadium catalysts at low temperatures for the oxidation of sulfur dioxide, in which refined carbonized mother liquor had been added, was investigated.Twenty minutes were needed to produce obvious cavitations when the catalyst raw material was treated in the 50 W ultrasonic generator. However, only 10 minutes would be needed in a 150 W ultrasonic generator.The higher the temperature of the wet material, the less time was needed to produce cavitations, and the optimal temperature was 60℃. The water content in the wet material mainly affected the quantity of cavitations. Ls-8 catalyst was prepared using ultrasonic. Its activity for conversion of SO2 reached to 52.5% at 410℃ and 4.2% at 350℃. The differential thermal analyses indicate that both endothermic peaks and exothermic peaks noticeably shifted forward compared with Ls catalyst prepared without ultrasonic, and SEM results show a uniform uore size distribution for Ls-8 catalvst.     

Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag／SiO2 Catalysts for CO Selective Oxidation in H2

The interactions of oxygen with pre~reduced silver catalysts as well as their catalytic propertiesfor CO selective oxidation in H2 after oxygen pre-treatment are studied in this paper. It is found that the pretreatment exerts a strong influence on the activity and selectivity of the silver catalyst. A drop in activity and selectivity is observed after treating a pre-reduced catalyst with oxygen at low temperatures,whereas a converse result is obtained after an oxidizing treatment at high temperatures (T≥350℃). O2-TPD results show that surface oxygen species adsorbs on silver surface after the oxygen treatment at low temperatures. However, penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile the surface oxygen species disappear. No other silver species except metallic silver are observed on all the catalysts by XRD, and the size of silver particle is not changed after the treatment with oxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also be removed by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorption and diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing the decrease in CO oxidation activity, in other words, it is important to obtain a clean silver surface for increasing the catalyst activity in CO removal from H2-rich feed gas. The differences in activity and selectivity due to the oxygen pretreatment at different temperatures axe discussed in terms of the changes in the surface/subsurface oxygen species of the silver particles.     

Effect of Catalyst Pretreatment on the Oxidation of Carbon Monoxide over Gold Catalysts Supported on Double Oxides

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Impact of the Spatial Organization of Bifunctional Metal–Zeolite Catalysts on the Hydroisomerization of Light Alkanes

Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one-dimensional zeolites (ZSM-22 and mordenite) and a γ-alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n-heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the “intimacy criterion” for the rational design of bifunctional catalysts for the conversion of low-molecular-weight reactants.     

Effect of Cr and Co Promoters Addition on Vanadium Phosphate Catalysts for Mild Oxidation of n-Butane

In this study, Cr and Co promoted, as well as unpromoted vanadium phosphate (VPO) catalysts were synthesized by the reaction of V2O5 and o-H3PO4 in organic medium followed by calcination in n-butane/air environment at 673 K. The physico-chemical properties and the catalytic behavior were affected by the addition of Cr and Co dopants. H2-TPR was used to investigate the nature of oxidants in the unpromoted and promoted catalysts. The results showed that both the Cr and Co promoters remarkably lowered the temperature of the reduction peak associated with V5 . The amount of oxygen species originated from the active phase, V4 , removed was significantly increased for Co and Cr-promoted catalysts. Both Cr and Co dopants improve strongly the n-butane conversion without sacrificing the MA selectivity. A good correlation was observed between the amount of oxygen species removed from V4 phase and the activity for n-butane oxidation to maleic anhydride. This suggested that V4 -O was the center for the activation of n-butane.