A. Pestryakov

Selective oxidation of alcohols over foam-metal catalysts

Abstract Catalysts based on the foam metals (silver and copper) were studied in the processes of partial oxidation of methanol, ethanol and ethylene glycol. The experiments showed that the foam catalysts have high gas permeability, mechanical strength, thermostability and catalytic properties exceeding the ones of the traditional crystal and granular metal catalysts. Electronic states of silver and copper on the surface of the catalysts were studied by the method of diffuse reflectance electron spectroscopy in UV–VIS range.

Influence of modifying additives on the electronic state of supported palladium

Abstract The influence of modifying additives of Ce, Zr, La and Cs oxides on the electronic state of palladium supported on γ-Al 2 O 3 has been studied by IR-spectroscopy of adsorbed CO, diffuse reflectance UV–visible spectroscopy, X-ray diffraction (XRD) and H 2 chemisorption. The modified supports have been prepared using impregnation, coprecipitation and sol–gel methods. It is established that Ce and Zr oxide additives increase the effective charge of palladium ions whereas La and Cs oxides lower it. The effect of metal–support interaction is stronger in samples prepared by sol–gel than by coprecipitation

Supported foam-silver catalysts for alcohol partial oxidation

Abstract Structural, mechanical, gas-dynamic and catalytic properties of silver catalysts supported on foam ceramics have been studied. The foam catalysts have high gas permeability, mechanical strength, and low density. Catalytic activity and selectivity of the foam catalysts in the process of oxidation of methanol to formaldehyde exceed the characteristics of the commercial crystalline and granulated catalysts. Different electronic states (ions, charged cluster, crystals) of silver on the catalyst surface have been studied by the method of UV–visible spectroscopy.

INFLUENCE OF Fe INTRODUCTION METHOD ON GOLD STATE IN NaY ZEOLITE

The present work is devoted to the study of some properties (size, electronic state, redox properties, interaction with matrix) of gold clusters and nanosized particles in Na-Y zeolite modified by iron. Two methods of iron introduction were applied: wet-impregnation and ion-exchange, which result in different structure and reducibility of iron species. Aggregation of iron species and their probable dissolution during gold deposition in samples prepared by wet-impregnation permits to form new Au, Fe and Au-Fe species in contrast to samples prepared by ion-exchange. The strong interaction of Au with Fe species in Au/Fe-imp/NaY changes noticeably a behavior of gold nanoparticles under heating.

FORMATION OF CATALYTICALLY ACTIVE COPPER NANOPARTICLES IN NATURAL ZEOLITES FOR COMPLETE OXIDATION OF HYDROCARBONS

Copper catalysts for complete oxidation of hydrocarbons supported on natural zeolites of different structure and origin were prepared by ion-exchange procedure. The catalytic experiments demonstrate that the temperature of beginning of hydrocarbons conversion is in the range of 170-300 °C, depending on the composition of the catalyst. The complete conversion can be observed for both zeolites, depending (probably) on Si/Al ratio of the zeolite matrix. Different states of the copper have been identified by the methods of UV-VIS and XPS spectroscopies and TPR by hydrogen. Whereas no changes in XRD and 27Al MAS NMR was observed under condition of catalytic runs, that supports conclusion about stability of bulk material, XPS spectroscopy reveals significant altering in surface composition under different treatments due to appearance of complicated nano-species of copper, which are responsible for catalytic activity.

Characterization of H and Cu mordenites with varying SiO2/Al2O3 ratios, by optical spectroscopy, MAS NMR of 29Si, 27Al and 1H, temperature programmed desorption and catalytic activity for nitrogen oxide reduction

H-mordenites (HMor) with variable SiO 2 /Al 2 O 3 molar ratio (MR) varying from 10 to 206 were incorporated with copper (CuMor). Maximum total acidity and maximum concentration of the strongest acid sites were found for MR-15 (HMor15). This sample has the lowest micropore and mesopore content, but also show strongly disordered Si sites in the crystalline lattice. A consistent finding has been the disappearance of the NMR line from extraframework 27 Al, whenever Cu is present. The reducibility of copper ions and stability of reduced species depend on MR. The MR also influences optical lineshapes from different reduced species of Cu. A plasmon resonance band at 580 nm, due to small Cu particles formed in the zeolite, occurs at low and high MR but not at MR=15. Catalytic tests of NO conversion reveal that the reduced Cu-mordenites with MR=15 are the most stable and active ones.

Study of electronic state of supported gold nanospecies by IR spectroscopy

The nature of different Au species supported on hexagonal mesoporous silica has been studied by infrared spectroscopy of adsorbed CO. Experiments revealed existence of the following states of supported gold: neutral metal particles Au°, ions Au⁺ and a number of partly charged states Au^δ+ with different effective charge. Redox pretreatments (vacuum, O₂ and H₂) of Au/SiO₂ at the different temperatures (100, 300 and 500°C) exert a significant effect on the electronic state of supported Au species. The experiments showed high stability of Au^δ+ states under all treatments; that may prove their active role in catalytic properties of gold.

Reduction of nickel ions in mordenites with different SiO 2 /Al 2 O 3 molar ratios

The aim of present work was to study the influence of SiO2/Al2O3 molar ratio (MR) on nickel behavior in the mordenites with wide variation of MR during reduction in hydrogen flow. It was found that during reduction treatment variation of MR in mordenite from 10 to 206 influences reducibility and mobility of reduced nickel species. Stability of the reduced samples during storage in air at ambient conditions also depends on molar ratio. Variation of MR of mordenite does not change crystal structure, but results in different ionic properties. This effect is explained by variation of acidity of zeolite matrix in line with variation of chemical composition.

Catalysts based on gold nanosized species incorporated into zeolites

Last years nanosized gold particles attract much attention as a component of industrially perspective catalysts for some reactions as CO oxidation, NO reduction etc. We studied several systems including gold based on different synthetic zeolites pure or doped with another metals (Fe, Na). It was shown by different techniques (XPS, UV-Vis spectroscopy, TPR) that intrinsic properties of zeolites used and gold system preparation method influence significantly on the contribution of different gold species (ions, clusters and particles). For mixed Au-Me-zeolites activity level and dynamic of CO conversion with time in steam and temperature depends on nature of zeolite and specificity of Au-Me interaction. All binary metal systems were found to be activated in different degree during catalytic activity test due to mutual interaction of gold with second metal. Extremely high level of CO conversion and low dependence of activity on temperature was observed for Au- Fe- H- and Na-Y zeolites. The change in contribution of gold nanoparticles was observed after sample contact with CO.

Neutralization of gas emissions on foam-metal catalysts

Catalysts of new structural type - foam metals - have been tested in the process of deep oxidation of hydrocarbons and neutralization of exhaust gases of automotive engines. Foam catalysts have physicochemical, gas-dynamic and catalytic characteristics exceeding the indices of the traditional granular and honeycomb catalysts.