Study of <Emphasis Type="Italic">n</Emphasis>-hexane isomerization on Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO₄/ZrO₂/Al₂O₃ catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al₂O₃ alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO₄/ZrO₂/Al₂O₃ superacid catalyst were used in this study. With the use of IR spectroscopy (CO_ads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.     

Adsorption and conversion of ethylene glycol on the surface of Ag-containing catalyst modified with phosphate

The interaction of ethylene glycol with the surface of Ag-containing catalysts modified with phosphates was studied by IR spectroscopy. It was found that ethylene glycol was adsorbed at the surface phosphate groups; the presence of water vapor increased the stability of adsorbed ethylene glycol to a temperature of 400°C. A study of the kinetics of oxidation of ethylene glycol showed that it was consecutively converted into glycolaldehyde and glyoxal at 400°C. At 500–550°C, glyoxal was formed upon both the consecutive and direct conversion of ethylene glycol. The presence of a stage of the consecutive conversion of ethylene glycol into glycolaldehyde and glyoxal was caused by the participation of surface phosphate groups in the adsorption of alcohol molecules to be oxidized.     

State of components in PdCu/Al2O3 catalysts obtained via anchored metal complexes

IRS and XPS data have shown that the reduction of pdCu/Al₂O₃ catalysts is followed by the formation of 30–40 Å homogeneous bimetallic particles with a surface enriched in copper atoms.     

Estimation of proton donor ability of surface hydroxy groups in terms of proton affinity

A method to estimate the proton donor ability of hydroxy groups in terms of proton affinity (PA) is suggested. The PA of hydroxy groups of aerosil and of decationated zeolite type Y have been determined.

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(PA). PA .

     

51V NMR Study of VOCl3Immobilized on the SiO2and MgCl2Surface

The magnetic shielding tensor and quadrupole interaction parameters, as well as the mutual orientation of tensors for the (SiO)VOCl₂complex obtained by the immobilization of VOCl₃on the SiO₂surface are determined. The state of VOCl₃on the surfaces of MgCl₂and modified SiO₂with all surface OH groups replaced by Cl atoms is studied. To prepare the modified SiO₂, CCl₄and SiCl₄are used as chlorinating agents. The formation of structurally similar pentavalent vanadium complexes on the surface of these supports is shown. A model for the coordination environment of vanadium on the chlorine-containing supports is proposed. The vanadium atom exists in the distorted pentahedral environment and is bound to the support through either two chlorine atoms or chlorine and oxygen atoms. A correlation between the coordination of VOCl₃and catalytic properties of VOCl₃/MgCl₂is assumed.     

Stoichiometry of Oxidation Reactions Involving α-Oxygen on FeZSM-5 Zeolite

The stoichiometry of the low-temperature reaction between surface -oxygen formed by decomposing N₂O over Fe-containing ZSM-5 zeolite and methane, hydrogen (deuterium), and carbon monoxide is studied. Methane and hydrogen react with -oxygen in stoichiometric ratios of 1 : 1.8 and 1 : 1.6, respectively. The observed stoichiometry is due to the mechanisms of the corresponding reactions. According to a mechanism proposed for the interaction of -oxygen with methane and hydrogen, this reaction is accompanied by the dissociation of CH₄and H₂molecules. For hydrogen, such a mechanism is supported by IR spectroscopic studies of resulting surface compounds, namely, of new hydroxyl groups that were formed on the zeolite surface in the course of the reaction. -Oxygen reacts with CO in the ratio of 1 : 1 to form CO₂in amounts equal to those of -oxygen on the surface.     

Promotion of Catalytic Properties of Sulfated Zirconium and Aluminum Oxides with Carbon Tetrachloride

The promoting effect of minor amounts of carbon tetrachloride on the catalytic activity and working life of sulfated zirconium and aluminum oxides is considered for the example of isobutane alkylation with butenes.     

Interaction of aromatics with Br?nsted sites in zeolites: Demarcation line between regions of stable existence of H-complexes and ion pairs for various types of bases

Interaction of naphthalene, α-methylnaphthalene, and hexamethylbenzene with OH groups of SiO₂, HNaY and H-ZSM-5 zeolites was studied by IR spectroscopy. The results are compared with data obtained for other types of organic bases. Specificity in the generation of H-complexes of olefins, arenes, naphthalenes, N- and O-bases with Br?nsted surface sites was elucidated. Each type of base appears to have its particular correlation of (PA^a-PA^b) and the shift of Δυ_OH band in H-complexes. It has been found that if (PA^a-PA^b) is less than 85±5 kcal/mol, the formation of ion pairs is thermodynamically more favorable than that of H-complexes for all types of organic compounds.     

Interaction of butylamines with protonic centers of HNaY zeolite

IR-spectroscopic studies of the interaction of tert-, sec- and n-butylamine with HNaY protonic centers at 373–725 K and P_amine=0.13–13.3 kPa indicate that the deamination proceeds through intermediate butylammonium ions whose decomposition is the rate-determining step and can provide directly ammonium ions. The temperature of incipient reaction increases in the series: tert-

- -, - - 373 723 0,13 13,3 . , . . : -<-<-.

     

Reaction of tetrahydrofuran with H2S in the presence of Na+/γ-Al2O3

Modification of -Al₂O₃ by sodium hydroxide promotes the increase of surface basicity but does not exert a strong effect on catalytic activity in the reaction of thiolane production from tetrahydrofuran and H₂S. Introduction of NaOH to -Al₂O₃ in small concentration increases the number of Lewis acid centers but decreases their strength. The activity of Na/-Al₂O₃ referred to one Lewis acid center drops.