Electron microscopic study of the structure of nickel catalysts modified with heteropoly compounds

The state of the active phase on the surface of low-percentage nickel catalysts on carbon supports in the presence of new modifiers, mixed series 12 heteropoly compounds (HPC), was investigated. The presence of a modifier causes an increase in the dispersion of the nickel, formation of nickel-HPC associates on the surface of the support, and determines the high dispersion and thermal stability of the Ni particles in reducing medium. Modified nickel catalysts have higher selectivity for coal oils during liquid-phase hydrogenation of coal, and the process takes place with less gas formation.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2705–2711, December, 1990.     

Selective hydrogenation of phenylacetylene on Ni and Ni-Pd catalysts modified with heteropoly compounds of the Keggin type

It is established that unmodified Ni catalysts and Ni catalysts modified with Mo- and W-heteropoly compounds (HPC) of the Keggin type (6 wt %) along with catalyst containing 6% K₄SiW₁₂O₄₀/Al₂O₃ appear to be active in the reaction of phenylacetylene (PA) hydrogenation. At low temperatures (100?C150°C), the selectivity of the process strongly depends on the nature of the modifier or second active metal (Pd). It is demonstrated that in the presence of 6% Ni-0.015% Pd/Al₂O₃ modified by HPC K₄SiMo₆W₆O₄₀, the conversion of PA at 100°C was 87% at a styrene: ethylbenzene ratio of 1: 1. The acidity of HPC is found to influence the side reactions of alkylation and condensation. Transmission electron microscopy demonstrates that Ni in modified HPC 6% Ni/Al₂O₃ is present in the form of the particles below 2 nm in size, and these particles of Ni become larger when affected by the reaction medium during PA hydrogenation.     

Hydrogenating Activity and Adsorption Capacity of Supported Nickel Catalysts Modified by Heteropoly Compounds

The catalytic activity, adsorption capacity, and pore structure of low-percentage nickel catalysts supported on -Al₂O₃or activated carbon and modified by tungsten heteropoly compounds are studied. The activity, selectivity, and thermal stability of the catalysts in the vapor-phase hydrogenation of olefins and aromatic hydrocarbons are higher than those for conventional nickel catalysts. The concentration of nickel in the catalysts is 10–15 times lower than that in commercial catalysts. However, the modified catalysts have higher specific surface areas of metal, higher dispersion, a uniform distribution of metal particles, and a pore-radius distribution other than in the support. The study of water adsorption and desorption showed that the heteropoly compound modifying the -Al₂O₃support covers the support surface completely, and supported nickel interacts with the active surface of the modifying agent rather than with Al₂O₃. A hydrogenation mechanism is proposed, which involves H₂dissociation on Ni particles and the subsequent diffusion of hydrogen atoms via a spillover mechanism to the adsorbed organic compound with the participation of the OH groups of the modifying agent.     

The Development and Use of New Hydrogenation Catalysts1

Advantages and drawbacks of commercial catalysts for gas-phase hydrogenation are considered. The use of modified catalysts, including nickel catalysts modified with heteropoly compounds, is promising. Data on the selective reduction of carbonyl compounds and hydrogenation of aromatic hydrocarbons over these catalysts are presented. Palladium films are shown to be the best catalysts for the selective reduction of acetylene compounds to olefins.     

Hydrodechlorination of chlorobenzene on Ni and Ni-Pd catalysts modified by heteropolycompounds of the Keggin type

Ni and Ni-Pd catalysts modified by heteropolycompounds (HPCs) of the Keggin type are shown to be active in the gas-phase hydrodechlorination of chlorobenzene. The dispersion of the metal and the degree of its interaction with the support are found to change upon the addition of HPCs. The activity of the modified catalysts changes depending on the HPCs?? composition, benzene and cyclohexane being present in the products of hydrodechlorination. The addition of Pd as a second active metal is found to change both the activity and selectivity of the produced catalysts (with benzene as the sole product).     

Kinetics of hydrogenation of 1-hexene in the presence of aromatic hydrocarbons on palladium sulfide catalyst

Conclusions A kinetic study has been made of 1-hexene hydrogenation on palladium sulfide catalyst at atmospheric pressure in the presence of benzene, toluene, or xylenes, and a kinetic model of the process has been established, according to which the aromatic hydrocarbons retard the reaction as a consequence of adsorptive displacement. The isomerization of hexene (double bond shift) under hydrogenation conditions proceeds at a considerably higher rate than does the hydrogenation.When hydrogen is replaced by deuterium, kinetic isotope effects are observed in both the hydrogenation and the isomerization; this indicates that hydrogen participates in the slow stages of both reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1243–1248, June, 1982.