Hydrogenating activity and adsorption capacity of supported nickel catalysts modified by heteropoly compounds

The catalytic activity, adsorption capacity, and pore structure of low-perc entage nickel catalysts supported on gamma -Al2O3 or activated carbon and m odified by tungsten heteropoly compounds are studied. The activity, selecti vity, and thermal stability of the catalysts in the vapor-phase hydrogenati on of olefins and aromatic hydrocarbons are higher than those for conventio nal nickel catalysts. The concentration of nickel in the catalysts is 10-15 times lower than that in commercial catalysts. However, the modified catal ysts have higher specific surface areas of metal, higher dispersion, a unif orm distribution of metal particles, and a pore-radius distribution other t han in the support. The study of water adsorption and desorption showed tha t the heteropoly compound modifying the gamma -Al2O3 support covers the sup port surface completely and supported nickel interacts with the active surf ace of the modifying agent rather than with Al2O3. A hydrogenation mechanis m is proposed, which involves H-2 dissociation on Ni particles and the subs equent diffusion of hydrogen atoms via a spillover mechanism to the adsorbe d organic compound with the participation of the OH groups of the modifying agent.