Hydrogen spillover effects in the hydrogenation of benzene over Pt/. gamma. -Al/sub 2/O/sub 3/ catalysts

A study has been made of the presence of hydrogen spillover on Pt/..gamma..-Al/sub 2/O/sub 3/ catalysts and its influence on the hydrogenation of benzene to cyclohexane. The specific activity, refered to Pt metal, increases with the degree of dilution of the catalysts with the ..gamma..-Al/sub 2/O/sub 3/ support up to 50/1 and remains almost constant in more diluted systems; this indicates that atomic hydrogen does not migrate beyond a certain distance, depending on the granulation and texture of the solid mixture. The results suggest that hydrogenation occurs both on the Pt/..gamma..-Al/sub 2/O/sub 3/ and on the diluent ..gamma..-Al/sub 2/O/sub 3/. The ratio between the specific conversion of diluted and undiluted catalysts is temperature independent and the Arrhenius plots for various (un)diluted catalysts all show an equal apparent activation energy value of 9.16 kcal/mol.A hypothesis for the hydrogenation mechanism of benzene over the ..gamma..-Al/sub 2/O/sub 3/ diluent is reported.