Selective C-C Hydrogenolysis of Alkylbenzenes to Methylbenzenes with Suppression of Ring Hydrogenation

Selective reduction of alkylbenzenes, which are supplied by refining heavy hydrocarbons, to methylbenzenes by selective C-C hydrogenolysis was accomplished by Ru/CeO2 catalyst. Hydrogenolysis of ethylbenzene was carried out with gas-phase fixed-bed flow reactor and various noble metal catalysts. The catalyst with high Ru loading (4wt%) on CeO2 support pre-calcined at high temperature (1073K; Ru(4)/CeO21073 catalyst) showed both good activity and selectivity to toluene. The yield of toluene reached 65%-C in the conditions of 533K and H-2 partial pressure of 0.075MPa. Hydrogenolysis of other alkylbenzenes including p-ethyltoluene, propylbenzene and cumene was also carried out. Hydrogenolysis of C-aryl-C-alkyl bond and hydrogenation of benzene ring was slow in all substrate cases. Hydrogenolysis of rho-ethyltoluene can give rho-xylene as the main product (highest yield: 53%-C). These high yields of methylbenzenes make a marked contrast to the traditional bifunctional hydrocracking systems which preferably dissociate C-aryl-C-alkyl bond in alkylbenzenes. Characterization of Ru catalysts suggests that the block-shaped Ru particles with small size (<2nm) in Ru(4)/CeO21073 give good catalytic performance. Too strong interaction between Ru species and CeO2 support induced by decreasing the loading amount rather gives ring-hydrogenation activity and decreases methylbenzenes selectivity.