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

Article abstract of DOI:10.1002/cctc.201801118

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 (4 wt%) on CeO₂ support pre-calcined at high temperature (1073 K; Ru(4)/CeO₂¹⁰⁷³ catalyst) showed both good activity and selectivity to toluene. The yield of toluene reached 65 %-C in the conditions of 533 K and H₂ partial pressure of 0.075 MPa. 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 p-ethyltoluene can give p-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 (<2 nm) 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.