Hydroisomerisation of n-alkanes over partially reduced MoO_3:Promotion by CoAlPO-11 and relations to reaction mechanism and rate-determining step

摘要

The reaction mechanism and the rate-determining step(RDS)of the isomerisation of n-alkanes(C_4-C_6)over partially reduced MoO_3 catalysts were studied through the effects of the addition of an alkene isomerisation catalyst(i.e.CoAlPO-11).When an acidic CoAlPO-11 sample was mechanically mixed with the MoO_3,a decrease of the induction period and an increase of the steady-state conversion of n-butane to isobutane were observed.These data support previous assumptions that a bifunctional mechanism occurred over the partially reduced MoO_3(a complex nanoscale mixture of oxide-based phases)during n-butane isomerisation and that the RDS was the skeletal isomerisation of the linear butene intermediates.The only promotional effect of CoAlPO-11 on the activity of partially reduced MoO_3 for C_5-C_6 alkane hydroisomerisation was a reduction of the induction period,as the RDS at steady-state conditions appeared to be dehydrogenation of the alkane in this case.However,lower yields of branched isomers were observed in this case,the reason of which is yet unclear.