SEMIHYDROGENATION OF 1,3-BUTADIENE ON ADSPECIES MODIFIED PD-NI, CO AND CU CATALYSTS

Selective semi-hydrogenation of 1,3-butadiene has been investigated in excess of hydrogen over Co, Cu and Pd-Ni catalysts. The results on 5 wt.-% Co/Al2O3 and Pd-Ni/Nb2O5 catalysts provide evidence that hydroca rbonaceous materials formed on these surfaces play an important role i n governing the competition between 1,3-butadiene and n-butenes. Simil ar results have been observed on 5 wt.-% Cu/SiO2 modified by preadsorp tion of n-butylamine. On the poisoned surface hydrogenation and isomer ization of n-butenes have been remarkably inhibited, but the sample re mains active in semi-hydrogenation of 1,3-butadiene. It is proposed th at the unusual high selectivity of alkene formation is ensured by firm ly held adspecies (FHA) formed from diene or n-butylamine. FHA cover a nd modify metal sites and do not allow adsorption of n-butenes as they apparently cannot compete with FHA. Hydrogenation of diene has been i nterpreted by a compression-displacement model, in which the high stre ngth of diene complexation plays a definite role. Butadiene 'pushes aw ay' FHA for reason of its high complexation strength and finds (create ) reaction sites for its semi-hydrogenation. Preadsorption of CH3OH on 5 wt.-% Cu/SiO2 affects the region selectivity of n-butenes: on the m odified surface the selectivity of cis-2-butene increases at the expen se of 1-butene. These results have been interpreted by electronic modi fication of Cu sites by intermediates formed from decomposition of met hoxy species.