Novel dual-bed reactors: utilization of hydrogen spillover in reactor design

Hydrogen spillover over macroscopic distances was demonstrated and exploited in the design of two novel catalytic reactors for 1-butene isomerization. A dual-bed reactor containing separate zones of noble metal and bimetallic catalysts yielded activities up to 2.7 times greater than that of the noble metal alone. The noble metal catalyst contained palladium supported on graphitic carbon. The bimetallic catalyst contained a base metal, either iron or cobalt, and a lanthanide metal, either cerium or praseodymium, also supported on graphitic carbon. The bimetallic catalysts by themselves had no measurable activity at the current experimental conditions. Results from a dual-bed, dual-feed reactor using the same catalysts showed dramatic activity increases relative to controls. In this reactor, the hydrocarbon never contacted the noble metal catalyst, yet substantial hydrocarbon conversion was measured. No hydrocarbon conversion was detected when blank support replaced the bimetallic catalyst or when no material at all was placed above the noble metal catalyst. In both reactors, the activity increase was attributed to hydrogen spillover. That is, molecular hydrogen adsorbed and dissociated on the noble metal catalyst. The adsorbed atomic hydrogen was then transported via surface diffusion to the bimetallic catalyst, activating those sites. The results also demonstrated that a catalytic reaction may occur at distinctly different reactive sites and that catalysts may be selected to promote specific steps within the reaction.