Dehydrogenation of lsopentane on Active Charcoal Catalysts with Transition Metals

Abstract

Dehydrogenation of isopentane at temperatures ranging from 400 to 500°C was studied with active charcoal catalysis impregnated with Fe, Co, Ni and Cu. Discussion was made mainly about the effect and the role of added transition metals. The catalytic activities of active charcoals containing those metals were several times higher than that of active charcoal itself: However the selectivities were independent of the additives. The catalytic activity increased at first almost linearly with the increase in the metal content, but above a certain critical value the activity- did not depend on the metal content. Although the critical value varied by the element, the saturated activities depended little on the metal species added. The dehydro- genation of paraffin on active charcoal is composed of the abstraction of hydrogen atoms by active charcoal from paraffin and the desorption of hydrogen atoms from active charcoal as hydrogen molecules. When those metals were impregnated on other supports (silica gel, porous glass), they exhibited little catalytic activies for the dehydrogenation of isopentane. Therefore, the metals added to active charcoal were thought to accelerate the recombination and desorption of hydrogen atoms which were known to be the rate-determining step of the reaction on active charcoal.
This is understood as the reverse process of ordinay spillover phenomenon which is the diffusion of hydrogen atoms to a support through metallic particles on the support. The new phenomenon observed in this work may be called"reverse-spillover".