Isotopic transient kinetic analysis of CO hydrogenation on Cu-modified Ru/SiO2

The effect of Cu decoration of Ru/SiO2 on CO hydrogenation at 1 atm has been studied by isotopic transient kinetics analysis for catalysts having Cu/Ru atomic ratios of 0-0.5. The abundances, coverages, and lifetimes of surface intermediates of the reaction were measured under reaction conditions using isotopic transient kinetic analysis. The effects of temperature and partial pressure of H-2 on these surface reaction parameters were also investigated. Activity distribution analysis showed that there were primarily two kinds of active methanation sites/intermediates (related to pools alpha and beta) as has previously been noted by a number of researchers. Cu preferentially blocked alpha-type sites. The surface abundance for pool alpha monotonically decreased with Cu loading while that for pool beta only decreased for Cu/Ru > 0.1. Some additional low activity sites for methanation may have been generated with Cu addition due to (a) the spillover of H and CHx from Ru to Cu permitting reaction to occur on the Cu, or (b) the creation of beta-type sites at the Ru-Cu interfaces. The surface abundance of CO measured during the reaction suggests that (a) there was significant spillover of CO from Ru to Cu, and (b) Cu not only blocked the Ru surface but may have possibly caused some reconstruction of it. The surface abundance of intermediates was independent of H-2 partial pressure in the range 18-55 kPa for all the catalysts. (C) 1996 Academic Press, Inc.