Temperature-programmed desorption and reaction of CO and H/sub 2/ on alumina-supported ruthenium catalyst

The temperature-programmed desorption of CO and temperature-programmed reaction of CO in flowing H/sub 2/ has been studied on a 5 wt% Ru/Al/sub 2/O/sub 3/ catalyst. CO adsorbs molecularly on Ru/Al/sub 2/O/sub 3/ at room temperature. Two distinct CO desorption peaks were observed. The activation energies of desorption were calculated to be 27 and 37 kcal/mole. Upon heating CO dissociates on Ru/Al/sub 2/O/sub 3/ at approximately 415/sup 0/K to form CO/sub 2/ and carbon. The carbon remaining on the catalyst surface enhanced the strength of adsorption of CO, probably by donating electrons to increase the degree of back bonding of the adsorbed CO. The surface carbon reacted reaidly with H/sub 2/ at 303/sup 0/C, forming CH/sub 4/ and small amounts of C/sub 2/H/sub 6/, whereas absorbed CO was inert to H/sub 2/ at this temperature. The surface carbon could easily be deactivated by heat treatment, and a very high temperature was required to remove the deactivated carbon from the catalyst surface with H/sub 2/. These results strongly suggest that carbon is a reactive intermediate and that the dissociation of CO is a necessary step in methanation and Fischer--Tropsch synthesis.