Keynote Address. Structural requirements and pathways in methane reactions catalyzed by supported metal clusters

FUEL 71

Mingshi Li, Jiangsu Polytechnic University, Changzhou, 94720, China, Ya-Huei Chin, chin@berkeley.edu, Department of Chemical Engineering, University of California, Berkeley, 201 Gilman Hall, Berkeley, CA 94720-1462, Junmei Wei, Engelhard Corporation, Iselin, NJ 08830, and Enrique Iglesia, iglesia@cchem.berkeley.edu, Department of Chemical Engineering, University of California, 201 Gilman Hall, Berkeley, CA 94720.
Kinetic and isotopic evidence for elementary steps is provided for CH4 reactions on Rh, Pt, Ir, Ru, Pd,and Ni clusters. Turnover rates for CH4 reforming with CO2 or H2O depend only on C-H activation rates on essentially uncovered surfaces. The elementary steps include rigorously those required for water-gas shift and Boudouard reactions. Reforming turnover rates increased with decreasing cluster size, because of the reactivity of low-coordination atoms prevalent in small clusters. With O2 co-reactants, C-H bonds react on Rh, Ru, and Pt clusters covered partially with oxygen (O*) through O*-O* or O*-* vacancy active pairs. O*-vacancy sites form as O2 is depleted and activate C-H bonds much faster than bare metal surfaces. Cluster size effects in CH4-O2 reactions reflect changes in surface coordination and in reactivity and binding of chemisorbed oxygen. H2 and CO were not detected when O2 was present; thus direct partial oxidation does not occur and H2-CO mixtures form via combustion-reforming pathways.
 

Advances in Hydrogen Production
8:30 AM-11:50 AM, Monday, 11 September 2006 Palace -- Marina Room, Oral

Division of Fuel Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006