The influence of dispersion on the interactions of H/sub 2/ and CO with Pd/SiO/sub 2/ has been investigated. The distribution of H/sub 2/ adstates changes with dispersion, due possibly to a change in the morphology of the Pd crystallites or in the coordination of adsorbed H atoms with the Pd atoms. The ratio of linearly held CO to bridge-bonded CO decreases with the dispersion, as does the ratio of Pd(100) to Pd(111) planes on the surfaces of the Pd crystallites. CO dissociation occurs preferentially from bridge sites and proceeds more readily with decreasing dispersion. Consistent with this, the turn-over frequency for methanation increases with decreasing dispersion. 34 references.
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