Dehydrogenation of methanol on Pd(100): comparison with the results of Pd(111)

Abstract

Dehydrogenation of methanol on Pd(100) is systematically investigated using self-consistent periodic density functional theory. The theoretical results are compared with those of the same reaction on Pd(111) published very recently [J. Phys. Chem. C, 2009, 113, 4188–4197]. Switching from (111) to (100), adsorptions are strengthened for most species except for CHO, CO and H at hollow sites. Moreover, Pd(100) affords relatively low energy barriers and higher rate constants for most elementary dehydrogenation steps as well as smaller desorption rates for the saturated adsorbates (methanol and formaldehyde), suggesting that the more open Pd surface indeed possesses the higher activity and selectivity for the complete dehydrogenation of methanol. At lower temperatures (e.g., 250 K), Pd(100) affords the same dehydrogenation path as Pd(111) for methanol, which is unchanged on the latter surface at both lower and higher temperatures; whereas at the typical steam re-forming (MSR) temperature (500 K), the path on Pd(100), i.e., CH₃OH → CH₃O and/or CH₂OH → CH₂O → CHO → CO, is different from the situation of Pd(111). In both cases, the initial bond scission process constitutes the rate-determining step.