Influence of preadsorbed oxygen on activated chemisorption of methane on Pd(110)

Dissociative chemisorption of methane on clean and oxygen modified Pd(110) has been studied by using molecular beam surface scattering. The absolute dissociation probability of CH4 (Stot) is found to increase exponentially with the incident normal energy (En) of CH4 and with surface temperature (TS) on clean Pd(110). The kinetic isotope effect is also found; namely, Stot of CD4 is 4 to 5 times smaller than Stot of CH4 throughout the entire range of En studied. These results are consistent with a direct dissociation mechanism. Measurements on preadsorbed oxygen on Pd(110) show that Stot of CH4 decreases linearly, as oxygen coverage is increased from 0 to 0.4 ML in good agreement with the first-order Langmuir kinetics when approximately two active sites are blocked by one oxygen atom. No influence of the oxygen induced surface reconstructions on the dissociative adsorption kinetics of CH4 is observed.