Kinetics of hydrogen oxidation to water on the Rh(111) surface using multiple source modulated molecular beam techniques

Article abstract of DOI:10.1016/0039-6028(91)90645-9

We have examined the kinetics of the oxidation of hydrogen to water on the Rh(111) surface using modulated molecular beam reactive scattering. For reactant pressures below 10^-4 Torr and temperatures from 450-1250 K we observe serial steps, with apparent activation energies of 2.5 ± 1 and 10 ± 1 kcal/mol. Pseudo-first-order preexponential factors are 10⁵ and 10⁷ s^-1, respectively, varying slightly with oxygen coverage. Reaction is inhibited by excess oxygen. Maximum water production occurs around 650 K. At lower temperatures the reaction becomes nonlinear. We use a new three-molecular-beam arrangement. Two continuous, independently adjustable beams establish steady-state surface concentrations, while a weaker modulated third beam induces small concentration perturbations around the selected steady state. With this technique we varied surface oxygen coverages, used isotopic substitution in the three beams to produce H₂O, D₂O and HDO, and linearized the HDO reaction.