Mechanism and Dynamics of CO2 Formation in Formic Acid Decomposition on Pt Surfaces

The final CO2 formation step in the decomposition of deuterated formic acid (DCOOH) on Pt surfaces is investigated using density functional theory (DFT) and ab initio molecular dynamics (AIMD) trajectories starting at the relevant transition states. The comparison of our AIMD simulations with the recent experimentally measured translational energy and angular distributions of the desorbed CO2 led us to the conclusion that the decomposition is dominated by the DCOO* intermediate, and the observed thermal and hyperthermal channels of the desorbed CO2 can be attributed to the reaction at terrace and step sites, respectively. The alternative HOOC* pathway is ruled out based on the poor agreement with the experimental distributions and other evidence. Furthermore, the CO2 product was found to have significant vibrational excitations, consistent with previous observations of chemiluminescence of CO2 produced by decomposition of formic acid. These product state distributions are rationalized by the sudden vector projection model.