Potential Energy Surface of Methanol Decomposition on Cu(110)

Combining the dimer saddle point searching method and periodic density functional theory calculations, the potential energy surface of methanol decomposition on Cu(110) has been mapped out. Each elementary step in the methanol decomposition reaction into CO and hydrogen occurs via one of three possible mechanisms: O−H, C−H, or C−O bond scission. Multiple reaction pathways for each bond scission have been identified in the present work. Reaction pathway calculations are started from an initial (reactant) state with methanol adsorbed in the most stable geometry on Cu(110). The saddle point and corresponding final state of each reaction or diffusion mechanism were determined without assuming the reaction mechanism. In this way, the reaction paths are determined without chemical intuition. The harmonic pre-exponential factor of each identified reaction is calculated from a normal-mode analysis of the stationary points. Then, using harmonic transition state theory, the rate constant of each identified reaction pathway in the entire reaction network is obtained. The most favorable decomposition route for methanol on Cu(110) is found as follows: CH3OH → CH3O → CH2O. The rate-limiting step in this decomposition route is the dehydrogenation of methoxy to formaldehyde. Our calculations are in agreement with previous experimental observations and theoretical results.