Atomic-Scale Mechanism for Hydrogenation of $o$-Cresol on Pt Catalysis*

Biofuels derived from lignocellulosic biomass have received significant attention lately due to increasing environmental concerns. With first-principles density-functional theory and \textit{ab initio} molecular dynamic simulations, we investigated the atomic-scale mechanism of $o$-cresol hydrogenation on the Pt(111) surface. The formation of 2-methyl-cyclohexanone (the intermediate product) was found to involve two steps. The first step is the dehydrogenation, that is, the H atom in the hydroxyl group moves to the Pt surface. The second step is the hydrogenation, that is, the H atoms on Pt react with the carbon atoms in the aromatic ring. The first step involves a smaller barrier, suggesting that dehydrogenation occurs first, followed by hydrogenation of the ring. In particular, tautomerization is found to occur via a two-step process over the catalyst. On the other hand, 2-methyl-cyclohexanol (the final product) is produced through two paths. One is direct hydrogenation of the aromatic ring. Another pathway includes partial hydrogenation of the ring, dehydrogenation of --OH group, finally hydrogenation of remaining C atoms and the O atom. Our theoretical results agree well with the experimental observations.