Hydrogenation of Hydrogen Cyanide to Methane and Ammonia by a Metal Catalyst: Insight from First-Principles Calculations

摘要

The adsorption and hydrogenation behaviors of hydrogen cyanide to methane and ammonia formation by W(111) catalyst were systematically investigated using the density functional theory method. Based on our calculated consequences, it is found that the WHCN(T,T-mu(2)-C,N) is calculated to be the most stable conformer, possessing an adsorption energy of -49.8 kcal/mol, among all calculated structures of HCN/W(111) system. To comprehend the electronic property of its interaction between the adsorbate and substrate, we calculated the electron localization functions, local density of states, and Bader charges; our results were consistent and explicable. Reaction paths in all possible mechanisms were explored in detail, involving the hydrogenation on different orientations of each adsorbate and the scission of the carbon nitrogen bond. Before forming an imine intermediate (H2CNH(a)), two adsorbed hydrogen atoms will sequentially react with the nitrogen and then carbon atoms in the first and second hydrogenation steps, and the corresponding activation barriers are calculated to be 37.4 and 16.3 kcal/mol, respectively. After yielding an imine intermediate (H2CNH(a)), however, the breaking of carbon-nitrogen bond is likely to proceed at this stage with a pertinent barrier height of 27.5 kcal/mol, forming CH2(a) + NH(a). At elevated temperatures, these resulted adsorbates could be desorbed by further consecutive hydrogenations to generate the final products of methane and ammonia. Our findings provide atomistic-level insight into the novel pathway for surface-assisted synthesis of methane and ammonia via facile hydrogenation reaction of HCN.