Nitric Oxide Decomposition via Selective Catalytic Reduction by Ammonia on a Transition-Metal Cluster of W 2 TcO 6 .

Decomposition of nitric oxide (NO) gas on a reactive transition-metal cluster of W 2 TcO 6 has been examined and investigated via selective catalytic reduction by ammonia (NH 3 -SCR) using the M06-L density functional method. The transition-metal cluster of W 2 TcO 6 can be employed to transform NO to N 2 gas efficiently over an active site of tungsten (W). A reaction mechanism of NO conversion based on the NH 3 -SCR process has been elucidated by a potential energy surface along the reaction pathways. The reaction pathways of this NH 3 -SCR process begin with adsorption of NH 3 , adsorption of NO to the cluster, formation of nitrosamine (NH 2 NO) and NHNO/NHNOH intermediates, and rearrangement of NHNO/NHNOH to obtain N 2 and H 2 O, respectively. Notably, a significant NH 2 NO as a key intermediate, namely, "nitrosamine", must be formed before further steps can take place in the generation of N 2 from NO, followed by the involvement of the NHNO or NHNOH intermediate. From our calculated results, the NHNO intermediate via TS3 a is found in pathway a , while NHNOH is found in pathway b via TS3 b . Pathway b has a lower energy barrier of 35.1 kcal/mol than pathway a with an energy barrier of 41.8 kcal/mol, indicating that pathway b should be more energetically favorable. The step for NHNO intermediate rearrangement is a rate-determining step for the reaction occurring through pathway a , which is found to be more difficult in accordance with a difficult N-H bond cleavage to form the NNOH intermediate before N 2 formation. The overall reaction is an exothermic process with thermodynamic and kinetic favors. Thus, this bimetallic W 2 TcO 6 cluster could be used as a promising and active catalyst for NO decomposition via the NH 3 -SCR process to an eco-friendly gas, that is, N 2 .