Theoretical Study on the Catalytic Reduction Mechanism of NO by CO on Tetrahedral Rh-4 Subnanocluster

摘要

The catalytic mechanism of 2NO + 2CO -> N-2 + 2CO(2) on Rh-4 cluster has been systematically investigated on the ground and first excited states at the B3LYP/6-311+G(2d),SDD level. For the overall reaction of 2NO + 2CO -> N-2 + 2CO(2), the main reaction pathways take place on the facet site rather than the edge site of the Rh4 cluster. The turnover frequency (TOF) determining transition states are characteristic of the second NO bond cleavage with rate constant k(4) = 1.403 x 10(11) exp (-181 203/RT) and the N-N bond formation for the intermediate N2O formation with rate constant k(2) = 3.762 x 10(12) exp (-207 817/RT). The TOF-determining intermediates of (NbRh4NO)-N-3 and (NbRh4Ob)-N-3(NO) are associated with the nitrogen-atom molecular complex, which is in agreement with the experimental observation of surface nitrogen. On the facet site of Rh-4 cluster, the formation of CO2 stems solely from the recombination of CO and O atom, while N-2 originates partly from the recombination of two N atoms and partly from the decomposition of N2O. For the N-O bond cleavage or the synchronous N-O bond cleavage and C-O bond formation, the neutral Rh-4 cluster exhibits better catalytic performance than the cationic Rh-4(+) cluster. Alternatively, for N-N bond formation, the cationic Rh-4(+) cluster possesses better catalytic performance than the neutral Rh-4 cluster.