Theoretical study on the gas-phase reaction mechanism between palladium monoxide and methane

✍ Scribed by Hua-Qing Yang; Chang-Wei Hu; Chao Gao; Meng-Yao Yang; Fang-Ming Li; Cai-Qin Li; Xiang-Yuan Li

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 894 KB
• Volume: 32
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.21926

✦ Synopsis

The gas-phase reaction mechanism between palladium monoxide and methane has been theoretically investigated on the singlet and triplet state potential energy surfaces (PESs) at the CCSD(T)/AVTZ//B3LYP/6-311þG(2d, 2p), SDD level. The major reaction channel leads to the products PdCH 2 þ H 2 O, whereas the minor channel results in the products Pd þ CH 3 OH, CH 2 OPd þ H 2 , and PdOH þ CH 3 . The minimum energy reaction pathway for the formation of main products (PdCH 2 þ H 2 O), involving one spin inversion, prefers to start at the triplet state PES and afterward proceed along the singlet state PES, where both CH 3 PdOH and CH 3 Pd(O)H are the critical intermediates. Furthermore, the rate-determining step is RS-CH 3 PdOH ! RS-2-TS1cb ! RS-CH 2 Pd(H)OH with the rate constant of k ¼ 1.48 Â 10 12 exp(À93,930/RT). For the first CAH bond cleavage, both the activation strain DE = strain and the stabilizing interaction DE = int affect the activation energy DE = , with DE = int in favor of the direct oxidative insertion. On the other hand, in the PdCH 2 þ H 2 O reaction, the main products are Pd þ CH 3 OH, and CH 3 PdOH is the energetically preferred intermediate. In the CH 2 OPd þ H 2 reaction, the main products are Pd þ CH 3 OH with the energetically preferred intermediate H 2 PdOCH 2 . In the Pd þ CH 3 OH reaction, the main products are CH 2 OPd þ H 2 , and H 2 PdOCH 2 is the energetically predominant intermediate. The intermediates, PdCH 2 , H 2 PdCO, and t-HPdCHO are energetically preferred in the PdC þ H 2 , PdCO þ H 2 , and H 2 Pd þ CO reactions, respectively. Besides, PdO toward methane activation exhibits higher reaction efficiency than the atom Pd and its first-row congener NiO.