Theoretical Investigation of Water Gas Shift Reaction Catalyzed by Iron Group Carbonyl Complexes M(CO)5 (M = Fe, Ru, Os)

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• 作者：Yu Chen ; Fuli Zhang ; Chunming Xu ; Jinsen Gao ; Dong Zhai ; Zhen Zhao
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：March 15, 2012
• 年：2012
• 卷：116
• 期：10
• 页码：2529-2535
• 全文大小：424K
• 年卷期：v.116,no.10(March 15, 2012)
• ISSN：1520-5215

文摘

We have investigated the mechanism of M(CO)₅ (M = Fe, Ru, Os) catalyzed water gas shift reaction (WGSR) by using density functional theory and ab initio calculations. Our calculation results indicate that the whole reaction cycle consists of six steps: 1 鈫?2 鈫?3 鈫?4 鈫?5 鈫?6 鈫?2. In this stepwise mechanism the metals Fe, Ru, and Os behave generally in a similar way. However, crucial differences appear in steps 3 鈫?4 鈫?5 which involve dihydride M(H)₂(CO)₃COOH^{鈥?/sup> (4鈥?/b>) and/or dihydrogen complex MH₂(CO)₃COOH鈥?/sup> (4). The stability of the dihydrogen complexes becomes weaker down the iron group. The dihydrogen complex 4_Fe is only 11.1 kJ/mol less stable than its dihydride 4鈥瞋Fe at the B3LYP/II(f)++//B3LYP/II(f) level. Due to very low energy barrier it is very easy to realize the transform from 4_Fe to 4鈥瞋Fe and vice versa, and thus for Fe there is no substantial difference to differentiate 4 and 4鈥?/b> for the reaction cycle. The most possible key intermediate 4鈥瞋Ru is 38.2 kJ/mol more stable than 4_Ru. However, the barrier for the conversion 3_Ru 鈫?4鈥瞋Ru is 23.8 kJ/mol higher than that for 3_Ru 鈫?4_Ru. Additionally, 4鈥瞋Ru has to go through 4_Ru to complete dehydrogenation 4鈥瞋Ru 鈫?5_Ru. The concerted mechanism 4鈥瞋Ru 鈫?6_Ru, in which the CO group attacks ruthenium while H₂ dissociates, can be excluded. In contrast to Fe and Ru, the dihydrogen complex of Os is too unstable to exist at the level of theory. Moreover, we predict Fe and Ru species are more favorable than Os species for the WGSR, because the energy barriers for the 4 鈫?5 processes of Fe and Ru are only 38.9 and 16.2 kJ/mol, respectively, whereas 140.5 kJ/mol is calculated for the conversion 4鈥?/b> 鈫?5 of Os, which is significantly higher. In general, the calculations are in good agreement with available experimental data. We hope that our work will be beneficial to the development and design of the WGSR catalyst with high performance.}