期刊論文

標題 Ab initio study of the reaction mechanism of CO2 with Ti atom in the ground and excited electronic states
學年 90
學期 2
出版(發表)日期 2002/04/01
作品名稱 Ab initio study of the reaction mechanism of CO2 with Ti atom in the ground and excited electronic states
作品名稱(其他語言)
著者 黃德彥; Hwang, Der-yan; Mebel, Alexander M.
單位 淡江大學化學學系
出版者 American Institute of Physics (AIP)
著錄名稱、卷期、頁數 Journal of chemical physics 116(13), pp.5633-5642
摘要 Density functional B3LYP/6-3111G(3d f )//B3LYP/6-31G* calculations of potential energy surfaces ~PES! have been performed for the Ti1CO2→TiO1CO reaction in the triplet, quintet, and singlet electronic states. The results indicate that in the ground triplet state the most favorable reaction mechanism involves insertion of the Ti atom into a CO bond @via a h2-C,O coordinated t-~TiOC!O complex# to produce a triplet t-OTiCO molecule with the energy gain of 43.9 kcal/mol and the latter can further dissociate to TiO(3D)1CO with the total reaction exothermicity of ;30 kcal/mol. The addition mechanism leading to the same TiO(3D)1CO products via a metastable h2-O,O complex t-cyc-TiCO2 is also feasible at ambient temperatures since the highest barrier on the reaction pathway is only 4.7 kcal/mol. The reaction mechanisms in excited singlet and quintet electronic states have many similar features with the ground state reaction but also exhibit some differences. In the singlet state, the reaction can follow 1A9 and 1A8 pathways, of those the insertion via a s-~TiOC!O (1A8) complex leading to s-OTiCO (1A8) and then to TiO(1D)1CO does not have an activation barrier. The insertion mechanism on the 1A9 PES depicts a low barrier of 1.8 kcal/mol and leads to s-OTiCO (1A9), which dissociates into TiO(1D)1CO. The addition pathways via h2-O,O coordinated complexes require to overcome significant barriers, 7.8 and 34.9 kcal/mol for the 1A9 and 1A8 states, respectively. In the quintet state, the reaction at low and ambient temperatures can proceed only by coordination of Ti(5F) toward CO2 with formation of h2-C,O q-~TiOC!O, h2-O,O q-cyc-TiCO2 , and h1-O q-TiOCO bound by 9.7, 6.1, and 4.6 kcal/mol, respectively, relative to the reactants. The h2-C,O and h1-O coordinations occur without barriers, while the h2-O,O coordination has an entrance barrier of 4.2 kcal/mol. The calculated PESs show that the carbon dioxide reforming into CO in the presence of Ti atoms should take place spontaneously.
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語言 英文
ISSN 0021-9606
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