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    題名: Ab initio study of the reaction mechanism of CO2 with Ti atom in the ground and excited electronic states
    作者: 黃德彥;Hwang, Der-yan;Mebel, Alexander M.
    貢獻者: 淡江大學化學學系
    日期: 2002-04-01
    上傳時間: 2009-12-01
    出版者: American Institute of Physics (AIP)
    摘要: Density functionalB3LYP/6-311+G(3df )//B3LYP/6-31G * calculations of potential energy surfaces (PES) have been performed for the Ti+CO 2 →TiO+CO 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 η 2 -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( 3 Δ)+CO with the total reaction exothermicity of ∼30 kcal/mol. The addition mechanism leading to the same TiO( 3 Δ)+CO products via a metastable η 2 -O,O complex t-cyc-TiCO 2 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 1 A ′′ and 1 A ′ pathways, of those the insertion via a s-(TiOC)O ( 1 A ′ ) complex leading to s-OTiCO ( 1 A ′ ) and then to TiO( 1 Δ)+CO does not have an activation barrier. The insertion mechanism on the 1 A ′′ PES depicts a low barrier of 1.8 kcal/mol and leads to s-OTiCO ( 1 A ′′ ), which dissociates into TiO( 1 Δ)+CO. The addition pathways via η 2 -O,O coordinated complexes require to overcome significant barriers, 7.8 and 34.9 kcal/mol for the 1 A ′′ and 1 A ′ states, respectively. In the quintet state, the reaction at low and ambient temperatures can proceed only by coordination of Ti( 5 F) toward CO 2 with formation of η 2 -C,O q-(TiOC)O, η 2 -O,O q-cyc-TiCO 2 , and η 1 -O q-TiOCO bound by 9.7, 6.1, and 4.6 kcal/mol, respectively, relative to the reactants. The η 2 -C,O and η 1 -O coordinations occur without barriers, while the η 2 -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.
    關聯: Journal of chemical physics 116(13), pp.5633-5642
    DOI: 10.1063/1.1453954
    顯示於類別:[化學學系暨研究所] 期刊論文


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