화학공학소재연구정보센터
Journal of Molecular Catalysis A-Chemical, Vol.424, 1-7, 2016
A density functional theory study of ethylene epoxidation catalyzed by niobium-doped silica
A mechanistic study of ethylene epoxidation by hydrogen peroxide catalyzed by niobium doped in a silica mesopore is reported. Density functional theory calculations at the M06-L/aug-cc-pVDZ level were used to investigate the catalytic pathway. A five-step cycle is proposed. The initial steps are the adsorption of H2O2 to the Nb center followed by coordination of ethylene to the hydrogen peroxide. The rate-limiting step is the subsequent epoxidation of ethylene via transfer of an oxygen atom, which has a calculated enthalpic barrier of 11.6 kcal/mol relative to the preceding intermediate. This is followed by desorption of the ethylene oxide product and dehydration to regenerate the catalyst. The reaction barrier is lower than reported for other catalysts in the literature, consistent with recent experimental reports of the efficacy of Nb-doped mesoporous silica catalysts [Catal. Sci. Technol., 2014, 4, 4433-4439].The mechanistic details elucidated in the present calculations may aid in the rational design of new epoxidation catalysts and thus the factors influencing the reaction, e.g., geometry and charge changes, are discussed. (C) 2016 Elsevier B.V. All rights reserved.