Density functional theory study of the oxidation of methanol to formaldehyde on a hydrated vanadia cluster |
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Authors: | P. González‐Navarrete L. Gracia M. Calatayud J. AndréS |
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Affiliation: | 1. Departament de Química Física i Analítica, Universitat Jaume I, Box 224, Castelló 12071, Spain;2. Laboratoire de Chimie Théorique, UMR 7616, Univ. P. et M. Curie Paris 06, Paris 75005, France;3. Laboratoire de Chimie Théorique, CNRS, UMR 7616, Paris F‐75005, France;4. MALTA Consolider Team, Departament de Química Física i Analítica, Universitat Jaume I, Box 2 24, Castelló 12071, Spain |
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Abstract: | Density functional theory was used to study the mechanism for the oxidation of methanol to formaldehyde. A vanadium oxide cluster O?V(OH)3 has been utilized to represent the catalytic system under hydrated conditions, i.e., in the presence of V? OH hydroxyl groups. Two types of methoxy‐intermediates have been considered: a penta‐coordinate methoxy‐intermediate (OH)4V(OCH3) and a tetrahedral methoxy‐intermediate (OH)2VO(OCH3)(H2O). The most plausible reaction pathway corresponds to the process involving first the formation of the tetrahedral methoxide, and a subsequent rate‐limiting step where hydrogen is transferred from the methoxy groups toward the oxygen atom of the vanadyl V?O site. The reaction mechanism is a typical two‐state reactivity process due to a change of the multiplicity (reactive singlet → product triplet) along the reaction coordinate accompanied by a reduction of the vanadium center from VV (d0) to VIII (d2). Minimum energy crossing points were localized and possible spin inversion processes are discussed by means of the intrinsic reaction coordinate approach to find the most favorable reaction pathways. The hydration effect is found to be mainly the destabilization of the methoxy intermediates. An alternative reaction pathway with a lower apparent barrier is presented. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 |
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Keywords: | hydration water B3LYP V2O5 open‐shell singlet spin‐crossing |
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