Density functional theory study of the oxidation of methanol to formaldehyde on a hydrated vanadia cluster

✍ Scribed by P. González-Navarrete; L. Gracia; M. Calatayud; J. AndréS

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 1013 KB
• Volume: 31
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.21543

✦ Synopsis

Density functional theory was used to study the mechanism for the oxidation of methanol to formaldehyde. A vanadium oxide cluster O¼ ¼V(OH) 3 has been utilized to represent the catalytic system under hydrated conditions, i.e., in the presence of VÀ ÀOH hydroxyl groups. Two types of methoxy-intermediates have been considered: a penta-coordinate methoxy-intermediate (OH) 4 V(OCH 3 ) and a tetrahedral methoxy-intermediate (OH) 2 VO(OCH 3 )(H 2 O). 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 V¼ ¼O 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 V V (d 0 ) to V III (d 2 ). 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.