Catalytic Mechanisms of Methanol Oxidation to Methyl Formate on Vanadia–Titania and Vanadia–Titania–Sulfate Catalysts

Abstract

Density functional theory calculations were carried out using both cluster and slab models to investigate the catalytic reaction network and the effect of sulfate promoter on methanol selective oxidation using the V2O5/TiO2 catalyst. The hemiacetal mechanism was reaffirmed to be the most favorable reaction pathway for the formation of methyl formate (MF) by the prediction of another reaction pathway involving formic acid. Molecular oxygen was found to assist the desorption of the reaction products from the reduced catalyst active site, both formaldehyde and methyl formate (MF). The mechanism of catalyst regeneration was elucidated based solely on first-principles calculations, which involve the conversion of another methanol molecule to formaldehyde over a peroxo species. This leads to our formulation of a complete catalytic reaction network for methanol selective oxidation to formaldehyde and MF on the V2O5/TiO2 catalyst. In addition, the detailed mechanism for the formation of formaldehyde and MF was also predicted on the sulfate-promoted V2O5/TiO2 catalyst. Based on the calculated reaction networks, the preferred formation of MF on the V2O5/TiO2-based catalysts was attributed to the lower energy barrier of the oxidative dehydrogenation (ODH) of the CH3OCH2O* intermediate than that of CH3O*. Furthermore, our calculated energy barriers also suggest that the sulfate-promoted V2O5/TiO2 catalyst has not only higher catalytic activity for methanol conversion but also higher selectivity of MF over CH2O, consistent with previous experimental observations. The sulfate promoter was found to increase the positive charge at the V site, leading to a lower energy barrier for the ODH of CH3O* than the unpromoted catalyst.

Oxidative esterification of acetol with methanol to methyl pyruvate over hydroxyapatite supported gold catalyst: Essential roles of acid-base properties

“…MPA here) is unlikely to play a major role under the alcohol solvent [29,48], which (namely pyruvic acid in this work) is indeed not observed in our case. Instead, the most likely pathway would probably proceed via first the formation of hemiacetal, and the subsequent oxidation to MPA, which is consistent with that proposed by the experimental and theoretical works based on the oxidative esterification of primary alcohols [29,[34][35][36]48]. Both of these two steps would take place rather rapidly, thus leaving the intermediates present with amounts below the detection limit during the entire reaction, which is also in agreement with the other's work involving PA and hemiacetal as the intermediates [29,48].…”

“…Instead, the amphoteric catalysts containing both basicity and proper acidity such as Au/ZrO2 [30], Au/ZnO [31], Au/β-Ga2O3 [32], and Au/Ga3Al3O9 [33] are more efficient for the overall oxidative esterification compared to the catalysts containing only basicity. This appears to be reasonable, as the favorable pathway is generally believed to proceed via the oxidation of primary alcohol to aldehyde, followed by the reaction with alcohol to form hemiacetal intermediate, which is then further oxidized to the corresponding ester [34][35][36]. It has been reported that the condensation of methanol and aldehyde to form hemiacetal has a low energy barrier in the presence of acid sites [35,36].…”

“…This appears to be reasonable, as the favorable pathway is generally believed to proceed via the oxidation of primary alcohol to aldehyde, followed by the reaction with alcohol to form hemiacetal intermediate, which is then further oxidized to the corresponding ester [34][35][36]. It has been reported that the condensation of methanol and aldehyde to form hemiacetal has a low energy barrier in the presence of acid sites [35,36]. In addition, gold nanoparticles can be better stabilized by the Lewis acid inherent on the supports [37].…”

CuO Nanoparticle-Decorated TiO2-Nanotube Heterojunctions for Direct Synthesis of Methyl Formate via Photo-Oxidation of Methanol

“…Therefore, methyl formate (MF), produced from methanol and containing a number of organic functional groups (aldehyde, ether, and methyl groups), has been considered as an important chemical intermediate and as environmentally benign chemicals in the emerging area of “green chemistry”. It is widely used in the chemical industry to produce dozens of chemicals and is exploited as an important precursor in the pharmaceutical and pesticide productions. − Generally, MF is produced via the carbonylation and dehydrogenation reactions of methanol at a high temperature (>100 °C). These thermal synthetic methods suffer from medium conversion ( e.g ., <50%) and a large lack of product selectivity ( e.g .…”

Recent Advances in Aerobic Photo‐Oxidation of Methanol to Valuable Chemicals

“…Methyl formate (MF, HCOOCH 3 ) and dimethoxymethane (DMM, CH 3 OCH 2 OCH 3 ), produced from methanol, have been considered as significant organic processing intermediates in C 1 based chemistry and as environmentally benign chemicals in the emerging area of “green chemistry”. They are widely applied for the production of chemicals, such as formic acid and formamide [3,4] . Both the MF and DMM, containing several organic substituents (e. g., aldehyde, ester, ether, and methyl groups), also is used as important precursors to produce pharmaceuticals and pesticides and as an additive to petroleum [5] .…”