First principles studies on the selectivity of dimethoxymethane and methyl formate in methanol oxidation over V2O5/TiO2-based catalysts

Na Li; Shibin Wang; Yuhan Sun; Shenggang Li

doi:10.1039/c7cp02326j

First principles studies on the selectivity of dimethoxymethane and methyl formate in methanol oxidation over V₂O₅/TiO₂-based catalysts

Phys Chem Chem Phys. 2017 Jul 26;19(29):19393-19406. doi: 10.1039/c7cp02326j.

Authors

Na Li¹, Shibin Wang², Yuhan Sun², Shenggang Li²

Affiliations

¹ CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai Advanced Research Institue, Chinese Academy of Sciences, 100 Haike Road, Shanghai 201210, China. [email protected] and Department of Chemistry, Shanghai University, 99 Shangda Road, Shanghai 200444, China.
² CAS Key Laboratory of Low-Carbon Conversion Science and Engineering, Shanghai Advanced Research Institue, Chinese Academy of Sciences, 100 Haike Road, Shanghai 201210, China. [email protected] and School of Physical Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210, China.

PMID: 28715018
DOI: 10.1039/c7cp02326j

Abstract

First principles calculations using both molecular cluster and periodic slab models were performed to reveal the mechanism for the formation of dimethoxymethane (DMM) from methanol over V₂O₅/TiO₂-based catalysts. Two different pathways were found, and the formation of DMM was predicted to be initiated by methanol chemisorption followed by a dehydration reaction with hemiacetal catalyzed by acidic sites. For unpromoted V₂O₅/TiO₂ catalysts, we predicted the energy barrier for the rate determining step (RDS) to follow the order formaldehyde (FA) > methyl formate (MF) > DMM, consistent with the experimental observation for the preferential formation of DMM at a relatively low temperature and that of MF at a relatively high temperature. For sulfate-promoted catalysts, the energy barriers were calculated to follow the order FA > DMM > MF, so the sulfate promoter was predicted to mainly enhance the selectivity of MF, consistent with our previous experiment in which very high yield of MF was obtained with the sulfate-promoted catalyst. Calculated rate constants for the RDS were further used for semi-quantitative predictions of the product selectivities, which were found to be in quite good agreement with some of the recent experimental data in the literature, showing the validity of our approach. We also investigated the effects of the titania support and the polymerization of the vanadia species on the reactivity of the V₂O₅/TiO₂ catalyst. Finally, we benchmarked several popular exchange-correlation functionals for calculating the reaction energies for the formation of FA, MF, and DMM from methanol oxidation, and the M06 hybrid functional was found to be superior to other semi-local and hybrid functionals studied.