Highly Efficient and Stable Vanadia-Titania-Sulfate Catalysts for Methanol Oxidation to Methyl Formate: Synthesis and Mechanistic Study

摘要

Vanadia-titania-sulfate nanocatalysts for methanol oxidation to methyl formate (ME) were prepared by coprecipitation. When calcinated at 400 degrees C, both methanol conversion and MF selectivity reached similar to 98.5% at reaction temperatures of 140-145 degrees C. Characterizations with several experimental techniques revealed the catalysts as highly dispersed vanadia supported by anatase titania with acidic sites of significant strength and density. The catalysts also showed very high stability with lifetime exceeding 4500 h. Extensive density functional theory calculations using both cluster and surface models revealed MF to form via the hemiacetal mechanism, involving the condensation of methanol and formaldehyde at acidic sites and methanol and hemiacetal oxidations at redox sites. The alternative formyl mechanism was predicted kinetically much less favorable, showing these catalysts to work in a distinct mechanism from the rutile titania photocatalyst. Interestingly, methanol chemisorption at redox sites leads to the formation of acidic sites capable of catalyzing the condensation reaction.