Methanol Oxidation to Formate on ALD-Prepared VOx/θ-Al2O3 Catalysts: A Mechanistic Study
journal contributionposted on 27.11.2017, 14:49 by Weiqiang Wu, Kunlun Ding, Jian Liu, Tasha Drake, Peter Stair, Eric Weitz
Well-defined supported VOx/θ-Al2O3 catalysts were prepared by atomic layer deposition (ALD) with vanadium coverages of 0.48, 1.20, and 3.40 wt %. In-situ Raman and UV–vis diffuse reflectance spectroscopy confirm that the monovanadate, VO4, is the predominant vanadium species at low loadings (0.48 and 1.20 wt %), while polyvanadate VO4 is the predominant vanadium species for the 3.40 wt % VOx/θ-Al2O3 catalyst. In-situ FTIR spectroscopy of methanol oxidation to formate, in the absence of gas-phase oxygen, on the 0.48 wt % VOx/θ-Al2O3, identified two different formates. A comparison of the frequencies for the formates adsorbed on just V2O5 and on just θ-Al2O3 demonstrates that one of these formates is located on aluminum sites of VOx/θ-Al2O3 while the other is located on vanadium sites. The oxidation state of vanadium for the VOx/θ-Al2O3 catalyst was determined by XPS after different reaction times. On the basis of the time dependence of the formate absorptions and the change in the oxidation state of vanadium in VOx/θ-Al2O3, a mechanism is proposed for methanol oxidation and we discuss the role of the alumina support in the mechanism.