1 research outputs found
Methanol Oxidation to Formate on ALD-Prepared VO<sub><i>x</i></sub>/θ-Al<sub>2</sub>O<sub>3</sub> Catalysts: A Mechanistic Study
Well-defined
supported VO<sub><i>x</i></sub>/θ-Al<sub>2</sub>O<sub>3</sub> 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, VO<sub>4</sub>, is the predominant vanadium species
at low loadings (0.48 and 1.20 wt %), while polyvanadate VO<sub>4</sub> is the predominant vanadium species for the 3.40 wt % VO<sub><i>x</i></sub>/θ-Al<sub>2</sub>O<sub>3</sub> catalyst. In-situ
FTIR spectroscopy of methanol oxidation to formate, in the absence
of gas-phase oxygen, on the 0.48 wt % VO<sub><i>x</i></sub>/θ-Al<sub>2</sub>O<sub>3</sub>, identified two different formates.
A comparison of the frequencies for the formates adsorbed on just
V<sub>2</sub>O<sub>5</sub> and on just θ-Al<sub>2</sub>O<sub>3</sub> demonstrates that one of these formates is located on aluminum
sites of VO<sub><i>x</i></sub>/θ-Al<sub>2</sub>O<sub>3</sub> while the other is located on vanadium sites. The oxidation
state of vanadium for the VO<sub><i>x</i></sub>/θ-Al<sub>2</sub>O<sub>3</sub> 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 VO<sub><i>x</i></sub>/θ-Al<sub>2</sub>O<sub>3</sub>, a mechanism
is proposed for methanol oxidation and we discuss the role of the
alumina support in the mechanism