The effect of support on redox properties and methanol-oxidation activity of vanadia catalysts

The effect of support composition on the catalytic properties of isolated mono-vanadates was studied using reaction rates for the methanol-oxidation reaction and oxygen binding from coulometric titration measurements on 2.5 wt%V(2)O(5)/ZrO(2), 2.5 wt%V(2)O(5)/TiO(2), and 5 wt%V(2)O(5)/Al(2)O(3). Although a review of the redox properties for the bulk oxides V(2)O(5), ZrV(2)O(7), AlVO(4), Mg(3)(VO(4))(2), and CeVO(4) showed that the environment surrounding the V cations can have a dramatic effect on the redox properties, the majority of sites on supported catalysts showed nearly identical properties, with Delta G of oxidation being -375 +/- 25 kJ/mol at 748K. The steady-state turnover frequencies for methanol oxidation were also similar (within a factor of 3) on each of the supports over the temperature range from 463 to 528 K. Finally, methanol-oxidation rates in the absence of oxygen over the oxidized vanadia/titania catalyst at 443 K demonstrated that all of the vanadia sites were active for the reaction and exhibited a similar rate to that observed in the presence of oxygen, showing that the reaction follows a Mars-van Krevelen mechanism. (C) 2010 Elsevier B.V. All rights reserved.