Method for quantifying redox site densities in metal oxide catalysts: Application to the comparison of turnover frequencies for ethanol oxidative dehydrogenation over alumina-supported VOx, MoOx, and WOx catalysts

Isothermal anaerobic titration with ethanol as a probe molecule is proposed as an accurate technique to quantify active redox site densities in supported metal oxide catalysts. It is shown that the number of active redox sites for VOx–Al2O3, MoOx–Al2O3, and WOx–Al2O3 catalysts is a function of both the metal atom and its oxide surface density, but the intrinsic redox rate per active site is independent of both of these factors. Thus, the difference in steady-state redox rates per metal atom is due only to differences in the number of redox sites under reaction conditions.