Oxidative dehydrogenation of propane on V_2O_5/A1_2O_3 and V_2O_5/TiO_2 catalysts:understanding the effect of support by parameter estimation

摘要

In this paper,the effect of the oxide support for supporting the vanadium oxide phase is studied by estimating the reaction parameters for the oxidative dehydrogenation of propane.To achieve this objective,several V_2O_5/A1_2O_3 and V_2O_5/TiO_2 catalysts were synthesized by an incipient-wetness-impregnation technique.The supported vanadium oxide catalysts were characterized and the surface area,monolayer coverage and reducibility were determined.The surface area of the catalyst samples was not significantly affected with supported vanadium oxide loading.It was observed that the catalysts contain only molecularly dispersed vanadium oxide species below monolayer coverage,and molecularly dispersed and crystalline V_2O_5 above monolayer coverage.TPR studies revealed that the V_2O_5/Al_2O_3 samples were more difficult to reduce relative to the V_2O_5/TiO_2 samples.The monolayer or near-monolayer catalysts,10% V_2O_5/A1_2O_3 and 4% V_2O_5/TiO_2,were selected for detailed kinetic analysis.A Mars-van Krevelen (MVK) model containing eight parameters was chosen for this purpose.The parameters were estimated using a genetic algorithm (GA),which optimizes a suitable objective function for a non-linear multi-response system.From the parameters estimated,it was determined that a similar catalytic cycle occurs independent of the oxide support.However,the rate at which the catalytic cycle occurs appears to be much faster on the more reducible titania support compared to the rate on the less reducible alumina support.The degree of reduction varies along the length of the reactor and depends on the support.Thus,the support has a significant effect on the reaction parameters for the oxidative dehydrogenation of propane over supported vanadium oxide catalysts.