Elucidating the Support-Size Effect on the Catalytic Stability of CrOx/Silicalite-1 for Oxidative Dehydrogenation of Propane with CO2

By impregnating 3 wt% Cr into the hydrothermally synthesized silicalite-1 with an average crystal size of 0.06-0.35 mu m, the effects of the silanol-group density on the dispersion, structural and electronic characteristics of Cr(VI) oxides are studied for the oxidative dehydrogenation of propane with carbon dioxide (CO2-ODP). Characterization results reveal that the CrOx species are highly dispersed over silicalite-1 irrespective of the crystal sizes, and the highest CrOx dispersion is achieved over silicalite-1 with an average crystal size of 0.15 mu m due to its highest density of the silanol nests. Moreover, the textural properties and the relative quantity of the Cr(VI) oxides with different structures are strongly affected by the crystal size of the zeolite. The catalyst by using 0.15 mu m silicalite-1 as the support shows the most stable performance for CO2-ODP indexed by the C3H6 yield, which is much superior to the remaining catalysts. The correlation of the characterization data of the fresh and representative spent catalysts with the reaction results rigorously reveals that the catalytic stability of CrOx/silicalite-1 for CO2-ODP is mainly determined by the dual functions of the deposited coke, which is basically originated from the interactions between Cr(VI) oxides and the support. These understandings on the stability of CrOx isilicalite-1 raised essentially from the density of silanol nests over silicalite-1 are beneficial for developing more efficient Cr-based catalysts for the non-oxidative & oxidative dehydrogenation of short alkanes including CO2-ODP. [GRAPHICS] .