Studies On The Selective Oxidation Of Propane Over SBA-15-supported V-and Mo-based Catalysts

The direct synthesize of propene and acrolein from propane is one of the important ways to optimize the light alkanes. Many researches have shown that Vanadium and Molybdenum oxides are the most important components for selective oxidation of light alkanes and the highly dispersed active sites can help the improvement of the selectivity of the products.In the present work, SBA-15-supported highly dispersed Vanadium and Molybdenum oxides catalysts were prepared for the selective oxidation of propane. The effects of different preparation methods, carriers and reaction conditions were investigated. Furthermore, the catalysts were characterized in details by XRD,TPR,Raman,BET,ICP,TEM,UV-Vis, etc to elucidate the structure-reactivity relationships. The main results are summarized as follows:1) SBA-15-supported vanadium oxide catalysts have been successfully prepared by a grafting/anion exchange method. The experimental result of XRD and the In-situ Raman Spectroscopy indicates that the order of the dispersed degree of Vanadium species prepared through different methods or carriers are in the following order: VO_x/SBA-15(G/E) > VO_x/SBA-15(wet-impregnant method) > VO_x/SiO₂ (wet-impregnant method)。2) This paper is the first time to use VO_x/SBA-15(G/E) catalysts in the selective oxidation of propane prepared through a grafting/ anion exchange method. In comparison with the SiO₂-supported vanadium oxide catalysts, SBA-15-supported vanadium oxide catalysts show higher catalytic performance for the oxidative dehydrogenation of propane to propene, furthermore, the catalysts prepared by the grafting/anion exchange method exhibit higher performance than those prepared by wet-impregnant method. From the results of the catalysts characteriazation and reaction, it is shown that the degree of dispersed VO_x species greatly influence the performance of surported vanadium oxide catalysts. 3) Vanadium-containing SBA-15 was first successfully synthesized through peroxo route. Our data suggest that the vanadium is inserted within the mesoporous framework with high metal dispersion. Compared with VO_x/SiO₂, VO_x/MCM-41 and VO_x/SBA-15 catalysts prepared by traditional wet-impregnant methods, the catalyst obtained in this way exhibits a better catalytic performance for ODH of propane. The highest propene yield obtained on the VO_x-SBA-15 catalyst prepared by peroxo route reaches more than 20% and propene space-time yield up to 3.4 kg·kgcat-1·h-1. The excellent catalytic performance is probably related to the high surface area, improved reducibility and well V-dispersion of the catalyst.4) Supported molybdenum oxides with different supports have been studied. The unique catalytic performance of MoOx/SBA-15 catalyst for propane oxidation to oxygenates has been found for the first time. Best result was obtained on the 9MoOx/SBA-15 with the yield of acrolein more than 5%. The characterization results showed that the improved reducibility and MoOx dispersion might answer for the high catalytic performance of MoOx/SBA-15 catalysts.