Bismuth-promoted （1% and 3%） vanadyl pyrophosphate catalysts were prepared by refluxing Bi（NO3）4.5H2O and VOPO4.2H2O in isobutanol. The incorporation of Bi into the catalysts lattice increased the surface area and...Bismuth-promoted （1% and 3%） vanadyl pyrophosphate catalysts were prepared by refluxing Bi（NO3）4.5H2O and VOPO4.2H2O in isobutanol. The incorporation of Bi into the catalysts lattice increased the surface area and lowered the overall V oxidation state. Profiles of temperature programmed reduction （TPR） in H2 show a significant shift of the maxima of major reduction peaks to lower temperatures for the Bi-promoted catalysts. A new peak was also observed at the low temperature region for the catalyst with 3% of Bi dopant. The addition of Bi also increased the total amount of oxygen removed from the catalysts. The reduction pattern and reactivity information provide fundamental insight into the catalytic properties of the catalysts. Bi-promoted catalysts were found to be highly active （71% and 81% conversion for 1% and 3% Bi promoted catalysts, respectively, at 703 K）, as compared to the unpromoted material （47% conversion）. The higher activity of the Bi-promoted catalysts is due to that these catalysts possess highly active and labile lattice oxygen. The better catalytic performance can also be attributed to the larger surface area.展开更多
In this study, Cr and Co promoted, as well as unpromoted vanadium phosphate （VPO） catalysts were synthesized by the reaction of V2O5 and o-H3PO4 in organic medium followed by calcination in n-butane/air environment ...In this study, Cr and Co promoted, as well as unpromoted vanadium phosphate （VPO） catalysts were synthesized by the reaction of V2O5 and o-H3PO4 in organic medium followed by calcination in n-butane/air environment at 673 K. The physico-chemical properties and the catalytic behavior were affected by the addition of Cr and Co dopants. H2-TPR was used to investigate the nature of oxidants in the unpromoted and promoted catalysts. The results showed that both the Cr and Co promoters remarkably lowered the temperature of the reduction peak associated with V^5＋. The amount of oxygen species originated from the active phase, V^4＋, removed was significantly increased for Co and Cr-promoted catalysts. Both Cr and Co dopants improve strongly the n-butane conversion without sacrificing the MA selectivity. A good correlation was observed between the amount of oxygen species removed from V^4＋ phase and the activity for n-butane oxidation to maleic anhydride. This suggested that V^4＋-O was the center for the activation of n-butane.展开更多
Four vanadium phosphate catalysts supported on γ-A1203 （20 wt%） were synthesized via wetness impregnation of VOHPO4.0.5H2O precursor and calcined for different durations （6, 10, 30 and 75 h） at 673 K in a reactio...Four vanadium phosphate catalysts supported on γ-A1203 （20 wt%） were synthesized via wetness impregnation of VOHPO4.0.5H2O precursor and calcined for different durations （6, 10, 30 and 75 h） at 673 K in a reaction flow of n-butane/air mixture. The samples calcined for 6 and 10 h produced only a single phase of （VO）2P2O7. However, the VOPO4 phase （β-VOPO4） was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination. All these pyrophosphate peaks disappeared after 75 h of calcination. The formation of V^5＋ phase was also observed in the SEM micrographs. The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H2-TPR analysis. Selective oxidation of n-butane to maleic anhydride （MA） over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V^4＋ to V^5＋ phases. An appropriate ratio of V^5＋/V^4＋ can enhance the performance of the VPO catalyst. However, a higher amount of V^5＋ and its associated oxygen species are responsible to promote the MA selectivity.展开更多
文摘Bismuth-promoted （1% and 3%） vanadyl pyrophosphate catalysts were prepared by refluxing Bi（NO3）4.5H2O and VOPO4.2H2O in isobutanol. The incorporation of Bi into the catalysts lattice increased the surface area and lowered the overall V oxidation state. Profiles of temperature programmed reduction （TPR） in H2 show a significant shift of the maxima of major reduction peaks to lower temperatures for the Bi-promoted catalysts. A new peak was also observed at the low temperature region for the catalyst with 3% of Bi dopant. The addition of Bi also increased the total amount of oxygen removed from the catalysts. The reduction pattern and reactivity information provide fundamental insight into the catalytic properties of the catalysts. Bi-promoted catalysts were found to be highly active （71% and 81% conversion for 1% and 3% Bi promoted catalysts, respectively, at 703 K）, as compared to the unpromoted material （47% conversion）. The higher activity of the Bi-promoted catalysts is due to that these catalysts possess highly active and labile lattice oxygen. The better catalytic performance can also be attributed to the larger surface area.
文摘In this study, Cr and Co promoted, as well as unpromoted vanadium phosphate （VPO） catalysts were synthesized by the reaction of V2O5 and o-H3PO4 in organic medium followed by calcination in n-butane/air environment at 673 K. The physico-chemical properties and the catalytic behavior were affected by the addition of Cr and Co dopants. H2-TPR was used to investigate the nature of oxidants in the unpromoted and promoted catalysts. The results showed that both the Cr and Co promoters remarkably lowered the temperature of the reduction peak associated with V^5＋. The amount of oxygen species originated from the active phase, V^4＋, removed was significantly increased for Co and Cr-promoted catalysts. Both Cr and Co dopants improve strongly the n-butane conversion without sacrificing the MA selectivity. A good correlation was observed between the amount of oxygen species removed from V^4＋ phase and the activity for n-butane oxidation to maleic anhydride. This suggested that V^4＋-O was the center for the activation of n-butane.
文摘Four vanadium phosphate catalysts supported on γ-A1203 （20 wt%） were synthesized via wetness impregnation of VOHPO4.0.5H2O precursor and calcined for different durations （6, 10, 30 and 75 h） at 673 K in a reaction flow of n-butane/air mixture. The samples calcined for 6 and 10 h produced only a single phase of （VO）2P2O7. However, the VOPO4 phase （β-VOPO4） was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination. All these pyrophosphate peaks disappeared after 75 h of calcination. The formation of V^5＋ phase was also observed in the SEM micrographs. The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H2-TPR analysis. Selective oxidation of n-butane to maleic anhydride （MA） over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V^4＋ to V^5＋ phases. An appropriate ratio of V^5＋/V^4＋ can enhance the performance of the VPO catalyst. However, a higher amount of V^5＋ and its associated oxygen species are responsible to promote the MA selectivity.
