Effect of direct ultrasound synthesis via a sesquihydrate route on bismuth-promoted vanadyl pyrophosphate catalysts |
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Authors: | Kang-Zhi Goo Yeow-Hong Yap Kuen-Song Lin Loong-Kong Leong |
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Institution: | 1. Department of Chemical Engineering, Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Kajang, Malaysia;2. Department of Chemical Engineering, Materials Science/Environmental Technology Research Center, Yuan Ze University, Taoyuan, Taiwan, ROC |
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Abstract: | A series of 1, 3, and 5% Bi-doped vanadium phosphate catalyst catalysts were prepared via sesquihydrate route using direct ultrasound method and were denoted as VPSB1, VPSB3, and VPSB5, respectively. These catalysts were synthesized solely using a direct ultrasound technique and calcined in a n-butane/air mixture. This study showed that catalyst synthesis time can be drastically reduced to only 2 hr compared to conventional 32–48 hr. All Bi-doped catalysts exhibited a well-crystallized (VO)2P2O7 phase. In addition, two V5+ phases, that is, β-VOPO4 and αII-VOPO4, were observed leading to an increase in the average oxidation state of vanadium. All catalysts showed V2p3/2 at approx. 517 eV, giving the vanadium oxidation state at approx. 4.3–4.6. Field-emission scanning electron microscopy micrographs showed the secondary structure consisting of thin and small plate-like crystal clusters due to the cavitation effect of ultrasound waves. VPSB5 showed the highest amount of oxygen species removed associated with the V5+ and V4+ species in temperature-programmed reduction in H2 analyses. TheX-ray absorption near edge structure (XANES) measurement showed the occurrence of vanadium oxide reductions in hydrogen gas flow, indicating the presence of V4+ and V5+ species. Higher average valence states of V5+, indicating more V5+ phases, were present. The addition of bismuth has increased the activity and selectivity to maleic anhydride. |
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Keywords: | bismuth butane oxidation direct ultrasound synthesis selective oxidation sesquihydrate vanadyl pyrophosphate catalyst |
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