Modification and Characterisation of Vanadium Phosphorus Oxide Catalysts for Selective Oxidation of Propane to Acrylic Acid

Vanadium phosphate catalysts synthesized via VOPO4∙2H2O were further reduced in isobutanol to produce VOHPO4∙0.5H2O precursor. Calcination of this precursor in propane/air environment (1% propane in air) transformed into activated (VO)2P2O7 catalysts. The morphology, structure, oxidant’s nature and catalytic performance for propane oxidation to acrylic acid over this catalyst strongly depended on the duration of calcination. The catalyst calcined for 36 h (VPD36P) exhibits low surface area. However, prolonged calcination promoted a higher surface area with better crystallization. VIII and VV phases are detected in all catalysts. The SEM micrographs showed that all propane/air catalysts gave rosebud type agglomerates with various sizes but in a uniform shape. A comparison of effect of calcinations environments on the vanadium phosphate catalyst in flow of both propane/air and butane/air, the latter calcinations environment produced catalyst with more platelet and higher surface area. Chemical analysis also shows that VPDB catalyst consist of higher amount of VV (26%) and 74% of VIV phase whereas VPDP only contains 76 and 9.8% of VIV and VV phases, respectively. Interestingly, VPDP also showed 14.2% of VIII phase. For n-butane oxidation at 673 K, VPDB gave 83% of conversion and 63% of MA selectivity whereas VPDP gave 75% of conversion and 64% of MA selectivity. The n-butane/air calcined catalyst, VPDB showed better activity (14.1%) in propane oxidation than the propne/air calcined catalyst, VPDP (7.9%). The addition of 1, 2 and 5 mol % of Zr into (VO)2P2O7 catalysts produced a single vanadyl pyrophosphate phase in VOPO4∙2H2O method with different degree of crystallinity. The presence of lower percentage of Zr (1 and 2%) improved the surface area of the catalysts; however, the surface area of the catalyst with 5% of Zr added is decreased. The SEM micrograph for all Zr modified catalysts gave roughed rosebud agglomerates as compared to the unpromoted catalyst. VPDZr1 catalyst was found to be the most selective catalyst among all the Zr doped catalysts in propane oxidation.

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