Vanadium–phosphorous oxide supported on mesoporous SBA-15 catalysts for ammoxidation of toluene to benzonitrile†
Abstract
Mesoporous silica (SBA-15)-supported vanadium–phosphorous oxide (VPO) catalysts with different VPO wt% synthesized by a deposition–precipitation method were studied for the direct synthesis of nitriles by a toluene ammoxidation process. The calcined catalysts were characterized by various analytical techniques to determine the phases present in the samples, oxidation states of vanadium, reducibility and acidity of the samples. The formation of various types of VOPO4 phases in both SBA-15-supported VPO samples and unsupported VPO samples is inferred from the XRD analysis results. However, UV-DRS and XPS studies reveal that the synthesized samples comprise both a vanadyl pyrophosphate phase and a vanadium orthophosphate phase in both supported and unsupported VPO samples. TPR analysis demonstrates that the reducibility of the supported VPO is higher than that of the pure VPO catalyst. Ammonia desorption studies suggest that the total acidity increases with VPO loading. The results for ammoxidation of toluene show that VPO/SBA-15 catalysts exhibit better catalytic properties than unsupported VPO catalysts and are well correlated with the reducibility of the catalysts.
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