Synthesis and properties of VPO catalysts for oxidation of n-butane to maleic anhydride

Bulk and supported vanadium-phosphorus oxide VPO catalysts were synthesized by traditional and barothermal methods. It was shown that the use of aerosil as a support for the VPO phase, depending on the time of its introduction into the reaction mixture. It can lead to the formation of catalyst precursor of vanadyl hydrogen phosphate VOHPO4 0.5H2O, or a phase of vanadyl pyrophosphate (VO)2P2O7 as already the catalytically active phase for selective oxidation of n-butane to maleic anhydride. The use of a modified aerosil gel formed from pyrogenic aerosol, as a support for the VPO phase, leads to the formation of VOHPO4∙0.5H2O phase. It has been found that the nature of support affects the features of formation of VOHPO4∙0.5H2O phase, in particular, the ratio of crystallographic planes in resulting VPO phase. The use of aerosil as a support leads to a decrease in the relative content of the basal plane, while use of aerosil gel leads to an increase in the relative content of the basal plane in applied VPO phase. The catalytic properties of bulk and supported VPO samples were studied in the selective oxidation of n-butane to maleic anhydride in standard (1.7 vol.%) and enriched (3.4 vol.%) n-butane mixtures. It has been found that in an enriched n-butane mixture for bulk samples, the n-butane conversion and selectivity for maleic anhydride are sharply reduced. It has been found that supported VPO samples have a higher specific rate of n-butane oxidation and higher productivity compared to bulk samples. It was shown that use of barothermal synthesis and aerosol gel as a support made it possible to increase the selectivity of maleic anhydride, which is associated with an increase in the relative content of the basal plane of VPO phase. The achieved improved catalytic properties of VPO catalysts supported with aerosol gel make recycling technology promising. This can make the production of maleic anhydride more economical.