The Catalytic Function of Phosphorus Enriched on the Surface of Vanadium‐based Catalysts in Selective Oxidations

In this work, the variation of the phosphorus content on the surface of vanadium-based bulk catalysts by atomic layer deposition is used to experimentally unravel its catalytic functionality in the selective oxidation of n-butane. The consecutive combustion of maleic anhydride is suppressed, due to a surface enrichment with phosphorus.

Abstract

Vanadium phosphates are established as the benchmark system for the selective oxidation of n-butane towards maleic anhydride. By varying the phosphorus content on the surface of three V-based catalysts with diverse performance, this study experimentally elaborates on the catalytic function of phosphorus. Contact time variation and cofeed studies revealed, that surface phosphates, deposited in sub-monolayers via atomic layer deposition, significantly contribute to an increased product selectivity. Furthermore, our results suggest that the phosphorus particularly suppresses the consecutive combustion of the (re-)adsorbed product. The recently introduced solid solution catalyst V_1-xNb_xOPO₄ with medium maleic anhydride selectivity could be tuned by the surface enrichment with phosphorus towards product selectivities of up to S_MAN=60 %, under optimized alkane-rich feed conditions. Therefore, PO_x-V_0.3Nb_0.7OPO₄ is introduced as promising catalyst, which is not based on vanadyl(IV) pyrophosphate, to access significantly higher MAN formation rates at increased alkane partial pressures of c _n-butane>10 %vol in n-butane oxidation.

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