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

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 V1‐xNbxOPO4 with medium maleic anhydride selectivity could be tuned by the surface enrichment with phosphorus towards product selectivities of up SMAN = 60%, under optimized alkane‐rich feed conditions. Therefore, POx‐V0.3Nb0.7OPO4 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 cn‐butane > 10%vol in n‐butane oxidation.