The nature of the active site of the (VO)2P2O7 catalyst: An investigation of the chemical composition and dynamics of the catalyst surface

Publisher Summary This chapter discusses the influence of water vapor on the chemical composition of the surface and on the activity and selectivity of an equilibrated (VO) 2 P 2 O 7 catalyst intending to get a better understanding of the dynamics of the catalyst surface and the nature of the active site of this catalyst. The surface layer of an equilibrated (VO) 2 P 2 O 7 catalyst consists of a vanadium phosphorus oxide (VPO) structure with a P:V ratio of about two and in the next subsurface layers also higher P:V ratios than one have to be assumed. To elucidate the structure of the active site of the (VO) 2 P 2 O 7 catalyst, some characteristics of the known active site models are given, usually the active center is described in terms of the bulk structure sometimes terminated in pyrophosphate groups stressing the role of edge-shared VO 6 double octahedra. However, the existence of these VO 6 double octahedra on the surface plane parallel to (100) has not been proven up to now for the equilibrated (VO) 2 P 2 O 7 catalyst, the surface of which is enriched in phosphorus, because of the formation of water in the butane oxidation.