Use of 31P NMR by Spin Echo Mapping to prepare precursors of Vanadium Phosphate catalysts for n-Butane oxidation to Maleic anhydride

Abstract

Vanadium phosphate oxide (VPO) catalysts perform the mild oxidation of n-butane to maleic anhydride. The preparation of the precursor of this catalyst, the vanadyl phosphate hemihydrate VOHPO 4 , 0.5 H 2 O, is very important in controlling the final properties of the VPO catalyst because the transformed precursor/vanadyl pyrophosphate (VO) 2 P 2 O 7 , which corresponds to the final active phase, is topotactic. Thus, it is possible to control the morphology of the final catalyst by controlling the morphology of its precursor. This chapter demonstrates the development of 31 P NMR by spin echo mapping to study VPO catalysts. 31 P NMR by spin echo mapping is a powerful technique that enables preparing VOHPO 4 , 0.5 H 2 O phase, the precursor of the VPO catalyst for n-butane oxidation to maleic anhydride. It also permits the detection of the transient appearance of intermediate hydrated VOPO 4 phases, which is difficult to be observed by X-ray diffraction (XRD). The hemihydrate is more easily detected by 31 P NMR by spin echo mapping as compared to XRD.