VPO catalyst transformations were investigated using in situ laser Raman spectroscopy. During reduction -oxidation step changes, (VO)2P2O7 was readily converted to αII-, δ-VOPO4, and ultimately to β-VOPO4 in O2/N2; these V5+ phases were eliminated in n-butane/N2. A wet N2 feed (5-10% H2O in N2) transformed (VO)2P2O7 and αI-, αII-, β-, δ-, γ-VOPO4 to V2O5 at temperatures above 400°C. The presence of water vapor facilitated the loss of oxygen atoms involved in V - O - P bonding, and separated vanadium oxide and phosphorus oxide species were formed. The isolated vanadium oxide species could be transformed to V2O5; phosphorus species likely diffused from the catalyst lattice in the form of acid phosphates.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry