Redox features of β-VOPO 4 catalyst using [formula omitted] tracer and laser Raman spectroscopy

Abstract

The oxygen ions of the β-VOPO 4 catalyst were exchanged with an 18 O tracer by a reduction–oxidation method and by a catalytic oxidation of but-1-ene using 18 O 2. The bands at 992 and 900 cm −1 were more shifted to lower frequencies than those at 1076 and 1002 cm −1. Applying the correlation between the Raman bands and stretching vibrations in the literature, the exchanged oxygen species were estimated. The results suggest that the P–O–V vacancies corresponding to 992 and 900 cm −1 were responsible for reoxidation and the VO oxygen corresponding to the 1002 cm −1 band of β-VOPO 4 was not. The (VO) 2P 2O 7 was oxidized to β-VOPO 4 by O 2 above 823 K. The insertion position of oxygen was determined at the bands at 992 and 900 cm −1 of β-VOPO 4 using 18 O 2, which is the same as the exchanged position.