TiP2O7catalysts characterised by in situRaman spectroscopy during the oxidative dehydrogenation of n-butane

Abstract

The structural and chemical stability of TiP₂O₇ has been investigated by Raman spectroscopy under an n-butane–O₂–He gas mixture (1∶1∶2). Titanium pyrophosphate powders with low and high specific surface areas have been characterised up to 560 °C. No structural transition or chemical decomposition was evidenced under the gas feed used. However, the overall intensity of the Raman spectrum decreased sharply at 400 °C in parallel with the deposition of disordered graphite at the surface and reappeared above 450 °C when the carboneous compound burned. This phenomenon was completely reversible on decreasing the temperature. The deposit appearing with the reduction of TiP₂O₇ could arise from the trapping of reaction intermediates by oxygen vacancies at the surface. Above 450 °C, the carboneous compound disappeared when the diffusion rate of oxygen vacancies increased. The same phenomenon was observed on high surface area TiP₂O₇ for which supplementary bands assigned to surface modes were observed.