Identification of Vanadium Oxide Species and Trapped Single Electrons in Interaction with the CeVO4 Phase in Vanadium−Cerium Oxide Systems. 51V MAS NMR, EPR, Raman, and Thermal Analysis Studies

Abstract

Vanadium−cerium oxide catalysts, with different V/Ce atomic ratios, were prepared using vanadyl oxalate (VOC2O4) impregnated on ceria (CeO2) as precursors. Subsequently, the freshly prepared solids were calcined under a flow of dried air at different temperatures from 400 to 800 °C. These solids have been characterized with different techniques: Raman spectroscopy, thermal analysis (TG-DSC), specific area measurements (BET), EPR, and solid-state 51V MAS NMR. Different vanadium species in the vanadium−cerium oxide catalysts have been evidenced. Polymeric V−O−V chains, vanadium tetrahedral surface species, and V2O5 phase are stabilized mainly when solids are calcined in the temperature range 400−500 °C. Their formation also depends on the vanadium content. For higher calcinations temperatures (≥500°C), CeO2 reacts with vanadium (V) species to form a CeVO4 mixed phase. Further to that formation, a single electron is trapped in an oxygen vacancy in the CeVO4 phase and can be considered as its probe.