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

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 degreesC. These solids have been characterized with different techniques: Raman spectroscopy, thermal analysis (TG-DSC), specific area measurements (BET), EPR, and solid-state V-51 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 400500 degreesC. Their formation also depends on the vanadium content. For higher calcinations temperatures (greater than or equal to 500degreesC), 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.