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 (VOC 2 O 4 ) impregnated on ceria (CeO 2 ) 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 solidstate 51 V MAS NMR. Different vanadium species in the vanadium-cerium oxide catalysts have been evidenced. Polymeric V-O-V chains, vanadium tetrahedral surface species, and V 2 O 5 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 (g500°C), CeO 2 reacts with vanadium (V) species to form a CeVO 4 mixed phase. Further to that formation, a single electron is trapped in an oxygen vacancy in the CeVO 4 phase and can be considered as its probe.

Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

“…The silica features are not observed since this is in amorphous form and the preferential formation of CeVO 4 indicates that supported vanadia interacts selectively with the ceria portion of the promoted support [26]. Similar studies with low surface area metal oxide supports suggest the formation of CeVO 4 and further crystallization even at 500 • C [27]. Crystallite size (Table 1) of silica promoted ceria is lowered compared to ceria.…”

Study of the Crystallization of Nanoporous Mixed Metal Oxide Phases

“…may occur during calcination, and therefore suggests the proximity of these ions in the pre-calcination solid (Matta et al 2002;Cousin et al 2007;Reddy et al 2004).…”

Effect of the physico-chemical properties of vanadia/praseodymia on cyclohexanol decomposition

“…To this, the finely powdered dried support was added, stirred for 6 h at room temperature and kept overnight. The excess water was evaporated by stirring, and the resulting material was oven dried at 110°C for 12 h and subsequently calcined at 500°C for 5 h in a muffle furnace in air atmosphere [10]. The catalysts composition was obtained from Stereoscan 440 Cambridge, UK energy dispersive X-ray analyzer.…”