Oxygen storage materials in automotive catalysts work to maximize catalytic conversion in dynamic oxygen activity conditions. The currently commercialized materials for this purpose, ceria-zirconia solid solutions, do not function well at temperatures below 300oC, resulting in large emissions of toxic and polluting gases upon cold-start of a vehicle. In previous work, vanadium sesquioxide (V2O3) in the metastable bixbyite crystal phase has been shown to undergo oxygen uptake and release at very low temperatures, with oxygen uptake occuring at temperatures as low as 100oC, owing to the intrinsic oxygen vacancies in the crystal lattice. In this work, bixbyite V2O3 has been synthesized with two aliovalent dopants. Titanium and manganese dopants have been successfully incorporated into V2O3, allowing us to investigate the effect of p- and n-type doping, respectively. Thermogravimetric analysis reveals a slight increase in oxygen storage capacity for both doped materials, along with an effect on the cycling stability after ten oxidation and reduction cycles. Ti-doped materials showed better cycling stability, while Mn-doped materials had minimal effect on cycling stability. Oxygen storage capacity drops significantly upon cycling for all tested materials, driven mainly by irreversible absorption of oxygen during the low temperature half-cycle. Ex situ X-ray diffraction performed on cycled materials show at least two mechanisms for material degradation: irreversible conversion of V2O3 to VO2 and destruction of the crystals to form amorphous material. These effects are strongest for Mn-doped and undoped V2O3, and density functional theory calculations show that negative lattice strain induced by the Ti4+ dopant decreases the formation energy of oxygen interstitials. Since these interstitials are stabilized, they are less likely to cause the formal oxidation of V3+ to V4+, causing transformation to VO2, or to cause destructive strain, resulting in amorphous VOx formation. Therefore, Ti4+ is a beneficial dopant for bixbyite V2O3 for use as an oxygen storage material in automotive catalysis.

Evaluating the effect of dopants on the oxygen storage behavior of bixbyite vanadium sesquioxide (V2O3) nanocrystals

2019 Fall National Meeting

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