Role of Oxygen Vacancies in Catalytic SO3 Decomposition over Cu2V2O7 in Solar Thermochemical Water Splitting Cycles

摘要

We report the structure-activity relationship of copper pyrovanadate (Cu2V2O7) as an efficient catalyst for SO3 decomposition in solar thermochemical water splitting cycles. Of the α, β and γ polymorphs of Cu2V2O7, the α-phase, which has a blossite-type structure, was stable under the catalytic reaction conditions. Spontaneous oxygen desorption accompanied by charge compensation through the reduction of Cu~(2+) to Cu~+ produced an oxygen deficiency corresponding to Cu_(16)V_(16)O_(55) at 600 °C. Density functional theory calculations based on these results showed that oxygen vacancy formation is more favorable on the Cu-O-V bridging sites than on the V-O- V site in the pyrovanadate unit. The oxygen vacancy formation energy of the (100) surface is considerably less than that of bulk Cu_(16)V_(16)O_(56). The reaction, Cu_(16)V_(16)O_(55) + SO3 → Cu_(16)V_(16)O_(56)+ SO2, is exothermic, suggesting that oxygen vacancies play a key role in catalytic SO3 decomposition over a Cu2V2O7 catalyst.