Catalytic SO3 Decomposition Activity of SiO2-Supported Alkaline Earth Vanadates for Solar Thermochemical Water Splitting Cycles

Alkaline earth vanadates (Ae-V: Ae = Ca, Sr, and Ba) were supported on mesoporous SiO2 by a wet impregnation method. The catalytic activity of the prepared materials for the decomposition of SO3 into SO2 and O-2, which is a key step in solar thermochemical water splitting cycles, was investigated. In the temperature range 700-800 degrees C, the Ae-V/SiO2 catalysts exhibited remarkably high activities, which were superior to those of supported Pt catalysts in a wide range of weight hourly space velocities (55-220 g-H2SO4 g(-1) h(-1)). Despite the melting points of the materials exceeding 1000 degrees C, the high activity was determined to be closely related to the unusual melting behavior of Ae-V. Under the reaction atmosphere, the Ae-V phase was converted to AeSO(4) and molten V2O5 (melting point = 690 degrees C) via facile solid-gas reactions between SO3 and alkaline earth elements displaying high basicity. Notably, upon contact with the molten V2O5 phase, the as-deposited AeSO(4) was immediately decomposed into SO2 and O-2 to regenerate the Ae-V phase. The catalyst, which solidified at lower temperatures (<690 degrees C), could not decompose the sulfate and was therefore unable to drive the catalytic cycles. Consequently, the SO3 decomposition rate at <690 degrees C was lower than that of an alkaline vanadate (Cs-V) with a melting point as low as 500 degrees C but higher than that of a rare earth vanadate (La-V) with the highest melting point (>1800 degrees C).

Automated summary

The study focused on the catalytic performance of alkaline earth vanadates supported on mesoporous SiO2 for the decomposition of SO3. The high activity of the catalysts was found to be closely related to the unusual melting behavior of Ae-V, allowing for efficient regeneration in the SO3 decomposition process at high temperatures.