Effects of coexisting oxoanions on SO₃ decomposition activity of molten-phase potassium metavanadate catalysts

Abstract

Molten-state potassium metavanadate (KVO 3 ) supported on mesoporous SiO 2 materials have emerged as active catalysts for SO 3 decomposition over a moderate temperature range (¯650 °C), which is a potential O 2 evolution reaction useful for solar thermochemical water splitting. The molten phase formed at ²520 °C contained tetrahedral VO 4 2¹ , which plays a vital role in accelerating the SO 3 uptake and conversion to SO 2 /O 2 . The present study aimed to reveal how the SO 3 decomposition activity is affected by adding other oxoanions such as borate (BO 3 3¹), carbonate (CO 3 2¹ ), and phosphate (PO 4 3¹ ) into the melt. Although borate showed a deteriorating effect, phosphate tended to improve the catalytic activity when the P/V molar ratio was equal to or less than 0.5. The addition of phosphate produced a mixed phosphate vanadate with a composition of KV 2 PO 8 , which consists of infinite tetrahedral PO 4 and pyramidal VO 5 linked by vertex sharing. Because of the congruent melting at temperature as low as ³530 °C, KV 2 PO 8 may be expected as another candidate of active molten phase catalyst for SO 3 decomposition.