Evaluating the chemical stability of metal oxides in SO 3 and applications of SiO 2 ‐based membranes to O 2 /SO 3 separation

The decomposition of sulfur trioxide to produce sulfur dioxide and oxygen using a catalytic membrane reactor is technology that promises to improve the economic viability of the thermochemical water‐splitting Iodine‐Sulfur (IS) process for large‐scale CO 2 ‐free hydrogen production. The chemical stability of membrane materials under SO 3 , however, is a significant challenge for this strategy. In this study, microporous membranes with a layered structure that consisted of a membrane support prepared from α‐Al 2 O 3 , an intermediate layer prepared from silica‐zirconia, and a top layer prepared from bis (triethoxysilyl)ethane‐derived organosilica sols, were examined for stability under SO 3 and for use in SO 3 /O 2 separation. An α‐Al 2 O 3 support that features SiO 2 –ZrO 2 intermediate layers with large pore sizes and a high Si/Zr molar ratio showed excellent resistance to SO 3 , which was confirmed by N 2 adsorption, Energy Dispersive X‐ray Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). These membranes also demonstrated a negligible change in gas permeance before and after SO 3 exposure. Subsequently, in binary‐component gas separation at 550°C, microporous organosilica‐derived membranes achieved an O 2 /SO 3 selectivity of 10 (much higher than the Knudsen selectivity of 1.6) while maintaining a high O 2 permeance of 2.5 × 10 −8 mol m –2 s –1 Pa –1 .