Binary iron cobalt oxide silica membrane for gas separation

Abstract

This work investigates the preparation, characterisation and performance of binary iron/cobalt oxide silica membranes by sol–gel synthesis using tetraethyl orthosilicate as the silica precursor, and cobalt and iron nitrates. It was found that cobalt and iron oxides were generally dispersed homogeneously in the silica structure, with the exception of a few minor patches rich in cobalt oxide. The sol–gel synthesis affected the micro-structural formation of binary metal oxide silica matrices. Increasing the iron content favoured condensation reactions and the formation of siloxane bridges, and consequently larger average pore sizes which lead to low He/N2 permselectivity values below 20. In the case of high cobalt content, a higher silanol to siloxane ratio was observed with tighter pore size tailoring, as evidenced by higher He/N2 permselectivities reaching 170. The binary metal oxide and silica interfaces proved to follow a molecular sieving mechanism characterised by activated transport where the permeance of the smaller gas molecules (He and H2) increased with temperature up to 500°C, whilst the permeance of larger gas molecules (CO2 and N2) decreased.