Characterization of co-doped silica for improved hydrothermal stability and application to hydrogen separation membranes at high temperatures

Co-doped silica sol solutions with varying Co composition (Co/(Si+Co)=10-50 mol%) were prepared from tetraethoxysilane and Co(NO(3))(2).6H(2)O. Subsequently, these solutions were used in the preparation of hydrogen separation microporous membranes with enhanced hydrothermal stability at 500 degrees C under a steam pressure of 300 kPa. At Co concentrations > 33%, the XRD pattern and peak intensity of the Co-doped silica preparations were similar and were not dependent on Co composition, suggesting that Co was incorporated into the silica network. The best H(2) permeation performance in a steam atmosphere (500 degrees C; steam pressure, 300 kPa) was obtained using silica doped with approximately 30 mol% Co. Co-doped silica membranes (Co 33 mol%) fired at 600 degrees C under a steam partial pressure of 90 kPa showed stable gaseous permeances and a H(2) permeance of approximately 2.00-4.00 x 10(-6) m(3)(STP).(m.s.kPa)(-1) with a selectivity of 250-730 (H(2)/N(2)), even after 60 h of exposure to steam (steam pressure, 300 kPa) at 500 degrees C.