Characterization of Co‐Doped Silica for Improved Hydrothermal Stability and Application to Hydrogen Separation Membranes at High Temperatures

Abstract

Co‐doped silica sol solutions with varying Co composition (Co/(Si+Co)=10–50 mol%) were prepared from tetraethoxysilane and Co(NO3)2·6H2O. Subsequently, these solutions were used in the preparation of hydrogen separation microporous membranes with enhanced hydrothermal stability at 500°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 H2 permeation performance in a steam atmosphere (500°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°C under a steam partial pressure of 90 kPa showed stable gaseous permeances and a H2 permeance of approximately 2.00–4.00 × 10−6 m3(STP)·(m·s·kPa)−1 with a selectivity of 250–730 (H2/N2), even after 60 h of exposure to steam (steam pressure, 300 kPa) at 500°C.

Preparation of particulate/polymeric sol–gel derived microporous silica membranes and determination of their gas permeation properties

“…The design/stabilization of silica membrane pore structures by the incorporation of transition metals has been recently studied in order to improve the hydro/thermal stability of the membranes [6][7][8][9][10][11]. Research on this subject is still in progress and it is stated that the enhanced hydrothermal stability may be due to the reduced motion of silanol groups through the formation of more stable bonds and a denser pore structure with transition metal addition.…”

Doped microporous hybrid silica membranes for gas separation

“…A possible approach to improve the gas permselectivity of these hybrid silica membranes is the incorporation of metal ions in the hybrid silica matrix. This approach was successfully implemented by doping the silica network with metal ions, such as aluminum and magnesium [16], zirconium [17,18], niobium [19,20], nickel [21] and cobalt [22,23]. For hybrid silica (i.e., BTESE), only the incorporation of niobia has been reported to date [24,25], where it is claimed that the introduction of niobia created surface active sites resulting in a reduced CO 2 permeance.…”

Ultra-microporous membrane separation using toluene to simulate tar-containing gases

“…In addition, membrane reactor configurations have been investigated, where WGSR catalysts and membranes are integrated into a single process unit for H 2 separation and the subsequent WGSR shifting, overcoming equilibrium limitations at the same time [25][26][27][28][29]. In general terms, metal oxide silica membranes have shown to be thermally stable [30] and deliver high H 2 purities of > 98 mol% for processing syngas downstream from the water gas shift reactors [31].…”