Highly hydrogen selective ceramic membranes: application to the transformation of greenhouse gases

This paper reports the preparation of modified Vycor glass membranes by sev eral methods: polymerization, dip coating, sol-gel impregnation, and chemic al vapor deposition (CVD). It was found that a membrane there called Nanosi l) formed by the high-temperature CVD of tetraethylorthosilicate (TEOS) in inert gas exhibited hydrogen selectivities of 100% with respect to CH4, CO, CO2 and H2O. The transport of hydrogen was not through Knudsen diffusion, but was activated, and probably involved atomic hydrogen species. The membr ane was also stable to hydrothermal stresses (10% H2O at 873 K and 1 bar) f or over 150 h of operation. The membrane was employed in a catalytic reacto r for the dry reforming of methane, CH4+CO(2)reversible arrow 2CO+H-2, usin g a 1% Rh/Al2O3 catalyst. As a result of simultaneous reaction and separati on, conversions were higher than those obtained in a packed-bed reactor ope rated at the same conditions, and exceeded equilibrium levels. (C) 2000 Els evier Science B.V. All rights reserved.