A novel microporous hybrid silica membrane for the separation of carbon dioxide, fabricated through sol-gel deposition of a microporous Nb-doped ethylene-bridged silsesquioxane layer on a multilayer porous support, was reported. Effect of the calcination temperature on H(2)/CO(2) separation properties of Nb-BTESE membrane was investigated. Low CO(2) permeance was imparted by doping acidic niobium centers into the hybrid silica networks. Denser hybrid silica networks as well as more Lewis acid sites were generated as the calcination temperature elevated, which imparted very low CO2 permeance to the novel hybrid membrane while retaining its relative high H(2) flux in the order of similar to 10(-7) mol m(-2) s(-1) Pa(-1) Dominant densification occurred in the Nb-doped hybrid silica networks when the calcination temperature was lower than 400 degrees C. Meanwhile, the Nb-BTESE membrane showed relatively weak acidity which was induced by niobium doping. Dual effects are working when the heat-treated temperature was higher than 400 degrees C. On the one hand, the increased surface acidity reduced the number of sites and/or affinity for adsorption of CO(2) as the calcination temperature elevated. On the other hand, membrane densification occurred during the calcination process. Therefore, the permselectivity of H(2)/CO(2) for Nb-BTESE membrane could be tuned by altering the calcination temperature. The Nb-BTESE membrane calcined at 450 degrees C showed both relative high hydrogen permeance (similar to 9.7 x 10(-8) mol M(-2) S(-1) Pa(-1)) and excellent H(2)/CO(2) permselectivity (220), as compared with Nb-BTESE membranes calcined at other temperatures. (C) 2011 Elsevier B.V. All rights reserved.