In a high-temperature catalytic membrane reactor, a plug-flow reactor is combined with a gas-separative membrane. By selectively removing one of the reaction products, the reaction mixture is prevented from reaching equilibrium, and a higher conversion can be obtained This concept is only valid for reactions that are limited by the thermodynamic equilibrium, such as the direct dehydrogenation of propane to propene. A tubular H-2-selective silica membrane;was characterized [alpha(H-2/C3H8 = 70-90 at 500 degrees C] and used as the gas-separative membrane. The membrane reactor was filled with a chromia/alumina catalyst. The kinetics of the catalyst was studied. At 500 degrees C the deactivation of the catalyst is slow, and the propene yield is almost constant for at least 10 h of operation. Under well-chosen process conditions, the propene yield is at least twice as high as the value obtained at thermodynamic equilibrium in a conventional reactor.