Stability improvement of Rh/γ-Al2O3 catalyst layer by ceria doping for steam reforming in an integrated catalytic membrane reactor system

Significant improvement over the equilibrium methane conversion level was achieved by performing the reforming of methane in a catalytic membrane reactor, which was prepared by integrating a microporous silica membrane with a sandwiched-type Rh/gamma-Al2O3 catalyst layer. However, the methane conversion activity decreased progressively owing to the deactivation of the intermediate catalyst layer under the reaction environments. On the other hand, addition of CeO2 as a promoter for the Rh/gamma-Al2O3 catalyst significantly improved the catalyst stability. The improvement was achieved probably by the kinetic and oxidative stabilization of the catalyst matrix with CeO2. However, compared to the nonpromoted system, the ceria-promoted systems displayed lower catalytic activities based on the Rh/Ce ratios. The results led to the conclusion that a controlled interplay of the catalytic potentiality of Rh and the stabilization effect of Ce are essential to obtain an acceptable system. The membrane quality and its performance decreased especially with high Ce incorporation in the catalyst layer, possibly as a result of the observed microstructural variations in the catalyst layer with the Ce addition. Therefore, a consensus between the activity and stability of the material as a catalyst and the textural characteristics of the catalyst layer as a support layer for the silica membrane is considered to be an important factor that decides the success of the approach. A possible mechanism has been suggested to explain the role of ceria as a promoter in the Rh/gamma-Al2O3 system.