Supported Rh nanoparticles on CaO-SiO2 binary systems for the reforming of methane by carbon dioxide in membrane reactors

A set of Rh catalysts supported on a binary CaO-SiO2 system with different CaO content was prepared to investigate their textural and structural properties, Rh particle size, and catalytic performance in the dry reforming of methane reaction. The Rh nanoparticles and nanocrystalline structures in the reduced catalysts were characterized through HRTEM and CO chemisorption. EDX mapping showed that CaO is uniformly distributed on SiO2 and that no segregation is detected between them. Rh nanoparticles of about 1-2.6 nm were observed. These particle sizes indicate that Rh is well dispersed on the catalyst surface and that no agglomeration exists. The incorporation of the promoter (CaO) to the silica support induced an increase in the metal dispersion from 8% in Rh/SiO2 to 22-80% in Rh/CaO-SiO2 catalysts. However, the Rh dispersion decreased as the CaO loading also increased in the binary supports. For the high CaO load solids, a high stability was observed after 80h on stream for the dry reforming of methane. In addition, the solid with 27% CaO presented the higher methane reaction rate. As a consequence, this solid was selected for its application in a membrane reactor under different conditions. The increase of methane conversion with reaction pressure at high sweep gas flow rate indicates that the separation efficiency of the Pd membrane is sufficiently high to dominate the performance of Pd membrane reactors under those conditions. (C) 2013 Elsevier B.V. All rights reserved.