Hydrogen production in membrane reactors using Rh catalysts on binary supports

The binary supports employed in this work were prepared by different methods. The Ti(7%)–MgO and the Ti(13%)–SiO2 were obtained using the grafting technique. The La(27%)–SiO2 was obtained through the incipient wetness impregnation with La(NO3)3 of Aerosil 300, previously calcined at 1173 K. The Rh was incorporated to these supports by wet impregnation. The catalysts were first evaluated for the CH4 + CO2 reaction in a fixed-bed reactor. They were found to be active and stable as to justify their use in the membrane reactor, which was operated at 823 K achieving methane conversions up to twice as much as the equilibrium values. In all cases, the activity of the Rh solids remained constant after 120 h on stream with very little formation of carbonaceous residues only detected through LRS. The catalysts were characterized through either hydrogen or carbon monoxide chemisorption, TPR, XRD, LRS and XPS. The Rh(0.6)/La–SiO2 catalyst showed a high metal dispersion that remained constant after use and the highest capacity to restore the CH4 + CO2 equilibrium when H2 was permeated out of the reaction section. The Rh(0.8)/Ti–MgO showed the highest Rh/oxide interaction associated with the lowest capacity to restore the reaction equilibrium. The Rh(0.8)/Ti–SiO2 exhibited an intermediate activity due in part to the partial segregation of the TiO2 upon calcinations and the subsequent appearance of small Rh° crystallites in the used catalysts.