Raman studies of Rh and Pt on La2O3 catalysts used in a membrane reactor for hydrogen production

Abstract

Rh and Pt catalysts supported on lanthanum oxide were prepared by wet impregnation. The solids were used in a Pd-Ag membrane reactor to produce hydrogen through the carbon dioxide reforming of methane. The effect of the sweep gas flow rate and W/F upon the conversions of CO2 and CH 4, as well as on the production of H2 was studied. The best performing catalyst was Rh (0.6%). It yielded a methane conversion 38% higher than the thermodynamic value and the highest H2 permeate flux across the membrane. Lanthanum phases on the support and the catalysts were characterized by Laser Raman spectroscopy, FTIR, and XRD. The support and the calcined fresh catalysts exhibited a mixture of phases which were influenced by the metal type. Furthermore, platinum seemed to favor the formation of Ia-La2O2CO3 after a short treatment in flowing CO2. However, the only remaining crystalline phase after 100h on stream was II-La2O2CO3. A small amount of graphitic carbon was detected using Laser Raman spectroscopy, despite the fact that no carbon deposition was observed through TGA measurements. The graphite crystallization order seemed to be dependent upon the contact time of the reactants.