Beneficial effects of the use of a nickel membrane reactor for the dry reforming of methane: Comparison with thermodynamic predictions

The development of a nickel composite membrane with acceptable hydrogen permselectivity at high temperature in a membrane reactor for the highly endothermic dry reforming of methane reaction was the purpose of this work. A thin, catalytically inactive nickel layer, deposited by electroless plating on asymmetric porous alumina, behaved simply as a selective hydrogen extractor, shifting the equilibrium in the direction of a higher hydrogen production and methane conversion. The main advantage of such a nickel/ceramic membrane reactor is the elimination or limitation of the side reverse water gas shift reaction. For a Ni/Al2O3 catalyst, containing free Ni particles, normally sensitive to coking, the use of the membrane reactor allowed an important reduction of carbon deposition (nanotubes) due to restriction of the Boudouard reaction. For a NiCo/Al2O3 catalyst, where the metallic nickel phase was stabilized by the alumina, the selective removal of the hydrogen significantly enhanced both methane conversion (+67% at 450 degrees C, +22% at 500 degrees C and 18% at 550 degrees C) and hydrogen production (+42% at 450 degrees C, +32% at 500 degrees C and +22% at 550 degrees C compared to the results obtained for a packed-bed reactor. The hydrogen selectivity during the catalytic tests at 550 degrees C, maintained with constant separation factors (7 for H-2/CH4, 8 for H-2/CO and 10 for H-2/CO2), higher than Knudsen values, attested to the high thermal stability of the nickel composite membrane. (C) 2007 Elsevier Inc. All rights reserved.