CO2 reforming of CH4 over La-Ni based perovskite precursors

LaNiO3 and La2NiO4 type perovskites were prepared by the self-combustion method and were used as catalyst precursors for the CO2 reforming Of CH4 reaction at 700 degrees C. The catalysts were tested in reduced and non-reduced form. High CH4 and CO2 conversion were obtained without carbon deposition. This result was explained by the occurrence of the RWGS (reverse water gas shift) reaction. The La2NiO4 perovskite used as precursor presents the smallest nickel particles after the reduction treatment. Consequently the catalytic activity is higher than that obtained with Ni/La2O3 or LaNiO3. When La2NiO4 is used without treatment prior to the reaction high methane and carbon dioxide conversions are reached but a carbon deposition is observed. The perovskite structure is not completely transformed and the presence of metallic nickel particles at the surface of La2NiO4 would be responsible for the carbon deposition. It is assumed that the role of the support is to allow the activation of carbon dioxide, which is favoured over La2O3 whereas it is limited over La2NiO4. Consequently the reaction between the complex C-Ni species (resulting from methane activation at the surface of the nickel particle) and gaseous CO2 is inhibited over Ni/La2NiO4 leading to a carbon accumulation at the surface of the catalyst. As soon as the perovskite structure is completely transformed, after reductive treatment or during the reaction, a high activity is reached and no carbon deposition was further observed, the catalytic performances being optimal when the average nickel particles size is the smallest, (C) 2006 Elsevier B.V. All rights reserved.