CO2 reforming of CH4 over Ni perovskite catalysts prepared by solid phase crystallization method

Ni-supported catalysts on perovskite-type oxides have been prepared by "solid phase crystallization" (spc) method and tested for CO2 reforming of CH4 into synthesis gas at 850 degrees C. The Ni catalysts were obtained in situ during the reaction from the oxides as the precursors in which nickel species were homogeneously incorporated in the perovskite structure. Ni/Ca0.8Sr0.2TiO3 and Ni/BaTiO3 catalysts showed high activity as well as high sustainability among the catalysts tested. The high activity may be due to highly dispersed and stable Ni metal particles (diameter < 1 nm) on the perovskite, where the nickel species thermally evolve from the cations homogeneously distributed in an inert perovskite matrix as the precursors during the reaction. Nickel species was partly incorporated in the perovskite structure by replacing the Ti site and partly separated as NiO from the structure after the calcination of the precursors, and the former species likely affords the highly dispersed Ni metal under the reducing atmosphere. The amount of NiO detected by XRD analyses was smaller on BaTiO3 than on Ca0.8Sr0.2TiO3, while that of surface Ni obtained by TGA was larger on Ca0.8Sr0.2TiO3 than on BaTiO3. It is thus likely that an incorporation of Ni was enhanced in BaTiO3 compared to Ca0.8Sr0.2TiO3, resulting in the higher dispersion of Ni metal particles on the former support. This well coincided with the activity of Ni/BaTiO3 being higher than that of Ni/Ca0.8Sr0.2TiO3 at high space velocity. The high sustainability against coke formation may be partly due to the mobile oxygen as well as due to the presence of alkaline earth metals in the perovskite supports. Oxygen mobility in the perovskite was further tested by CO2 pulse reactions, suggesting an easy migration of oxygen over the perovskite structure. It is most likely that the oxygen easily migrates from the supports to the surface of fine Ni particles, where the coke material can be oxidized into carbon oxides. (C) 1999 Elsevier Science B.V. All rights reserved.