The CO2 reforming of CH4 over Ni/La2O3/alpha-Al2O3 catalysts: The effect of La2O3 contents on the kinetic performance

The aim of this work is to quantitatively investigate the effect of La2O3 contents on the intrinsic activity of Ni active sites for the CO2 reforming of CH4 on Ni/La2O3 (1, 2, 4, and 6 wt%)/alpha-Al2O3 Catalysts using steady and pulse kinetic methods. The Ni particle sizes were decreased with increasing La,03 contents. And the 4-La catalyst had the most Ni-H species. The Ni active sites on the 4-La catalyst showed the highest reforming activity and the lowest activation energy. Among CH4, CO2, CO, and H-2, only CH4 reaction orders were not zero and they were affected by the La2O3 contents. In 550-600 degrees C, the CH4 dissociation is a rate-determining step for the reforming reaction on the Ni/La2O3/alpha-Al2O3 catalysts. The 4-La catalyst gave the highest reforming activity because the CH4 dissociation was a structure sensitive reaction and 4-La catalyst has the most suitable Ni particle size. In 650-750 degrees C, the CH4 dissociation and the formation of Ni-H reached equilibration and the reaction between CHx species with La2O2CO3 became the rate-determining step. The 4-La catalyst with the most Ni-H could keep the highest x value of CHx intermediates, leading to the highest reforming activity in 650-750 degrees C. Therefore, the La2O3 contents on the catalysts tuned the Ni particle sizes and Ni-H amounts on the catalysts, which lead to higher reforming activity on the 4-La catalyst. (C) 2007 Elsevier B.V. All rights reserved