Interactions between Ni and La2O3 in Ni/La2O3 catalysts prepared using different Ni precursors

The role of the anion (NO3- or Cl-), used in the preparation via impregnation of unreduced Ni/La2O3 catalysts, in the interactions between Ni and La2O3 was investigated using XRD, TPR, and ESCA experiments. The following results have been obtained: In the 20 wt% Ni/La2O3 prepared using Ni(NO3)(2) as precursor, LaNiO3 and La(OH)(3) were the only compounds identified by XRD in the sample calcined in O-2, and La2NiO4 and La(OH)(3) were the only compounds identified in the sample calcined in He. At lower Ni contents, the L(2)O(3) phase was additionally identified. For the 20 wt% Ni/La2O3 prepared using Ni chloride as precursor, LaOCl was the only compound detected by XRD; no phase containing Ni was identified by XRD in the samples calcined in O-2 or He. At lower Ni chloride contents, LaNiO3 was additionally detected in the sample calcined in O-2 and La2NiO4 in that calcined in He. A comparison between the XRD spectra and the TPR curves suggested the presence of amorphous NiO in the samples based on Ni chloride. It is also shown that the Ni precursor employed in the preparation of the catalyst plays a role in the CO2 reforming of CH4. During the CO2 reforming of methane, the unreduced Ni/La2O3 catalysts, based on Ni nitrate, had a high initial CO yield but a low time stability; in contrast, the unreduced Ni/La2O3 catalysts, based on chloride, had a high stability. A possible explanation of this behavior, based on ESCA analysis and on the reaction between CH4 and catalysts, is provided. (C) 1996 Academic Press, Inc.