The influence of lanthanum oxide added to a Ni/Al2O3 catalyst has been studied in the carbon dioxide reforming of methane. The samples were prepared by variable pH coprecipitation, with different La2O3 contents: 0, 4, 8, and 12 wt.%. Although the NiO reducibility was not altered, the presence of La increased the metallic dispersion (XPS, XRD, TEM), slightly increased conversion levels, and also enhanced the catalyst stability due to a substantial decrease in coke formation during reaction. An increase in Ni dispersion in samples containing La leads to more metallic particles with diameters less than 10 nm that contribute to the catalytic conversion without producing large amounts of coke in filaments. However, there is a limit to the amount of lanthanum oxide (between 8 and 12 wt.%) above which metallic dispersion is not favored, and therefore coke filament formation and quick catalyst deactivation cannot be controlled. This is probably due to the poor La2O3 dispersion in these materials (XPS), leading to a loss in the improvement of Ni-Al-La catalyst properties. La atoms are included in the metallic nickel lattice after 4 h of reaction. After a long reaction time La is segregated and the Ni particle size increases, leading to greater coke production (in filaments). (C) 2004 Elsevier B.V. All fights reserved.