High stability of Ce-promoted Ni/Mg-Al catalysts derived from hydrotalcites in dry reforming of methane

Ce-promoted Ni/Mg-Al catalysts were synthesized by means of a methodology that involves the doping of Ni-Mg-Al mixed oxides derived from hydrotalcites with Ce(EDTA)]⁻ and subsequent thermal decomposition. The effect of the nominal load of Ce in the catalytic performance of the materials was studied. The solids were characterized by means of XRD, BET area, TPR-H₂, TPD-CO₂, chemical analysis by ICPs, TGA, SEM and TEM and were evaluated in CO₂ reforming of methane at 700 °C. The results indicate the partial reconstruction of the periclase phase during the doping with Ce(EDTA)]⁻ and the formation of a mixture of crystalline periclase and fluorite phases after the calcination. Catalysts with particle sizes of Ni⁰ between 5 and 9 nm were obtained. Ce presents a promote effect in the degree of reduction of Ni and the amount and strength of the basic sites. It was evident a beneficial effect of cerium in the catalytic activity and selectivity of the doped materials. The increase of the nominal Ce load between 1 and 10% causes no considerable effect in the catalytic activity and selectivity or in the size of crystallite in these materials but in the inhibition of the coke formation. The catalysts show excellent catalytic performance under drastic conditions of reaction and long operation times. The Ce-doped Ni/Mg-Al catalyst is stable up to 100 h of reaction using a feed mixture of CH₄/CO₂/He 10/10/80 at 24 L g⁻¹ h⁻¹, up to 20 h of reaction using CO₂/CH₄ 20/20 at 48 L g⁻¹ h⁻¹ and up to 15 h of reaction using CO₂/CH₄ 40/40 at 96 L g⁻¹ h⁻¹. The filamentous coke formation is demonstrated on the surface of the catalyst when gas of dilution in the reactants is not used. The developed method of synthesis becomes an interesting methodology for obtaining catalysts for CO₂ reforming of methane.