Design of Ni-based catalysts supported over binary La-Ce oxides: Influence of La/Ce ratio on the catalytic performances in DRM

CeO2 and binary La2O3-CeO2 oxides, with different La/Ce atomic ratios (1:4; 1:1; 4:1), were synthesized using sol-gel method in the presence of citric acid in ammonia solution, at pH~9, and Ni (10 wt%) was added by wetness impregnation method. The physical-chemical properties, catalytic activity and long-run stability of the prepared catalysts were evaluated in DRM reaction. Characterizations of both fresh and spent catalysts were carried out using low-temperature N2 adsorption, XRD, TGA, TPR, Raman and TEM analyses. The DRM gradient catalytic tests performed in the range of 400–800 °C revealed higher catalytic conversions for Ni/La2O3-CeO2 catalysts, especially for those with La/Ce ratio 1:4 and 1:1. The stable conversions of CH4 and CO2 (long run at 650 °C for 24 h) registered for such Ni/La2O3-CeO2 catalysts were attributed to the presence of small Ni crystallites. During long run tests, Ni/La2O3-CeO2 catalysts, with La/Ce atomic ratios 1:4 and 1:1, formed the same types of carbon, both as filaments and layered carbon with graphene structure, but their catalytic activity was retained. Ni/CeO2 showed the smallest content of carbon, however, exhibited lower CH4 and CO2 conversions in comparison with the Ni-La2O3-CeO2 systems, due to the presence of big Ni particles with sizes of up to 0.5 µm.