The optimization of Ni–Al2O3 catalyst with the addition of La2O3 for CO2–CH4 reforming to produce syngas

A series of La₂O₃–NiO–Al₂O₃ catalysts promoted by different loading of lanthanum were prepared via the hydrolysis-deposition method to improve the catalytic performance of nickel-based catalyst for CO₂–CH₄ reforming. The catalysts were characterized by N₂ adsorption - desorption, XRD, H₂-TPR, TG-DTG, TEM, Raman and TPH techniques. Results showed that the precursor of active component was mainly in the form of NiAl₂O₄ spinel, which almost disappeared after reduction process from XRD characterization, suggesting well reduction performance. The catalyst with La loading of 0.95 wt% (La–Ni-1) presented a small average Ni grain size of 7.71 nm and exhibited well catalytic performance at 800 °C, with CH₄ conversion of 94.37%, CO₂ conversion of 97.15%, H₂ selectivity of 75.01% and H₂/CO ratio of 0.92. The Ni grain size of La–Ni-1 increased only 5.84% to 8.16 nm after performance test, which was lower than that of others and indicated a well structure stability. Additionally, the strong carbon diffraction peak over La–Ni-0.5 and La–Ni-2 catalysts suggested the presence of crystalline carbon species accumulated on the catalysts, while there was no carbon peak over La–Ni-1 sample. A 150 h stability test for La–Ni-1 demonstrated that the conversion of CH₄ was around 95%, higher than that of La–Ni-0 (without lanthanum addition) and La–Ni-4 (with La content of 3.82 wt%). The carbon deposition rate of La–Ni-1 was only 1.63 mg/(g_cat·h), lower than that of La–Ni-4 (2.20 mg/(g_cat·h)), showing both high activity and well stability. Therefore, the “confinement effect” of La₂O₃ to Ni crystalline grain would inhibit the sintering of active component, prevent the carbon deposition, and improve the catalytic reforming performance.