Performance evaluation and coke formation analysis of nickel-based catalysts for the diesel surrogate steam reforming to produce hydrogen for SOFCs

Diesel steam reforming presents a promising and cost-effective method for supplying H2 and CO for solid oxide fuel cells avoiding the problem of hydrogen storage. However, the requirement of costly noble metal catalyst and carbon deposition remain challenges. In this study, three Ni-based catalysts, namely Ni-Al2O3, Ni-Al2O3-La2O3 and Ni-Al2O3-CeO2, are separately prepared to investigate the effects of promoters on Ni catalyst structure, performance, stability, and carbon deposition in a diesel surrogate steam reforming. Fresh and spent catalysts are characterized by H2-temperature programmed reduction, X-ray diffraction, transmission electron microscopy and thermogravimetric analysis. The results show that the addition of La and Ce increases the dispersion of Ni, which is favorable for promoting the interaction of the catalyst with the reactants. Thermogravimetric analysis confirms that the modified catalysts exhibit lower levels of carbon deposition. However, the addition of La leads to the formation of La2O2CO3, which may block the reaction sites of the catalyst surfaces and thereby affect the fuel conversion rate. On the other hand, the addition of Ce does not result in performance loss and can even improve the performance of the surrogate fuel reforming. Density functional theory calculations demonstrate that both La and Ce doping increase the activation energy of the carbon deposition reaction, which is pivotal in improving the catalyst resistance against coke formation. Moreover, the CO/CO2 ratio is proposed as an in-time indicator to monitor the catalyst carbon deposition.