Interconnection between feed composition and Ni/Co ratio in (La-Ni-Co-O)-based perovskites and its effects on the stability of LPG steam reforming

Nickel-based perovskites (La-Ni-O) partially substituted with cobalt were tested for steam reforming of Liquefied Petroleum Gas (LPG), and analyzed by a series of in situ techniques. In situ X-ray diffraction (XRD) analyses showed that, depending on the fraction of substituted Ni, the perovskites go through one or two reduction stages before decomposing into Ni-0/Co-0 and La2O3. Extended X-ray absorption fine structure (EXAFS) data indicated that the nanoparticle's surface are enriched with Co after reduction, but the Ni atoms migrate to the surface and overlay the former Co shell soon after feeding the LPG steam reforming mixture. In samples synthesized with a low Co/Ni ratio, the Ni surface layer oxidizes after a few hours under reaction conditions, showing signs of deactivation. The oxidation could be prevented by decreasing the water/LPG feed ratio, which reactivated the catalyst. The use of a proper water/LPG feed ratio coupled with the suitable Co/Ni ratio in the synthesis of perovskite precursors is essential to keep the catalysts active during LPG steam reform.