Stability of (La-Ni-Co-O)-based perovskites in LPG steam reforming: assessment of gas composition and Ni/Co ratio

Steam reforming of Liquefied Petroleum Gas (LPG) is a viable option for producing hydrogen in isolated regions. Catalysts prepared from perovskite precursors may retain metal particles dispersed and decrease sintering due to the high interaction particle-support, but even so the oxidation rate of carbon deposits is still high. Partial substitution of Ni or Co in the B-site of ABO₃-type perovskites may increase reducibility and stability while maintaining high hydrogen yield. In order to understand the reasons for high carbon deposition rates on these catalysts and to attempt to control the deposition process, Ni/Co bimetallic catalysts synthesized from La-based perovskite precursors were tested for LPG steam reforming. IN-SITU XRD analyses showed that, depending on the fraction of substituted Ni, the perovskites go through one or two reduction steps before decomposing into bimetallic Ni/Co particles supported on La₂O₃. EXAFS data indicated that the nanoparticle's surface are enriched with Co after reduction, but Ni atoms migrate to the surface and overlay the former Co shell soon after feeding the LPG steam reforming mixture. In samples synthesized with low Co/Ni ratio, the Ni surface layer oxidizes after a few hours during reaction operation, showing signs of deactivation. 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 reforming. (author)