Ru-Ni modified LaMnO3 perovskites for H2 production via CH4-CO2 chemical looping: Structure-activity effect

Ni and Ru-Ni modified LaMnO3 perovskites were investigated in CH4-CO2 chemical looping (CL) with the aim to produce H₂ from CH4, valorising CO2 used as oxidant. Samples were synthesized by sol-gel and microwave-assisted routes and thoroughly characterized by XRD, N2 physisorption (BET), H2/CH4-TPR, Raman spectroscopy, HRTEM/EDX, XPS and TGA. The incorporation of Ni and Ru enhanced surface area, oxygen mobility and reducibility with respect to the unpromoted perovskite. Under CL conditions, Ni/LaMnO3 underwent structural degradation and Ni exsolution, whereas Ru addition stabilized the perovskite lattice, suppressed Ni segregation, and mitigated carbon accumulation. Microwave-assisted synthesis yielded smaller crystallites and promoted faster CO2-driven reoxidation, improving redox reversibility. CL experiments were carried out at 550 °C over both, Ru-Ni and Ni catalysts, moreover the monometallic Ni samples were tested also at 690 °C, according to CH4-TPR profiles. Notably, Ni/LaMnO3 sol-gel is the most active catalyst, delivering the highest H2 production during the CH4 step, while incurring a broader redox window and increased lattice strain. The improved stability of the Ru-Ni system was attributed to a moderate Ni exsolution, likely favored by interaction with ruthenium which promoted the formation of finely dispersed Ni-Ru ensembles, mitigated coke deposition, and yielded a confined and well reversible redox window. Consistently, post-cycling XRD analyses confirmed the structural stability and minimal coking of the Ru-Ni systems.