Advanced PGM-free nanocomposite catalysts for the activation of inert C1 molecules: exploration of Ni- and Cu-loaded ferrite and manganite perovskites

The growing emissions of greenhouse gases, mainly CO2 and CH4, and the consequent potentially catastrophic global warming, call for a rapid decarbonization of the global energy system by replacing fossil fuels with renewables. Solar and wind energy are the most promising options for large-scale decarbonization, but their intermittency requires storage solutions and complementary energy sources, among them biofuels and synthetic fuels. Biogas, obtained from anaerobic digestion of waste organic matter and manly composed of CH4 and CO2, can be upgraded to biomethane by CO2 separation, or further valorised either by CO2 methanation using renewable H2, or by CH4-CO2 dry reforming to yield bio-syngas. Capturing waste CO2 from industrial exhausts and converting it into synthetic fuels (among them CH4) is also a promising energy storage route. However, the carbon-neutral use of methane requires post-combustion treatments to oxidize residual CH4, a stronger greenhouse gas than CO2. These processes demand efficient and robust catalysts able to activate such inert C1 molecules at the lowest possible temperature, while also ensuring long-term operation. Noble metals – Pd for CH4 combustion, Ru and Rh for CH4 dry reforming and CO2 methanation – are effective but costly, making cheaper alternatives highly desirable. This work focuses on the design of nanocomposite catalysts based on LaMnO3 and LaFeO3 perovskites loaded with Ni and Cu, thanks to their thermal stability, tuneable composition, and presence of redox-active species. After optimizing sol-gel citrate combustion synthesis for the preparation of nanocrystalline perovskites, Ni and Cu were incorporated to further increase catalytic activity, via two different strategies: i) lattice doping and subsequent exsolution, and ii) Ammonia-driven deposition-precipitation (ADP), both yielding metallic nanoparticles after reduction. The prepared materials were tested as thermo-catalysts in the three target reactions, also adopting a photo-thermal approach to enhance activation of CH4 dry reforming. Catalytic behaviour was found to depend on perovskite type (Mn or Fe), loaded metal (Ni or Cu), incorporation method (exsolution or ADP), and type of pre-treatment (oxidative or reductive). Extensive physicochemical characterizations allowed a global understanding of the catalytic trends in relation with the catalysts structural, morphological and chemical properties, as well as their evolution under reaction conditions provided by in situ/operando techniques. At the end, Ni-LaMnO3 nanocomposites emerged as particularly promising, showing versatile functionality across all processes, but with different activity and stability arising from different Ni-loading methods and thus metal-support interaction. This work represents a step forward the design and development of cost-effective and versatile catalysts for a variety of industrially relevant chemical processes.