Femtosecond Laser Generation of LaCoO₃ Perovskite Nanocatalysts for Preferential CO Oxidation

Green synthesis and defect engineering of LaCoO₃ model nanocatalysts by femtosecond pulsed laser ablation in liquid (fs-PLAL) led to the formation of two types of nanoperovskites: stoichiometric LaCoO₃ and nonstoichiometric cobalt-rich nanoparticles. Micro-Raman analysis revealed pronounced second-order phonon scattering, suggesting a high defect density. The defect spatial distribution was evaluated by high-resolution electron microscopy, employing Fourier filtering and image reconstruction. Increasing the laser fluence increases the surface defect density due to the fast cooling of primary nanoparticles, a process intensified by the inherently ultrashort pulses. Laser-produced nanoparticles exhibited internal defects, a characteristic absent in those produced by a chemical method. Chemically derived nanoparticles, originally perfectly crystalline, formed grain/twin boundaries during calcination when their irregular shapes coalesced. Compared to a chemically synthesized reference catalyst, nanoparticles laser-synthesized at 5.8 J cm^-2 showed the highest CO conversion during PROX in excess H₂ at 400 °C. Perovskite produced at 5.8 J cm^-2 and 5.1 J cm^-2 also showed higher CO₂ selectivity (89% and 83%, respectively, versus 28% of the reference), as well as excellent stability at 350-400 °C.