Sonochemically Prepared Ni-Based Perovskites as Active and Stable Catalysts for Production of COx-Free Hydrogen and Structured Carbon

A sonochemical method is employed to synthesize LaNiO3 perovskites as catalysts for methane decomposition to produce clean COx-free hydrogen and structured carbon. The catalytic activities of perovskites prepared under various sonochemical conditions (different power densities and exposure times) are contrasted with those of LaNiO3 prepared by a conventional sol–gel method. The results show that a sonochemically prepared catalyst presents a methane conversion of up to 60% after 16 h of reaction, while the conventional sol–gel LaNiO3 catalyst deactivates quickly, reaching 1% methane conversion after 30 min of reaction. Structural characterization of the as-prepared materials indicates that under certain sonochemical conditions (low-intensity sonication for 8 h) it is possible to obtain NiO inclusions in the LaNiO3 perovskite structure, which are not present when employing the conventional synthesis technique. Upon activation of these materials under reducing conditions, it is found that the presence of the sonochemically formed NiO inclusions facilitates exsolution of the reduced Ni species to the surface of the catalyst particles, improving the catalyst activity in methane decomposition. The sonochemically synthesized catalysts, which exhibit coexistence of LaNiO3 phase and NiO inclusions, also seem to exhibit autocatalytic properties as they steer the methane decomposition reaction toward formation of non-encapsulating carbon nanotubes, which not only enhance catalyst stability but also increase the catalyst activity over long reaction times.