Enhanced Methane Oxidation over Co3O4-In2O3-x Composite Oxide Nanoparticles via Controllable Substitution of Co3+/Co2+ by In3+ Ions

Composite oxide nanoparticles are promising candidates for catalytic applications to reduce the usage of expensive noble metals. However, the associated inferior low-temperature activity imposes major challenges on the rational design and modulation of compositions. Herein, we reported for the first time the successful synthesis of Co3O4-In2O3 composite oxides with the nanoparticle size of 10-20 nm for methane combustion via a modified precipitation method adopting the organic base N-butylamine as a precipitator to eliminate the negative effects resulting from conventional inorganic base precipitators. The doped In3+ would first occupy octahedral sites of the spinel Co3O4 and then tetrahedral sites, resulting in the increase of Co2+ ratio on the surface when the doped molar ratio (n(In)) was 0-0.2 and decrease with excessive doping (nIn of 0.2-0.4). The increment of Co2+ ratio was essential for the formation of abundant reactive oxygen species, improvement of reducibility, and optimization of surface acidity, which synergistically contributed to superior catalytic activity with a T99 of 395 degrees C. The catalytic activity of the tailored Co-In-0.2 nanocatalyst is among the best of the state-of-the-art Co-based catalysts; meanwhile, it also exhibits excellent stability and water resistance.