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 Co 3 O 4 –In 2 O 3 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 In 3+ would first occupy octahedral sites of the spinel Co 3 O 4 and then tetrahedral sites, resulting in the increase of Co 2+ ratio on the surface when the doped molar ratio ( n In ) was 0–0.2 and decrease with excessive doping ( n In of 0.2–0.4). The increment of Co 2+ 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 T 99 of 395 °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.