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

Abstract

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.

Irregularly Shaped NiO Nanostructures for Catalytic Lean Methane Combustion

“…Among the series of catalysts for the elimination of volatile organic chemicals, − noble metal-supported catalysts have received tremendous attention because of their excellent catalytic activities and high reaction rates in methane combustion, ,, especially for Pd-based catalysts. − ,,,− Although noble metal-supported catalysts have high efficiencies, their high price, low availability, and easy sintering at high temperatures limit their large-scale industrial applications. ,, Therefore, transition metal oxide catalysts are fast becoming the focus of researchers due to their lower cost and comparable catalytic activity to noble metal catalysts. − In the reaction course of methane catalytic combustion, the activation of the C–H bond is a key step, and NiO is considered to be one of the potential transition metal oxide nanoparticles capable of replacing noble metal catalysts due to its excellent performance in the activation of C–H bonds. ,,,, Consequently, interest in the fabrication of various NiO nanomaterials as high-efficiency and low-cost catalysts in lean methane catalytic combustion has been growing. , …”

Zr-Doped NiO Nanoparticles for Low-Temperature Methane Combustion

“…1,2 However, the associated release of unburnt methane could cause serious environmental problems since it is a powerful greenhouse gas with a high global warming potential. 3,4 Catalytic combustion of methane has been recognized as a promising way to reduce methane emissions in industrial processes, 5,6 yet it presents profound challenges due to the stable molecular structure of methane and the unfavorable reaction conditions. For example, the exhaust from NGVs has a low residual methane concentration (0.1−1 vol %), large amounts of water vapor (5−15%), a relatively low temperature (<500−550 °C), and a high throughput.…”

“…As an alternative to traditional fossil fuels, natural gas has been widely applied in gas turbine and natural gas vehicles (NGVs) because of its high energy efficiency and low pollutant emissions. , However, the associated release of unburnt methane could cause serious environmental problems since it is a powerful greenhouse gas with a high global warming potential. , Catalytic combustion of methane has been recognized as a promising way to reduce methane emissions in industrial processes, , yet it presents profound challenges due to the stable molecular structure of methane and the unfavorable reaction conditions. For example, the exhaust from NGVs has a low residual methane concentration (0.1–1 vol %), large amounts of water vapor (5–15%), a relatively low temperature (<500–550 °C), and a high throughput. − Therefore, it is imperative to develop high-performance catalysts with excellent low-temperature activity and stability. − …”

Hydrothermal Microwave Synthesis of Co3O4/In2O3 Nanostructures for Photoelectrocatalytic Reduction of Cr(VI)

“…Indium oxide (In 2 O 3 ) is an n-type semiconductor that has superior electrical conductivity and excellent photoelectrochemical stability. Up to now, In 2 O 3 nanorods, nanoribbons, and nanowires have been prepared to supply a greater specific surface area for reinforced photoelectrochemical reactions . P-CuO-N-In 2 O 3 quantum dot heterojunction photocatalysts for long-wavelength visible light photocatalysis were reported .…”