Volatile organic compounds (VOCs) are toxic and are considered the most important sources for the formation of photochemical smog, secondary organic aerosols (SOAs), and ozone. These can also greatly affect the environment and human health. For this reason, VOCs are removed by applying various technologies or reused after recovery. Catalytic oxidation for VOCs removal is widely applied in the industry and is regarded as an efficient and economical method compared to other VOCs removal technologies. Currently, a large amount of VOCs are generated in industries with solvent-based processes, and the ratio of aromatic compounds is high. This paper covers recent catalytic developments in VOC combustion over noble-metal-based catalysts. In addition, this report introduces recent trends in the development of the catalytic mechanisms of VOC combustion and the deactivation of catalysts, such as coke formation, poisoning, sintering, and catalyst regeneration. Since VOC oxidation by noble metal catalysts depends on the support of and mixing catalysts, an appropriate catalyst should be used according to reaction characteristics. Moreover, noble metal catalysts are used together with non-noble metals and play a role in the activity of other catalysts. Therefore, further elucidation of their function and catalytic mechanism in VOC removal is required.

Due to the increasing attention focused on global warming, many studies on reducing CO₂ emissions and developing sustainable energy strategies have recently been performed. One of the approaches is CO₂ methanation, transforming CO₂ into methane. Such transformation (CO₂ + 4H₂ → CH₄ + 2H₂O) provides advantages of carbon liquification, storage, etc. In this study, we investigated CO₂ methanation on nickel–magnesium–alumina catalysts both experimentally and computationally. We synthesized the catalysts using a precipitation method, and performed X-ray diffraction, temperature-programmed reduction, and N₂ adsorption–desorption tests to characterize their physical and chemical properties. NiAl₂O₄ and MgAl₂O₄ phases were clearly observed in the catalysts. In addition, we conducted CO₂ hydrogenation experiments by varying with temperatures to understand the reaction. Our results showed that CO₂ conversion increases with Ni concentration and that MgAl₂O₄ exhibits high selectivity for CO. Density functional theory calculations explained the origin of this selectivity. Simulations predicted that adsorbed CO on MgAl₂O₄(100) weakly binds to the surface and prefers to desorb from the surface than undergoing further hydrogenation. Electronic structure analysis showed that the absence of a d orbital in MgAl₂O₄(100) is responsible for the weak binding of CO to MgAl₂O₄. We believe that this finding regarding the origin of the CO selectivity of MgAl₂O₄ provides fundamental insight for the design methanation catalysts.

We synthesized cerium-doped cobalt-alumina (Co_xCe_y/Al₂O₃) catalysts for the propane steam reforming (PSR) reaction. Adding cerium introduces oxygen vacancies, and the oxygen transfer capacity of the Ce promoter favors CO to CO₂ conversion during PSR, inhibiting coke deposition and promoting hydrogen production. The best PSR activity was achieved at 700 °C using the Co_0.85Ce_0.15/Al₂O₃ catalyst, which showed 100% propane (C₃H₈) conversion and about 75% H₂ selectivity, and 6% CO, 5% CO₂, and 4% CH₄ were obtained. In contrast, the H₂ selectivity of the base catalyst, Co/Al₂O₃, is 64%. The origin of the difference in activity was the lower C₃H₈ gas desorption temperature of the Co_0.85Ce_0.15/Al₂O₃ catalyst compared to that of the Co/Al₂O₃ catalyst; thus, the PSR occurred at low temperatures. Furthermore, more CO was adsorbed on the Co_0.85Ce_0.15/Al₂O₃ catalyst, and subsequently, desorbed as CO₂. The activation energy for water desorption from the Co_0.85Ce_0.15/Al₂O₃ catalyst was 266.96 kJ/mol, higher than that from Co/Al₂O₃. Furthermore, the water introduced during the reaction probably reacted with CO on the Co_0.85Ce_0.15/Al₂O₃ catalyst, increasing CO₂ generation. Finally, we propose a mechanism involving the Co_0.85Ce_0.15/Al₂O₃ catalyst, wherein propane is reformed on Co_xCe_y sites, forming H_2, and CO, followed by the conversion of CO to CO₂ by water on CeO₂ sites.