Copper-manganese oxide catalysts for low-temperature oxidation of indoor pollutants

Indoor air purification is crucial for preserving health and well-being in enclosed spaces. This study presents the successful low-temperature oxidation of CO and ethylene, considered as indoor air pollutants, achieved without employing expensive precious metals. A series of binary CuMnOx samples, with a Cu/(Cu+Mn) ratio of 15 wt%, were prepared using various synthesis procedures and thoroughly characterized to understand their physico-chemical and their link with catalytic properties. The findings revealed that copper significantly enhanced the performance of all samples when compared to the pure MnOx materials. For all the pollutants investigated, the best-performing catalyst was the Cu-Mn mixed oxide obtained through a redox route, which achieved complete CO oxidation at room temperature and maintained high activity for over 250 h. For ethylene, it demonstrated superior low-temperature catalytic oxidation compared to the other samples, reaching a T10 equal to 85 °C. These remarkable performances were attributed to enhanced oxygen mobility, increased reducibility, and the synergy between copper and manganese, which played a pivotal role in VOC oxidation. Notably, long-term stability tests under continuous flow, variation of GHSV, pollutant and oxygen concentrations, and catalytic performance under wet conditions confirmed the excellent durability and versatility of the catalyst, even at extremely low catalyst loadings. Further catalytic testing and spent catalyst analysis revealed that the low-temperature oxidation mechanism involves a Mars-van Krevelen-like reaction pathway with parallel involvement of both reactive surface oxygen species and molecular oxygen, all of which play a crucial role in the reaction process. Finally, this work provides a systematic correlation between catalytic activity (in terms of both T100 and reaction rate) and structural, redox, acid-base, and electronic properties, demonstrating that the decisive factors differ for CO and C2H4 oxidation.