Two-step hydrothermal synthesis of highly active MnOx-CeO2 for complete oxidation of formaldehyde

MnOx-CeO2 catalysts prepared by either a two-step hydrothermal (HT) method or a deposition–precipitation (DP) method were evaluated for completely oxidation of formaldehyde (HCHO). MnOx-CeO2(HT) exhibited an excellent HCHO oxidation activity. The reaction rate of MnOx-CeO2(HT) was almost six times that of MnOx-CeO2(DP) at 100 °C after excluding the effect of specific surface area. XPS study suggests that MnOx-CeO2(HT) catalyst possessed higher contents of Ce3+ and Mn4+ species than MnOx-CeO2(DP) catalyst due to the synergistic interaction between MnOx and CeO2 (Ce4+ + Mn3+ ↔ Ce3+ + Mn4+). The high Mn4+ content on the surface could provide sufficient HCHO oxidation active sites. The generation of Ce3+ species could lead to abundant chemisorbed oxygen species, which were further determined by in situ DRIFTs, EPR, O2-TPD and H2-TPR studies, and were mainly responsible for the excellent HCHO oxidation activity. DFT simulation also proved these results, which suggests that the Mn loading on CeO2 (1 1 0) plane could promote the generation of oxygen vacancy derived from Ce-O-Mn, while the (1 1 0) plane was one of the main exposure plane on the surface of Mn-Ce(HT) catalyst. This work provides a simple strategy to design highly active Mn-Ce catalysts for HCHO oxidation. We believe this non-precious catalyst will provide a cost-effective solution for catalytic oxidation of HCHO and other organic pollutants.