New insights into alkaline metal modified CoMn-oxide catalysts for formaldehyde oxidation at low temperatures

Although CoMn oxides have shown promising catalytic properties in HCHO oxidation, their activities have a large space to improve especially at low temperatures (<70 °C). In the present study, Na or K doping into CoMn oxides was found to greatly enhance the low temperature activities, being one of the most active catalysts among non-noble metal catalysts. Na or K doping into CoMn oxides generates additional surface adsorbed oxygen and the amount of which has a linear relationship with the HCHO oxidation rate at 30 °C and 40 °C, which gives clear evidence of the crucial roles of surface adsorbed oxygen in HCHO oxidation. What is more, the positive effect of K doping was boosted when H₂O was co-existed in the feed gas. The surface hydroxyl species generated from H₂O dissociation directly participate in the HCHO oxidation, which provides a low activation energy pathway and increase the low temperature activity.