Alkali Metal Doped MnOx Catalysts for Formaldehyde Oxidation

The catalytic oxidation of formaldehyde to CO2 and H2O under low temperature is of great significance and insistent demand for indoor air purification. In this work, through alkali metal doping, we significantly improved the formaldehyde oxidation activity of Mn-based catalysts. At a temperature as low as 97 degrees C, 300 ppm of formaldehyde can be completely eliminated over 5%Cs/MnOx. The results showed that the presence of alkali metals markedly increased the redox ability of MnOx catalyst and the proportion of reactive oxygen species. The adsorption and reaction path of formaldehyde on the surface of the catalysts were studied by in-situ infrared spectroscopy. It was found that the adsorption form of formaldehyde on the surface of alkali metals doped MnOx catalyst was different from that of MnOx, except for monodentate formate detected over MnOx, more easily decomposed bridged adsorbed formate was another prominent adsorbed species over 5%Na/MnOx and 5%Cs/MnOx catalysts. The difference in reaction paths may be the key to the higher activities of alkali doped MnOx catalysts. This finding may provide some new ideas for the design of low temperature formaldehyde oxidation catalysts.Graphical AbstractThe intermediate species during formaldehyde oxidation on MnOx and Na+/Cs+-doped MnOx are different, which may be the key reason why the latter exhibit higher activities than MnOx.