Sodium Rivals Silver as Single-Atom Active Centers for Catalyzing Abatement of Formaldehyde

The development of efficient alkali-based catalysts for the abatement of formaldehyde (HCHO), a ubiquitous air pollutant, is economically desirable. Here we comparatively study the catalytic performance of two single-atom catalysts, Na<sub>1</sub>/HMO and Ag<sub>1</sub>/HMO (HMO = Hollandite manganese oxide), in the complete oxidation of HCHO at low temperatures, in which the products are only CO<sub>2</sub> and H<sub>2</sub>O. These catalysts are synthesized by anchoring single sodium ions or silver atoms on HMO(001) surfaces. Synchrotron X-ray diffraction patterns with structural refinement together with transmission electron microscopy images demonstrate that single sodium ions on the HMO(001) surfaces of Na<sub>1</sub>/HMO have the same local structures as silver atoms of Ag<sub>1</sub>/HMO. Catalytic tests reveal that Na<sub>1</sub>/HMO has higher catalytic activity in low-temperature oxidation of HCHO than Ag<sub>1</sub>/HMO. X-ray photoelectron spectra and soft X-ray absorption spectra show that the surface lattice oxygen of Na<sub>1</sub>/HMO has a higher electronic density than that of Ag<sub>1</sub>/HMO, which is responsible for its higher catalytic efficiency in the oxidation of HCHO. This work could assist the rational design of cheap alkali metal catalysts for controlling the emissions of volatile organic compounds such as HCHO.