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, Na₁/HMO and Ag₁/HMO (HMO = Hollandite manganese oxide), in the complete oxidation of HCHO at low temperatures, in which the products are only CO₂ and H₂O. 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 Na₁/HMO have the same local structures as silver atoms of Ag₁/HMO. Catalytic tests reveal that Na₁/HMO has higher catalytic activity in low-temperature oxidation of HCHO than Ag₁/HMO. X-ray photoelectron spectra and soft X-ray absorption spectra show that the surface lattice oxygen of Na₁/HMO has a higher electronic density than that of Ag₁/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.