Constructing hollow urchin-like Ag-K/Co3O4-MnO2 spheres with low Ag loading as a highly efficient catalyst for formaldehyde oxidation

Hollow urchin-like Co 3 O 4 -MnO 2 spheres were synthesized via hydrothermal method, followed by co-impregnation with 3 wt% Ag and K (3, 5, 7 wt%). The optimized Ag-5 K/Co 3 O 4 -MnO 2 catalyst achieved complete HCHO conversion at 50 °C under 150 ppm HCHO, 21 vol% O 2 /N 2 , RH = 30 %, and WHSV = 36,000 mL g cat -1 h −1 . Systematic parameter studies (0 ∼ 80 % RH, 50 ∼ 350 ppm HCHO, 5 ∼ 21 vol% O 2 , 36,000 ∼ 144,000 mL g cat -1 h −1 WHSV) demonstrated the robust catalytic performance of Ag-5 K/Co 3 O 4 -MnO 2 across wide operational ranges. Remarkably, Ag-5 K/Co 3 O 4 -MnO 2 demonstrated excellent stability and nearly 100 % HCHO conversion over a continuous period of 100 h with the WHSV of 36,000 mL g cat -1 h −1 . The hollow architecture enhanced reactant diffusion, while interconnected nanorod arrays provided abundant Ag/K anchoring sites. Potassium doping increased Ag/Ag + , (Mn 2+ + Mn 3+ )/Mn 4+ and Co 3+ /Co 2+ ratios via strengthened Ag-support interactions, promoting oxygen activation. Mechanistic analysis indicated HCHO oxidation proceeds via HCHO → DOM → HCOO – + OH – →CO 2  + H 2 O route.