Insights into the roles of superficial lattice oxygen in formaldehyde oxidation on birnessite.

K + -modified birnessite materials were constructed to remove formaldehyde (HCHO) in this work. The introduction of K + led to weakening of the Mn-O bonds and enhanced the migration of superficial lattice oxygen, resulting in improved redox properties and catalytic activity. MnO 2 -3K with the largest specific surface area and greatest abundance of superficial lattice oxygen showed the best catalytic performance at 30-130 °C. The operando analyses reveal that HCHO is primarily activated to dioxymethylene (DOM) and subsequently converted to formate species (*COOH). The accumulation of formate species caused a decline in catalytic performance during extended testing at 30 °C, a challenge that could be mitigated by raising the temperature. Theoretical studies disclose that the *COOH → *H 2 CO 3 step with the largest energy barrier is the rate limiting step for HCHO deep decomposition. Molecular oxygen could be activated at oxygen vacancies to replenish the depleted lattice oxygen after decomposition of carbonate species (*H 2 CO 3 ) and CO 2 and H 2 O desorption. The adsorbed oxygen and water did not limit the deep oxidation of HCHO. This research presents a promising approach for designing highly efficient, non-noble metal catalysts for formaldehyde degradation.