Mesoporous Ag-Al2O3-m and Ag-K-Al2O3-m catalysts were fabricated by a one-pot technique based on an evaporation-induced self-assembly method. Among them, Ag-3 K-Al2O3-m exhibited the highest activity, achieving 100 % HCHO conversion at 40 °C. The catalyst’s performance was notably impacted by RH conditions, which showed improved activity at 30 % RH, due to the formation of active –OH groups. As the K loading increased, the aggregation of Ag particles gradually occurred. According to DFT computation, the presence of K promoted the adsorption and activation of HCHO, O2 and H2O on the catalyst surface. The superior low-temperature reducibility, adequate surface active oxygen and surface –OH groups were identified as key roles to the enhanced catalytic performance of Ag-K-Al2O3-m. Both Ag-Al2O3-m and Ag-K-Al2O3-m operated through the same oxidation mechanism for HCHO oxidation.