Steering the Reaction Pathway of Tandem Catalytic Oxidation of HCHO Under Ambient Condition via Methanol Intermediate.

Tandem catalytic systems for HCHO oxidation are generally regarded as a relay process comprising intermediate (e.g., Methyl formate, MF) generation on zeolites and subsequent intermediates-to-CO2 conversion on supported metal catalysts. Here, a new cascade pathway mediated by the secondary intermediate methanol (CH3OH) over ZSM-5/Pt-γ-Al2O3 tandem catalyst is proposed, which is composed of physically mixed ZSM-5 and Pt-γ-Al2O3 with an overall Pt content of only 0.3 wt%. In this system, the CH3OH is generated directly via MF decomposition on acidic ZSM-5 and subsequently serves as the primary active intermediate on Pt-γ-Al2O3 catalyst, enabling efficient HCHO-to-CO2 complete conversion under ambient conditions. The deep studies with Pd- and Ag-based tandem systems further reveal that the reaction pathway is steered by the intrinsic reactivity of intermediates on supported metal catalysts: CH3OH-mediated cascade routes dominate in Pt- and Pd-containing systems, whereas MF remains the sole reactive intermediate over Ag-based tandem catalysts. Additionally, we demonstrate that the molecular diffusion of key intermediate within ZSM-5 plays a decisive role in proximity-dependent catalytic behavior. Specifically, the strong adsorption affinity and interfacial accumulation of CH3OH on ZSM-5 necessitate close spatial proximity between the zeolite and Pt catalyst, in contrast to the weaker adsorption affinity of MF.