H ₂ O-Enabled Reversible SO ₂ Resistance on Separately Dual-Functional Pd–W Sites for Low-Temperature Hydrocarbon Oxidation

Sulfur dioxide (SO 2 ) poisoning remains a critical challenge for noble-metal catalysts in hydrocarbon oxidation, particularly under industrial humid conditions. H 2 O is commonly regarded as a detrimental component in SO 2 -containing exhaust streams where sulfur-water synergistic deactivation prevails. Here we prove that, when combined with rational active-site design, H 2 O molecules can instead promote SO 2 -resistance in hydrocarbon oxidation catalysis. A Pd/W–Al 2 O 3 catalyst with spatially separated Pd and W sites exhibits superior low-temperature methyl ethyl ketone (MEK) oxidation activity and unprecedented resistance to SO 2 poisoning under both dry and humid conditions. In the absence of water, SO 2 is selectively immobilized as SO 3 2– species on W sites, preventing competitive adsorption on Pd and preserving MEK oxidation pathways. Under humid conditions, however, SO 2 can be transformed into HSO 3 – species that interact directly with Pd-bound ketone intermediates. Spectroscopic and theoretical investigations reveal that HSO 3 – functions as a dynamic proton shuttle, enabling a proton-bridge-assisted C–C bond cleavage pathway that facilitates intermediate conversion and drives reversible recovery from SO 2 poisoning. This work demonstrates how H 2 O molecules fundamentally reshape SO 2 -catalyst interactions and highlights a general strategy for converting SO 2 poisons into reaction promoters through spatially separated dual-functional active sites.