H₂O-Enabled Reversible SO₂ Resistance on Separately Dual-Functional Pd-W Sites for Low-Temperature Hydrocarbon...

Sulfur dioxide (SO₂) poisoning remains a critical challenge for noble-metal catalysts in hydrocarbon oxidation, particularly under industrial humid conditions. H₂O is commonly regarded as a detrimental component in SO₂-containing exhaust streams where sulfur-water synergistic deactivation prevails. Here we prove that, when combined with rational active-site design, H₂O molecules can instead promote SO₂-resistance in hydrocarbon oxidation catalysis. A Pd/W-Al₂O₃ catalyst with spatially separated Pd and W sites exhibits superior low-temperature methyl ethyl ketone (MEK) oxidation activity and unprecedented resistance to SO₂ poisoning under both dry and humid conditions. In the absence of water, SO₂ is selectively immobilized as SO₃^2- species on W sites, preventing competitive adsorption on Pd and preserving MEK oxidation pathways. Under humid conditions, however, SO₂ can be transformed into HSO₃^- species that interact directly with Pd-bound ketone intermediates. Spectroscopic and theoretical investigations reveal that HSO₃^- 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 SO₂ poisoning. This work demonstrates how H₂O molecules fundamentally reshape SO₂-catalyst interactions and highlights a general strategy for converting SO₂ poisons into reaction promoters through spatially separated dual-functional active sites.