Palladium-based　catalysts　have　long　been　considered　the　benchmark　for　methane　combustion;　however,　the　authentic　phase　of　catalytic　active　sites　remains　a　subject　of　ongoing　debate.　Additionally,　challenges　like　water-poisoning　and　long-term　stability　need　to　be　addressed　to　advance　catalyst　performance.　Herein,　we　investigate　Pd　on　Co3O4　nanorods　as　a　highly　effective　catalyst　for　catalytic　oxidation　of　methane,　demonstrating　long-term　stability　and　water　tolerance　during　a　100-h　continuous　operation　at　350　°C.　Comprehensive　characterizations　reveal　the　presence　of　an　active　Pd-oxygen　vacancy　(Ov)-cobalt　interface　in　Pd/Co3O4,　which　effectively　adsorbs　molecular　O2.　The　absorbed　oxygen　species　on　this　interface　are　activated　and　directly　participate　in　methane　combustion.　Moreover,　near-ambient　pressure　X-ray　photoelectron　spectroscopy　demonstrates　that　Pd　nanoparticles　undergo　a　rapid　phase　transition　and　predominantly　remain　in　the　metallic　state　during　the　reaction.　This　behavior　is　attributed　to　the　electronic　metal-support　interaction　between　Pd　and　Co3O4.　Furthermore,　in　situ　Fourier　transformed　infrared　spectrum　reveals　that　under　reaction　conditions,　HCO3*　species　are　formed　initially　and　subsequently　transformed　into　formate　species,　indicating　that　the　formate　pathway　is　the　dominant　mechanism　for　CH4　oxidation.　©　2025　Dalian　Institute　of　Chemical　Physics,　the　Chinese　Academy　of　Sciences