Pretreatment　under　specific　atmosphere　is　a　general　strategy　to　activate　catalysts.　How　physicochemical　properties　of　supports　are　modulated　during　activation　process　and　their　influence　on　active　sites　are　still　the　ongoing　topic.　Herein,　the　effect　of　reaction　gas　treatment　on　performance　of　phosphorus　modified　Pd/Al2O3　catalysts　in　lean　methane　oxidation　was　studied.　The　pretreated　Pd/P-doped　Al2O3　catalyst　exhibited　a　full　conversion　of　CH4　at　∼400　°C,　excellent　stability　under　both　dry　and　wet　conditions.　Characterization　results　reveal　that　the　uniform　and　stable　P　species　in　Al2O3　enhanced　the　metal-support　interaction　and　availability　of　oxygen　in　support.　Under　reaction　gas　condition,　PdO-support　connection　was　further　promoted　to　favor　generation　of　oxygen　vacancies　on　support　with　the　help　of　CH4,　leading　to　weakened　Pd–O　bond,　facile　reformation　and　increased　fraction　of　PdO.　These　facilitated　formation　of　intermediates　and　surface　dehydroxylation　and　mitigated　the　deactivation　caused　by　thermodynamic　decomposition　of　PdO.　©　2023　Hydrogen　Energy　Publications　LLC