The　superbasic　ZrO2　(ZrO2-KOH)　with　high　surface　area　was　prepared　by　reflux-digestion　of　ZrO(OH)(2)　gel　in　mother　liquor　and　examined　as　a　support　promoting　ammonia　synthesis　by　particulate　Ru.　The　TEM　image　of　Ru/ZrO2-KOH　catalyst　indicates　that　the　size　of　Ru　particles　is　in　the　range　of　1.5-3.2　nm,　which　is　the　optimum　size　of　Ru　particles　for　the　maximum　number　of　B-5-type　sites.　Additionally,　the　characterizations　including　CO2-TPD,　XPS　and　N-2-TPD　demonstrate　that　the　Ru　particles　supported　on　ZrO2-KOH　exhibit　higher　electron　density　compared　to　that　of　Ru/ZrO2　catalyst.　As　a　result,　the　dissociative　adsorption　of　N-2　over　Ru/ZrO2-KOH　is　more　facile　than　that　over　Ru/ZrO2　catalyst.　Thus,　the　Ru/ZrO2-KOH　catalyst　shows　an　excellent　activity　for　ammonia　synthesis　especially　under　the　conditions　of　low　temperature　and　pressure.　The　highest　reaction　rate　of　Ru/ZrO2-KOH　is　16.91　mmol/(g　h)　at　698　K　and　3.0　MPa,　which　is　much　higher　than　that　of　various　Ru　catalysts　supported　on　other　supports.　Crown　Copyright　(c)　2013　Published　by　Elsevier　B.V.　All　rights　reserved.