Ru/AC　catalysts　with　K　promoter　were　prepared　by　impregnation　of　the　samples　with　different　amounts　of　KOH.　The　catalysts　were　characterized　using　a　variety　of　techniques,　including　X-ray　diffraction,　X-ray　photoelectron　spectroscopy,　transmission　electron　microscopy,　CO　chemisorption　and　temperature-programmed　desorption.　The　presence　of　K　promoter　had　a　limited　effect　on　the　size　of　Ru　particles,　but　significantly　enhanced　the　amount　of　adsorbed　hydrogen,　nitrogen　and　ammonia.　A　new　desorption　peak　of　nitrogen　and　ammonia　at　low　temperature　can　be　observed　in　their　TPD　profiles　for　Ru　catalysts　with　K　promoter.　We　propose　that　the　presence　of　K　promoter　not　only　improved　the　adsorption　properties　of　hydrogen,　nitrogen　and　ammonia　for　Ru　catalyst　supported　on　activated　carbon,　but　also　weakened　the　adsorption　strength　of　nitrogen　and　ammonia.　The　change　in　the　chemisorptive　properties　of　reactant　gases　including　hydrogen,　nitrogen　and　ammonia　may　be　responsible　for　K　promoter　enhanced　ammonia　synthesis　activity　of　Ru/AC　catalyst,　more　than　just　the　electronic　properties　of　K　promoter.　©　2013　The　Royal　Society　of　Chemistry.