Uniformly　carbon-covered　alumina　(CCA),　which　was　prepared　by　pyrolysis　of　sucrose,　was　used　as　support　of　ruthenium　catalyst.　Carbon　did　not　significantly　influence　on　the　ammonia　synthesis　activities　of　Ru　catalysts　by　changing　their　Ru　particle　sizes　or　Ru　3d5/2　binding　energies.　Residual　chlorine　severely　suppressed　ammonia　synthesis　by　decreasing　the　amount　of　hydrogen　with　the　desorption　peak　at　medium　temperatures.　Carbon　also　inhibited　the　adsorption　of　this　hydrogen　species　for　chlorine-free　Ru　catalysts,　but　did　not　change　their　activities.　On　the　other　hand,　carbon　can　increase　the　ammonia　synthesis　activities　of　containing-chlorine　Ru　catalysts　by　decreasing　the　disadvantageous　effect　of　chlorine　on　H2　adsorption.　©　2011　Elsevier　B.V.　All　rights　reserved.