Ru/Al2O3　catalysts　with　different　Ru　particle　sizes　were　prepared　by　changing　the　metal　loading,　the　treatment　temperature　in　hydrogen　or　the　calcination　temperature　in　air.　It　is　found　that　the　catalysts　obtained　by　different　methods　cannot　directly　be　used　to　study　the　correlation　between　particle　sizes　and　the　catalytic　activity.　The　difference　in　treatment　conditions　of　Ru/Al2O3　catalysts　affected　the　ammonia　synthesis　activity　of　Sm-promoted　Ru/Al2O3　not　only　by　affecting　the　sizes　and　the　shapes　of　Ru　particles,　but　also　by　changing　the　properties　of　some　active　sites　available　for　gas　adsorption.　(C)　2013　Elsevier　B.V.　All　rights　reserved.