Size-dependent selectivity and activity of silver nanoclusters in the partial oxidation of propylene to propylene oxide and acrolein: A joint experimental and theoretical study

Model silvernanocatalystsbetween9and23nminsizewerepreparedbysize-selectedclusterdeposition from afreeclusterbeamonamorphousaluminafilmsandtheirsize-dependentcatalyticperformance studied inthepartialoxidationofpropyleneunderrealisticreactionconditions.Smallerclusterspref- erentially producedacrolein,whilethe23nmparticleswereconsiderablymoreselectivetowardsthe formation ofpropyleneoxide,atreactionratesfarexceedingthosepreviouslyreportedforlargersilver particles. Theactivityofclustersdroppedsignificantlywithincreasingparticlesize.First-principlecalcu- lations, oftheactivationenergiesforoxygenadsorptionanditsdissociation,atvariablesurfacecoverage yielded surfaceenergieswhichresultedinparticleshapesresemblingtheexperimentallyobservedshapes of partiallyoxidizedsilverclusters.Thecalculatedactivationbarriersforpropyleneoxideandacrolein formation onvariousfacetsandontheedgesofthenanoparticlesprovideddetailedinformationabout the energeticsofthecompetingreactionpathways.Thesize-andcorrespondingmorphology dependent theoretical activityandselectivity are in good accord with experimental observations.