The　catalytic　decomposition　of　N2O　using　Au19Pd　and　Au19Pt　clusters　as　catalysts　with　optimized　geometries　was　studied　using　density　functional　theory　(DFT).　The　optimized　geometries　of　the　Au19Pd　and　Au19Pt　clusters　were　obtained　as　a　function　of　structural　and　thermodynamic　analyses,　in　which　the　heteroatoms　are　on　the　surfaces　of　the　clusters.　We　selected　the　Au19Pd　cluster　as　a　model　cluster　to　investigate　the　reaction　mechanism　of　N2O　decomposition.　There　are　two　reaction　pathways　to　be　considered:　Eley-Rideal　(ER)　and　Langmuir-Hinshelwood　(LH).　We　found　that　the　first　N2O　decomposition　needs　to　surmount　an　energy　barrier　of　1.118　eV,　and　is　exothermic　by　-0.371　eV.　The　elimination　of　the　residual　oxygen　atom　on　the　surface　has　an　energy　barrier　of　1.920　eV　along　the　ER　pathway　after　N-2　desorption,　which　is　higher　than　that　along　the　LH　channel　(1.669　eV).　The　adsorption　energy　of　the　oxygen　atom　on　the　surface　is　3.203　eV,　and　the　oxygen　atom　diffusion　on　the　surface　needs　to　surmount　an　energy　barrier　of　0.113　eV　along　the　LH　pathway.　This　indicates　that　the　oxygen　atom　is　prone　to　transfer　on　the　cluster　to　promote　the　generation　of　the　O-2　molecule,　and　therefore　the　LH　is　the　optimized　reaction　pathway.　We　investigated　the　catalytic　activity　of　Au19Pt　for　N2O　decomposition　along　the　LH　pathway　in　comparison　with　the　Au19Pd　cluster.　Both　platinum　and　palladium　have　catalytic　activities　for　N2O　decomposition,　especially　the　palladium　in　this　study.　Comparison　between　this　work　and　the　theoretical　study　on　periodic　systems　shows　that　these　two　clusters　can　be　used　as　better　catalysts　for　N2O　decomposition,　especially　the　Au19Pd　cluster.　Furthermore,　the　O-2　desorption　is　no　longer　the　main　barrier　to　the　reaction,　which　further　enhances　the　catalytic　activities　of　these　two　clusters　for　N2O　decomposition.