Au-Cu Composite Catalysts For Preferential Oxidation Of CO In Hydrogen-rich Gas

The polymer-electrolyte membrane fuel cell(PEMFC) utilizes high purity hydrogen as a fuel,and hydrogen is usually produced by steam reforming of methanol and other hydrocarbons.However, the anode of PEMFC is prone to be poisoned by CO contained in the reformed gas,resulting in the damage of battery performance seriously. Preferential oxidation (PROX) has beenrecognized as oneofthe most promising and cost effective methodsto remove the smallamount ofCO in hydrogen-rich gas. Thus, high activity and selectivityare the key factorsto choose a suitablePROXcatalystthatconvertCOcompletelywithminimizingorwithoutconsumptionofhydrogen.Supported gold catalysts have well known ambient temperature activity for CO oxidation andasagoodchoiceforthePROXsystem. Previousstudieshaveshowedthatthereweresomewhat lowselectivityandpoor stabilityfor supportedAu catalyst inCO-PROXreaction, however,theeffectivecombination of Au and Cu can present a synergistic effect, not only enhance the activity andselectivity but also improve the stability. Based on this, in this thesis we studied the catalyticperformanceofAu-CucompositecatalystsforCO-PROXreaction.Inthe first part ofthis thesis, aseries ofAu-Cu-FLAcatalysts,thereinAu as active ingredient,Cu aspromoter depositedonto thecomposite metaloxide carrier FeLaOx-Al2O3pre-prepared, wereprepared by modified deposition-precipitation method. The catalysts were characterized by XRD,BET, H2-TPR, XPS and TEM techniques, and investigated their catalytic activity for CO-PROXreactioninhydrogen-richgas.Themainconclusionsaredrawnasfollows:(1) Effects of the addition of several Mn, Ni, Cu, Zn transition metals on the performance ofAu-FLA for CO-PROX were investigated. It was found that introducing Cu into Au-FLAcatalystcanenhancecatalyticperformances,confirmingthecooperativeeffect betweencopperandgold.(2) Cu content has a great influence onthe catalytic properties of Au-Cu-FLAcatalyst. Inourinvestigation, Au-Cu-FLAplays the optimal catalytic performance when Cu content is1.04%, with100%ofCOconversionandabove60%ofselectivityat80℃。(3) In comparison with the parent catalyst Au-FLA, the Au-Cu-FLA catalysts have a bettercapacityresistanceto watervaporandCO2andabetterstabilityofcontinuousreactionbecauseofthe presenceofCucanabletolimit thegrowthofgoldnanoparticles.GiveninthetraditionofAu-Cu catalysts,Cu speciespalyeitherpromoteroramorphouscarrier,in the second part of this thesis, we controllably synthesized two kinds of Cu2O with differentmorphologies, andobtained Au-Cu2O catalysts by modified deposition-precipitation method. XRD,SEM,BET,H2-TPR,XPStechniquesareperformedtocharacterizethestructureandcompositionofthecatalysts,andinvestigatedtheircatalyticactivityforCO-PROX.Themainconclusionshavebeendrawnasfollowing:(1) Two different morphologies Cu2O nanomaterials (Cubic and Cub-Octahedron) werecontrollably synthesized bychemical precipitation methods. The amount of the surfactant added isthemajorfactorinmorphologyofcuprousoxide.(2) The effects of preparation methods of Au-Cu2O catalysts such as co-precipitation method,modified deposition-precipitation method and sol method on the catalytic properties of Au-Cu2Owere investigated, and the catalytic performance order is M-DP> CP> Sol, demonstrating that theM-DPmethodisthebestmethodforpreparingtheAu-Cu2Ocatalysts.(3)XRDandSEMresultsshowthatnano-Auparticlesdidnot entertheCu2Ocrystallattice,butattachedto thesurfaceofthecuprousoxidecarrier, well maintained specific morphologyandcrystalstructureofCu2O.(4) The morphologies ofCuOx have a certain effect onthe catalytic performanceofAu-CuOxfor CO-PROX reaction. During the preparation process, the oxidation-reduction reaction occurredbetween Au3+and Cu+, Au and Cu species are mixed valence, and this mixed state promoted thecatalyticpropertiesofAu-CuOxcatalysts.Thisisthekeyreasonforthewellcatalyticperformance.