A First-principle Study On The Direct Synthesis Of Hydrogen Peroxide From Hydroxide And Oxygen On Palladium Single Atom Catalyst Supported On Alumina

Hydrogen peroxide is an environmental friendly oxidant because its oxidation product is water.At present,H2O2 has been widely used in papermaking,textile,daily detergent and other industries.The current method of synthesizing H2O2 is indirect synthesis using the anthraquinone method,which is well known for its complicated process,high energy consumption,and huge pollution.Therefore,people have paid much interest on how to synthesize H2O2 directly through hydrogen and oxygen.Among the various catalysts,Pd-based catalysts show good catalytic activity for this reaction,Pure palladium and its alloys(Au,Pt,Ag,Sn,Ni and so on)exhibit excellent performance.Despite the above significant progress,the selectivity and activity of the currently discovered palladium-based alloy systems still cannot reach the industrial demand at the same time.Single atom catalysts have broad prospects for high atomic utilization of active components and high activity.Isolated Pd atom shows better selectivity for direct synthesis of H2O2.Single Pd atom catalysts may be more effective than pure palladium and Pd-based nanoalloy particles.In this thesis,based on Pd-based catalysts and the use of density functional theory(DFT),the properties of bulk Pd,AuPd(111),and Pd1/?-Al2O3(100)single-atom catalyst for direct synthesis of hydrogen peroxide were studied.Our results indicate that rather than adsorbed,single Pd prefer to be embedded on the surface.The three catalysts are very active for the dissociation of H2.The adsorption of O2 on Pd1/?-Al2O3(100)is very stable,O2 stay molecular state on it and can't dissociate,while Pd(111)and AuPd(111)show dissociative activity for the adsorbed O2.The energy barrier indicates that on Pd1/?-Al2O3(100)the main reaction energy barrier of H2O2 is lower than the side reaction,showing the main reaction is more profitable,but Pd and AuPd(111)all show strong dissociation activity for OOH,resulting low selectivity.The performance of the catalyst is Pd(111)<AuPd(111)<Pd1/?-Al2O3(100).Microkinetic analysis suggests that Pd1/?-Al2O3(100)has the highest H2O2 production rate and selectivity among the three catalysts,showing excellent performance.The good performance of Pd1/?-Al2O3(100)single-atom catalyst is attributed to oxidation state of Pd that is more active for the generation of H2O2 on the surface and the 2?*orbital of the O-O bond of each adsorbate on Pd1/?-Al2O3(100)is less likely to be attacked by electrons which enhances its stabilitythe and.What's more,the isolated adsorption of Pd lack additional active site for cleavage of O-O bond,which limit side reaction and raise selectivity.The DFT theoretical calculation method was used to make a comparable study of the direct synthesis of hydrogen peroxide for Pd(111),AuPd(111),and Pd1/?-Al2O3(100).The results show that the Pd1/?-Al2O3(100)single atom catalyst has good performance in both activity and selectivity.