Preparation Of Cu Based Alloy Catalysts By LDHs Precursor Method And Its Mechanism In Hydrogenation/Hydrogen Production Reaction

With the increasing global energy demand and environmental problems,it is urgent to vigorously develop clean and sustainable energy.Hydrogen energy（H₂）is regarded as the clean energy with the most development potential in the 21st century and will occupy an important position in the world energy structure.However,due to the high requirements for energy storage medium,hydrogen energy is also very valuable and needs to be used reasonably.In addition to the efficient utilization of hydrogen energy,improving the activity of hydrogen production is also an effective way.Supported metal catalysts are widely used in the field of high-efficiency hydrogenation and hydrogen production.Among them,metal Cu has attracted much attention as a catalyst or promoter because of its low cost and unique electronic arrangement（half full 4s orbit）.Compared with single metal catalysts,alloy catalysts usually show excellent catalytic performance,which is due to their overall,ligand and geometric effects.Alloy catalysts have various structures,including random alloys,intermetallic compounds and single atom alloys.Alloys with different structures have different properties in specific reactions.Therefore,it is of great significance to select appropriate preparation methods to design and construct matching alloy structures according to the characteristics of different types of catalytic reactions.Layered composite metal hydroxides（LDHs）are a class of anionic layered compounds.Because of their adjustable composition and compatibility,the atomic dispersion of layered metals and their structural topological effects,LDHs show significant advantages in the preparation of supported metal catalysts.At the same time,LDHs are also an ideal research platform for constructing different types of alloy catalysts.Selective hydrogenation of acetylene impurities in ethylene feed gas is an important reaction process in the field of petrochemical industry,and it is also an important embodiment of efficient utilization of green hydrogen energy.Supported Pdbased catalyst is a widely used catalyst for selective hydrogenation of acetylene.However,although traditional Pdbased catalysts have high activity,their ethylene selectivity is usually low.In addition,as a typical strong exothermic reaction（the total reaction enthalpy is-175.7 k J/mol）,the thermal effect of catalytic micro zone also has an important impact on the selectivity and stability of ethylene.Therefore,aiming at improving the selective hydrogenation performance of C≡C bond in the selective hydrogenation of acetylene,based on the topological effect of LDHs structure,PdCu single atom alloy catalyst was prepared by electric displacement method,and two kinds of PdCu bimetallic catalysts with different dispersion structures were prepared by adjusting the Cu content as reference samples.At the level of intrinsic dynamics and micro thermal effect,the essential effect of the structure of SAAs on the selective hydrogenation of acetylene was clarified.The distribution of Pdin single atom on the surface of Cu nanoparticles was proved by AC-HAADF-STEM and in-situ CO-IR.Through comparison,it is found that in the intrinsic dynamics,PdCu-SAA catalyst shows excellent ethylene selectivity（100%）,which is mainly due to the highly dispersed Pdsites changing the adsorption mode of intermediates and reducing the desorption energy.In the non-intrinsic dynamics,the high ethylene selectivity of SAAs catalyst was maintained（>97%）,but the selectivity of the two reference samples decreased significantly（the selectivity was61.31%and 79.08%respectively）.The excellent catalytic performance of SAAs catalyst benefited from the collaborative control of heat generation and heat transfer in micro zone.Combined with chemical adsorption,transient plane source method and reaction heat calculation,the relationship between Pddispersion with the heat reaction and Cu atom continuity with thermal conductivity are established respectively.From the perspective of reaction heat,the extremely high Pddispersion（96.3%）in SAAs is conducive to disperse the heat generated by a single active center,making the reaction heat per unit point from 41.1 k J/（g·s）decreased significantly to 21.3 k J/（g·s）,effectively avoiding the generation of hot spots.From the perspective of thermal conductivity,the continuity of Cu atoms in PdCu-SAA catalyst is high,and the thermal conductivity is from0.4 W?m^-1?K^-1 increased to 0.6 W?m^-1?K^-1,enhancing the heat conduction efficiency.With the development of hydrogen production technology,photocatalytic H₂ evolution is considered to be a promising hydrogen energy development method.However,due to the limitation of photocatalyst carrier recombination rate,the efficiency of this process is not ideal.Therefore,introducing hole scavenger to improve hydrogen evolution efficiency is a common strategy,but it inevitably leads to the increase of production cost and the waste of hole oxidation capacity.Using renewable biomass resource 5-hydroxymethylfurfural（5-HMF）to replace the traditional sacrificial agent can improve the efficiency of hydrogen production and realize the high-value transformation of biomass resources.In photocatalytic reaction,Cu catalysts show surface plasmon resonance（SPR）effect because of its unique physical and chemical properties,which can significantly improve the light absorption capacity,but the hydrogen adsorption capacity is low.To solve this problem,in this paper,Pt with high work function was selected as the second metal component and alloyed with Cu to control the preparation of Pt Cu random alloy photocatalytic hydrogen production coupled biomass oxidation catalyst,and the catalytic mechanism was revealed.Specifically,Pt Cu alloy catalyst was prepared by improved co-precipitation method based on structural topology transformation effect of LDHs,and single metal Pt and Cu catalysts were prepared as reference.HRTEM,EDS and H₂-TPR characterization results confirmed the successful construction of Pt Cu alloy structure and the strong interaction between Pt and Cu.The performance evaluation results showed that the hydrogen production rate of Pt Cu photocatalyst can reach1160.8μmol?g^-1?h^-1,and the yields of 2,5-furandicarboxylic acid（FDCA）and furan-2,5-dicarbaldehyde（DFF）were 129.6μmol/g and46.0μmol/g respectively,which are much higher than the two reference samples.HRTEM and in-situ CO-IR characterization results confirmed that the high catalytic activity of Pt Cu alloy catalyst was due to its high metal dispersion（78.6%）and linear adsorption ratio.In addition,XPS and in-situ CO-IR further showed that the unique electron interaction between Pt and Cu atoms in Pt Cu alloy（i.e.the total electron number of Pt atoms increased after alloying,but the d electron density was small）was helpful to enhance the photocatalytic oxidation ability and hydrogen production activity.Further tested by UV-Vis spectrum,photoelectrochemistry and PL spectrum showed that Pt Cu alloy could effectively improve the light absorption capacity and promote the separation and photo charges transfer,so as to improve the coupling reaction performance of 5-HMF photocatalytic oxidation to DFF and FDCA with aquatic H₂.