Research On Surface And Interface Regulation Of Supported Metal Catalysts And Their Catalytic Performance Toward Hydrogen Generation From Liquid Phase Organic Hydrogen Carriers

As a new type of green energy,hydrogen energy has shown great potential in achieving the dual-carbon goal and sustainable development,which has become an important part of the global deep decarbonization as well as the transformation of fossil energy to sustainable energy.The entire chain of hydrogen energy study including hydrogen generation,hydrogen storage,and hydrogen consumption;Among them,the efficient preparation,safe storage and transportation of hydrogen are the key issues affecting the large-scale application of hydrogen energy industry chain.In recent years,through the development of hydrogen production by low carbon alcohol reforming and hydrogen storage based on nitrogen heterocyclic liquid alkane,much research attentions have been focused on the integration of hydrogen energy production,storage,transportation and real-time supply.In spite of much progress in this field,the following key issues and challenges remain unresolved.Structural design of efficient catalysts and fine-structure regulation so as to meet the requirements of practical application are rather difficult.Catalyst deactivation and rate decrease in hydrogen generation during long-term operation is a great challenge.The structure of intrinsic active center,catalytic reaction path and reaction mechanism have not been fully revealed,which restricts the structure design and performance enhancement of heterogeneous catalysts.To solve the above problems,in this dissertation,three supported metal catalysts with interface synergistic effect(Cu⁰-Cu⁺,Rh-Ni^δ--O_v-Ti³⁺and Pd⁰-Pd^δ+)were designed and prepared.They have shown excellent catalytic performance in three types of organic liquid phase media for hydrogen production:methanol steam reforming for hydrogen production,ethanol steam reforming for hydrogen production,and 12H-N ethyl carbazole dehydrogenation,respectively.Through fine regulation of the surface/interface geometric and electronic structure,the O-H,C-H and C-C bond breaking as well as deep dehydrogenation were promoted.The intrinsic active sites,structure-property correlation and catalytic mechanism were revealed at the atomic/molecular level based on kinetic analysis,in situ spectroscopy characterizations and theoretical calculations.This work provides a theoretical basis on the structure design and performance optimization of efficient catalysts for hydrogen production from organic liquid phase medium,which shows important scientific significance and application prospect.The specific main research contents are as follows:1.Cu⁰-Cu⁺co-catalyzed C-H bond fracture to promote hydrogen production from methanol steam reformingA y Cu/Cu（Al）O_x catalyst with specific Cu⁰-Cu⁺dual sites（y represents Cu/Al total mass ratio）was designed and prepared by co-precipitation followed by subsequent hydrogen reduction process,whose structure was characterized by Cu₂O modified Cu nanoparticles supported on amorphous alumina,achieving efficient catalytic conversion of low-temperature methanol steam reforming（MSR）for hydrogen production.The 4.25Cu/Cu（Al）O_x sample displays methanol conversion of more than 99%,H₂ production rate of 110.8μmol s^-1 g_cat^-1 and cycling stability of 300 h at 240°C,which is significantly superior to the catalysts reported in the literature.Kinetic studies,in situ spectroscopy characterization and operando pulse analysis verify that MSR reaction involves three main processes:dehydrogenation of CH₃OH,hydrolysis of HCOOCH₃ and decomposition of HCOO*,in which C-H bond breaking of CH₃O*and HCOO*intermediates is the rate-determining step.STEM-EELS,isotope kinetic analysis,in situ XAFS spectroscopy and DFT theoretical calculations confirm:the Cu⁰-Cu⁺dual sites derived from the Cu-Cu（Al）O_x interface as the intrinsic active center,CH₃O*and HCOO*exhibit oxygen terminal bridge adsorption configuration at the interface（moderate adsorption strength）,promoting electron transfer from the catalyst surface to the reaction intermediates,significantly reducing the C-H bond breaking energy barrier（rate determining step）,and achieving a significant performance improvement in methanol reforming for hydrogen production.This work reveals the structure-activity relationship between interfacial structure and catalytic performance at the molecular/atomic level,and providing a certain theoretical basis for the structural design of efficient catalysts and having potential application prospects.2.RhNi-TiO₂ catalyst with bimetal-support interaction towards hydrogen production from ethanol steam reformingA RhNi/TiO₂ catalyst with strong bimetal-support interaction（SBMSI）was designed and prepared based on the topological transformation process of RhNi Ti-LDHs precursor,which exhibited excellent catalytic performance towards hydrogen production from ethanol steam reforming（ESR）.CO-DRIFT and STEM-EDS analysis confirm that Rh tends to be atomically dispersed on the surface of Ni nanoparticles,accompanied with a reversible TiO₂ coating on the surface of RhNi bimetallic particles.Quasi-in-situ XPS and XAFS spectra demonstrated:at the Rh-Ni^δ--O_v-Ti³⁺interface,electron transfers from TiO_2-xto Ni and then to Rh corresponding to a multi-channel electron transfer mode,breaking the traditional single channel electron transfer mode between metal and support.The 0.5RhNi/TiO₂ catalyst（0.5 wt.%Rh loading）achieves ethanol conversion of 99.7%,H₂ yield of 61.7%and hydrogen generation rate of 12.2 L h^-1 g_cat^-1 at 400°C,and maintains a good stability within 300 h,which exceeds the catalysts reported in the literature.Kinetic analysis,in situ characterizations（XAFS and FT-IR）and DFT theoretical calculations prove:the interface site(Rh-Ni^δ--O_v-Ti³⁺)as the intrinsic active sites promoting the coupling of OH^-and C-H bond to generate formate intermediates（rate-determining step）.In addition,the presence of SBMSI also reduces the strong adsorption properties of species with COO^-structure（CO₂,carbonate or formate）.This accelerates the transformation of reaction intermediate and the regeneration of active site,which significantly improves the hydrogen yield and catalytic stability.This work provides a refined structural control approach for strong bimetallic support interactions,which can be extended to the structural design of efficient catalysts in other structurally sensitive reaction systems.3.Pd⁰-Pd^δ+synergistic catalysis for high efficiency dehydrogenation from dodecahydronitrogen-ethyl carbazoleAn aluminum oxide supported Pd catalysts（Pd/Al₂O₃）with tunable Pd⁰-Pd^δ+interface sites were prepared through fine regulation of the crystal phases structure（amorphous,γ,δandα）of rod-like Al₂O₃,which was used for the dehydrogenation reaction of 12H-N-ethylcarbazole（12H-NECZ）,achieving a significant increase in H₂ release rate.The optimized 3Pd/Al₂O₃-γcatalyst shows12H-NECZ conversion of 100%,NECZ selectivity of more than 99%,TOF value of 281.2 min^-1 and H₂ generation rate of 0.66 mol _H2 g _Pd^-1 min^-1（180°C,2 h）.The catalytic performance dose not display obvious decline within five cycles of testing,demonstrating a satisfactory stability,which is in the leading level of literature reports.The results of ²⁷Al MAS NMR,XPS and CO-DRIFT spectra verify that the content of pentacoordinate aluminum and the proportion of Pd^δ+/Pd⁰ decrease gradually as the crystal phase structure of alumina changes from amorphous（Al₂O₃-A1 and Al₂O₃-A2）toγ（Al₂O₃-γ）,δ（Al₂O₃-δ）andα（Al₂O₃-α）.As demonstrated by in situ characterizations（FT-IR and TPSR-MS pulse experiment）,kinetic analysis,H/D isotope exchange and DFT theoretical calculations,the surface Pd⁰ site with a high d electron density is conducive to the activation adsorption of substrate molecule,which reduces the energy barrier of C-H bond fracture.Moreover,the low electron density at the interface Pd^δ+site promotes the rapid desorption of H₂ and NECZ.Thus,the Pd⁰-Pd^δ+interface synergistic catalysis significantly enhances the deep dehydrogenation of 12H-NECZ.This study provides a successful paradigm for the surface/interface structure tuning of dehydrogenation catalysts,and revealed the synergistic catalytic dehydrogenation mechanism,which has certain guiding significance for the development of high-performance dehydrogenation catalyst...