The Auto Synthesis Methode And Regulation Of Catalytic Active Site For Layered Double Hydroxides-based Materials

Heterogeneous catalysts play an important role in our society,through the effective regulation of catalysts to improve the efficiency of the catalytic reaction is the goat that people pursue.Currently,the catalytic efficiency is limited by the fact that the active sites are easy to aggregate,and the dispersion of the active sites are not uniform.It is a challenge and opportunity for researchers to optimize the defect structure and electronic structure of active sites to achieve efficient and highly selective catalytic reactions.As a family of highly ordered two-dimensional functional materials,layered double hydroxides(LDHs)has the characteristics of adjustable lamellar element type and proportion,variable interlamellar anion,controllable particle size and thickness.Besides,the trivalent metal elements(M3+)are highly dispersed by bivalent metal elements(M2+),leading to the ordered distribution of both the M2+ and M3+ ions in the LDH framework.Moreover,through the topological transformation,LDHs can be transformed into mixed metal oxide(MMO)with specific crystal facet exposure,abundant interface structures,and defect structures.Those characteristics make LDHs become a model catalytic system.Based on the LDHs system,we have carried out a series of studies Firstly,to achieve the fine preparation of LDHs materials,we successfully realized the automatic synthesis of LDHs on a laboratory scale by using the continuous automatic device.Then,based on the auto synthesis device and inspired by the ordered distribution structural feature of LDHs,the LDHs based single-atom catalyst was precisely synthesized.Advanced spectroscopy characterization further reveals the structure-activity relationship.Finally,through the topological transformation of NiAl-LDH,NiO nanosheets with an abundant Ni and O vacancies(VNi&O)were constructed.As increasing the concertation of(VNi&O),the selectivity of the CO2 photoreduction reaction can be regulated.This thesis provides new ideas and methods for the fine preparation of LDHs based materials and paves a new way for the regulation of catalytic active sites.The details studies are listed as follows:1.Firstly,we designed and built a set of automatic synthesis device.Then,we designed and wrote corresponding computer software to control the automatic synthesis device.Through this automatic system,We have successfully realized the fine synthesis of LDHs materials.More importantly,the remote and long-distance LDHs synthesis can also be achieved by this automatic system.The syntheses procedure are captured as digital code,which can be published,versioned,and easily transformed,thereby greatly enhancing reproducibility and further improving the development of LDHs based materials.The software designed and assembled in this chapter also provides new ideas and powerful tools for the future synthesis of inorganic materials.2.Based on the LDHs automatic synthesis device and ordered distribution structural feature of LDHs.We fabricated single Ru atoms supported on monolayer NiFe-LDH(denoted as Ru1/mono-NiFe)catalysts through a facile one-step coprecipitation method.Detailed characterization(XAFS,XPS,STEM,etc.)and density functional theory(DFT)calculations verify that single ruthenium atoms are uniquely anchored on the top of the iron atoms via coordination with three oxygen atoms.The Ru1/mono-NiFe catalyst shows high catalytic activity in the hydrazine electrooxidation reaction.Furthermore,DFT calculations indicated that the excellent catalytic activity is because the single Ru atoms can stabilize the hydrazine electrooxidation intermediates(*N2H3 and*N2H)and further decrease the bandgap energy(Eg).The loading amount of the single ruthenium atoms on the LDH with a precise location can go up to 7.0 wt%.Moreover,the LDHs with different compositions(NiAl-LDH,MgAl-LDH)can be also applied as supports for single ruthenium atoms due to the advantage of the unique LDH structure.3.To study the defect structure of the catalyst and realize the strengthening of the process for the catalytic reaction.NiO nanosheets with an abundant Ni and O vacancies(VNi&O)were constructed through the topological transformation of NiAl-LDH.The selectivity of CO2 photoreduction under visible light irradiation could be tuned by controlling the concentration of VNi&O.NiAl-275 possesses the highest concentration of VNi&o and shows the highest CH4 selectivity of 22.8%.More interestingly,under irritation wavelength ?>600 nm,the hydrogen evolution reaction can completely be suppressed and the selectivity of CH4 can be further improved to 38.5%.Comprehensive catalyst characterization studies(XAFS,XPS,HRTEM,etc.)and DFT calculations revealed that the existence of VNi&O can lower the Gibbs free energy barrier of CO2 reduction.Under the irradiation wavelength ?>600 nm,NiO with VNi&O showed a driving force that could only overcome the Gibbs free energy barrier of CO2 reduction to CH4 and CO(0.519 eV),rather than that of H2 evolution(0.605 eV),so it inhibits the side reaction of hydrogen evolution.