Topotactic Transformation Mechanism From Layered Double Hydroxides To Copper-cobalt Bimetallic Catalysts And The Struture Regulations

For a complex catalytic reaction,it often requires a synergistic catalysis by multiple active centers.The surface/interfacial structure of the multicomponent catalysts plays a crucial role in the synergistic catalysis.,Taking the advantages structural features of layered double hydroxides(LDHs)that the metal cations of the LDH layer are highly dispersed at an atomic level,and the composition and molar ratio are adjustable,and the composition and size of the intercalated anions within the 2D interlayer space are adjustable,LDHs materials has been employed as the precursors to prepare uniformly dispersed supported metal catalyst with tailored nanostructures.However,during the topolofical transformation process,the mechanism of migration and aggregation of metal ions on the LDHs layers or within the confined interlayer space remains unclear.Therefore,in this paper,supported CoCu catalysts with control structures have been prepared derived from CoCu based LDHs.The work mainly focuses on the lattice confinement effect of LDHs,especially for the transformation mechanism for the Cu2+ and Co2+ active sites confined in the 2D lattices,confined in 2D lattices or 2D interlayer space,or confined in both 2D lattices and 2D interlayer space,to Cu,Co,or CuCo nanoparticles for and the meso-scale structure for the final formed supported metal catalysts.The main work is displayed as follows:1.WO42-intercalated CuCoMgAl-LDHs(CuCoMgAl-WO42--LDHs)was first employed as the precursor to prepare supported CoCu catalysts by in-situ calcination/reduction process.Cu2+ and Co2+ active sites are confined in the 2D lattices during the transformation process,and the interlayer WO42-could effectively restrict the migration and aggregation of Cu2+ and Co2+ along the caxis direction.CuCo alloy phase with low Co content and sole Co nanoparticles have been observed in uniformly dispersed nanoparticle distrtibution with a particle size of 3.1 nm.While for the traditional impregnation method,Co,Cu,CuCo heterostructure and CuCo alloy nanoparticles have been detected in uneven distribution with dual particle size of 5.1 nm and 18.5 nm.It reveals the confinement effect for the LDH layer effectively constrains the migration and aggregation of metal active sites.2.Through tailoring the calcination/reduction conditions including the reduction method,the reduction temperature,or the heating rate,the nanostructures of the supported CoCu catalysts from CuCoMg Al-W042--LDHs have been controlled.The migration and aggregation mechnism of metal active sites has been investigated in detail.3.CuCoMgAl-CO32--LDHs were employed as the precursor to prepare supported CoCu catalysts with Cu2+ and Co2+ active sites migrating in 3D directions during the transformation process.CuCo alloy phase with low Co content and sole Co nanoparticles have been observed in uniformly dispersed nanoparticle distrtibution with a larger particle size of 6.9 nm,compared to the CuCoMgAl-WO42--LDHs as precursor.It indicates that the migration of the metal active sites along the c axis intensifies the aggregation of the nanoparticles.4.Through tailoring the length/diameter ratio of the LDH nanosheets,the nanostructures of the supported CoCu catalysts from CuCoMgAl-WO4 2-LDHs have been controlled.The migration and aggregation mechnism of metal active sites has been investigated in detail.5.Co complex anions intercalated CuMgAl-LDHs(CuMgAl-Co(intercalated)-LDHs)and Cu complex anions intercalated CoMgAl-LDHs(CoMgAl-Cu(intercalated)-LDHs)were employed as precursors to prepare supported CoCu catalysts by in-situ calcination/reduction process in confined interlayer space.It is found that for CuMgAl-Co(intercalated)-LDHs,a core-shell nanostructure with Cu0.49Co0.51(301)as shell and Cu0.4gCo.52(111)as core has been observed;for CoMgAl-Cu(intercalated)-LDHs,a core-shell nanostructure with Cu(200)as shell and Co(111)as core has been observed.It indicates the migration rate for Cu active site on the LDH layer and Co active site within the LDH interlayer space exhibits better matching than that for the condition of Co active site on the LDH layer and Cu active site during the transformation process.6.The obtained supported CuCo catalysts have been applied in the synthesis of ethanol and higher alcohol from syngas.The relationships between the lattice structure,the particle distribution,and also the particle size and the conversion of syngas,the total selectivity of alcohol,and the selectivity of C 2+ alcohol.