Design And Synthesis, Catalytic Performance And Computer Simulation Of Layered Double Hydroxides

Layered double hydroxides(LDHs) have been attracting attention of scientists and academe as a kind of materials with special structure and properties.It is generally expressed in the formula:[M²⁺_1-x M³⁺_x(OH)₂](A^n-)_x/n·mH₂O.Because M²⁺ and M³⁺ in the layer-sheets and anions(A^n-) in the gallery are flexibly controllable,and the structure and properties of LDHs are changeable,it can be used for the design of functional materials.LDHs are widely used in catalysis,adsorption-separation, medicine,PVC stability,dope,oil-exploitation and so on.Under the guide of hydrogen production from aqueous-phase reforming of ethylene glycol and "in situ" hydrogenation of methyl benzoate,the design and synthesis, catalytic performance and computer simulation of layered double hydroxides were carried out.The total thesis was divided into four sections:(1) The design and synthesis of LDHs based under the guide of hydrogen production and hydrogenation reactionAccording to the catalytic requirement of hydrogen production from aqueousphase reforming of ethylene glycol and "in situ" hydrogenation of methyl benzoate or benzoic acid,we designed and filtered the activation components of catalysts. Changing the mol.ratio of metal ions,a series of NiSnAl,NiMgAl,and CuMnAl-LDHs materials were synthesized with a coprecipitation method.And then,the structure,thermal stabilities,and reductive properties were characterized by XRD, TG-DTA,BET,TPR-MS,SEM,EDS technologies.LDHs materials must be changed into the metal supported catalysts in the hydrogen production and hydrogenation reaction.The traditional pathway of LDHs derived catalysts was that LDHs containing transition metals are first calcined,and then are reduced under H₂ atmosphere.In this study,a new-typed reductive method,direct H₂ reduction of LDHs,was proposed to construct the metal supported catalysts.The performance was obviously promoted using the catalysts reduced by direct H₂ reduction method.At last,the reduction and activation mechanism of LDHs based metal supported catalysts was proposed against the XRD and TPR-MS characterization results.(2) Hydrogen production from aqueous-phase reforming of biomass-derived hydrocarbonsRecently,the clean and effective hydrogen energy is produced by glycose or alcohol as the reactant,which is the hotspot of research for hydrogen production.In this study,hydrogen production by aqueous-phase reforming of biomass-derived ethylene glycol(EG) was tested at near 500 K over the modified NiAl-LDHs derived catalysts.The results showed that the activity and selectivity of H₂ were improved when Sn or Mg modified to Ni/Al-LDHs.The reasons for H₂ production selectivity and activation promoted,the former was likely related with the Ni₃Sn alloy conformed,and the later was likely related with the alkali supports.H₂ selectivity reached near 100%and H₂ production rate was 292.01μmol/min over Ni₂₀SnAl₇-HT derived catalyst.Moreover,the catalyst displayed a good stability, reaching above 120 h.The H₂ selectivity and stabilities of Sn modified Ni-LDHs derived catalyst were equal to the performance of Pt/γ-Al₂O₃ and Sn-Raney Ni catalysts reported by Dumesic et al.(3) 'In situ' hydrogenation of methyl benzoate(benzoic acid) to benzaldehydeThe coupling reaction between hydrogen production from steaming reforming of methanol and hydrogenation of methyl benzoate(benzoic acid),for the first time,was proposed to produce benzaldehyde.In order to realize this new-typed coupling reaction,the Cu component was designed for steaming reforming of methanol,and the Mn component was designed for hydrogenation of methyl benzoate(benzoic acid). The bi-functional catalysts were prepared with CuMnAl-LDHs as precursors.Cu-Mn catalyst displayed a good catalytic performance,and the selectivity of benzaldehyde reaches 95.63%,which was superior to the traditional hydrogenation methods.The mechanism of 'in situ' hydrogenation was proposed according to the production distribution and catalysts characterization.'In situ' hydrogenation method could predigest the reaction craftwork because it needn't additional H₂,so it can avoid the difficulty in production,transport,and storage of H₂.(4) Computer simulation of the structure and properties of LDHsThe structure of LDHs was complicated because the layers existed electrovalent bond and covalent bond,and the interactions of host-guest included static electricity effect,hydrogen bonding and van der waals force.So theoretical studies of the structure and properties of LDHs were difficult with single model and method.The structure parameters and energies of LDHs were calculated with density functional theory(DFT),molecular dynamics(MD),and electrostatic potential model(EPM) from different dimensions and accuracies.The interlayer structure characters, host-guest interaction,electron transfer of CO₃^2-,SO₄^2-,CrO₄^2-,F^-,Cl^-,Br^-,I^-,OH^-, NO₃^- and drug molecule(DIF) intercalated LDHs were studied.Moreover,the distribution,hydrogen-bonding of interlayer anions and water molecules were discussed.And ion-exchange properties,heat stabilities,hydration and swelling properties were concluded according to the calculational and experimental results. The computer simulation provided theoretical supporting for molecule design of new-typed LDHs materials.