Studies On Design And Catalytic Performance Of Copper-based Catalysts For The Synthesis Of Ester Chemicals From Methanol

The clean and efficient utilization of coal occupies an extremely important position in the sustainable development strategy in China.The development of synthesis chemicals from coal and environment-friendly catalytic materials and technologies have unique practical value and strategic significance.Methanol is one of the major chemicals produced from coal.Methanol can be used to produce some downstream chemicals such as olefins,gasoline,aldehydes,organic acids,esters and so on by further processing.Among ester chemicals produced from methanol,dimethyl carbonate（DMC）and methyl formate（MF）have high economic value and can act as important intermediates in organic synthesis,which have been widely employed in chemical,medicine and dyestuff industries etc.In the processes of the DMC synthesis via oxidative carbonylation of methanol and the MF production from methanol dehydrogenation,copper was used as an effective catalyst.It is found that controlling the grain size and the dispersion of copper nanoparticles,and preventing the agglomeration of copper nanoparticles become key factors to enhance the catalytic performance of Cu-based catalysts in the reaction.In recent years,it has become one of the research hotspots in the field of heterogeneous catalysis to tune the catalytic performance of nanomaterials based on the spatially confined effect.In view of the common problems of supported copper catalysts in synthesis of DMC and MF from methanol,copper nanoparticles are introduced into the inner cavity of nitrogen-doped hollow carbon spheres and mesoporous channels of ordered mesoporous silica for constructing composite catalysts.Controling the microstructure of copper nanoparticles can improve the catalytic performance effectively.Main contents of this work are following aspects:1.Mono-dispersed Si O₂ microspheres were synthetized by St?ber method using tetraethoxysilane（TEOS）as silicon source.The composite structure of nitrogen-containing resorcinol-formaldehyde resin（RF）coated with SiO₂（SiO₂@RF）was prepared using self-assembly of RF under hydrothermal conditions.SiO₂@RF is calcined at high temperature and nitrogen-doped hollow carbon spheres（NHCSs）are obtained by etching Si O₂ using HF solution.The SEM and TEM results showed that the average diameter of NHCSs was about240 nm with a shell thickness of¹7 nm,which displayed a perfect spherical morphology and uniform size.After hydrothermal impregnation,the copper salt precursor was introduced into the inner cavity of NHCSs and the Cu@NHCSs catalysts were obtained through reduction at a N₂/H₂ atmosphere;2.In the preparation of NHCSs,formaldehyde,3-aminophenol and resorcinol were polymerized to form phenolic resin.By adjusting the amount of3-aminophenol,the nitrogen doping content can be effectively controlled.The relationship between the nitrogen content and morphology was explored on the basis of the CO₂-TPD results.It is found that the introduction of nitrogen into the carbon shell produce basic centers.When the nitrogen content is increased to about 5.4 wt%,more basic centers results in the uneven encapsulation of phenolic resin on the template surface and the NHCSs were damaged due to the reject effect between the Si O₂ spheres with negative charge surface and the basic centers.The emergence of the pot-shaped morphology was particularly evident when nitrogen content reaches to 7.2%.3.The Cu@NHCSs catalysts show high catalytic performance in the synthesis of DMC.With the increase of nitrogen content,the catalytic activity of Cu@NHCSs displayed a volcanic curve.The space-time yield(STY_DMC)and TOF value over Cu@NHCSs-3 reached 1528 mg/（g·h）and 11.0 h^-1,respectively,which was nearly 5 times higher than that without nitrogen doping.The thinner shell and uniform mesopore provide favorable conditions for the diffusion of reactants and products.In addition,when pyridic nitrogen and graphitic nitrogen doping into NHCSs,it can effectively improve the electronic properties of the shell layer and increase the dispersion of Cu species.The size of copper particles is 7.4 nm in Cu@NHCSs-3,therefore it displays high intrinsic catalytic activity on the nanometer scale.4.Using SBA-15 as support,n-hexane is organic phase and copper-zinc aqueous solution militate against is inorganic phase.During the preparation process,the active components can effectively enter the mesoporous channel of SBA-15 through the interaction of two solvents.Then the supported copper-zinc composite catalyst was obtained after N₂/H₂ reduction.5.The catalytic performance of Cu-Zn/SBA-15 in MF synthesis by dehydrogenation of methanol has been studied.After addition of Zn,the catalytic activity and MF selectivity are obviously improved.When the reduction temperature is 300°C,mole ratio of Cu/Zn is 10 and methanol of liquid hourly space velocity is 7.9 h^-1,the catalyst exhibits the best catalytic performance,and the methanol conversion and MF selectivity reach 29.8%and93.7%,respectively.It is concluded that active components can effectively immerse into the pores of SBA-15 by the double-solvent impregnation method,which is helpful to enhance the stability of the resulting catalyst.Moreover,the addition of Zn makes copper species more stable and better dispersion.Because of the synergism between Cu and Zn components,the side reactions can be greatly reduced and the catalyst performance is significantly improved.