Ordered Mcsoporous Composites And Templated Carbon Materials:Design,Synthesis And Catalytic Performance

Ordered mesoporous material is a class of porous materials whose pore sizes are between2 and 50 nm and the pore channels are arranged in long-range order.Owing to its high specific surface area,uniform and adjustable pore size,easy modification and good stability,ordered mesoporous material has been widely used in the fields of hetergeneous catalysis,adsorption and separation,environmental protection and electrochemistry.It is great significance to explore more potential applications by utilizing the characteristics of easily modified inner surface of mesoporous materials to get functional materials.This paper mainly investigates the application of ordered mesoporous composites and templated carbon in solid acid catalysis and electrocatalytic reduction of CO₂.Ordered mesoporous composite materials ZrMo-KIT-6 and metal oxide NiO-Al₂O₃ were synthesized by soft template method.The former was used as solid acid catalyst for acetalization of glycerol with acetone,and the latter was used as hard template to prepare templated carbon materials Ni-N-C-?T?for the electrocatalytic reduction of CO₂ by chemical vapor deposition?CVD?method.Furthermore,replacing hard template,we directly used carbon paper with porous structure to support Ni to prepare integrated eletrodes by CVD method for the electrocatalytic reduction of CO₂.The main research contents are as follows.1.Design,synthesis and catalytic performance of ordered mesoporous solid acid ZrMo-KIT-6:A series of solid acid catalysts?ZrMo-KIT-6?with different Zr and Mo contents were synthesized by one-pot hydrothermal synthesis.The influences of Zr and Mo contents and calcination temperature in ordered mesoporous structure and existing states of introduced Zr and Mo species were systematically researched by XRD,N₂-physisorption,TEM,TG-DSC,XRD,Raman,UV-vis and XPS techniques.The results indicated that Zr and Mo species were incorporated into the skeleton of material as designed and existed as a highly dispersed state when the content was below 7%.NH₃-TPD and pyridine infrared measurements showed that ZrMo-KIT-6?5-700?had the highest acid content,and there existed both Br?nsted and Lewis acid sites.The ZrMo-KIT-6?5-700?material showed optimal catalytic performance?conversion of glycerol was 85.8%and selectivity of solketal was 97.8%?,and there was no obvious decline in catalytic performance even after five cycles.2.Templated carbon was preparated by taking ordered mesoporous NiO-Al₂O₃ as template for electrocatalytic reduction of CO₂:ordered mesoporous NiO-Al₂O₃ was synthesized by one-pot evaporation-induced self-assembly?One-pot EISA?method.In view of the confined effect of its channels,the templated carbon materials Ni-N-C-?T?were prepared by CVD method with acetonitrile used as C and N source.The results of XRD,SEM,TEM,XPS and electrochemical measurements showed that Ni-N-C-?600?materials had high N content?3 at%?and pyridine N accounted for 40%of the total N content,Ni nanoparticles were closely encapsulated by N-doped carbon nanotubes.The Ni-N-C structure at the interface of the two materials and pyridine N were conducive to CO₂RR reaction.The Ni-N-C-?600?material showed optimal catalytic performance(FE_CO?%?and current density respectively reaches 62%,11.6 mA cm^-2 at-0.76 V vs.RHE)and good stability(FE_CO?%?still has 40%at the reaction time 5 h).By controlling the synthesis temperature of Ni-N-C materials and adjusting the electrode potential,the ratio of CO/H₂ in syngas can be adjusted between 0.25 and1.5.3.One-step CVD method synthesis of Ni-NCNTs/CP electrodes for electrocatalytic reduction of CO₂:commercial carbon fiber paper which has uniform porous structure and good conductivity is taken to load Ni species with different contents.With utilizing acetonitrile as sources of C and N,X-Ni-NCNTs/CP-T as integrated electrode was prepared by CVD method for electrocatalytic reduction of CO₂ to syngas.The results of XRD,SEM and XPS indicated that there are abundant Ni nanoparticles encapsulated by N-doped carbon nanotubes?Ni-NCNTs?on the surface of carbon paper.Carbon fibers can be closely wrapped by Ni-NCNTs,which directly avoid being exposed to electrolyte.Therefore,HER can be effectively inhibited.Pyridine N and Ni-N-C structure on the electrode surface can adsorb and active CO₂ molecules,while graphite N has little contribution to CO₂RR.2.5-Ni-NCNTs/CP-700 has the best catalytic performance(FE_CO?%?and current density respectively reaches 54%,13.6 mA cm^-2 at-0.86 V vs.RHE)and FE_CO?%?still has 30%at reaction time 6 h.By selecting suitable eletrodes and adjusting the electrode potential,the ratio of CO/H₂ in syngas can be adjusted between 0.25 and 1.5.