One-pot Route Synthesized Highly Ordered Nitrogen-doping Mesoporous Carbon Supported Pd and Ag Catalysts for Liquid-phase Hydrogenation Reactions

Author:Li Zuo Zuo

Supervisor:li xiao nian

Database:Doctor

Degree Year:2017

Download:253

Pages:131

Size:11664K

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Highly ordered mesoporous carbon(OMC)due to its large specific surface area and pore volume are widely used in the field of catalysis,hydrogen storage materials and electrode materials,while introducing nitrogen can significantly improve its structure,conductivity,acid-base properties and other characteristics.A new class of highly thermal stability,high nitrogen loading and recyclable N-doped highly ordered mesostructures carbon(NOMC)was synthesized by one-pot route.Adjusting and controlling of C-N atomic ratio and accumulation regulation by changing nitrogen source and synthesis methods.The NOMC were used as supports to immobilize Pd nanoparticles,which provided a unique platform to investigate the influence for hydrodechlorination of 4-chlorophenols to phenol.A single-site Ag-NOMC catalyst was obtained by one-pot route.Meanwhile,the relationship of N-doped ordered mesoporous carbons and hydrodechlorination properties was studied,the outcome of this project will provide a foundation for other doped materials,and to broaden the nitrogen carbon materials in other catalytic application provide enlightenment.Adjusting and controlling of NOMC by changing temperature,template used,nitrogen source and synthesis methods.The results show that material specific surface area and pore volume increased with the increase of calcination temperature,and template agent(1,3,5-trimethylbenzene TMB)and temperature will affect the nitrogen species.The calcined samples of 500℃ and 900℃ with TMB addition,the different N species can get,such as carbon nitride,pyridinic N,pyrrolic N and graphitic N.While at higher temperature with TMB addition,it is easier to form pyrrolic N which is helpful for the improvement of catalytic activity.The amount of nitrogen doping is higher after TMB addition.This may be due to TMB generated after two-dimensional hexagonal(p6m)structure which can form nice pore structure for nitrogen doping.But if the calcined temperature was at 350 ℃ or 500 ℃ the amount of nitrogen doping as high as 51.54%.The results of FI-IR and TG may illustrate that most of the nitrogen is come from melamine which did not join into the lattice of carbon.Different precursors(resorcinol,cyanuric acid,melamine,phloroglucinol and urea)were investigated respectively.The results show that when using resorcinol and cyanuric acid as precursor,the material specific surface area is better than others.The catalyst shows better activity performance when using resorcinol and melamine as precursor than others,but while using phloroglucinol instead of melamine show the lowest activity performance.The N groups may lost when calcining at high temperature,since the thiocyanate radical can not polymerize with resorcinol well.Pd catalysts supported on N-doped or B-doped ordered mesoporous carbons(NOMC or BOMC)have been prepared and tested in the hydrodechlorination(HDC)of chlorophenols with H2.The NOMC or BOMC could be readily obtained by one-pot route synthesis with nitrogen which is containing molecules to achieve materials with well preserved mesopore structure.The difference from the previous methods is that the used urea as nitrogen source via one-pot route.This target compound allows complete dechlorination at mild operating conditions(303 K and atmospheric pressure).The catalyst with small PdNPs gave the excellent catalytic activity and selectivity under mild conditions.In addition,the stability of the catalysts was checked and the conversion of 4-CP was still maintained at 100%without apparent deactivation in the 6 times.This catalytic performance could be attributed to the synergetic effects of the active center P-N,N-doped supports,and the stabilized small PdNPs.The Ag@NOMC could be obtained by one-pot route synthesis with nitrogen which is containing molecules to achieve materials with well preserved mesopore structure.Different precursors,template agent and the different Ag loading amount were investigated,and as prepared catalysts tested in the hydrogenation of nitrophenol in water.The results show that material pore structure and catalytic activity m-aminophenol better than resorcinol as precursors.When using template agent(1,3,5-trimethylbenzene TMB),the pore structure and catalytic activity are all better.The catalytic activity is not increase with the Ag loading amount,but when the Ag loading is 1 wt%,shows the best catalytic activity.The H2-TPR also gave the evidence that the 1 wt%Ag have more active site than others.As a result of a single atom site may have been formed Ag-N structure.The characterization of XRD,EDX and TEM can not find the Ag nanoparticles when the Ag loading is 0.5 wt%or 1 wt%,but compared the catalytic activity 1 wt%Ag is better than 10 wt%Ag,The characterization of the material confirmed the atomic dispersion of the Ag phase throughout the sample.It can effectively save the dosage of the catalyst active component.