Boron/Nitrogen-rich Carbon Materials For Chemical Fixation Of CO₂ Into Cyclic Carbonates

Carbon dioxide?CO₂?is not only the common greenhouse gas in the air,but also one of the most important carbon resources on Earth.Its capture and conversion have received extensive attention.Converting CO₂ into chemical products with high value-added chemical product by chemical process is of great significance to protecting the environment and improving economic returns.The cycloaddition reaction between propylene oxide and carbon dioxide can not only effectively fix carbon dioxide but also meet the requirements of green chemistry,and the development of suitable catalysts has become a research hotspot.There are many types of catalysts used in this reaction.Although most of them exhibit relatively high catalytic activity,there are also problems,such as low recycling rate and heavy metal pollution.Among these catalysts,as one of the most promising catalysts,carbon materials have an excellent chemical inertness in the recycling of natural advantages,the surface chemistry can be controled to make it more suitable for catalytic reactions.In view of the application of carbon materials in cycloaddition reactions,based on the idea of acid-base synergistic,the work includes the following parts:?1?Polyacrylonitrile contents the more nitrogen,and after carbonization we can obtain a carbon material with high N content.Besides,graphene oxide?GO?is a two-dimensional carbon material that rich in oxygen-containing functional groups.So GO can be used in producing regular nitrogen-containing carbon materials.In the experiments,we use GO as a substrate,GO/polyacrylonitrile composites is prepared by in-situ polymerization in the solution.After GO/polyacrylonitrile composites is pre-oxidated and carbonized,we obtain the nitrogen-doped carbon material.And the relationship between the N content,N species,and pore structure is further studied.The experimental study that the material which pre-oxidized at 270^? and carbonized at 500 ^? obtain the best catalytic activity.In the experiment,when the amount of catalyst is 0.2 g,TBAB is 1 mol%of substrate,and reaction temperature is 120 ^?,the pressure of CO₂ is 2 MPa,the yeild of PC reaches 62.9%and the specific activity reaches3.25g g^-1h^-1 after 5 h reaction.We found that the effect of nitrogen content is more significant than the pore structure on the activity of the catalyst.The higher the content of unsaturated nitrogen?such as amino,pyridine nitrogen and pyrrole nitrogen?in the catalyst,the better the activity is.?2?In order to improve the catalytic activity of the carbon material,we prepare the boron-nitrogen co-doping carbon material.Based on the idea of acid-base synergistic catalysis,we use L-glutamic acid as the carbon source and nitrogen source,and boric acid as the boron source.Both of them are mechanically mixed by a simple and effective ball-milling method,.By investigating different carbonization temperatures and mixing ratios,we discover that when the ratio of glutamic acid to boric acid was 1:6 and carbonization temperature is 900°C,the catalyst activity is the highest.The XPS analysis showed that the nitrogen content is 8.93 at%and the boron content is 7.16 at%.In the experiment,when the amount of catalyst is 0.02 g,TBAB is1 mol%of substrate,the reaction temperature is 160 ^?,and carbon dioxide pressure is 2 MPa,the yeild of PC reaches 90.2%,and the specific activity reaches 23.5 g g^-1h^-1.Furthermore,it has excellent recycling ability and actual application value.