Biomass Derived Nitrogen-enriched Active Carbon For Catalytic Reduction Of Nitroaromatics And Selective Adsorption Of CO₂

Nitrogen-enriched active carbons have been widely concerned in the fields of energy storage and conversion,gas adsorption,water purification and catalyst support due to its rich surface functional groups,high specific surface area,excellent conductivity,low cost and environmental friendliness.Nitrogen-enriched biomass are rich in nitrogen compounds,which are excellent precursors for the preparation of nitrogen-enriched active carbon.Biomass have the advantages of renewable,rich resources and low-price.Using nitrogen-enriched biomass as carbon source to prepare active carbon can realize the effective utilization of resources,improve the added value of biomass,reduce the environmental pollution caused by the direct burning of biomass waste,which has the characteristics of energy saving,value-added,environmental protection.In this paper,tobacco stems and coffee grounds were used as raw materials to prepare nitrogen-enriched active carbon by pre-carbonization and KOH activation.1.Tobacco stems derived nitrogen-enriched active carbons（TACs）were prepared by KOH activation.The effects of activation temperature and ratio of KOH/C on pore structure and surface nitrogen content of TACs were studied.The results show that TACs-3-800 has high specific surface area(S_BET=2938 m²·g^-1),large pore volume(V_total=1.60 cm³·g^-1)and high nitrogen content（1.34%）.TACs were also used as a metal free catalyst for reduction of nitroarenes.The results show that the TACs-3-800 has the highest catalytic activity for the reduction of nitroaromatics(conversion of nitrobenzene was 99.9%,selectivity for aniline nearly 100%,initial reaction rate 2.32×10^-2 mol·g^-1·h^-1).The effects of pore structure and nitrogen on the reaction were also research.The results show that large pore structure and specific surface area are help for the reaction,and pyridine nitrogen is the possible active site of reaction.In addition,TACs-3-800 has remarkable activity and durability in reducing aniline.2.Nitrogen-enriched microporous activated carbons（CACs）was successfully prepared with coffee grounds as precursor and KOH as activator.The morphology and surface elements of CACs were characterized.The results show that CACs has abundant microporous pore structure,and shows high specific surface area of micropores and large narrow pore volume.Among them,CACs-2-800 has a higher specific surface area of micropores(S_mic=1138 m²·g^-1)and a larger pore volume of narrow pores(V_0.8=0.34 cm³·g^-1,V_0.6=0.27 cm³·g^-1).The nitrogen enriched activated carbon was used as adsorbent for CO₂adsorption.The adsorption capacity of CACs-2-800 was the highest,which was 6.22 mmol·g^-1 at 273 K and 3.82 mmol·g^-1 at 298 K.Even at low pressure,CACs-2-800 still has high adsorption capacity,which is 2.37 mmol·g^-1 at 273 K.CACs-2-800 also showed high CO₂/N₂selectivity(S_CO2/N2=33)and good adsorption/desorption cycle stability.It is an excellent adsorbent with high selectivity and stability,which are conducive to the adsorption and conversion of CO₂ from industrial flue gas.High nitrogen content and suitable narrow pore diameter are the main reasons for the high selectivity of CACs-2-800.In addition,CACs-2-800 has high catalytic activity for cycloaddition of epichlorohydrin and CO₂.This greatly broadens its application in CO₂ capture and conversion after combustion.