Research On Reaction Mechanism Of CO₂ Desorption By Covalent Organic Frameworks Catalysts

CO2 emissions and climate change have attracted widespread attention,and they are attributed to the excessive consumption of fossil fuels.The post-combustion capture of CO2 from the flue gas of fossil fuels is a crucial route for controlling CO2 emission and achieving the global target of carbon neutralization.The application of amine-based solvents in chemisorption is a highly mature technology that provides the advantages of stable reliability,high absorption efficiency,and highly scalability(for industrial applications).However,this technology also has a high energy penalty(4 GJ/t CO2),especially for solvent regeneration(approximately 70%of total energy consumption)at between 120-140℃.Therefore,developing novel strategy is necessary to achieve energy-efficient solvent regeneration that allows for low-cost CO2 capture.Covalent organic frameworks(COF)are superior candidates because of their controllable frame structure,super high surface area,and large pore volume.The various covalent bonds in COF can effectively provide binding sites for the formation of welldistributed coordination structures with various metals that promote the stability of catalytic sites,and this technique is widely applied in catalysis.The reasonable matching of a metal oxide with COF to improve acidic active sites,which provides unique structural advantages.Catalytic amine-based solvent regeneration with COF-based solid acid is a feasible option for reducing energy consumption of CO2 capture,which is beneficial for designing material structures and understanding reaction mechanisms.The main research contents are as follows:(1)Inducing efficient proton transfer through Fe/Ni@COF catalystHerein,we cover the nanoscale NiFe2O4 cluster with COF support,to prepare solid acid catalysts.The pristine chemical bonds of Ni(Fe)-O and Ni(Fe)-Ni(Fe)are substituted by Ni(Fe)-N and Ni(Fe)-N-Ni(Fe)by targeting the anchoring of NiFe2O4 cluster over COF.The created coordination state stimulates the production of Bronsted acid sites.The obtained nanomaterials achieve a considerable improvement in CO2 desorption of up to 290.1 mmol/(min·g)at 88℃ for spent monoethanolamine(MEA)solvent,representing a substantial increase of 540%relative to traditional thermal desorption.Consequently,the energy consumption of MEA generation is reduced by approximately 58%.Intermediate species(HCO3-,CO32-,and RNHCOO-)and reaction pathways are established by combining operando Raman spectroscopy and ex situ 13C NMR spectrum measurements.Theoretical calculations are performed to clarify the transformation mechanism of the acid sites around Ni/Fe atoms and its intrinsic role in the adsorption equilibrium of solvent regeneration.(2)Synergistic promotion for solvent regenerantion by CoSAC@NC catalystUsing COF as catalysts support for enhancing mass transfer and boosting aminebased solvent regeneration is a promising option for both resources recycling and efficient carbon capture.Here,the effect of CoSAC-N-C prepared by Co atoms anchored in COF derivatives was firstly investigated on CO2 desorption reaction at 88℃.The Brownian motion and shuttle effect of submicron or micron CoSAC-N-C particles play a positive role in reducing the concentration boundary layer and updating the CO2-species concentration of liquid/gas film,which is beneficial for mass transfer enhancement.Additionally,the single metal sites of CoSAC-N-C catalyst abundant acid/base active sites for water dissociation,which can promote the proton transfer and boost carbamate decomposition.Therefore,the maximal desorption rate(1.57 mmol/min)increases by 200%and relative heat duty decreases to 67%.The results offer a favorable technology for reuse of industrial solid waste in the field for low-energy carbon capture.(3)Sulfonic-coordinated Co-N-C solid acid catalystsAtomically dispersed Co-N-C coordination is a promising strategy for providing acidic activity sites for catalytic amine solvent regeneration,but the control of the coordination environment remains a major challenge.Here,we report the use of COFderived catalysts with single-atom cobalt to boost the carbamate breakdown reaction.The sulfo group(-SO3H)introduced into the framework was demonstrated to improve the CoN-C coordination and morphology of COF supports,and it served as the bridge for proton transfer.Experimental characterizations suggest that-SO3H extends the COF layer,resulting in increased surface areas(696 m2/g)that are beneficial for anchoring cobalt atoms.Moreover,the new coordination configuration(Co-N/C/O)significantly increased the acidic activity of the COF catalysts with single-atom Co.Density functional theory calculations revealed that the Co sites enhanced by the sulfo group were favorable for both carbamate breakdown and acid site generation.The sulfonic-coordinated Co-NC(S-Co/NC)catalysts exhibited superior spent solvent regeneration activity at lower concentrations compared with previously described catalysts.Moreover,the maximum desorption rate(3.74 CO2 mmol/min)considerably increased by 733%compared with the catalyst-free reaction,resulting in approximately 39%lower relative heat duty.This study presented an efficient and feasible method for atomic-level tuning of the Co-N-C catalyst for developing excellent solid acid catalysts for energy-efficient amine solvent regeneration.In summary,for the post-combustion capture of CO2,the high regeneration temperature hampered the practice application of chemisorption involving the use of an alkanolamine absorbent.In the present study,three kind of acid catalyst based on COF framework were prepared to achieve the efficient regeneration of CO2 solvent through a heterojunction engineering strategy.An experimental-theoretical method was also developed to investigate the structure-activity relationship during catalytic carbamate decomposition.The results revealed that the coordination between metal and COF supporter played a key role in forcing LASs to transform into BASs and increasing surface areas and pore sizes.The proposed methods provided an effective strategy for developing high-performance catalysts for solvent regeneration;they could represent a practical and promising technique route for using amine-based solvent to capture CO2 from industrial flue gas at a low cost.