Investigation of metal-organic frameworks as adsorbents for CO₂ capture from flue gas

Coordination compounds;Organometallic compounds;Carbon sequestration;Flue gases--Purification

Kahr, Juergen ; Wright, Paul Anthony ; Wright, Paul Anthony

University:University of St Andrews

Department:Chemistry (School of)

关键词: Coordination compounds;    Organometallic compounds;    Carbon sequestration;    Flue gases--Purification;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/7045/JuergenKahrPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

The post-synthetic modification of CPO-27(Mg) by introducing nickel cations into theframework is described. A combination of surface sensitive XPS analysis, synchrotron powder X-ray diffraction and selected area and bulk EDX measurements revealed the distribution of Ni²⁺ throughout the crystal with the highest concentration towards the external surface forming a nickel-rich rim. By adding nickel acetate and chloride salts in combination with a weak acid, Ni²⁺ contents of up to 67% for the bulk material were achieved via a one-pot preparative procedure. A combined mechanism of overgrowth and isomorphous cation exchange is proposed. The study led to an improvement of porosity to N₂ (77 K) up to 17 mmol g⁻¹, close to values achieved elsewhere via complex activation procedures. High values for the adsorption of carbon dioxide of up to 6.7 mmol g⁻¹ at temperatures and partial pressure relevant for carbon capture from post-combustion power plants were accomplished (298 K, 0.1 bar) and were shown to be repeatable over cycles under dry conditions.The synthesis, structure and adsorption properties of a series of zinc imidazolatezeolitic imidazolate framework, ZIF, materials was also investigated. Structuraldetails of the zinc nitroimidazolate ZIF-65(Zn) were determined by Rietveldrefinement. Heating experiments of as prepared ZIF-65(Zn) revealed a partialtransformation from a cubic framework to an unknown structure, shown to bereversible. The new phase possess high porosity to nitrogen and showed stepped,hysteretic adsorption and desorption isotherms for at 77 K and CO₂ at 298 K. Usingmethanol instead of DMF in synthesis yielded a novel dense non-porous zinc nitroimidazolate structure.A series of novel structures was prepared via synthesis including a mixture of 2-nitroimidazole (NIm) and purine with different zinc metal sources. Two MOFstructures were found to consist of purine linkers only, but could not be renderedporous. By changing the metal source or solvent an isoreticular structure of the ZIF-68 (GME) family was obtained, composed of purine and NIm, as well as a novel formof a mixed linker ZIF with the RHO topology with Im-3m symmetry that exhibitslarge pores and exo-Zn and exo-NIm moieties decorating the cavity walls. Thenitrogen uptake (77 K) of 6.5 mmol g⁻¹could be increased to 12.5 mmol g⁻¹ byremoving exo-moieties through water washing.The use of a diamino functionalised purine linker (DAP) together with NIm gave anew ZIF material, STA-17, with a novel topology. The structure was found to exhibitporosity to nitrogen (77 K) of 6.5 mmol g⁻¹ and carbon dioxide at (198 K) of 5 mmolg⁻¹, but shows weak interaction with CO₂ at 298 K. Indexing from synchrotronpowder XRD data gave a hexagonal unit cell with a = b = 29.725 Å and c = 18.606 Å.Subsequent analysis of the composition using NMR, TGA and IR techniques revealedthe presence of both linkers in the structure and a linker ratio of 2:1 (NIm : DAP).Although crystals of suitable quality for single crystal X-ray diffraction were notobtained, a partial model for the structure is proposed via analogy with a hypotheticalzeolite structure and analysis of powder X-ray diffraction data.