Carbon dioxide adsorption on MIL-10

Carbon dioxide adsorption on MIL-100(M) (M = Cr, V, Sc) metal–organic frameworks: IR spectroscopic and thermodynamic studies Carlos Palomino Cabello, Paolo Rumori, Gemma Turnes Palomino⇑
Department of Chemistry, University of the Balearic Islands, 07122 Palma de Mallorca, Spain
a r t i c l e i n f o
Article history: Received 13 December 2013 Received in revised form 24 January 2014 Accepted 5 February 2014 Available online 14 February 2014
Keywords: Carbon capture and storage Metal-organic frameworks IR spectroscopy Thermodynamics
abstract
Interaction between carbon dioxide and the coordinatively unsaturated Cr(III), V(III) and Sc(III) cationic centers in MIL-100(Cr), MIL-100(V) and MIL-100(Sc), respectively, was studied by means of variable-tem- perature infrared (VTIR) spectroscopy, a technique that affords determination of standard adsorption enthalpy (DH0) and entropy (DS0) from analysis of IR spectra recorded over a temperature range while simultaneously measuring equilibrium pressure inside a closed IR cell. DH0 was found to be 63, 54 and 48 kJ mol1 for MIL-100(Cr), MIL-100(V) and MIL-100(Sc), respectively, which are among the high- est values so far reported for CO2 adsorption on metal–organic frameworks containing open metal sites. Corresponding values for DS0 resulted to be 210, 198, and 178 J mol1 K1, thus showing a positive correlation between DH0 and DS0. The observed values of standard adsorption enthalpy are discussed in the broader context of corresponding data reported in the literature for the adsorption of carbon dioxide on other MOFs, as well as on zeolites.  2014 Elsevier Inc. All rights reserved.
1. Introduction
Carbon-based fossil fuels provide about 80% of the world’s en- ergy needs [1], but their combustion is one of the major contribu- tors to the rising levels of carbon dioxide in the atmosphere, and hence to greenhouse effect and its adverse consequences on cli- mate. Despite increasing development of renewable and cleaner energy sources, a fast move away from fossil fuels is unlikely to oc- cur in the mid-term. Consequently, there is a need to develop effi- cient technologies that could allow us to continue using fossil fuels while reducing CO2 emissions. Carbon capture and storage (CCS) has been proposed as a means of limiting CO2 emissions from fossil fuel burning (both in power plants and in other stationary sources), thus mitigating greenhouse effects [2–5]. Current technology for CCS uses mainly liquid amine-based chemical absorbents, but besides the high amount of energy re- quired for regenerating the sorbent, that technology poses some corrosion problems and environmental hazards derived from waste processing, unintentional emissions and accidental release [6–10]. To overcome the drawbacks of amine aqueous solutions, several types of porous adsorbents that can reversibly capture and release CO2 (in temperature- or pressure-swing cycles) are currently under active investigation as a means to facilitate CO2
capture from flue gases of stationary sources [11–13]. For cost- effective gas separation, main adsorbent requirements are large adsorption capacity (specially at a low pressure), stability over a large number of adsorption–desorption cycles, fast kinetics, and favorable adsorption thermodynamics, meaning that, in order to facilitate CO2 capture and release, the corresponding adsorption enthalpy should be neither too low nor too high. The main types of porous materials currently under active re- search for CO2 separation are porous carbons [14,15], zeolites [16–18], and metal–organic frameworks (MOFs) and related com- pounds [19–24]. Among these, MOFs have attracted significant interest during last years, mainly because metal–organic frame- works and related materials have the advantage of showing a large variety of structural types and chemical composition, which facil- itates rational design of chemical synthesis aimed at optimizing gas adsorption properties [25–27]. The large number of structures that can be obtained by changing either the organic linker or the metal endows MOFs with a high versatility for tuning not only pore size and surface area but also adsorption enthalpy, which is a main factor determining preferential gas adsorption, and hence separa- tion, from gas mixtures. MOFs having unsaturated metal cation centers are particularly promising in this context. Removal of the coordinated solvent molecules (which act as terminal ligands for the metal cations embedded within the porous framework) by thermal treatment under a vacuum generates localized carbon dioxide adsorption centers which show enhanced gas–solid
http://dx.doi.org/10.1016/j.micromeso.2014.02.015 1387-1811/ 2014 Elsevier Inc. All rights reserved.
⇑ Corresponding author. Tel.: [phone]; fax: [phone]. E-mail address: [e-mail] (G.T. Palomino).
Microporous and Mesoporous Materials 190 (2014) 234–239
Contents lists available at ScienceDirect
Microporous and Mesoporous Materials
journal homepage: www.elsevier.com/locate/micromeso
interaction energy, thus facilitating selective uptake of CO2 at a low pressure [19,20,24,28,29]. As a part of a systematic study on the thermodynamics of car- bon dioxide adsorption on MOFs having unsaturated metal cations in their framework, and with a view to increase knowledge about prospective carbon dioxide adsorbents for CCS, we report for the first time on variable temperature IR (VTIR) [30,31] studies on the interaction of CO2 with three members of the MIL-100 isostructural series (MIL-100(Cr), MIL-100(V) and MIL-100(Sc)). MIL-100(M) are mesoporous MOFs that have the chemical composition M3O(F/ OH)(H2O)2[C6H3(CO2)3]2nH2O. They are metal(III) carboxylates built from trimers of metal octahedra sharing a common oxygen atom which are linked together by trimesate rigid ligands (Fig.1).ThereisalsoaterminalH2O ligand that can be removed by appropriate thermal treatment, to leave an open (coordinatively unsaturated) cationic site. After solvent removal, the framework structure (which is cubic) shows two types of empty mesoporous cages having free apertures of approx. 2.9 and 3.4 nm, accessible through microporous windows of approx. 0.55 and 0.86 nm, respectively [32–35].TheVTIRmethodhastheadvantageofbeing able to give not only the IR spectroscopic features of gas adsorption complexes, but also the corresponding values of standard adsorp- tion enthalpy and entropy that rule the thermodynamics of the adsorption process, thus allowing a detailed description of the interaction between the gas and the adsorbent which could be very
useful in the choice of an optimal adsorbent. The results are dis- cussed in the broader context of relevant data for carbon dioxide adsorption on cation-exchanged zeolites and on other metal–or- ganic frameworks.
2. Materials and methods
The MIL-100(M) (M = Cr, V and Sc) samples used were synthesized under solvothermal conditions following procedures reported in the literature [32–35].Thenecessaryreagents(1,3,5-benzenetricarb- oxylic acid (Aldrich, 95%), triethyl-1,3,5-benzenetricarboxylate (Aldrich, 97%), chromium(VI) oxide (Sigma–Aldrich, 99%), vana- dium(III) chloride (Aldrich, 97%), scandium(III) nitrate hydrate (Aldrich, 99.9%), N,N-dimethylformamide (Scharlau, 99.5%), hydro- fluoric acid (Sigma–Aldrich, 40%), ethanol (Scharlau, 96%), and acetone (Scharlau, 99.5%)) were comercially available and used as received. MIL-100(Sc) was prepared by dissolving 0.204 g of Sc(NO3)3xH2O and 0.084 g of trimesic acid in 15 ml of N,N-dimethylformamide (DMF). The reaction mixture was stirred at room-temperature for 30 min. Then, the mixture solution was transferred into a Teflon- lined autoclave (23 ml) and heated at 423 K for 36 h. After cooling to room temperature, the white powdered product was collected by filtration, washed with DMF, and dried at room temperature. In order to remove the DMF resided in the pores of MIL-100(Sc), the as-synthesized sample was solvothermally treated in ethanol at 373 K for 16 h and then collected by filtration, and dried at room temperature. MIL-100(V) was synthesized by mixing 0.628 g of VCl3 and 0.588 g of triethyl-1,3,5-benzenetricarboxylate in 5 ml of deionized water. The synthesis was carried out in a Teflon-lined autoclave (23 ml) at 493 K for 72 h. The product was retained by filtration as a greenish powder and washed with hot ethanol in order to re- move the unreacted ligand. Finally it was washed with deionized water and dried at 373 K under air. MIL-100(Cr) was prepared by mixing 0.5 g of CrO3, 1.05 g of trimesic acid, and 1.0 ml of a 5 M hydrofluorohydric solution in 24 ml of deionized water. The slurry was stirred for a few minutes at room temperature and then introduced in a Teflon-lined auto- clave (45 ml) and set for 96 h at 493 K. The resulting green solid was washed with deionized water and acetone and dried at room temperature under air atmosphere. The synthesized materials were checked by X-ray powder dif- fraction. The diffractograms of the obtained products showed in
Fig. 1. View of the structure of MIL-100: (a) Trimer of metal octahedra, and (b) schematic tridimensional representation of the supertetrahedra built up from trimers of metal octahedra and trimesate rigid ligands. Metal, carbon and oxygen atoms are depicted as blue, gray and red spheres, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
5 10 15 20 25 30 35
(c)
(b)
2-theta (degree)
(a)
Fig. 2. X-ray diffraction diffractograms (Cu-Ka radiation) of: (a) MIL-100(Cr), (b) MIL-100(Sc) and (c) MIL-100(V) samples.
C.P. Cabello et al./Microporous and Mesoporous Materials 190 (2014) 234–239 235
all cases good cristallinity, and all diffraction lines could be as- signed to the corresponding structural types, as shown in Fig. 2. For infrared spectroscopy, thin self-supported wafers of the MOF samples were prepar

Kết quả (Việt) 1:

Điôxít cacbon hấp phụ trên MIL-100(M) (M = Cr, V, Sc) khung kim loại-hữu cơ: IR quang phổ và nhiệt học Carlos Palomino Cabello, Paolo Rumori, Gemma Turnes Palomino⇑Vùng của hóa học, trường đại học thuộc quần đảo Balears, 07122 Palma de Mallorca, Tây Ban Nhar t i c l e tôi n f oBài viết lịch sử: nhận được 13 tháng 12 năm 2013 đã nhận trong hình thức sửa đổi ngày 24 tháng 1 năm 2014 chấp nhận 5 tháng 2 2014 có sẵn trực tuyến 14 tháng hai 2014Từ khóa: Cacbon chụp và lưu trữ kim loại hữu cơ khung IR phổ học nhiệt động lực họctóm tắtInteraction between carbon dioxide and the coordinatively unsaturated Cr(III), V(III) and Sc(III) cationic centers in MIL-100(Cr), MIL-100(V) and MIL-100(Sc), respectively, was studied by means of variable-tem- perature infrared (VTIR) spectroscopy, a technique that affords determination of standard adsorption enthalpy (DH0) and entropy (DS0) from analysis of IR spectra recorded over a temperature range while simultaneously measuring equilibrium pressure inside a closed IR cell. DH0 was found to be 63, 54 and 48 kJ mol1 for MIL-100(Cr), MIL-100(V) and MIL-100(Sc), respectively, which are among the high- est values so far reported for CO2 adsorption on metal–organic frameworks containing open metal sites. Corresponding values for DS0 resulted to be 210, 198, and 178 J mol1 K1, thus showing a positive correlation between DH0 and DS0. The observed values of standard adsorption enthalpy are discussed in the broader context of corresponding data reported in the literature for the adsorption of carbon dioxide on other MOFs, as well as on zeolites.  2014 Elsevier Inc. All rights reserved.1. IntroductionCarbon-based fossil fuels provide about 80% of the world’s en- ergy needs [1], but their combustion is one of the major contribu- tors to the rising levels of carbon dioxide in the atmosphere, and hence to greenhouse effect and its adverse consequences on cli- mate. Despite increasing development of renewable and cleaner energy sources, a fast move away from fossil fuels is unlikely to oc- cur in the mid-term. Consequently, there is a need to develop effi- cient technologies that could allow us to continue using fossil fuels while reducing CO2 emissions. Carbon capture and storage (CCS) has been proposed as a means of limiting CO2 emissions from fossil fuel burning (both in power plants and in other stationary sources), thus mitigating greenhouse effects [2–5]. Current technology for CCS uses mainly liquid amine-based chemical absorbents, but besides the high amount of energy re- quired for regenerating the sorbent, that technology poses some corrosion problems and environmental hazards derived from waste processing, unintentional emissions and accidental release [6–10]. To overcome the drawbacks of amine aqueous solutions, several types of porous adsorbents that can reversibly capture and release CO2 (in temperature- or pressure-swing cycles) are currently under active investigation as a means to facilitate CO2capture from flue gases of stationary sources [11–13]. For cost- effective gas separation, main adsorbent requirements are large adsorption capacity (specially at a low pressure), stability over a large number of adsorption–desorption cycles, fast kinetics, and favorable adsorption thermodynamics, meaning that, in order to facilitate CO2 capture and release, the corresponding adsorption enthalpy should be neither too low nor too high. The main types of porous materials currently under active re- search for CO2 separation are porous carbons [14,15], zeolites [16–18], and metal–organic frameworks (MOFs) and related com- pounds [19–24]. Among these, MOFs have attracted significant interest during last years, mainly because metal–organic frame- works and related materials have the advantage of showing a large variety of structural types and chemical composition, which facil- itates rational design of chemical synthesis aimed at optimizing gas adsorption properties [25–27]. The large number of structures that can be obtained by changing either the organic linker or the metal endows MOFs with a high versatility for tuning not only pore size and surface area but also adsorption enthalpy, which is a main factor determining preferential gas adsorption, and hence separa- tion, from gas mixtures. MOFs having unsaturated metal cation centers are particularly promising in this context. Removal of the coordinated solvent molecules (which act as terminal ligands for the metal cations embedded within the porous framework) by thermal treatment under a vacuum generates localized carbon dioxide adsorption centers which show enhanced gas–solidhttp://dx.doi.org/10.1016/j.micromeso.2014.02.015 1387-1811/ 2014 Elsevier Inc. All rights reserved.
⇑ Corresponding author. Tel.: [phone]; fax: [phone]. E-mail address: [e-mail] (G.T. Palomino).
Microporous and Mesoporous Materials 190 (2014) 234–239
Contents lists available at ScienceDirect
Microporous and Mesoporous Materials
journal homepage: www.elsevier.com/locate/micromeso
interaction energy, thus facilitating selective uptake of CO2 at a low pressure [19,20,24,28,29]. As a part of a systematic study on the thermodynamics of car- bon dioxide adsorption on MOFs having unsaturated metal cations in their framework, and with a view to increase knowledge about prospective carbon dioxide adsorbents for CCS, we report for the first time on variable temperature IR (VTIR) [30,31] studies on the interaction of CO2 with three members of the MIL-100 isostructural series (MIL-100(Cr), MIL-100(V) and MIL-100(Sc)). MIL-100(M) are mesoporous MOFs that have the chemical composition M3O(F/ OH)(H2O)2[C6H3(CO2)3]2nH2O. They are metal(III) carboxylates built from trimers of metal octahedra sharing a common oxygen atom which are linked together by trimesate rigid ligands (Fig.1).ThereisalsoaterminalH2O ligand that can be removed by appropriate thermal treatment, to leave an open (coordinatively unsaturated) cationic site. After solvent removal, the framework structure (which is cubic) shows two types of empty mesoporous cages having free apertures of approx. 2.9 and 3.4 nm, accessible through microporous windows of approx. 0.55 and 0.86 nm, respectively [32–35].TheVTIRmethodhastheadvantageofbeing able to give not only the IR spectroscopic features of gas adsorption complexes, but also the corresponding values of standard adsorp- tion enthalpy and entropy that rule the thermodynamics of the adsorption process, thus allowing a detailed description of the interaction between the gas and the adsorbent which could be very
useful in the choice of an optimal adsorbent. The results are dis- cussed in the broader context of relevant data for carbon dioxide adsorption on cation-exchanged zeolites and on other metal–or- ganic frameworks.
2. Materials and methods
The MIL-100(M) (M = Cr, V and Sc) samples used were synthesized under solvothermal conditions following procedures reported in the literature [32–35].Thenecessaryreagents(1,3,5-benzenetricarb- oxylic acid (Aldrich, 95%), triethyl-1,3,5-benzenetricarboxylate (Aldrich, 97%), chromium(VI) oxide (Sigma–Aldrich, 99%), vana- dium(III) chloride (Aldrich, 97%), scandium(III) nitrate hydrate (Aldrich, 99.9%), N,N-dimethylformamide (Scharlau, 99.5%), hydro- fluoric acid (Sigma–Aldrich, 40%), ethanol (Scharlau, 96%), and acetone (Scharlau, 99.5%)) were comercially available and used as received. MIL-100(Sc) was prepared by dissolving 0.204 g of Sc(NO3)3xH2O and 0.084 g of trimesic acid in 15 ml of N,N-dimethylformamide (DMF). The reaction mixture was stirred at room-temperature for 30 min. Then, the mixture solution was transferred into a Teflon- lined autoclave (23 ml) and heated at 423 K for 36 h. After cooling to room temperature, the white powdered product was collected by filtration, washed with DMF, and dried at room temperature. In order to remove the DMF resided in the pores of MIL-100(Sc), the as-synthesized sample was solvothermally treated in ethanol at 373 K for 16 h and then collected by filtration, and dried at room temperature. MIL-100(V) was synthesized by mixing 0.628 g of VCl3 and 0.588 g of triethyl-1,3,5-benzenetricarboxylate in 5 ml of deionized water. The synthesis was carried out in a Teflon-lined autoclave (23 ml) at 493 K for 72 h. The product was retained by filtration as a greenish powder and washed with hot ethanol in order to re- move the unreacted ligand. Finally it was washed with deionized water and dried at 373 K under air. MIL-100(Cr) was prepared by mixing 0.5 g of CrO3, 1.05 g of trimesic acid, and 1.0 ml of a 5 M hydrofluorohydric solution in 24 ml of deionized water. The slurry was stirred for a few minutes at room temperature and then introduced in a Teflon-lined auto- clave (45 ml) and set for 96 h at 493 K. The resulting green solid was washed with deionized water and acetone and dried at room temperature under air atmosphere. The synthesized materials were checked by X-ray powder dif- fraction. The diffractograms of the obtained products showed in
Fig. 1. View of the structure of MIL-100: (a) Trimer of metal octahedra, and (b) schematic tridimensional representation of the supertetrahedra built up from trimers of metal octahedra and trimesate rigid ligands. Metal, carbon and oxygen atoms are depicted as blue, gray and red spheres, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
5 10 15 20 25 30 35
(c)
(b)
2-theta (degree)
(a)
Fig. 2. X-ray diffraction diffractograms (Cu-Ka radiation) of: (a) MIL-100(Cr), (b) MIL-100(Sc) and (c) MIL-100(V) samples.
C.P. Cabello et al./Microporous and Mesoporous Materials 190 (2014) 234–239 235
all cases good cristallinity, and all diffraction lines could be as- signed to the corresponding structural types, as shown in Fig. 2. For infrared spectroscopy, thin self-supported wafers of the MOF samples were prepar