Confinement of AlF3 in MOF derived structures for the formation of 4-fold coordinated Al and significantly improved dehydrofluorination activity

doi:10.1016/j.cej.2020.124946

Chemical Engineering Journal

Volume 394, 15 August 2020, 124946

https://doi.org/10.1016/j.cej.2020.124946 Get rights and content

Highlights

•
AlF₃ particles are confined in quasi MOF structures (MIL-101) with (NH₄)₃AlF₆ as the precursor.
•
AlF₃ is stabilized by the confinement and interaction with CUS of Cr in quasi MOF.
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Large amounts of 4-fold coordinated Al in AlF₃ are achieved due to the interaction.
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Reaction rate of confined AlF₃ is about 9 times higher than that of supported AlF₃.
•
It provides a potential strategy for preparation of metal fluoride Lewis acid catalysts.

Abstract

Dehydrofluorination is the major process for the production of fluorinated monomers and treatment of synthetic greenhouse gases. It is usually catalyzed by the Lewis acids, such as AlF₃, MgF₂ and fluorinated Cr₂O₃. The activity and stability remain the challenges of catalysts. For metal fluorides, Lewis acidic sites are derived from the unsaturated coordination of metal sites. This work reports the confinement of AlF₃ into the cavity of quasi MOF structures. Due to the confinement effect and interaction of AlF₃ with coordinatively unsaturated Cr-O nodes (oxygen vacancy), significant amounts of 4-fold coordinated Al in AlF₃ can be achieved. Consequently, the Lewis acidity of AlF₃ could be dramatically enhanced. As the catalyst of the gas-phase dehydrofluorination of HFC-245fa (1,1,1,3,3-pentafluoropropane) to tetrafluoropropene (HFO-1234ze, a new generation of green refrigerant) at 350 °C with the GHSV of 750 h⁻¹, it exhibited the activity of 9 times higher than that of supported AlF₃. After reaction of 35 h, no noticeable deactivation was detected. The present work provides a potential strategy for the preparation of metal fluoride Lewis acid catalysts with high efficiency.

Graphical abstract

Introduction

At present, global warming is one of the major challenges both in academic and social community. In addition to notorious CO₂, hydrofluorocarbons (HFCs) are also the main contributors of greenhouse gases [1]. Consequently, significant efforts have been initiated. As a response, the European Union’s new F-gas Regulation prohibits the application of HFCs with global warming potential (GWP) higher than 150 as the commercial refrigerants [2], [3]. As the ozone depleting substances, the refrigerants including chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have already been phased out [4]. Therefore, it necessitates the development of new substitutes for CFCs, HCFCs and HFCs. Hydrofluoroolefins (HFOs) are suggested to be appropriate alternatives, which usually exhibit short atmospheric lifetime, zero ozone depletion potential (ODP) and low GWP [5]. Among all the HFO compounds, 1,3,3,3-tetrafluoropropene (HFO-1234ze) is considered as a potential candidate for the replacement of HFC-134a (1,1,1,2-tetrafluoroethane). With the GWP of 1300, HFC-134a is currently one of the most widely applied refrigerants, especially in automobile air conditioners [6], [7]. By contrast, the GWP of HFO-1234ze is only 6 with an atmospheric lifetime of less than 15 days, zero ozone depletion potential and low flammability. The physical properties of HFO-1234ze are very similar as that of HFC-134a [8]. In addition, HFO-1234ze can also be widely used in various areas, e.g. using as foaming agent, heat pump agent and solvent [9], [10].

Among various routes of HFO-1234ze preparation, gas-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa, with the GWP of 858) to HFO-1234ze is the most promising and environmentally friendly [11], [12]. Clearly, this process converts greenhouse gas into value-added and environmentally benign product. In addition, this route is relatively simple and efficient. Presently, HFC-245fa is widely adopted as the key blowing agent in polyurethane foam. Under the regulation of F-gases, this process provides a potential solution for the excess capacity of HFC-245fa [13], [14].

Due to the high dissociation energy of C–F bond, the dehydrofluorination of HFCs is usually carried out with suitable catalysts and high reaction temperatures because of the highly endothermic characteristics. However, the formation of extremely corrosive HF byproduct would result in significant challenge for the catalysts [15], [16], [17], [18]. Consequently, for any catalytic reactions involving HF, the choice of the catalysts is limited to metal fluorides and other HF resistant materials. Aluminum fluoride (AlF₃), magnesium fluoride and fluorinated Cr₂O₃ (F-Cr₂O₃) are the most common catalysts for gas-phase dehydrofluorination of HFCs [19], [20]. Although the traditional AlF₃ and F-Cr₂O₃ catalysts are active for the dehydrofluorination reactions, they deactivate rapidly due to the coke deposition over the strong acidic sites [21], [22]. MgF₂ possesses relatively weak Lewis acid and therefore low coke formation. Unfortunately, it also undergoes fast deactivation due to the significant sintering at temperatures above 280 °C [23]. Introduction of air in the feed was found to be effective for the improvement of catalytic stability for F-Cr₂O₃ [24]. However, it usually leads to low selectivity and extra cost for separation. Currently, the development of new catalytic materials with high activity and extremely long-term stability is the major topic of studies regarding dehydrofluorination reaction processes.

For catalysts, the coordinatively unsaturated metal site (CUS) is generally accepted to be the catalytic center [25]. Facilitated by high surface area, metal–organic frameworks (MOFs) are favorable for the formation of CUS, which are constructed by metal nodes with organic linkers [26]. In addition, the interaction of metal nodes and organic linkers attributes to the regular arrangements of metal centers in the developed pore channels [27]. Consequently, the guest molecule or atom cluster can be immobilized in CUS [28]. For instance, Jiang et al. reported that the Au@Ag nanoparticles were confined to 2–6 nm following the confining effect of the pore/surface structure of ZIF-8 [29]. It exhibited excellent activity for the hydrogenation of 4-nitrophenol. Corma et al. immobilized Au (III) (2 wt%) to a modificatory MOF which catalyzes a domino three coupling and cyclization to indoles efficiently [30].

However, the CUS usually is easy to be separated from the guest molecule or atom cluster due to the organic ligands, resulting in the weak interaction between host (CUS) and guest (molecule or atom cluster) [31]. In order to enhance the interaction, partially removing the organic ligands can expose more coordinatively unsaturated inorganic metal sites [32]. In our previous work, we have reported the preparation of quasi MIL-101 by calcination in N₂ atmosphere, which exhibited excellent stability towards gas dehydrofluorination [33]. Following the partial removal of the organic ligands, the quasi MOFs could show significant amounts of CUS.

In this work, we report the fabrication of highly dispersed AlF₃ nanoclusters in the quasi MIL-101 by impregnating the (NH₄)₃AlF₆ to the fresh MIL-101 in water. Then the (NH₄)₃AlF₆@MIL-101 sample was calcined under inert atmosphere at 350 °C. AlF₃ nanoclusters encapsulated in the quasi MIL-101 were achieved. The structure-activity relationship between host (CUS of calcined MIL-101) and guest (AlF₃ nanoclusters) was investigated in detail. SEM, TEM and BET were adopted for analysing the distribution of AlF₃ in the calcined MIL-101. Furthermore, the interaction between CUS and AlF₃ nanoclusters were also characterized by XRD, XPS, MAS NMR, EPR and FT-IR. And the NH₃-TPD was conducted to measure the acidic properties of virous catalysts. As the AlF₃ nanoclusters are confined in porous quasi MOF structures, coke formation was inhibited. Consequently, high and stable catalytic performance for gas dehydrofluorination of HFC-245fa was obtained.

Section snippets

Synthesis of MIL-101

MIL-101 was prepared according to our previous work [33]. Cr(NO₃)₃·9H₂O (8.002 g, 20.0 mmol), terephthalic acid (3.322 g, 20.0 mmol) and HF (0.9 mL, 40 wt%) were added to 160 mL deionized water. The mixed solution was first transferred into a 250 mL Teflon-lined autoclave and heated at 250 °C for 8 h. Then, the mixture was cooled to room temperature slowly and then the green paste was separated from the solution by centrifugation. The green paste was washed thoroughly with ethanol, DMF, aqueous

Results and discussions

The textural properties of catalysts were determined by N₂ physisorption experiments. As displayed in Fig. 1a, both the MIL-101 and (NH₄)₃AlF₆@MIL-101 show type I isotherms and H4 hysteresis which are usually found over microporous solids. Actually, MOF structures are well known microporous materials. As listed in Table S1, MIL-101 prepared in the present work possesses the surface area and pore volume of about 2965 m² g⁻¹ and 1.49 cm³ g⁻¹, respectively. The pore size is centered at 2 nm (Fig.

Conclusion

In summary, we propose a novel strategy for the preparation of metal fluoride Lewis acid catalyst. After the preparation of MIL-101, Al was loaded to the cavities using (NH₄)₃AlF₆ as the precursor. Calcined at 350 °C to 550 °C in N₂ atmosphere, (NH₄)₃AlF₆ and MIL-101 converts to AlF₃ and quasi MIL-101 respectively. During calcination, MIL-101 undergoes partial carbonization and deligandation of the organic linkers. However, the developed pore and the connection of metal nodes with ligands are

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was supported by Zhejiang Provincial Natural Science Foundation of China under grant no. LY19B060009 and LY19B050004, National Natural Science Foundation of China (21978265).

References (57)

R. Akasaka et al.
Thermodynamic property modeling for 2,3,3,3-tetrafluoropropene (HFO-1234yf)
Int. J. Refrig. Revue Internationale Du Froid
(2010)
W.Z. Jia et al.
Effect of calcination temperature and fluorination treatment on NiF₂-AlF₃ catalysts for dehydrofluorination of 1,1,1,2-tetrafluoroethane to synthesize trifluoroethylene
Appl. Catal. A-General
(2019)
A. Mota-Babiloni et al.
A review of refrigerant R1234ze(E) recent investigations
Appl. Therm. Eng.
(2016)
W. Mao et al.
A facile sol-gel synthesis of highly active nano alpha-aluminum fluoride catalyst for dehydrofluorination of hydrofluorocarbons
Appl. Catal. B: Environ.
(2017)
X.X. Fang et al.
Dehydrofluorination of 1,1,1,3,3-pentafluoropropane over C-AlF₃ composite catalysts: improved catalyst stability by the presence of pre-deposited carbon
Appl. Catal. A-General
(2019)
J.-W. Luo et al.
Catalytic dehydrofluorination of 1,1,1,3,3-pentafluoropropane to 1,3,3,3-tetrafluoropropene over fluorinated NiO/Cr₂O₃ catalysts
Appl. Surf. Sci.
(2018)
W. Mao et al.
Highly efficient gas-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane to 1,3,3,3-tetrafluoropropene over mesoporous nano-aluminum fluoride prepared from a polyol mediated sol-gel process
Appl. Catal. A-General
(2018)
J.D. Song et al.
High performance V₂O₅/MgF₂ catalysts for gas-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane: support-induced evolution of new active sites
J. Catal.
(2018)
T.Y. Song et al.
Dehydrochlorination of 1,1,2-trichloroethane over SiO₂-supported alkali and transition metal catalysts: tunable selectivity controlled by the acid-base properties of the catalysts
Appl. Catal. B: Environ.
(2018)
W.F. Han et al.
Reverting fluoroform back to chlorodifluoromethane and dichlorofluoromethane: intermolecular Cl/F exchange with chloroform at moderate temperatures
Chem. Eng. J.
(2019)

S. Lim et al.

Catalytic dehydrofluorination of 1,1,1,2,3-pentafluoropropane (HFC-245eb) to 2,3,3,3-tetrafluoropropene (HFO-1234yf) using in-situ fluorinated chromium oxyfluoride catalyst

Catal. Today

(2017)

N. Tsumori et al.

Quasi-MOF: exposing inorganic nodes to guest metal nanoparticles for drastically enhanced catalytic activity

Chem

(2018)

B. Kesanli et al.

Chiral porous coordination networks: rational design and applications in enantioselective processes

Coord. Chem. Rev.

(2003)

X. Zhang et al.

Gold(III) – metal organic framework bridges the gap between homogeneous and heterogeneous gold catalysts

J. Catal.

(2009)

J.H. He

Fractal calculus and its geometrical explanation

Results Phys.

(2018)

X.X. Li et al.

Nanoscale adhesion and attachment oscillation under the geometric potential. Part 1: the formation mechanism of nanofiber membrane in the electrospinning

Results Phys.

(2019)

X.W. Hu et al.

Thermal decomposition of ammonium hexafluoroaluminate and preparation of aluminum fluoride

Trans. Nonferrous Met. Soc. China

(2011)

K.L. Yap et al.

Characterization of the 13-cis-retinoic acid/cyclodextrin inclusion complexes by phase solubility, photostability, physicochemical and computational analysis

Eur. J. Pharm. Sci.

(2005)

A. Hess et al.

ESCA, XRD and IR characterization of aluminum-oxide, hydroxyfluoride, and fluoride surfaces in correlation with their catalytic activity in heterogeneous halogen exchange-reactions

J. Catal.

(1994)

Z.H. Jia et al.

Hollownano-MgF₂ supported catalysts: Highly active and stable in gas-phase dehydrofluorination of 1,1,1,3,3-pentafluoropropane

Appl. Catal. B: Environ.

(2018)

O. Bose et al.

XPS analysis of –AlF₃ phases with Al successively substituted by Mg to be used for heterogeneously catalyzed C1/F exchange reactions

Chem. Eng. J.

(1997)

V. Scalise et al.

Mechanochemical synthesis of low-fluorine doped aluminum hydroxide fluorides

J. Solid State Chem.

(2016)

G.J.M. Velders et al.

Preserving Montreal protocol climate benefits by limiting HFCs

Science

(2012)

G.J.M. Velders et al.

The large contribution of projected HFC emissions to future climate forcing

Proc. Natl. Acad. Sci. U.S.A.

(2009)

S.A. Montzka et al.

An unexpected and persistent increase in global emissions of ozone-depleting CFC-11

Nature

(2018)

M.K. Vollmer et al.

First observations of the fourth generation synthetic halocarbons HFC-1234yf, HFC-1234ze(E), and HCFC-1233zd(E) in the atmosphere

Environ. Sci. Technol.

(2015)

Z.Y. Wang et al.

Impacts of the degradation of 2,3,3,3-tetrafluoropropene into trifluoroacetic acid from its application in automobile air conditioners in China, the United States, and Europe

Environ. Sci. Technol.

(2018)

Y.L. Zhang et al.

Leakage rates of refrigerants CFC-12, HCFC-22, and HFC-134a from operating mobile air conditioning systems in Guangzhou, China: tests inside a busy urban tunnel under hot and humid weather conditions

Environ. Sci. Technol. Lett.

(2017)

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Confinement of AlF3 in MOF derived structures for the formation of 4-fold coordinated Al and significantly improved dehydrofluorination activity

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of MIL-101

Results and discussions

Conclusion

Declaration of Competing Interest

Acknowledgements

Int. J. Refrig. Revue Internationale Du Froid

Appl. Catal. A-General

Appl. Therm. Eng.

Appl. Catal. B: Environ.

Appl. Catal. A-General

Appl. Surf. Sci.

Appl. Catal. A-General

J. Catal.

Appl. Catal. B: Environ.

Chem. Eng. J.

Catal. Today

Chem

Coord. Chem. Rev.

J. Catal.

Results Phys.

Results Phys.

Trans. Nonferrous Met. Soc. China

Eur. J. Pharm. Sci.

J. Catal.

Appl. Catal. B: Environ.

Chem. Eng. J.

J. Solid State Chem.

Preserving Montreal protocol climate benefits by limiting HFCs

Science

The large contribution of projected HFC emissions to future climate forcing

Proc. Natl. Acad. Sci. U.S.A.

An unexpected and persistent increase in global emissions of ozone-depleting CFC-11

Nature

First observations of the fourth generation synthetic halocarbons HFC-1234yf, HFC-1234ze(E), and HCFC-1233zd(E) in the atmosphere

Environ. Sci. Technol.

Impacts of the degradation of 2,3,3,3-tetrafluoropropene into trifluoroacetic acid from its application in automobile air conditioners in China, the United States, and Europe

Environ. Sci. Technol.

Leakage rates of refrigerants CFC-12, HCFC-22, and HFC-134a from operating mobile air conditioning systems in Guangzhou, China: tests inside a busy urban tunnel under hot and humid weather conditions

Environ. Sci. Technol. Lett.

Confinement of AlF₃ in MOF derived structures for the formation of 4-fold coordinated Al and significantly improved dehydrofluorination activity