Catalytic activity of metal organic framework Cu3(BTC) 2 in the cycloaddition of CO2 to epichlorohydrin reaction

Article abstract of DOI:10.1016/j.cattod.2012.03.034

We demonstrate the novel, catalytic activity of metal organic framework of Cu₃(BTC)₂ catalysts in the synthesis of chloropropene carbonate from CO₂ and epichlorohydrin. The catalysts display moderate epoxide conversions, and moderate selectivities to chloropropene carbonate at 100 °C. No solvents or co-catalysts were required. It is suggested that Lewis acid copper (II) sites in the Cu₃(BTC) ₂ framework promoted the adsorption of carbon dioxide on the solid surface and its further conversion to the carbonate.

Full text of DOI:10.1016/j.cattod.2012.03.034

Catalysis Today 198 (2012) 215–218
Contents lists available at SciVerse ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Catalytic activity of metal organic framework Cu (BTC) in the cycloaddition of
3
2
CO to epichlorohydrin reaction
2
a
a
b,∗
Eugenia E. Macias , Paul Ratnasamy , Moises A. Carreon
a
Conn Center for Renewable Energy Research, University of Louisville, Louisville, KY, 40292 United States
Department of Chemical Engineering, University of Louisville, Louisville, KY, 40292 United States
b
a r t i c l e i n f o
a b s t r a c t
Article history:
3 2
We demonstrate the novel, catalytic activity of metal organic framework of Cu (BTC) catalysts in the
Received 26 January 2012
Received in revised form 14 March 2012
Accepted 15 March 2012
Available online 18 April 2012
synthesis of chloropropene carbonate from CO2 and epichlorohydrin. The catalysts display moderate
epoxide conversions, and moderate selectivities to chloropropene carbonate at 100 C. No solvents or
co-catalysts were required. It is suggested that Lewis acid copper (II) sites in the Cu3(BTC)2 framework
promoted the adsorption of carbon dioxide on the solid surface and its further conversion to the carbonate.
◦
Keywords:
Metal organic frameworks
Cu3(BTC)2
Published by Elsevier B.V.
CO2 conversion
Cyclic carbonates
1
. Introduction
The utilization of CO2 as a renewable raw material for the pro-
units, which give an intersecting 3D-channel system with microp-
ore diameter of 0.7–0.8 nm [14].
Some examples on the potential of Cu (BTC) as heterogeneous
3
2
duction of useful chemicals is an area of great interest. In particular,
the conversion of CO2 into cyclic carbonates, which are useful
chemical intermediates employed for the production of plastics
and organic solvents, represents an attractive route for the effi-
catalyst have been reported [15–21]. Cu (BTC)2 is an active cat-
3
alyst for the liquid phase cyanosilylation of benzaldehyde [15],
isomerization of terpene derivatives [16], CO oxidation [17], syn-
thesis of quinolines [18], p-xylene acylation [19], cyclopropanation
of alkanes [20], and aldol condensation [21]. Herein, we report, the
cient use of carbon dioxide. The catalytic conversion of CO to cyclic
2
carbonates and polycarbonates over conventional solid catalysts,
including zeolites and mesoporous oxides has been described by
Ratnasamy et al. [1–11]. Recently, we have reported the catalytic
activity of zeolitic imidazolate framework-8, ZIF-8, catalysts in the
synthesis of chloropropene carbonate from CO2 and epichlorohy-
drin [12].
Solid catalysts for CO2 conversion require high CO2 adsorp-
tion capacity and Lewis acid sites to catalyze the reaction of CO2
with epoxides (like epichlorohydrin, and styrene oxide) to give
cyclic carbonates and other precursors of carbonates [6–8,10].
catalytic performance of the metal organic framework Cu (BTC)2
3
catalysts in the synthesis of chloropropene carbonate from CO and
2
epichlorohydrin. The catalysts displayed moderate epoxide con-
versions, and moderate selectivities to chloropropene carbonate at
◦
100 C. To our best knowledge, the catalytic activity of Cu (BTC)
3
2
in the Lewis acid catalyzed cycloaddition reactions has not been
reported, so far.
2. Experimental
The metal organic framework, Cu (BTC)2 (BTC = benzene-1,3,5-
2.1. Catalyst preparation
3
tricarboxylate) [13–15], is an appealing material to employ as
catalyst for the CO conversion to cyclic carbonates due to the pres-
ence of Lewis acid coordination sites (Cu) in its framework and due
Cu (BTC)2 was prepared by a modified method reported by
2
3
Schlichte et al. [15]. In a typical synthesis, 3.5 g of copper (II) nitrate
hemi(pentahydrate) were dissolved in 48 ml of deionized water.
To this solution, 1.68 g of 1,3,5-benzenetricarboxylic acid, 98% dis-
solved in 48 ml of ethanol were added. The resultant solution
was loaded in a 250 ml stainless steel high pressure Parr reac-
tor, Model 4576A. The synthesis was carried out under stirring at
to its high CO2 adsorption capacity. Cu (BTC)2 is a porous metal
3
organic framework which forms a face-centered cubic crystalline
structure which is composed of dimeric cupric tetracarboxylate
◦
∗ Corresponding author.
E-mail address: macarr15@louisville.edu (M.A. Carreon).
120 C for 8 h. The solid particles were separated from the solu-
tion by centrifugation at 3000 rpm and washed with ethanol. The
0
920-5861/$ – see front matter Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.cattod.2012.03.034

2
16
E.E. Macias et al. / Catalysis Today 198 (2012) 215–218
centrifugation-washing step was repeated 3 times. The resultant
◦
Cu (BTC) crystals were dried overnight at 100 C. All chemicals
3
2
were bought from Alfa-Aesar.
.2. Characterization
The morphology of Cu (BTC)2 was inspected with a FE-SEM
2
3
(
FEI Nova 600) with an acceleration voltage of 6 kV. Powder XRD
patterns were collected using a Bruker D8-Discover diffractome-
ter at 40 kV, 40 mA with Cu K␣ radiation. The surface area and
adsorption–desorption isotherm measurements were carried out
with a Micromeritics Tristar 3000 porosimeter at 77 K using liquid
◦
nitrogen as coolant. The samples were degassed at 150 C for 3 h
before the measurements. The relative surface acidity of the cata-
lysts was measured by the adsorption of dipropyl amine. In a typical
◦
experiment, 1 g of catalyst was evacuated overnight at 220 C and
equilibrated with a 1 wt% solution of dipropylamine in toluene at
◦
2
5 C for 3 h. The fraction of the dipropyl amine adsorbed at equi-
librium was determined by gas chromatography of the supernatant
solution.
2.3. Catalytic studies
Fig. 1. X-ray diffraction patterns of the (a) as-synthesized and (b) recycled Cu3(BTC)2
crystals.
The catalytic activity of Cu (BTC) was evaluated in the cycload-
3
2
dition of CO2 to epichlorohydrin to form chloropropene carbonate.
In a typical reaction, 18 mmol of epichlorohydrin and 100 mg of
Cu (BTC) were placed in a 250 ml stainless steel high pressure
3
2
Parr reactor, Model 4576A. The reactor was pressurized with CO2
◦
at 7 bar, and the reaction was carried out at 70–100 C for 4 h.
After the reaction, the reactor was cooled to room temperature, the
unreacted CO2 was vented out, the catalyst was separated by cen-
trifugation, and the products were analyzed by GC–MS in a HP 5890
Gas Chromatograph equipped with 5970 Mass Selective Detector,
3
0 m × 0.32 mm HP-5 column coated with 5% phenyl poly siloxane
stationary phase. The temperature ramp rate during the GC analysis
was as follows: 70–220 C at 15 C/min.
◦
◦
3
. Results and discussion
The XRD pattern of the as-synthesized Cu (BTC)2 catalyst,
3
shown in Fig. 1a, corresponds to the typical known structure of
Cu (BTC) [15,16]. Small changes in the relative intensities of
3
2
the XRD peaks are due to variations in the degrees of hydra-
tion [15]. In particular, the similar I200/I220 ratio as well as the
absence of the (3 1 1) reflection in our sample suggests a hydrated
state [15]. The morphological features of Cu (BTC)2 crystals were
3
Fig. 2. Representative SEM of Cu3(BTC)2 crystals employed as catalysts in the
investigated by SEM (Fig. 2), which shows well-defined octahedral
crystals of ∼1–1.5 ␮m. This octahedral-like morphology is typical
for Cu (BTC) [14,16,22]. The BET surface area of the Cu (BTC)
crystals was 995 m /g, in agreement with previous reports [13,14].
As shown in Fig. 3, N2 adsorption–desorption isotherms indicate
cycloaddition of CO2 to epichlorohydrin.
3
2
3
2
mesoporous solid acid catalysts, this reaction usually occurs at tem-
2
◦
peratures at or above 100 C [1–11]. The chloropropene carbonate
◦
yield at 100 C was ∼33%. Lewis acid sites are known to catalyze
the porous nature of the Cu (BTC)2 crystals. The pore size distribu-
3
the reaction of carbon dioxide with epoxides to give propylene
carbonates and other precursors of polycarbonates [6,8]. In the
case of Cu (BTC) , it is likely that the Lewis acid copper (II) sites
tion (not shown) confirms the microporous nature of the crystals.
The cycloaddition of CO2 to epichlorohydrin yielded chloro-
propene carbonate, diols and dimers of epichlorohydrin. Controlled
experiments under our reaction conditions confirmed that the reac-
tion did not proceed to a significant extent in the absence of the
Cu (BTC) catalyst. Different from other metal organic frameworks
3
2
play an important role in catalyzing the cycloaddition of CO2 to
Table 1
3
2
Catalytic performance of Cu3(BTC)2 in the cycloaddition of CO2 to epichlorohydrin.
in which most of the coordination sites are blocked by the organic
ligand, in Cu (BTC) the Lewis acid coordination sites (copper sites)
Reaction
temperature ( C)
Epichlorohydrin
conversion (%)
Selectivity (%)
3
2
◦
are accessible for potential catalytic conversions [15]. Table 1 shows
the catalytic performance of Cu (BTC) as a function of temperature
Chloropropene
carbonate
Diol
Dimer
3
2
in the cycloaddition of CO2 to epichlorohydrin reaction.
Cu (BTC) was catalytically selective to chloropropene carbon-
70
80
100
35.0
24.6
63.8
0.0
0.0
51.8
68.2
100
33.9
31.8
0.0
14.3
3
2
◦
ate only at 100 C (Table 1). Only diols of the epoxide and dimers
о
of epichlorohydrin were observed below 100 C. Over zeolites and

E.E. Macias et al. / Catalysis Today 198 (2012) 215–218
217
Table 2
Selected physicochemical properties of the catalysts.
Catalyst
Physicochemical properties
Surface area
Pore volume
(cc/g)
Relative
aciditya
2
(
m /g)
Beta
451
995
1173
390
394
585
0.44
0.53
0.52
0.42
0.28
0.33
1.6
1.5
1.2
0.8
1.7
1.5
Cu3(BTC)2
ZIF-8
SBA-15
TS1
HY
a
Moles of dipropylamine adsorbed/g of dry catalyst (×10−8).
to reported literature [26]. ZIF-8 was prepared as described in our
previous report [12]. Of all these catalysts, zeolite beta shows the
highest yield to chloropropene carbonate at ∼82%. The relatively
high catalytic activity of zeolite beta is interesting. The Cu (BTC) ,
3
2
ZIF-8, HY and SBA-15 catalysts formed significant amounts of car-
bonaceous deposits during this reaction (see results of recycle
experiments below). The absence of such carbonaceous deposits
over the beta zeolite during the reaction can, perhaps, account for
the greater yield of the chloropropene carbonate over this catalyst.
The lower yield of the chloroprene carbonate over TS-1 is due to
the absence of strong acid sites on its surface. The lower formation
of carbonaceous deposits over beta zeolite and its greater stability
in hydrocarbon reactions as compared to other large pore zeolites,
like HY, HX and mordenite is well known.
Fig. 3. Nitrogen adsorption-desorption isotherms of Cu3(BTC)2 crystals.
epichlorohydrin. In addition, the partial positive charges on the
unsaturated copper metal sites of Cu (BTC)2 promote the bind-
3
ing and activation of the polar carbon-oxygen bonds of carbon
dioxide, resulting in high CO2 adsorption capacities. Unsaturated
cooper metal sites have been identified by theoretical and experi-
mental investigations as CO2 adsorption sites [23]. CO2 adsorption
capacities for Cu (BTC)2 range from 8.0 to 12.7 mol/kg at room
3
The catalytic performance of Cu (BTC)2 is better than zeolites
temperature and 15 bar [14,24,25]. The copper acid sites, probably,
promote the adsorption of carbon dioxide on the solid surface and
its further conversion to the carbonate. The significant formation
3
TS1, HY and SBA-15 and comparable to that of ZIF-8. For zeolites TS-
1
1
, and HY, the only observed product was diol. The yield to diol was
8%, and 32% for TS-1 zeolite, and HY zeolite, respectively. Although
of the diols over Cu (BTC)2 even at low temperature is probably
3
a clear correlation between surface area, pore volume or relative
acidity as a function of catalytic activity is not observed (Table 2),
related to the presence of a hydrophilic interior (with 12 water
molecules per pore) in the catalyst wherein the Cu2+ ions (in the
in general, catalysts with larger pore volumes (Beta, Cu (BTC) and
binuclear Cu2 cluster) are connected through a weak bond and the
residual axial coordination site is filled by a weakly bound water
molecule. The weakly bound water molecules pointing towards
the center of the pore are, probably, active in the hydration of the
epoxide to the diols.
3
2
ZIF-8) led to higher yields to chloropropene carbonate.
We have also investigated the catalytic performance of the
Cu (BTC)2 catalyst after use in a first run and subsequent recy-
3
cling. In the recycle experiments, the catalyst, after use in the
cycloaddition reaction, was washed with ethanol and acetone, cen-
We have compared the activity of Cu (BTC)2 vs zeolites beta,
3
◦
trifuged and air dried before reuse. The catalytic activity of the
TS-1, and HY, mesoporous silica SBA-15 and ZIF-8 at 100 C and
◦
recycled Cu (BTC)2 catalyst was evaluated at 100 C. The yield to
7
bar for 4 h (Fig. 4). Zeolites beta (SiO /Al O = 28), TS-1 and HY
3
2
2
3
chloropropene carbonate decreased from ∼33% (fresh) to ∼23%
were provided by Sud-Chemie Inc. SBA-15 was prepared according
(
recycled). The XRD of the recycled Cu (BTC) catalyst (Fig. 1b)
3 2
suggests that the Cu (BTC)2 structure is preserved. However, the
3
absence of the (1 1 1) and (3 3 1) planes of the recycled catalyst
as well as the presence of less intense XRD reflections as com-
pared to the as-synthesized catalyst may indicate that although
90
80
70
60
50
40
30
20
10
0
the Cu (BTC)2 crystals maintained long-range crystallinity, its
3
framework may have a greater degree of local structural dis-
order. Therefore the reduced activity of recycled catalyst can
be attributed, in part, to this local structural disorder and to
active site/pore blocking by residual carbonaceous deposits formed
during the reaction. Similar phenomena have been observed
for SBA-15 [6] and ZIF-8 [12] catalysts also for this particular
reaction.
In summary, we have demonstrated the novel catalytic activity
of metal organic framework Cu (BTC)2 catalysts in the synthesis of
3
chloropropene carbonate from CO and epichlorohydrin. Cu (BTC)
2
3
2
displayed moderate epoxide conversions, and moderate selectivi-
◦
ties to chloropropene carbonate at 100 C. Lewis acid copper (II)
sites in the Cu (BTC)2 framework promote the adsorption of car-
3
Beta Cu3(BTC)2 ZIF-8
SBA-15
TS1
HY
bon dioxide on the solid surface and its further conversion to the
carbonate. The activity of recycled Cu (BTC)2 catalyst decreased,
in part due to active site pore blocking by residual carbonaceous
deposits.
3
Fig. 4. Catalytic performance of Cu3(BTC)2 as compared to representative zeolites,
mesoporous SBA-15, and ZIF-8 in the synthesis of chloropropene carbonate from
◦
CO2 and epichlorohydrin. Reaction conditions: 100 C and 7 bar for 4 h.

2
18
E.E. Macias et al. / Catalysis Today 198 (2012) 215–218
Acknowledgments
[12] C.M. Miralda, E.E. Macias, M. Zhu, P. Ratnasamy, M.A. Carreon, ACS Catalysis 2
(
2012) 180.
[
13] S.S.Y. Chui, S.M.F. Lo, J.P.H. Charmant, A.G. Orpen, I.D. Williams, Science 19
This work was supported by a Kentucky Science and Engineer-
ing Foundation grant (KSEF-2361-RDE-014). We thank Sud-Chemie
Inc. for providing zeolites beta, TS-1, and HY.
(
1999) 1148.
[14] Q.M. Wang, D. Shen, M. Bulow, M.L. Lau, S. Deng, F.R. Fitch, N.O. Lemcoff, J.
Semanscin, Microporous Mesoporous Materials 55 (2002) 217.
[
15] K. Schlichte, T. Kratzke, S. Kaskel, Microporous Mesoporous Materials 73 (2004)
1.
8
References
[16] L. Alaerts, E. Seguin, H. Poelman, F. Thibault-Starzyk, P.A. Jacobs, D.E. De Vos,
Chemistry: A European Journal 12 (2006) 7353.
[
[
[
17] J. Ye, C. Liu, Chemical Communications 47 (2011) 2167.
18] E. Perez-Mayoral, J. Cejka, ChemCatChem 3 (2011) 157.
19] L. Kurfirtova, Y.-K. Seo, Y.K. Hwang, J.S. Chang, J. Cejka, Catalysis Today 179
[
[
[
1] R. Srivastava, D. Srinivas, P. Ratnasamy, Catalysis Letters 89 (2003) 81.
2] R. Srivastava, D. Srinivas, P. Ratnasamy, Catalysis Letters 91 (2003) 133.
3] R. Srivastava, D. Srinivas, P. Ratnasamy, Studies in Surface Science and Catalysis
(
2012) 85.
20] A. Corma, M. Iglesias, F.X.L.I. Xamena, F. Sanchez, Chemistry: A European Journal
6 (2010) 9789.
21] N.B. Pathan, A.M. Rathatgaonkar, M.S. Chorghade, Catalysis Communications
2 (2011) 1170.
22] J. Gascon, S. Aguado, F. Kapteijn, Microporous Mesoporous Materials 113 (2008)
32.
1
54C (2004) 2703.
4] R. Srivastava, M.D. Manju, D. Srinivas, P. Ratnasamy, Catalysis Letters 97 (2004)
1.
[
[
[
[
[
[
1
4
[5] D. Srinivas, R. Srivastava, P. Ratnasamy, US Patent 7,405,319 (2008).
[6] R. Srivastava, D. Srinivas, P. Ratnasamy, Journal of Catalysis 233 (2005) 1.
[7] R. Srivastava, D. Srinivas, P. Ratnasamy, Applied Catalysis A: General 289 (2005)
1
1
1
28.
8] R. Srivastava, D. Srinivas, P. Ratnasamy, Microporous and Mesoporous Materials
0 (2006) 314.
9] R. Srivastava, D. Srinivas, P. Ratnasamy, Tetrahedron Letters 47 (2006) 4213.
23] L. Grajciar, A.D. Wiersum, P.L. Llewellyn, J.-S. Chang, P. Nachtigall, Journal of
Physical Chemistry C 115 (2011) 17925.
[
9
24] A.R. Millward, O.M. Yaghi, Journal of the American Chemical Society 127 (2005)
[
17998.
[
[
10] P. Ratnasamy, D. Srinivas, in: G. Ertl, H. Knozinger, F. Schuth, J. Weitkamp (Eds.),
Handbook of Heterogeneous Catalysis, vol. 7, 2nd ed., Wiley-VCH, 2008, p. 3717
[
[
25] Z. Liang, M. Marshall, A.L. Chaffee, Energy Fuels 23 (2009) 2785.
26] M. Kruk, M. Jaroniec, Chemistry of Materials 12 (2000) 1961.
(
chapter 14).
11] D. Srinivas, R. Srivastava, P. Ratnasamy, US Patent 7,375,224 (2008).