Catalytic performance of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) in the isomerization of endo- to exo-dicyclopentadiene

Article abstract of DOI:10.1016/j.catcom.2015.10.006

MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr), metal-organic frameworks (MOFs), have been assessed in solvent-free isomerization of dicyclopentadiene (DCPD) from the endo- to exo-form. In the isomerization reaction, the conversion of endo-DCPD and selectivity for the exo-dimer strongly depend on the nature of the active metal center. The MIL-100 (Fe) catalyst possessing more acid sites shows the highest catalytic activity among the MILs and it was readily recoverable and reusable in subsequent reaction cycles for the isomerization. The effects of reaction parameters such as temperature, reaction time, and catalyst loading on the reactivity were also investigated.

Full text of DOI:10.1016/j.catcom.2015.10.006

Catalytic performance of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) in the
isomerization of Endo- to exo-dicyclopentadiene
Dong-Woo Kim, Hyeon-Gook Kim, Deug-Hee Cho
PII:
DOI:
Reference:
S1566-7367(15)30102-3
doi: 10.1016/j.catcom.2015.10.006
CATCOM 4464
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
8 April 2015
30 September 2015
5 October 2015
Please cite this article as: Dong-Woo Kim, Hyeon-Gook Kim, Deug-Hee Cho,
Catalytic performance of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) in the isomer-
ization of Endo- to exo-dicyclopentadiene, Catalysis Communications (2015), doi:
10.1016/j.catcom.2015.10.006
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

ACCEPTED MANUSCRIPT
Catalytic Performance of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) in the
Isomerization of endo- to exo-Dicyclopentadiene
Dong-Woo Kim, Hyeon-Gook Kim, and Deug-Hee Cho*
Division of Ulsan Research Center for Green Fine Chemicals, Korea Research Institute of
Chemical Technology, Ulsan 681-802, Republic Korea
*Corresponding author: dhcho@krict.re.kr
1

ACCEPTED MANUSCRIPT
ABSTRACT
MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr), metal-organic frameworks (MOFs), have been
assessed in solvent-free isomerization of dicyclopentadiene (DCPD) from the endo- to exo-
form. In the isomerization reaction, the conversion of endo-DCPD and selectivity for the exo-
dimer strongly depend on the nature of the active metal center. The MIL-100 (Fe) catalyst
possessing more acid sites shows the highest catalytic activity among the MILs and it was
readily recoverable and reusable in subsequent reaction cycles for the isomerization. The
effects of reaction parameters such as temperature, reaction time, and catalyst loading on the
reactivity were also investigated.
Keywords: MOF, Isomerization, Dicyclopentadiene, Solvent-free, Acidic catalysis
* Corresponding author. Tel.: +82 52 241 6040; fax: +82 52 241 6049.
E-mail address: dhcho@krict.re.kr
2

ACCEPTED MANUSCRIPT
1. Introduction
Metal-organic frameworks (MOFs) constitute an emerging class of hybrid inorganic-
organic porous materials, which have attracted considerable attention owing to a unique
combination of properties, such as crystalline open structures, extremely high surface areas
and pore volumes, and regular and accessible pores and functionality [1]. These porous
materials are promising for potential applications in gas storage, separation, and
heterogeneous catalysis [2], [3] and [4]. Most MOFs potentially combine advantages of both
homo- and heterogeneous catalysts because their structures consist of isolated metal clusters
or atoms connected by polydentate organic ligands to form a rigid porous framework [5]. The
presence of coordinatively unsaturated metal sites (CUS) in some of these MOFs enables
their interactions with substrates, the metal ion or cluster acting as a Lewis acid or redox
center [6] and [7].
MIL-100 (Fe) demonstrated catalytic activity in the oxidations of diphenylmethane and
triphenylmethane with tert-butyl hydroperoxide (TBHP) [8] and in Friedel-Crafts benzylation
of benzene [9]. Iron coordinated to 1,3,5-benzenetricarboxylate (BTC), [Fe(BTC)] metal-
organic framework, has been commercialized by BASF under the trade name of Basolite
F300. Although the exact crystal structure of Fe(BTC) is still unknown, it likely has a
structure similar to that of MIL-100 (Fe). [Fe(BTC)] is an effective catalyst for aerobic
oxidations of cyclooctane [10] and styrene [11]. In turn, MIL-100 (Cr) operates effectively as
a Lewis acid catalyst in various organic transformations [12]. MIL-101 (Cr) is able to
catalyze the cyanosilylation of benzaldehyde [13], carboxylation of epoxides [14], benzylic
oxidation of tetralin [15], sulfoxidation of thioethers with H2O2 [16], oxidation of
cyclohexane [17], and allylic oxidation of alkenes with TBHP [18] or O2 [19].
3

ACCEPTED MANUSCRIPT
Dicyclopentadiene (DCPD) is generally formed via the combination of cyclopentadiene
(CPD) molecules through the Diels-Alder reaction and is composed of two stereoisomers,
namely, the endo- and exo-isomers; the former constitutes approximately 99.5% and the latter
only 0.5% [20]. DCPD has been widely used as the monomer or feedstock for various resins,
rubbers, and high-energy fuels [21]. Recently, exo-DCPD has attracted increasing interest
because of its superior performance in the preparation of polymers and high-energy fuels. For
example, the ring-opening metathesis polymerization (ROMP) of exo-DCPD arises much
faster than that of endo-DCPD, and the produced polymer is more rigid [22]. In addition, the
hybrid of exo-DCPD, JP-10, which is a widely used missile fuel, shows much better low-
temperature performance than does hydrogenated endo-DCPD [21]. Therefore, it is necessary
to transform the endo-isomer to the exo-isomer.
The isomerization of endo- to exo-DCPD is not new, but the efficiency and strategies
must be improved. Bartlett and Goldstein first reported a two-step method [23]. The double
bond in the norbornene unit of endo-DCPD is mixed with HI, and then the HI is eliminated
with alcoholic potassium hydroxide, whereby the endo-structure is converted into its exo-
counterpart. Nelson and Kuo modified this process by using HBr to replace HI; this has been
widely accepted for laboratory preparations [24]. Herndon et al. found that some exo-DCPD
is formed when endo-DCPD is heated at 205 °C for a prolonged period [25]. Baldwin
suggested a dissociation-recombination mechanism to explain this phenomenon [26]. Zhang
et al. conducted this transfer at a milder temperature but higher pressure, and the yield of exo-
DCPD was significantly improved [27]. However, the use of solvents and reagents brings
about environmental concerns; also, the operation is too complicated for industrial
applications. Hence, Bakke and Morten presented a one-step catalytic isomerization of endo-
4

ACCEPTED MANUSCRIPT
DCPD in gas phase over Pt-containing silica alumina catalysts, but this resulted in extremely
low yields [28].
Thus, the exploration of new heterogeneous catalysts that are efficient under mild
reaction conditions without solvents remains highly desirable. This paper presents the
solvent-free isomerization of endo- to exo-DCPD using MOF catalysts, MIL-100 (Fe, Cr) and
MIL-101 (Fe, Cr). The synthesis of MIL catalysts is much easier and more convenient than
those of conventional zeolitic materials. To improve the understanding of the isomerization,
the influence of the acidic properties of the MIL catalysts on the synthesis of exo-DCPD was
evaluated. In addition, the effects of the reaction time, reaction temperature, and catalyst
loading are discussed. The MIL catalysts were subjected to a recycle test and hot catalyst
filtration in order to examine their stabilities.
2. Experimental
2.1. Materials
Iron powder (>99%), metallic chromium (>99%) and other chemicals (>99%), which are
used as raw materials to prepare metal-organic frameworks, were purchased from Aldrich.
Endo-dicyclopentadiene of 98% purity (Aldrich) was used without further purification.
2.2. MOF synthesis and characterization
MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) were synthesized according to the literature [5],
[7], [9] and [16] with some modifications. For details, see the Electronic Supplementary
Information.
2.3. Isomerization of endo- to exo-DCPD
5

ACCEPTED MANUSCRIPT
The isomerization of the endo- to the exo-dimer was carried out in a 100-mL glass
reactor equipped with a magnetic stirrer and condenser (Scheme 1). In a typical reaction, the
catalyst and reactant were charged into the reactor. When the desired temperature was
attained, the reaction was initiated by stirring under atmospheric pressure. The products and
reactant were identified using a gas chromatograph (BRUKER 450-GC) equipped with a
flame ionization detector (FID) and a capillary column (HP-5, (5% phenyl)-
methylpolysiloxane). The conversion was calculated based on the assumption that endo-
DCPD was the limiting reactant using an internal standard method with benzene as the
standard.
3. Results and discussion
3.1. Characterization of MIL catalysts
The as-synthesized MILs were characterized by XRD, FT-IR, low N2 sorption
measurements, and TGA. The XRD patterns (Fig. S1) [7], [9] and [16] and FT-IR spectra
(Fig. S2) [29] and [30] of all of the materials were in accordance with the literature. The N2
sorption isotherms shown in Fig. S3 gave BET surface areas of 1976.5 m2 g−1, 1599.5 m2 g−1,
2686.3 m2 g−1, and 2276.1 m2 g−1 for MIL-100 (Fe), MIL-100 (Cr), MIL-101 (Fe), and MIL-
101 (Cr), respectively. As shown in Fig. S4, the TGA curves of the MILs demonstrate that all
of the samples show good thermal stability up to 350 °C, which is much higher than the
reaction temperature for the isomerization of endo- to exo-DCPD.
The differences in the acidic properties of the MIL catalysts were evaluated based on the
TPD of NH3. The NH3-TPD profiles of the MIL catalysts are shown in Table 1 and Fig. S5.
These show that the acidity can be classified into two groups [31]: a weak-to-medium group,
6

ACCEPTED MANUSCRIPT
323–523 K; and a strongly acidic group, 473–623 K. Table 1 also summarizes the observed
and calculated metal content as active center in MILs, amount of metal (calculated value) are
19.81 (27), 19.11 (26), 16.73 (24) and 16.53 (23) wt % in MIL-100 (Fe), MIL-100 (Cr), MIL-
101 (Fe), and MIL-101 (Cr), respectively. This difference in the metal content from the
calculated and observed ones is most likely due to the presence of the unreacted linkers and
solvent molecules inside the pores of the MOF. The presence of extra molecules in the MILs
was evident from the regular degradation pattern of TGA also (Fig. S4) [32].
3.2. Reactivity of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) catalysts
The effects of the structures (different metals) of the Fe- and Cr-containing MIL-100 and
MIL-101 catalysts on the solvent-free isomerization of the endo- to the exo-dimer were
studied under atmospheric pressure over a reaction time of 3 h at 140 °C (Table 2). In the
absence of a catalyst, the conversion of endo-DCPD was limited to 1.0% with 0% selectivity
for the exo-dimer (Table 2, entry 1). However, the MIL catalysts exhibited improved
catalytic performances for the isomerization of endo- to exo-DCPD. For comparison under
the similar reaction condition, the catalytic activities of reported zeolite materials, Hand
HY, are given in Table 2, entries 2 and 3. The results indicated that the MIL catalysts
showed higher selectivity toward exo-DCPD than did the zeolite catalysts even though
conversion of endo-DCPD remained higher for the H and HY catalysts.
The MIL catalysts showed disparities in their catalytic activities depending on the
number of acid sites. MIL-100 (Fe) was found to be the most efficient catalyst, showing
17.3% conversion of endo-DCPD and 48.6% selectivity for exo-DCPD (Table 2, entry 4)
under the employed reaction conditions. The other MOFs, MIL-100 (Cr), MIL-101 (Fe), and
7

ACCEPTED MANUSCRIPT
MIL-101 (Cr), were also active, showing conversions of 7.3% (Table 2, entry 6), 4.3%
(Table 2, entry 7), and 4.2% (Table 2, entry 8), respectively, with similar selectivity. As
revealed in Table 1, MIL-100 (Fe) owns a greater number of total acid sites, and this catalyst
displayed better activity than did the other MIL catalysts. The catalysts arranged in order of
isomerization activity are MIL-100 (Fe) > MIL-100 (Cr) > MIL-101 (Fe) > MIL-101 (Cr),
which corresponds to the number of acid sites in each catalyst (MIL-100 (Fe, Cr) and MIL-
101 (Fe, Cr) exhibited the order of total acid site such that: MIL-100 (Fe) (3.60 mmol g-1) >
MIL-100 (Cr) (3.02 mmol g-1) > MIL-101 (Fe) (2.52 mmol g-1) > MIL-101 (Cr) (2.47 mmol
g-1)).
Moreover, the reactivity of the catalysts was evaluated based on the acetalization [33] of
benzaldehyde with ethanol, which is a reaction catalyzed solely by acidic centers.
Acetalization was performed via the reaction between 10 mmol benzaldehyde and 20 mmol
ethanol without solvent for 2 h at 60 °C using 1 wt% of MIL catalysts to yield 1,1-
diethoxymethylbenzene. The amount of product was estimated using gas chromatography to
find the initial rate (ro) value for acetalization. The results of acetalization using catalysts
with different acid pairs are presented in Fig. 1. The initial rates of reaction for MIL-100
(Fe), MIL-100 (Cr), MIL-101 (Fe), and MIL-101 (Cr) were 1.94, 1.28, 0.71, and 0.53 mmol
min−1 g−1, respectively. Thus, the relative reactivities are consistent with those derived from
the isomerization of endo- to exo-DCPD.
As is clear from the BET analysis, the MIL-101 (Fe, Cr) catalysts exhibited higher
surface areas than MIL-100 (Fe, Cr). However, MIL-100 (Fe, Cr) performed better as
catalysts for the endo- to exo-DCPD isomerization than did MIL-101 (Fe, Cr). This can be
attributed to the higher number of weak-medium acid sites in the MIL-100 (Fe, Cr) catalysts;
8

ACCEPTED MANUSCRIPT
between them, the Fe-containing MIL displayed more activity than its Cr counterpart, which
supplements the above rationale. In a previous report [34], the catalytic activity in the
isomerization of endo- to exo-DCPD over zeolite catalysts strongly depended on the acidic
properties; weak acid sites play a more important role in the isomerization of endo-DCPD.
From these observations, we surmise that in this endo- to exo-DCPD isomerization,
which is a liquid-phase reaction, the acidic properties play a more significant role than does
the surface area of the catalyst. Should this observation be generalized, it proposes syntheses
of MOFs with tunable acid sites rather than focusing on the surface features for catalytic
purposes, which generally works through opportunistic catalysis at the struts, nodes, defect
sites, or some combination thereof.
3.3. Parameter Study
Fig. 2 shows the effects of the reaction temperature on the isomerization of endo- to exo-
DCPD in the presence of MIL-100 (Fe). The conversion of endo-DCPD significantly
increased as the temperature increased from 100 to 180 °C. The selectivity toward exo-DCPD
was maintained with temperature at approximately 49.0% for MIL-100 (Fe) at 140 °C;
however, the selectivity decreased sharply when the temperature exceeded 140 °C. When the
temperature was above 140 °C, exo-DCPD reversibly decomposed into CPD [26]. Moreover,
in this process, thermal oligomerization (TCPD/TeCPD) of endo-DCPD has been reported to
be one of the main factors responsible for the low selectivity toward the exo-dimer [26] and
[34].
The reaction time also had a prominent influence on the catalytic activity in the
isomerization of endo- to exo-DCPD. The effect of reaction time on the isomerization was
9

ACCEPTED MANUSCRIPT
studied by keeping the reaction conditions constant (at 140 °C under atmospheric pressure).
As shown in Fig. 3, increased reaction time promoted the conversion of endo-DCPD;
however, the selectivity for exo-DCPD after 4 h decreased, likely because of the
oligomerization of exo-DCPD. A reaction time from 2 to 4 h appears to be more favorable for
the isomerization of the endo- to the exo-dimer.
The effect of the catalyst loading on the yield was investigated using MIL-100 (Fe) at
140 °C for 3 h under atmospheric pressure. As shown in Fig. 4, the selectivity for exo-DCPD
and the endo-DCPD conversion increased continuously as the catalyst loading increased up to
5 wt%. Further increase in the concentration of MIL-100 (Fe) did not significantly enhance
the conversion, probably due to the presence of excess catalyst that resulted in restricted
dispersion in the reaction mixture, which eventually limited mass transfer between the active
sites and the reactants [35].
The stability of the MIL-100 (Fe) catalyst was evaluated through recycling experiments.
For each cycle, the used catalyst was separated by filtration, washed with ethanol to remove
products adhering to the catalyst surface, dried at room temperature, and then reused directly
for the next run without regeneration. The activity of the reused MIL-100 (Fe) catalyst is
summarized in Table 3. Although the conversion of endo-DCPD decreased slightly with the
catalyst used for three cycles, the selectivity toward exo-DCPD was nearly identical to that
achieved with the fresh catalyst. To determine whether the active metal center underwent
leaching from the MIL-100 (Fe) during the recycling test, XRD analysis of fresh MIL-100
(Fe) catalyst and that used for three cycles was performed (Fig. 5). The characteristic peaks of
MIL-100 (Fe) were similarly present for the recycled and fresh catalysts and the ICP-OES
confirmed that no significant amount of iron (≤ 0.2 ppm) was leached into the reaction
10

ACCEPTED MANUSCRIPT
mixture. Therefore, it can be concluded that the MIL-100 (Fe) catalyst could be recycled for
up to three consecutive cycles without considerable loss of its initial activity. However, some
new peaks can be found in this sample, especially the large peak at around 16 degree to be the
result of the interaction of remaining reactant or product with some of the metal sites within
the pores during the repeated uses. In order to check for a possible contribution of
homogeneous catalytic action from active metal leached into solution, a hot catalyst filtration
test was performed after 3 h of reaction. As shown in Fig. 3, no further endo-DCPD
conversion in the filtrate occurred after catalyst removal at the reaction temperature,
indicating that catalysis was not due to leached species.
4. Conclusions
The MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) catalysts were successfully synthesized and
characterized according to previous literature. The MIL structures are easily synthesizable,
green, and reusable catalysts for solvent-free isomerization of endo- to exo-DCPD with
higher selectivity. The catalytic activity in the isomerization depended on the nature of the
active metal site. Among the MIL catalysts, MIL-100 (Fe) exhibited the highest catalytic
activity in the isomerization of endo- to exo-DCPD under mild reaction conditions due to the
higher number of weak-medium acid sites, which play a more important role in the
isomerization of endo-DCPD. The catalyst was also easily recovered and reused without
considerable loss of the initial activity. The solvent-free isomerization of the endo- to the
exo-dimer is distinguished by various advantages such as environmental friendliness, simple
work-up process, and easy availability of materials.
Acknowledgements
11

ACCEPTED MANUSCRIPT
This study was supported by the Korea Research Institute of Chemical Technology
program (SI-1510).
References
1. G. Férey, Chem. Soc. Rev. 37 (2008) 191.
2. A.U. Czaja, N. Trukhan, U. Muller, Chem. Soc. Rev. 38 (2009) 1284.
3. M. Yoon, R.S. balaji, K. Kim, Chem. Rev. 112 (2012) 1196.
4. H.C. Zhou, J.R. Long, O.M. Yaghi, Chem. Rev. 112 (2012) 673.
5. O.A. Kholdeeva, I.Y. Skobelev, I.D. Iivanchikova, K.A. Kovalenko, V.P. Fedin, A.B.
Sorokin, Catal. Today 238 (2014) 54.
6. J.W. Yoon, Y.K. Seo, J.S. Hwang, J.S. Chang, H. Leclerc, S. Wuttke, P. Bazin, A.
Vimont, M. Daturi, E. Bloch, P.L. Llewellyn, C. Serre, P. Horcajada, J.M. Grenèche,
A.E. Rodrigues, G. Férey, Angew. Chem. Int. Ed. 49 (2010) 5949.
7. K.M.L. T. Pashow, J.D. Rocca, Z. Xie, S. Tran, W. Lin, J. Am. Chem. Soc. 131 (2009)
14261.
8. A. Dhakshinamoorthy, M. Alvaro, Y.K. Hwang, Y.K. Seo, A. Corma, H. Garcia, Dalton
Trans. 40 (2011) 10719.
9. P. Horcajada, S. Surblé, C. Serre, D.Y. Hong, Y.K. Seo, J.S. Chang, J.M. Grenèche, I.
Margiolaki, G. Férey, Chem. Commun. (2007) 2820.
10. A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Chem. Eur. J. 17 (2011) 6256.
11. A. Dhakshinamoorthy, M. Alvaro, H. Garcia, ACS Catal. 1 (2011) 836.
12. L. Mitchell, B.G. Santiago, J.P.S. Mowat, M.E. Gunn, P. Williamson, N. Acerbi, M.L.
Clarke, P.A. Wright, Catal. Sci. Technol. 3 (2013) 606.
13. A. Henschel, K. Gedrich, R. Kraehnert, S. Kaskel, Chem. Commun. (2008) 4192.
14. O.V. Zalomaeva, A.M. Chibiryaev, K.A. Kovalenko, O.A. Kholdeeva, B.S. Balzhin-
Imaev, V.P. Fedin, J. Catal. 298 (2013) 179.
15. J. Kim, S. Bhattacharjee, K.E. Jeong, S.Y. Jeong, W.S. Ahn, Chem. Commun. (2009)
12

ACCEPTED MANUSCRIPT
3904.
16. Y.K. Hwang, D.Y. Hong, J.S. Chang, H. Seo, M. Yoon, J. Kim, S.H. Jhung, C. Serre, G.
Férey, Appl. Catal. A: Gen. 358 (2009) 249.
17. N.V. Maksimchuk, K.A. Kovalenko, V.P. Fedin, O.A. Kholdeeva, Chem. Commun. 48
(2012) 6812.
18. N.V. Maksimchuk, K.A. Kovalenko, V.P. Fedin, O.A. Kholdeeva, Adv. Synth. Catal.
352 (2010) 2943.
19. I.Y. Skobelev, A.B. Sorokin, K.A. Kovalenko, V.P. Fedin, O.A. Kholdeeva, J. Catal. 298
(2013) 61.
20. M.E. Jamróz, S. Gałka, J.C. Dobrowolski, J. Molec. Struct.: Theochem. 634 (2003) 225.
21. J.J. Zou, X. Zhang, J. Kong, L. Wang, Fuel 87 (2008) 3655.
22. C. Bergström, J. Koskinen, E. Halm, M. Lindström, M. Perälä, UP No. 6294706B1
(2001).
23. P.D. Bartlett, I.S. Goldstein, J. Am. Chem. Soc. 69 (1947) 2553.
24. G.L. Nelson, C.L. Kuo, Synthesis 2 (1975) 105.
25. W.C. Herndon, C.R. Grayson, J.M. Manion, J. Org. Chem. 32 (1967) 526.
26. J.E. Baldwin, J. Org. Chem. 31 (1966) 2441.
27. X. Zhang, K. Jiang, Q. Jiang, J. Zou, L. Wang, Z. Mi, Chin. Chem. Lett. 18 (2007) 673.
28. J.M. Bakke, L. Morten, Acta Chem. Scand. 44 (1990) 860.
29. F. Zhang, J. Shi, Y. Jin, Y. Fu, Y. Zhong, W. Zhu, Chem. Eng. J. 259 (2015) 183.
30. S. Wang, L. Bromberg, H.S. Gibson, T.A. Hatton, ACS Appl. Mater. Interfaces 5 (2013)
1269.
31. J. Kim, S.N. Kim, H.G. Jang, G. Seo, W.S. Ahn, Appl. Catal. A: Gen. 453 (2013) 175.
32. X. Zhou, W. Huang, J. Shi, Z. Zhao, Q. Xia, Y. Li, H. Wang, Z. Li, J. Mater. Chem. A 2
(2014) 4722.
33. A.C. Kathalikkattil, D.W. Kim, J. Tharun, H.G. Soek, R Roshan, D.W. Park, Green
Chem. 16 (2014) 1607.
13

ACCEPTED MANUSCRIPT
34. H. Han, J.J. Zou, X. Zhang, L. Wang, L. Wang, Appl. Catal. A: Gen. 367 (2009) 84.
35. Y. Zhao, C. Yao, G. Chen, Q. Yuan, Green Chem. 15 (2013) 446.
14

ACCEPTED MANUSCRIPT
List of Tables
Table 1 The amount of acid site and metal content of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr)
Table 2 Reactivity of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr)
Table 3 Recycling test of MIL-100 (Fe) on the isomerization of endo- to exo-DCPD
15

ACCEPTED MANUSCRIPT
Table 1 The amount of acid site and metal content of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr)
NH3-TPD (mmol g-1)
Metal content c (%)
Catalyst
Weak-medium
acid a
Strong
acid b
Total
(calcd)
(calcd)
3.60
(3.2)
19.81
(27)
MIL-100 (Fe)
MIL-100 (Cr)
MIL-101 (Fe)
MIL-101 (Cr)
3.45
2.75
1.13
0.92
0.15
0.27
1.39
1.55
3.02
(3.3)
19.11
(26)
2.52
(2.9)
16.73
(24)
2.47
(2.9)
16.53
(23)
a 323 ~ 523 K
b 473 ~ 623 K
c by ICP-OES
Table 2 Reactivity of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr)
Entry
Catalysts
Blank
Conversion (%)
Selectivity (%)
0.0
Reference
This work
33
1
2
3
4
5
6
7
8
< 1.0
20.5
11.2
17.3
20.3
7.3
H zeolite a
HY zeolite a
MIL-100 (Fe)
MIL-100 (Fe) b
MIL-100 (Cr)
MIL-101 (Fe)
MIL-101 (Cr)
38.3
20.5
33
48.6
This work
This work
This work
This work
This work
40.5
41.2
4.3
40.5
4.2
40.7
Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = 5 wt%, Temp. = 140 oC, Reaction time = 3 h
a 25g endo-DCPD, Cat./endo-DCPD = 5 wt%, Temp. = 150 oC, Reaction time = 3 h
b 5g endo-DCPD, Cat./endo-DCPD = 5 wt%, Temp. = 150 oC, Reaction time = 3 h
16

ACCEPTED MANUSCRIPT
Table 3 Recycling test of MIL-100 (Fe) on the isomerization of endo- to exo-DCPD
Entry
Recycle
Fresh
1st
Conversion (%)
Selectivity (%)
1
2
3
4
17.3
16.4
14.3
10.7
48.6
49.1
48.3
46.0
2nd
3rd
o
Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = 5 wt% MIL-100 (Fe), Temp. = 140 C,
Reaction time = 3 h
17

ACCEPTED MANUSCRIPT
List of scheme and figures
Scheme 1 Isomerization of endo- to exo-DCPD.
Fig. 1 Relative activity of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) on the acetalization of
benzaldehyde with ethanol.
[Reaction conditions: 10 mmol of benzaldehyde with 20 mmol of EtOH (1 wt% of cat., 60 °C, 2 h)]
Fig. 2 Effect of reaction temperature on the isomerization of endo- to exo-DCPD.
[Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = 5 wt% MIL-100 (Fe), Reaction time = 3 h]
Fig. 3 Effect of reaction time on the isomerization of endo- to exo-DCPD.
[Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = 5 wt% MIL-100 (Fe), Temp. = 140 oC]
Fig. 4 Effect of catalyst amount on the isomerization of endo- to exo-DCPD.
o
[Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = x wt% MIL-100 (Fe), Temp = 140 C,
Reaction time = 3 h
Fig. 5 XRD pattern of (a) fresh and (b) 3rd reused MIL-100 (Fe).
18

ACCEPTED MANUSCRIPT
Scheme 1 Isomerization of endo- to exo-DCPD.
19

ACCEPTED MANUSCRIPT
Fig. 1 Relative activity of MIL-100 (Fe, Cr) and MIL-101 (Fe, Cr) on the acetalization of
benzaldehyde with ethanol.
[Reaction conditions: 10 mmol of benzaldehyde with 20 mmol of EtOH (1 wt% of cat., 60 °C, 2 h)]
20

ACCEPTED MANUSCRIPT
Fig. 2 Effect of reaction temperature on the isomerization of endo- to exo-DCPD.
[Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = 5 wt% MIL-100 (Fe), Reaction time = 3 h]
21

ACCEPTED MANUSCRIPT
Fig. 3 Effect of reaction time on the isomerization of endo- to exo-DCPD.
[Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = 5 wt% MIL-100 (Fe), Temp. = 140 oC]
22

ACCEPTED MANUSCRIPT
Fig. 4 Effect of catalyst amount on the isomerization of endo- to exo-DCPD.
o
[Reaction conditions: 5g endo-DCPD, Cat./endo-DCPD = x wt% MIL-100 (Fe), Temp = 140 C,
Reaction time = 3 h]
23

ACCEPTED MANUSCRIPT
Fig. 5 XRD pattern of (a) fresh and (b) 3rd reused MIL-100 (Fe).
24

ACCEPTED MANUSCRIPT
Graphical abstract
25

ACCEPTED MANUSCRIPT
Highlights
 MILs catalysts were successfully synthesized and characterized.
 MILs have been confirmed its potential as catalyst for the isomerization.
 The acidic properties of MILs play a more significant role in the isomerization.
 MILs were easily reused without any considerable loss of the initial activity.
26