Catalytic cyclohexene oxidation in the nano channels of a copper silicate material

Article abstract of DOI:10.1016/j.apcata.2019.01.019

Herein we examined the catalytic activity of the copper silicate material SGU-29 for the aerobic partial oxidation of cyclohexene under mild conditions (1 bar of O₂ at 70 °C). In particular, the catalytic properties of the active sites provided by [CuO₄] square planar units in SGU-29 were investigated for cyclohexene oxidation to generate three main oxidation products (i.e., 2-cyclohexene-1-ol, 2-cyclohexene-1-one, and cyclohexene hydroperoxide). Based on the molecular sieving effect of SGU-29, we especially investigated the intrazeolitic reaction, a catalytic cyclohexene oxidation occurring only in nanochannels of SGU-29. A conversion yield of 42% was obtained for the aerobic cyclohexene oxidation occurring only in SGU-29 nanochannels under 1 bar of O₂ at 70 °C for 12 h. We demonstrated unequivocally that catalysis occurred only within the inner channels of SGU-29, rather than on its external surface or within the solvent, and we highlighted the special role of [CuO₄] square planar units in catalysis.

Full text of DOI:10.1016/j.apcata.2019.01.019

Accepted Manuscript
Title: Catalytic Cyclohexene Oxidation in the Nano Channels
of a Copper Silicate Material
Authors: Dong Hyeon Lee, Hyun Sung Kim
PII:
S0926-860X(19)30036-5
DOI:
Reference:
https://doi.org/10.1016/j.apcata.2019.01.019
APCATA 16959
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
8 October 2018
6 December 2018
26 January 2019
Please cite this article as: Lee DH, Kim HS, Catalytic Cyclohexene Oxidation in the
Nano Channels of a Copper Silicate Material, Applied Catalysis A, General (2019),
https://doi.org/10.1016/j.apcata.2019.01.019
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Catalytic Cyclohexene Oxidation in the Nano Channels of a Copper Silicate Material
Dong Hyeon Lee, Hyun Sung Kim*
Department of Chemistry, Pukyong National University, Busan 48513, Korea
*
E-mail: kimhs75@pknu.ac.kr
Correspondence should be addressed to
Hyun Sung Kim; kimhs75@pknu.ac.kr
AUTHOR INFORMATION
Corresponding Author
*
Hyun Sung Kim. Tel:+82-51-629-5596. Fax:+82-51-629-5583.
E-mail: kimhs75@pknu.ac.kr
Graphical Abstract
Highlights
Copper silicate, SGU-29 possesses 1-dimensional square planner CuO 2
unit array in
-
•
4

the framework.
2
-
•
Square planner CuO
4
unit works as catalytic active site for aerobic partial oxidation
of cycloalkene.
•
•
The molecular sieving effect of SGU-29 for catalytic performance was studied.
Aerobic partial oxidation of cycloalkene has been investigated to be occurred in
nanochannel of SGU-29.
ABSTRACT
Herein we examined the catalytic activity of the copper silicate material SGU-29 for the
aerobic partial oxidation of cyclohexene under mild conditions (1 bar of O
2
at 70 °C). In
particular, the catalytic properties of the active sites provided by [CuO ] square planar units
4
in SGU-29 were investigated for cyclohexene oxidation to generate three main oxidation
products (i.e., 2-cyclohexene-1-ol, 2-cyclohexene-1-one, and cyclohexene hydroperoxide).
Based on the molecular sieving effect of SGU-29, we especially investigated the intrazeolitic
reaction, a catalytic cyclohexene oxidation occurring only in nanochannels of SGU-29. A
conversion yield of 42.2% was obtained for the aerobic cyclohexene oxidation occurring only
in SGU-29 nanochannels under 1 bar of O
2
at 70 °C for 12 h. We demonstrated
unequivocally that catalysis occurred only within the inner channels of SGU-29, rather than
on its external surface or within the solvent, and we highlighted the special role of [CuO
4
]
square planar units in catalysis.
Keywords
Copper silicate; Heterogeneous Catalyst; Cyclohexene; Aerobic Oxidation; Zeolite
Introduction.
In the fine chemical industry, the allylic oxidation of olefins has gained crucial importance in
activating raw chemicals to form high value–added intermediates [1-4]. One class of raw
materials used in this regard is cyclic olefins such as cyclohexene. Cyclohexene can be
oxidized to a variety of oxygen–containing derivatives depending on the type of oxidant used
in the reaction. For example, cyclohexene can form epoxy cyclohexane or adipic acid if

hydroperoxide [5,6], NaOCl [7,8], or PhIO [9,10], are used as the oxidant. Additionally, use
of the bulky tert–butyl hydroperoxide (TBHP) [11-15] as the oxidant for cyclohexene
oxidation gives 2–cyclohexene–1–ol and 2–cyclohexene–1–one, which are important
intermediates in the fragrance industry and organic synthesis. However, these aforementioned
oxidants are environmentally unfriendly and increase production costs due to their hazardous
nature and the need for additional purification steps. In terms of the environment, oxygen is
an ideal green oxidizing agent since it is free, forms water as the only by–product, and
contains the maximum oxidizing weight percentage [16]. Until now, much progress has been
made on the aerobic oxidation of cyclohexene, particularly using noble metal nanoparticles
[17,18], carbon nanotubes [19], and mesoporous materials [20,21]. However, for
heterogeneous catalytic systems, there are still many aerobic oxygenation reactions for which
a general catalyst has yet to be found. Yet as interest in this area increases, the number of
studies on these catalysts has grown substantially. One promising class of candidates to
function as a heterogeneous catalyst includes microporous materials such as zeolites [22,23]
and metal–organic frameworks (MOF) [24-28]. These materials can provide specifically
tailored catalytic sites in confined nano–sized spaces, which may not only accelerate
chemical reaction rates but also control reactant and product selectivity. In particular, the use
of microporous zeotype materials, where a transition metal is substituted into an Al and/or Si
atom location in the zeolite framework, has been studied intensively as catalysts. For instance,
Potter and co–workers extended the family of transition metal–doped aluminophosphate
(AlPO) frameworks [29,30] to obtain isomorphous incorporation of bimetallic active centers
that display superior catalytic activity in oxidation reactions
As an important class of zeotypes, the copper silicate material SGU–29 has recently been
synthesized and characterized [31,32]. The structure of SGU–29 is noteworthy as it
comprises 1–dimensional [CuO ] square planar units array supported by four surrounding
4
SiO4 tetrahedrons, which are arranged almost parallel to each other with distances of 3.629
and 3.732 Å, as shown in Figure 1. The unique structural features of SGU-29 are associated
with excellent moisture-independent CO
2
sorption. The vacant space between each [CuO ]
4
square planar units, which can be termed an intra–crystalline copper(II) center, is able to
deliver a specific catalytic function for various chemical reactions. The effective window size
of the channel in SGU–29 is 4.5 × 7.3 Å, which is sufficient for cyclohexene (estimated size:
5
.7 × 3.8 Å, S1(a) in Supplementary Material) to enter as a substrate for subsequent allylic
oxidation. Herein, for the first time, we present the catalytic activity of SGU–29 for aerobic

partial oxidation of cyclohexene under mild conditions.
Experimental
Preparation of SGU-29 (Copper silicate). SGU-29 was synthesized according to the
previous report as follows [31]. The silicon source solution was prepared by dissolving
sodium silicate (40 g, 10.6% Na
12 g) and NaCl (18.5 g), in distilled deionized water (DDW, 60 g). The mixture was
continuously stirred at room temperature for 1 h. Separately, for the preparation of the copper
source solution, CuSO (9.0 g) was completely dissolved in DDW (30 g) containing conc.
SO (1.2 g, 95%). The copper source solution was then slowly added dropwise into the
silicon source solution while stirring. The mixture was aged with continuous stirring for 15 h
at room temperature, and the pH was adjusted to 10.66 by adding aqueous H SO solution
10 mM). ETS-10 (100 mg, ~100 nm size) nanopowders were added as seeds and well
2
O, and ~26.5% SiO
2
, Sigma-Aldrich), NaOH (1.3 g), KCl
(
4
H
2
4
2
4
(
dispersed by continuous stirring for 20 min. And the prepared gel was placed into Teflon-
lined autoclaves (capacity: 25 ml) and kept in a preheated oven at 220 °C for 24 h in a static
condition. After hydrothermal reaction, the light purple crystals obtained were collected by
centrifugation at 9000 rpm, and washed with copious amounts of water until the pH of the
supernatant solution was neutral. The collected SGU-29 powder sample was dried at 80 °C
for 6 h in the oven.
Catalytic test for cyclohexene aerobic oxidation.
Cyclohexene oxidation was performed in a magnetically stirred 25-mL Teflon-lined autoclave
reactor with integrated K-type thermocouple and pressure gauge (Berghof, model: BR-25).
The probe of the thermocouple was submerged in the reactant liquid to measure the real
reaction temperature. Typically, 4.0 g of cyclohexene, 4.8 g of acetonitrile, and 1.0 g of
toluene as an internal standard and 0.01 g of untreated SGU-29 powder as the catalyst were
placed in the Teflon reaction vessel and tightly sealed in the autoclave reactor. Before
reaching the desired reaction temperature, the reactor was flushed several times with high-
purity (99.999%) N2. Then, the reactor was heated and stabilized at the desired temperature;
subsequently, high-purity (99.999%) O was fed into the reactor to maintain the desired
2
pressure. After oxidation was terminated, the reactor was quickly cooled in water, and the
oxygen was released until ambient pressure was reached.
The catalyst was removed from the reaction mixture by centrifugation and the products in the
supernatant solution were analyzed by gas chromatography (model: Agilent 5890 series II)

equipped with a flame ion detector (FID). In detail, a quantitative determination of the
reactant consumed (i.e., cyclohexene) and the oxidation products (i.e., cyclohexene oxide, 2-
cyclohexene-1-ol, 2-cyclohexene-1-one, and cyclohexenyl hydroperoxide) was achieved
using standard calibration curves. (S2 in Supplementary Material) For examples, the
calibration curves for cyclohexene was realized by adding variable concentrations of the
corresponding cyclohexene to diethyl ether (0.1mL, 0.45, 0.90, 1.35, 1.80, and 2.70 mM,
respectively). The mixture was added with the internal standard (toluene, 0.1 mL from a 0.6
mM stock solution) and analyzed by GC.
To determine the content of cyclohexenyl hydroperoxide, the samples were analyzed twice,
before and after reducing cyclohexenyl hydroperoxide to 2-cyclohexene-1-ol with triphenyl
phosphine (Acros, 99%) according to previous reports. [33]
Instrumental Analysis. Scanning electron microscopy (SEM) images of pristine SGU-29
and catalytic reacted microcrystal were obtained with FE-SEM (MIRA 3 LMH In-Beam
Detector, TESCAN) at an acceleration voltage of 40 kV. X-ray diffraction (XRD) patterns for
the identification of the SGU-29 were obtained with X-Ray Diffractometer (PHILIPS/X'Pert-
MPD System) using Ni-filtered monochromatic Cu K radiation. N adsorption-desorption
2
isotherms were measured in a BELsorp-Max (BEL, JAPAN) at 77 K. The surface areas and
pore sizes of the samples were calculated using the Brunauer–Emmett–Teller (BET) and
nonlocal density functional theory (NL-DFT) model with the slit pore geometry method,
respectively. X-ray photoelectron spectroscopy (XPS) studies were carried out using a VG
Multilab 2000 spectrometer (Thermo VG Scientific, UK) using an Al Kα excitation source
with a photon energy of 1487 eV. The data was acquired in the hybrid mode.
Electron paramagnetic resonance (EPR) spectra were collected with a Bruker (EMXplus-
9
.5/2.7) electron spin resonance spectrometer at room temperature, with a frequency of 9.41
GHz and microwave power of 2.00 mW. The center field value was 3348.760 G and sweep
width was 400.000 G.
Results and Discussion
Using the procedure described in the Experimental section, we synthesized microporous
SGU–29 with a square bipyramidal crystal morphology, as shown by the scanning electron
microscopy (SEM) images in Figure 2a. The crystallinity and purity of SGU–29 were
confirmed by XRD analysis (Figure 2b.); the patterns obtained matched well with those
reported previously [31]. On the basis of Brunauer–Emmett–Teller (BET) analysis of the N2

2
adsorption isotherm at 77 K, the surface area of SGU–29 was calculated to be 411m /g
Figure 2c.), which is consistent with previous observations [31].
We investigated whether the [CuO ] square planar units in the confined channels of SGU-29
(
4
were capable of oxidizing cyclohexene to 2-cyclohexene-1-ol, 2-cyclohexene-1-one, and/or
cyclohexene-1-peroxide using oxygen as the oxidant. As a test for catalytic activity, the
catalytic performance of SGU-29 for oxidation of cyclohexene under mild reaction
conditions (i.e., 1 bar of O at 70 °C for 12 h) was evaluated. The cyclohexene conversion
2
yield was 47.8%, and the major product selectivities of 2-cyclohexene-1-ol (1), 2-
cyclohexene-1-one (2), and cyclohexene hydroperoxide (3) were found to be 20.1, 46.4, and
2
7.5%, respectively, as shown in Table 1.
Cyclohexene oxide, which is a well–known oxidative product, formed in such a minute
quantity that it could be safely ignored, especially since it formed via a different mechanism
from that of 1, 2, and 3.
The oxidation yield includes products from reactions occurring within the channels (denoted
as inner zeolitic conversion), on the external surface (denoted as external zeolitic conversion),
and in the surrounding solvent (denoted as conversion in solvent), which occurs via an auto-
oxidation process as shown Figure 3a. In this way, the obtained conversion yield of 47.8% for
1
2 h is the sum of the conversion yields of cyclohexene oxidation from these three distinct
regions.
In order to distinguish the catalytic effect of the [CuO ] square planar units in the SGU–29
4
nanochannels, we need to consider only inner zeolitic conversion. To examine this type of
conversion, we first hypothesized that each conversion yield of aerobic cyclohexene
oxidation corresponded to a specific reaction site, which we investigated by employing
control experiments using differently sized radical scavengers. First, the radical nature of the
catalytic oxidation of cyclohexene by SGU–29 was verified by testing the effect of the radical
scavenger. Specifically, addition of the well–known radical scavenger hydroquinone, whose
size (estimated diameter: 5.3 Å, S1(a) in Supplementary Material) is amenable for entry into
the channels of SGU–29, completely suppressed the oxidative conversion of cyclohexene in
all three potential catalytic regions, and no oxidation of cyclohexene was apparent. This
result clearly indicates that aerobic oxidation proceeds via a radical mechanism.
By comparison, addition of the bulky radical scavenger octadecyl–3–(3,5–di–tertbutyl–4–
hydroxyphenyl)–propionate (OBHP, estimated diameter: 9.5 Å S1(b) in Supplementary
Material), whose large size precludes entry into the SGU–29 window channel (4.5  7.3 Å),

quenched only the radicals in solution. Therefore, OBHP inhibited conversion of cyclohexene
on the external surface of SGU–29 and in the solvent. OBHP could not participate in
inhibiting the inner zeolitic conversion of cyclohexene, as its bulky nature precluded its full
entry into the channels of SGU–29. With OBHP as the radical scavenger under reaction
conditions of 1 bar of O2 at 70°C for 12 h, the obtained conversion yield of cyclohexene was
found to be 42.2%, with 23.3, 47.7, and 29.0% product selectivities for 1, 2, and 3,
respectively. These values were estimated from pure inner zeolitic conversion for
cyclohexene oxidation.
To determine the extent of cyclohexene conversion in the solvent, a control experiment under
identical conditions (i.e., 1 bar of O at 70 °C for 12 h) in the absence of SGU-29 was
2
performed. The obtained yield was 4.9%.
In this way, the conversion yield of cyclohexene on the SGU–29 external surface was
determined arithmetically as 0.7% (≈ 0%) by subtracting the yields from inner zeolitic
conversion and conversion in solvent from the total conversion yield. This indicates that the
oxidative conversion of cyclohexene catalyzed by the SGU–29 surface contributes very little
to the overall conversion yield. When OBHP was employed in the catalytic reactions, all the
results for SGU–29 clearly indicated that a heterogeneous catalytic reaction occurred inside
the channel of the SGU–29 frameworks. Figure 3b displays the conversion yield for the three
reaction regions.
Consequently, we could determine the catalytic performance of purely inner zeolitic
conversion. Table 1 lists the conversion yield and selectivity of main products of aerobic
cyclohexne oxidation occurred in nanochannel of SGU-29. Figure 4a. and Table 1. show the
inner zeolitic catalytic effect of the reaction time on cyclohexene oxidation with OBHP at 1
bar of O
selectivity of the three products changed. The maximum cyclohexene conversion yield was
52.2% after 24 h. Notably, formation of other by-products such as cyclohexene oxide,
2
and 70°C. As seen, the conversion yield gradually increased with reaction time as

adipic acid, and succinate acid from over-oxidation during the reaction was observed to have
a low selectivity. Up to 12 h, it was lower than 5%, and as the reaction time increased after
2
4h, the portion of by-products increased up to 26%. This indicated that over-oxidation of the
product occurred, leading to the formation of by–products.
The influence of O pressure on the catalytic performance of SGU–29 in the aerobic
oxidation of cyclohexene was also investigated, using various O pressures (from 1 to 4 bar)
at 70°C (Figure 4b and Table 1). The conversion yield and sum of the three major products
2
2

remained constant above 2 bar of O
the percentage of the peroxide (3) and by-products in the oxidation product mixture increased
with O pressure, and cyclohexene oxide was not detected at high oxygen pressures.
Moreover, the ratio of by-products increased. The maximum cyclohexene conversion yield
was 46.6% at an O pressure of 4 bar, with the main reaction products being 2–cyclohexene
2
pressure. Remarkably, in terms of product selectivity,
2
2
peroxide, followed by cyclohexene–1–one and 2–cyclohexene–1–ol.
The temperature-dependent conversion yields with the three major product selectivities in the
SGU-29 channels are shown in Figure 4c and Table 1 under the indicated conditions. The
conversion yield increased with temperature, and at 70°, SGU–29 displays an outstanding
conversion yield for products 1, 2, and 3; however, the conversion yield does not increase
above 80°C, and preformation of byproducts is increased. Interestingly, the number of moles
of cyclohexene consumed and the number of moles of the three products does not differ at
temperatures of <80 °C, indicating that over-oxidation does not occur.
Ensuring the stability of a catalyst is a crucial consideration for its practical application. To
evaluate the stability of SGU–29 for cyclohexene oxidation, recycling tests were performed
five consecutive times under identical conditions using molecular oxygen as the oxidant.
After each reaction, the catalyst was repeatedly washed with fresh acetonitrile and
centrifuged until no reactant and product from the supernatant solution were detected via gas
chromatography. The results of these recycling tests are shown in Figure 4d. Clearly, the
SGU–29 catalyst exhibits consistent performance, with no appreciable difference in its
conversion yield and product selectivity after five consecutive cycles. Further, the structural
stability of SGU–29 following consecutive reactions was established by XRD, SEM, and
BET analyses, which indicated no significant difference between pristine SGU–29 and that
used five times as indicated in Figure 2. This demonstrated that the structural integrity of
SGU–29 was well retained, thereby contributing to its excellent continuous catalytic
performance.
The reaction rate constants for cyclohexene oxidation over inner SGU–29 conversion and
auto–oxidation in acetonitrile were obtained in accordance with the indicated reaction
temperatures, which ranged from 40 to 70°C as shown S3(a) in supplementary material.
S3(b) displays the corresponding Arrhenius plots for cyclohexene oxidation of the pseudo–
first order plot kinetics. The activation energy of inner SGU–29 conversions for cyclohexene
oxidation (45.9 kJ mol−1) was much less than that associated with solvo–oxidation (58.5 kJ

mol−1). This indicates that the [CuO ] square planar units in the channels of SGU–29
4
function as the catalytic active sites for cyclohexene oxidation.
Turnover number (TON), which is defined as the molar ratio of converted substrate to
catalyst, is an important parameter to evaluate the catalytic performance of a catalyst. We
determined the TON of a [CuO
under mild reaction conditions (i.e., 1 bar of O
molar ratio of the product yield from inner zeolitic conversion to that from the [CuO
4
] square planar units in the SGU–29 channels for oxidation
at 70°C for 12 h) to be 986 by calculating the
] square
2
4
planar units in the SGU–29 channels. Reported conversation yields and TON values for
cyclohexene aerobic oxidation using various types of porous catalysts are listed in Table S1.
Notably, the obtained TON value (986) from SGU-29 is higher than those from various
embedded transition metal elements in other porous catalysts such as MOF. This
demonstrates that SGU-29 with the unique structure of arrays of [CuO
possesses superior catalytic performance.
4
] square planar units
The turnover frequency (TOF) was also calculated to reveal the intrinsic activity of the
catalytic site. The TOF of the [CuO ] square planar units in the SGU–29 frameworks were
4
–
1
found to be 82.1 h . Thus, we were able to obtain the conversion yield, TON, and TOF for
the inner zeolitic conversion of cyclohexene using the SGU–29 catalysts under various
reaction conditions, as summarized in the procedure for obtaining TON and TOF in S4-
Supplementary material.
To clarify the roles of the [CuO ] square planar units as the catalytic sites and the
4
enhancement of the reaction as a result of the confined nanospaces within the SGU–29
framework, we ran control experiments using isostructural zeotypes of SGU–29 such as
ETS–10 and AM–6. ETS–10 and AM–6 are a unique class of microporous transition metal
oxide silicates that possess a 1–dimensional (1D) quantum wire of MO
octahedra within their framework (as shown in Figure 1). Structurally, SGU–29 differs from
ETS–10 and AM–6 only by having 1D arrays of [CuO ] square planar units instead of 1D
quantum wires. As mentioned above, the axial positions of [CuO ] square planar units, which
are present in the confined spaces between two [CuO ] square planar units in SGU–29,
provide distinct active sites for the SGU–29 catalysts, which are not present in ETS–10 and
AM–6. In order to verify the role played by the axial positions of [CuO ] square planar units,
we evaluated the catalytic performance of ETS–10 and AM–6 under identical mild reaction
conditions (i.e., 1 bar of O at 70°C for 12 h). The conversion yields of ETS–10 and AM–6
revealed that they demonstrate minute catalytic activities of 4.5 and 5.0%, respectively
6
(M = Ti and V)
4
4
4
4
2

(
Figure 5a and entry 14-16 of Table 1). These values are comparable to the extent of
conversion via solvo–oxidation (4.9%) in the absence of the catalyst. The negligible catalytic
activity arises from the absence of axial active sites around the MO (M= Ti and V) octahedra
in ETS–10 and AM–6. Additionally, cyclohexene oxidation did not occur with ETS–10 and
AM–6 in the presence of OBHP. These control experiments indicate that the [CuO ] square
6
4
planar units in the SGU–29 frameworks are likely to be the active sites for cyclohexene
oxidation.
Besides cyclohexene, we tested using other cycloalkene series such as cyclopentene,
cycloheptene, and cis-cyclooctene under 1 bar of O at 70 °C for 12 h in the presence of
2
OBHP, as shown in Figure 5a. As seen, cyclopentene and cycloheptene were oxidized within
the nanochannel of SGU-29 with conversion yields of 28.5% and 24.0%, respectively as
shown in Figure 5b. Because the estimated size of cis-cyclooctene (6.2 × 4.5 Å, as seen S5 in
Supplementary material) is almost identical to the window size of SGU-29 (7.3 × 4.5 Å), it is
difficult for the cis-cyclooctene molecule to enter the channels of SGU-29. Furthermore, the
reactant selectivity of SGU-29 could be confirmed by observing only cyclohexene oxidation
during the control experiment conducted by employing the reactant mixture of 1:1
cyclohexene and cis-cyclooctene. As expected, only cyclohexene was oxidized, as shown in
Figure 5c.
On the basis of previous literature [34], it appears that the aerobic oxidation of cyclohexene
in the presence of SGU–29 proceeds via a classic Haber–Weiss radical–chain sequence
mechanism. In terms of the Haber–Weiss oxidation mechanism during the initiation period,
an increase in ROOH can also be observed in the SGU–29 catalytic systems. This is then
followed by either homolytic or heterolytic cleavage of the O–O bond in ROOH, depending
on the oxidation state of [CuO ] square planar units in the SGU–29 frameworks, as illustrated
4
by the proposed mechanism in Scheme 1.
To determine the change in the chemical oxidation state of Cu as a catalytic center in SGU–
2
9, XPS spectra were recorded for the Cu 2p3/2 core levels of a pristine SGU–29 sample and
for a sample used for five cycles. For Cu 2p3/2 in the case of pristine SGU–29, the oxidation
state of Cu could be defined as +2 from the peak at 933.7 eV, with strong two satellite peaks
2
+
corresponding to Cu , as shown in Figure 6a. On the other hand, in the Cu 2p3/2 core level
spectra of the SGU–29 sample that was used for five cycles, the peak at 932.3 eV
+
2+
+
corresponding to Cu was observed [35]. We noted that the ratio of Cu to Cu increased
with the number of consecutive catalytic reactions and remained constant above five cycles

(
Figure 6b), which was attributed to the role of the Cu as catalytic sites for peroxide cleavage,
as described in Scheme 1. To explore this possibility further, electron spin resonance (ESR)
analysis using the radical trap reagent, phenyl–N–tbutylnitrone (PBN), which was used as a
free radical spin trapping agent that is capable of forming stable radical adducts, was used to
identify the radical intermediates after homolytic/heterolytic cleavage of the ROOH
(R=cyclohexenyl) species generated during oxidation.
From Scheme 1, we expect four types of radical adducts to be generated during oxidation. As
predicted, the deconvolution of the ESR spectra obtained during oxidation in the presence of
SGU–29 revealed four types of spin adducts, corresponding to mixtures of ROO/PBN,
RO/PBN, R/PBN (R=cyclohexenyl) which formed as shown in Figure 6a, and O/PBN
from PBN itself oxidation [36]. The ESR spectra of four spin adducts observed were clearly
distinguished owing to sufficiently different hyperfine splitting constants, as tabulated in
Table S2[37,38].
In contrast, without SGU–29, only two ESR signals corresponding to RO/PBN and
ROO/PBN from the auto–oxidation products of the ROOH in solution were observed, as
shown in Figure 6b. The ESR study indicated that [CuO ] in the SGU–29 initiated the
4
generation of homolytic/heterolytic cleavage of ROOH species to form RO and ROO
radicals, and accelerated the oxidation of cyclohexene. The mechanistic insight suggested in
Scheme 1 is consistent with the above results, which were ascertained through XPS and ESR
analyses.
Conclusion
In summary, during our investigation of the catalytic properties of the [CuO ] square planar
4
units in SGU–29 for cyclohexene oxidation, we discovered that cyclohexene is oxidized to 2–
cyclohexene–1–ol (1), 2–cyclohexene–1–one (2), and cyclohexene hydroperoxide (3) only
within the inner channels of SGU–29, in yields reaching 40% and with TON and TOF of 986
and 82.1 h–1, respectively. Notably, there was no physical or chemical destruction of SGU–
2
9. This is the first effort that examines the catalytic properties of SGU–29 and establishes
the [CuO ] square planar units as the active oxidation sites. Overall, we believe that these
4
findings will be of great benefit in utilizing the novel catalytic properties of the [CuO ] units
4
in SGU–29 for application to various organic reactions.
ACKNOWLEDGMENT

This work (NRF-2016R1A2B4013157) was supported by Mid-Career Researcher Program
through NRF grant funded by the MEST.
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Figure 1. Schematic structural illustration of (left side) SGU–29 with [CuO
4
] square planar
units and (right side) ETS–10 (M=Ti) and AM–6 (M=V) with MO octahedral unit
6

Figure 2. (a) SEM images (b) XRD patterns and (c) surface area from BET analysis of
pristine SGU-29 (top) and reused SGU-29 (bottom) after catalytic reaction as indicated.

Figure 3. (a) Schematic illustration of possible three places (in solvent, external and inner
SGU-29) for cyclohexene aerobic oxidation catalyzed by SGU29 and (b) each conversion
yield of indicated three places and total conversion yield. Reaction condition: 4.0g
cyclohexene, 4.8g acetonitrile, 1.0g toluene (internal standard), 0.1g octadecyl–3–(3,5–di–
tertbutyl–4–hydroxyphenyl)–propionate (OBHP, bulky scavanger) and 10mg catalyst.
Conversion yield = (amount of initial cyclohexene – amount of cyclohexene after
reaction)/amount of initial cyclohexene.

Figure 4. Conversion yield and product selectivity for aerobic oxidation of cyclohexene-
catalyzed SGU–29 dependences on (a) reaction time (b) O2 pressure (c) reaction temperature,
and (d) reusability of the SGU–29. Reaction condition: 4.0g cyclohexene, 4.8g acetonitrile,
1
.0g toluene (internal standard), 0.1g octadecyl–3–(3,5–di–tertbutyl–4–hydroxyphenyl)–
propionate (OBHP, bulky scavanger) and 10mg catalyst. Conversion yield = (amount of
initial cyclohexene – amount of cyclohexene after reaction)/amount of initial cyclohexene.

Figure 5. (a) Comparison of conversion yields of ETS-10, AM-6 and SGU-29 for aerobic
oxidation without OBHP, (b) various cycloalkane and (c) reactant mixture of 1:1 cyclohexene
and cis-cyclooctene as indicated. Reaction condition: 4.0g cyclohexene, 4.8g acetonitrile,
1
.0g toluene (internal standard), 0.1g octadecyl–3–(3,5–di–tertbutyl–4–hydroxyphenyl)–
propionate (OBHP, bulky scavanger) and 10mg catalyst. Conversion yield = (amount of
initial cyclohexene – amount of cyclohexene after reaction)/amount of initial cyclohexene.

Figure 6. XPS Cu 2p3/2 spectra of CuO 2
-
in SGU–29 (a) as prepared and (b) after five
4
2
catalytic cycles (reaction conditions: 1 bar of O at 70°C for 12 h)

Figure 7. ESR absorption spectra (upper) and the collected first derivative spectra (lower) of
the observed PBN spin adducts in catalytic reaction with (a) and without (b) SGU–29, as
indicated

Scheme 1. Proposed pathway for the aerobic oxidation of cyclohexene by SGU–29 and
radical species (red) generated during oxidation.

o
b
c
Entry Catalyst
Time/h
O
2
/bar
Temperature / C Conversion /%
Selectivity /%
side-by-
products
d
1
2
3
4
5
6
7
8
9
0
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
SGU-29
4
8
1
1
1
1
1
2
4
6
8
1
1
1
1
1
1
1
1
70
70
70
70
70
70
70
70
70
40
50
60
80
70
70
70
70
13.7
26.6
42.2
49.1
52.2
45.0
46.7
46.5
46.6
~0
19.5
39.6
43.5
47.8
4.5
25.8
24.6
23.3
16.7
16.5
18.4
14.7
14.6
14.9
-
31.7
24.0
19.1
20.1
5.9
58.3
49.2
47.7
37.4
32.9
35.8
35.2
34.3
34.4
-
48.9
47.8
42.5
46.4
14.8
13.5
12.4
15.4
23.1
29.0
30.2
24.3
32.7
39.0
38.9
39.6
-
19.0
24.1
27.7
27.5
79.3
80.1
81.5
1.5
3.1
5.9
15.7
26.3
12.9
12.0
12.4
12.9
-
0.4
2.1
10.7
6.0
-
12
16
24
12
12
12
12
12
12
12
2
1
1
1
1
1
1
1
1
1
2
3
4
5
6
7
e
12
12
12
12
e
ETS-10
e
AM-6
5.0
4.9
6.4
6.2
-
-
Blanke
a
Table 1. Conversion yields and products selectivity for aerobic oxidation of cylclohexene in this work .
a
reaction condition: 4.0g cyclohexene, 4.8g acetonitrile, 1.0g toluene (internal standard), 0.1g octadecyl–3–(3,5–di–
tertbutyl–4–hydroxyphenyl)–propionate (OBHP, bulky scavanger) and 10mg catalyst.
b
conversion yield:(amount of initial cyclohexene − amount of cyclohexene after reaction)/amount of initial cyclohexene.
selectivity: amount of individual product/ amount of consumed cyclohexene
c
d
e
(amount of consumed cyclohexene − amount of three main products)/ amount of consumed cyclohexene
catalytic reaction without OBHP

Supplementary material
Contents
1
2
3
4
5
6
7
. Kinetic size of scavengers used in this study --------------------------------------- S1
. Calibration curves for quantitative analysis by GC------------------------------ S2
. Arrhenius Plot --------------------------------------------------------------------------- S3
. Calculation TON and TOF ------------------------------------------------------------ S4
. Kinetic size of cis-cyclooctene used in this study --------------------------------- S5
. Table 1S ----------------------------------------------------------------------------------- S6
. Table 2S ----------------------------------------------------------------------------------- S7

S1. Estimated size of (a) hydroquinone and (b) OBHP (octadecyl–3–(3,5–di–tertbutyl–4–
hydroxyphenyl)–propionate) used as scavengers in this study as indicated: The chemical structures of
molecules were first drawn by ChemDraw Ultra 12.0 and then the structure files were imported into
Chem3D Ultra 12.0. The chemical structures of scanvangers were optimized by the process Molecular
Mechanics 2 (MM2) Minimize Energy. Minimum RMS Gradient was set to 0.01 from ChemDraw3D
structures after MM.

cyclohexene
cyclohexane-1-ol
cyclohexane-1-one
S2. Calibration curve for cyclohexene, cyclohexane-1-ol and cyclohexane-1-one products.

S3. Plots between ln(C/C0) vs. time (a) with and (b) without SGU-29, and Arrhenius plots for
aerobic oxidation (c) with and (d) without SGU-29

S4. Calculation TON and TOF
(1) The unit cell composition of pristine SGU-29 is Na1.15
K
0.84CuSi
5
O
12
(
2) The number of water molecules contained in SGU-29 was obtained from TGA analysis. The
portion (weight loss % is 5.5% as indicated), between 50 C and 300 C represents desorption of
loosely bound SGU-29 water. So the actual weight could be calculated to be 9.45mg by subtracting
from10mg of SGU-29 to the amount of water, 0.55mg.
100
99
98
97
96
95
94
5.5%
50
100
150
200
250
300
350
400
Temperature / C
(3) Molecular weight of SGU-29’s unit cell
-
1

455.25g∙mol
(4) The number of square unit, [CuO
4
] in 9.45mg of SGU-29
-
5

= 2.08  10 mole
5) The number of consumed cyclohexene
conversion yield (42.2 % )  initial mole of cyclohexene (4.00g, MW: 82.14g∙mol )
(
(
-
1

-
2
=
2.05  10 mole
6) Turnover Number (TON) using 9.45mg of SGU-29 (under1 bar of O
2
at 343 K for 12 h)
= 985.6

=
(
7) Turnover Number (TON) using 9.45mg of SGU-29 (1 bar of O
2
at 343 K for 12 h)
-
1

Turnover Number (TON)/ reaction time (h) = 985.6/12h = 82.1h

S5. Estimated size of cis-cyclooctene: The chemical structures of molecules were first drawn by
ChemDraw Ultra 12.0 and then the structure files were imported into Chem3D Ultra 12.0. The
chemical structures of scanvangers were optimized by the process Molecular Mechanics 2 (MM2)
Minimize Energy. Minimum RMS Gradient was set to 0.01 from ChemDraw3D structures after MM.