S. Chen et al. / Journal of Catalysis 338 (2016) 38–46
39
ous solution (5.7 mL, 23.4 wt.%) of Al2(SO4)3 and an aqueous solu-
tion (5.95 mL, 18.2 wt.%) of NaAlO2 and NaOH (9.2 wt.%) were
added. The mixture was stirred at room temperature for 60 min,
producing a viscous aluminosilicate gel. The gel was transferred
into a Teflon-coated stainless steel autoclave for crystallization at
100 °C for 24 h. After filtration and washing, the sample was dried
overnight at 120 °C and calcined in air at 550 °C.
The Cu-containing mesoporous zeolite ZSM-5 (Cu-MZSM-5)
was synthesized using silane of N,N-dimethyl-N-octadecyl-N-(3-t
riethoxysilylpropyl)ammonium bromide (TPOAB) as a mesoscale
template according to our previous work [35]. The molar ratio of
various compositions was 1 Al2O3/1 Na2O/2.5 CuO/69 SiO2/15.1
TPAOH/13.2 TPOAB/1552 H2O. Typically, NaAlO2 (0.16 g) was dis-
solved in water (18.0 mL), followed by addition of tetrapropylam-
monium hydroxide (TPAOH, 12.0 mL) and tetraethyl orthosilicate
(TEOS, 15.0 mL). After the mixture was stirred at room tempera-
ture for 4.5 h, Cu(NO3)2Á3H2O (0.6 g) was then introduced and the
reaction mixture was stirred at 75 °C for another 5 h. Finally,
TPOAB (7.5 mL) was added dropwise and stirred for 1 h to yield
an aluminosilicate gel. The gel was transferred into a Teflon-
coated stainless steel autoclave for static crystallization at 180 °C
for 72 h. The resultant product was filtered, washed, dried over-
night at 120 °C, and calcined in air at 550 °C for 5 h.
Cu(I)
OH
COOH
Ph
Ph
CO2
TBHP
HO
Ph
COOCu(II)
TBHP
Ph
COOCu(II)
OH
OH
Key
Step
Fig. 1. Mechanism of decarboxylative coupling of CA with ethanol.
reasonable goal to synthesize transition metal-doped zeolite X
with Lewis basic and metal sites for decarboxylative coupling of
CAs with alcohols, alkylbenzenes, cycloalkanes, and cyclic ethers.
Here, we synthesized Cu-doped zeolite X (Cu-X) and envisioned
its use to catalyze the decarboxylative coupling reaction in high
activity. For comparison, Cu-doped zeolite Y (Cu-Y) and meso-
porous ZSM-5 (Cu-MZSM-5) were also prepared. Compared with
the Cu, Cu2O, and CuBr2 catalysts reported in the literature [29],
the Cu-Y, Cu-MZSM-5, and especially the Cu-X catalysts show
extraordinarily high activity at very low Cu content (the mole ratio
of the substrate to Cu is 336:1). This should be attributed to the
fact that the Cu-X catalyst not only possesses active Cu+ and Cu2+
sites but also provides abundant Lewis basic sites. The strong inter-
action between Cu species and the zeolite framework benefits the
transformation of Cu2+ and Cu+ in the reaction, and the Lewis basic
sites as electron donors enhance the electron density of the C@C
bond in the CA molecule, which greatly facilitates the C@C bond
Y and MZSM-5 were exchanged with 1 M NH4NO3 solution at
80 °C for 4 h. After filtration, the samples were dried overnight at
120 °C and calcined at 500 °C for 4 h, transforming to acidic H-
form zeolite Y (HY) and H-form zeolite MZSM-5 (HMZSM-5).
2.2. Characterization
The X-ray powder diffraction (XRD) pattern was recorded on a D/
MAX 2500/PC powder diffractometer (Rigaku) using a Cu Ka radia-
radical addition with electrophilic a-carbon-centered radicals. Fur-
thermore, this catalyst design concept was also applied to synthe-
tion source operated at 40 kV and 200 mA. Nitrogen physisorption
was conducted at À196 °C on a Micromeritics ASAP 2020M appara-
tus. The sample was degassed at 300 °C for 8 h before the measure-
ment. Specific surface area was calculated from the adsorption data
using the Brunauer–Emmett–Teller (BET) equation. The Cu content
and the Si/Al ratios were determined by inductively coupled plasma
optical emission spectroscopy (ICP-OES) with a Perkin-Elmer
3300DV emission spectrometer. The transmission electron micro-
scopy (TEM) image was obtained on a JEM-2100F microscope with
a limited line resolution capacity of 1.4 Å at 200 kV. Before charac-
terization by TEM, the sample was cut into thin slices and dropped
onto a Ni grid coated with a carbon membrane. X-ray photoelectron
spectroscopy (XPS) experiments were performed on an ESCALAB MK
II system. The basicity of the zeolite samples was measured on a Bru-
ker TENSOR 27 infrared spectroscope (IR) equipped with a reactor
cell. Before being dosed with pyrrole, the sample was outgassed
overnight at 400 °C and 10À3 Pa. After cooling to room temperature,
the sample was exposed to pyrrole vapor until saturated, followed
by evacuation at 65 °C for 60 min. The spectrum was recorded at
65 °C with a 2 cmÀ1 resolution and using a 32-scan spectrum. The
UV–vis diffuse reflectance (UV–vis) spectrum was obtained on a
Perkin-Elmer Lambda 25 spectrometer with an integration sphere.
The IR spectrum of the CA-chemisorbed Cu-X (Cu-X-CA) sample
was obtained on a Bruker TENSOR 27 infrared spectroscope
equipped with a reactor cell. Before measurement, the Cu-X-CA
sample was evacuated to 10À3 Pa at 100 °C for 20 h, and then the
temperature was increased to 110 °C. The spectrum was obtained
in the absorbance mode and was shown after subtraction of a back-
ground spectrum obtained on the Cu-X sample. For comparison, the
size Fe-, Co-, and Ni-doped zeolite X as highly active catalysts for
the preparation of very useful
a,b-epoxy ketone compounds via
direct oxidative coupling of alkenes with aldehydes.
2. Experimental
2.1. Materials synthesis
Cu-containing zeolite X (Cu-X) was prepared from a starting
aluminosilicate gel with molar ratio 1 Al2O3/3.5 Na2O/3 SiO2/0.08
CuO/186 H2O. In a typical run, water glass (9.9 mL) was mixed with
an aqueous solution (25.4 mL, 7.7 wt.%) of NaOH under vigorous
stirring for 1 h. Then the aqueous solution (27.0 mL, 11.8 wt.%) of
NaAlO2 was added and further stirred for 1 h at room temperature.
After that, the reaction mixture was stirred at 75 °C for another 4 h.
Finally, an aqueous solution (2.0 mL, 0.3467 g) of Cu(NO3)2Á3H2O
was added dropwise and stirred for 1 h to yield an aluminosilicate
gel. The gel was transferred into a Teflon-coated stainless steel
autoclave for static crystallization at 100 °C for 84 h. After filtration
and washing, the sample was dried overnight at 120 °C and cal-
cined in air at 550 °C. Fe-, Co-, and Ni-containing zeolite X (Fe-X,
Co-X, and Ni-X) were also synthesized in similar procedures by
the addition of Fe2(NO3)3Á9H2O (0.6693 g), Co(NO3)2Á6H2O
(0.456 g), and Ni(NO3)2Á6H2O (0.4622 g), respectively.
Cu-containing zeolite Y (Cu-Y) was prepared from a starting
aluminosilicate gel with molar ratio 1 Al2O3/4 Na2O/9 SiO2/0.32
CuO/170 H2O. In a typical preparation, water glass (19.4 mL),
H2O (3.6 mL), and a solution (3.4 mL) of zeolite Y seed (prepared
by mixing NaAlO2 (1.409 g), H2O (18.1 mL), NaOH (5.0776 g), and
water glass (17.3 mL), followed by aging at room temperature for
24–36 h) were mixed. After 30 min of stirring at room tempera-
ture, an aqueous solution (2.0 mL, 0.3467 g) of Cu(NO3)2Á3H2O
was added dropwise and further stirred for 1 h. After that, an aque-
IR spectrum of CA was also recorded at room temperature. The 13
C
solid-state NMR spectra of Cu-X-CA and CA were obtained on a Bru-
ker AVANCE III 400WB spectrometer operated at 9.4 T with a fre-
quency of 100.62 MHz. The Cu-X-CA sample was pre-outgassed
overnight at 100 °C and 10À1 Pa and then packed into a 4 mm zirco-