Materials characterization
Powder X-ray diffraction (XRD) patterns of all samples were obtained by
employing a Bruker D8 Advance X-ray diffractometer (Bruker AXS Inc.,
Germany) with Ni-filtered Cu Kα radiation (λ=1.5418 Å) operated at 40 kV
and 40 mA. The 2θ scanning angle recorded ranges from 5 to 60°
with a step size of 0.02 and a rate of 5o per minute.
All XRD patterns were analyzed using Jade 6.0 and ICSD database for
phase identification. Furthermore, the relative crystallinity was
evaluated.
The sample morphology was evaluated using a Nova NanoSEM 450 scanning
electron microscope (SEM; FEI, USA) with an accelerating voltage of 15
kV and a beam current of 10 nA. Elemental analysis was carried out on a
Falcon energy-dispersive spectrometer (EDS) (EDAX Inc., USA). A sputter
coating with a thin layer of platinum was adopted to avoid charging. Six
measurement points were selected at different positions to obtain the
average elemental composition for each sample.
High resolution transmission electron microscopy (HRTEM) analyses were
carried out on a JEM-2100 electron microscope (JEOL Co., Ltd., Tokyo,
Japan) with an accelerating voltage of 200 kV. All samples were
dispersed in absolute ethanol by ultrasonic treatment. Subsequently, the
particle-suspended solution was dropped onto copper TEM grids coated
with a holey carbon film and dried at room temperature.
The pore structure of each sample was measured by N2adsorption at 77 K using a 3H-2000PM2 automatic surface analyzer
(BeiShiDe Instrument Co., Ltd., Beijing, China). The specific surface
areas, micropore and mesopore volumes were calculated using the
Brunauer−Emmett−Teller (BET), Harvath−Kawazoe (H-K) and
Barrett-Joyner-Halenda (BJH) method, respectively. Vapor adsorption of
1-hexene on zeolite X samples was determined under
P/P0=0.85 at 298 K using a 3H-2000PW gravimetric vapor
adsorption analyzer (BeiShiDe Instrument Co., Ltd., Beijing, China). All
samples were outgassed at 573 K for 12 h prior to adsorption
measurements.
Raman spectra were collected by using a Renishaw InVia Reflex Lase
Micro-Raman Spectrometer (Renishaw Plc., U.K.) equipped with a 325 nm
argon ion laser. Data were recorded from 1200 to 200
cm−1 with a spectral resolution of 1.6
cm-1 and using a grating of 2400
lines·mm-1.
Solid-state 29Si and 27Al magic
angle spinning nuclear magnetic resonance (MAS-NMR) spectra were
recorded on a Bruker Avance-III 500 MHz super conducting Fourier NMR
spectrometer (Bruker AXS Inc., Germany) with a 4 mm MAS probe. The
chemical shifts of 29Si and 27Al MAS
NMR were externally referenced to tetramethylsilane (0 ppm) and 1M
AlCl3 aqueous solution (0 ppm), respectively.