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.