2.2. Catalyst characterization
X-ray diffraction (XRD) analysis was carried out in a Japan Science D/max-IIIA diffractometer in the scan range of 2u between 58 and 908 using Cu Ka as source at 30 kV, 20 mA. The morphology of the samples was examined by scanning electron microscope (SEM) (S-360 from Cambridge University Cambridge Company) at 1.0 kV.
The acidity strength and its distribution were analyzed by NH3 adsorption and NH3-TPD using TP-5000 multi-function instrument adsorption (Tianjin Instrument Co., Ltd.). 0.1 g catalyst sample was heated at 150 8C, and then at this temperature for impulse NH3 adsorption. When saturated adsorption was achieved, temperature was first decreased to 50 8C for 60 min, then programmed to increased to 800 8C under the heating up rate of 10 8C/min. The specific surface areas and the pore distribution of the catalysts were determined by the nitrogen physisorption using the BET method in NOVA 4000 instruments (Quantachrome Instruments,USA).