
Effect of SiO2/Al2O3 ratio on the conversion of methanol to olefins over molecular sieve catalysts
Qian WANG, Lei WANG, Hui WANG, Zengxi LI, Xiangping ZHANG, Suojiang ZHANG, Kebin ZHOU
Front. Chem. Sci. Eng. ›› 2011, Vol. 5 ›› Issue (1) : 79-88.
Effect of SiO2/Al2O3 ratio on the conversion of methanol to olefins over molecular sieve catalysts
A series of SAPO-34 molecular sieves with different SiO2/Al2O3 ratios have been synthesized for the methanol-to-olefin (MTO) reaction. Their physico-chemical properties are characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and N2 adsorption-desorption. The results are compared with those of the commercial HZSM-5, which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO2/Al2O3 ratio. The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO2/Al2O3 ratio of 0.4 exhibits the highest BET surface area. FT-IR spectra indicate that HZSM-5 has both Brǿnsted and Lewis acid sites and Brǿnsted acid sites are stronger, whereas SAPO-34 samples are dominated only by Lewis acid sites. When the SiO2/Al2O3 ratio increases, propylene and butylenes become the predominant product of the MTO reaction over HZSM-5. In contrast, the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene. According to the product distribution, the reaction mechanism over HZSM-5 catalysts is proposed.
HZSM-5 / SAPO-34 / methanol-to-olefin (MTO) / SiO2/Al2O3 ratio
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