Effect of SiO2/Al2O3 ratio on the conversion of methanol to olefins over molecular sieve catalysts

Abstract

A series of SAPO-34 molecular sieves with different SiO 2 /Al 2 O 3 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 N 2 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 SiO 2 /Al 2 O 3 ratio. The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO 2 /Al 2 O 3 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 SiO 2 /Al 2 O 3 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.

Altering C2H4/C3H6 yield in methanol to light olefins over HZSM-5, SAPO-34 and SAPO-34/HZSM-5 nanostructured catalysts: influence of Si/Al ratio and composite formation

“…Several parameters including gel composition, synthesis procedure, weight proportion and framework Si/Al ratio can affect the properties of SAPO-34/ HZSM-5 composites as well as catalytic activity. [36][37][38] The number and distribution of Si atoms in the framework of zeolites may affect the structure, acidity and catalytic performance of catalysts. Hence, the Si/Al ratio present in the reactant gel is believed to be a dominant factor in governing which structure is obtained.…”

“…Hence, the Si/Al ratio present in the reactant gel is believed to be a dominant factor in governing which structure is obtained. 15,36,[39][40][41] An optimum ratio of Si/Al in the starting gel of the composite can adjust the acidity so as to reduce the rate of coke formation to produce the highly desired ethylene and propylene derived products. 36,42,43 Wang et al investigated the effect of Si/Al ratio on the conversion of methanol to olens over HZSM-5 and SAPO-34 molecular sieves.…”

Incorporation of mono and bimetallic MnNi into SAPO‐34 framework used in conversion of methanol to ethylene and propylene: Alteration of acidic properties and catalytic performance

“…Furthermore, the acid site of the zeotype is undoubtedly significant to obtain valuable information on the reaction mechanism. Thus, the result of some researches regarding the reaction mechanism of light olefins formation on MeAPSO‐34 catalyst is summarized in Figure . According to this mechanism, methanol molecules are adsorbed on Brønsted acid sites of the MeAPSO‐34 catalysts.…”

Preparation of NaA Zeolite from High Iron and Quartz Contents Coal Gangue by Acid Leaching—Alkali Melting Activation and Hydrothermal Synthesis

“…Setting the reaction system to n(SiO2)/n(Al2O3) = 2.0; n(H2O)/n(Na2O) = 60; aging at 50 °C for 1 h; crystallization at 94 °C for 4 h; and changing n(Na2O)/n(SiO2) = 1.2, 1.7, 1.9, and 2.1, respectively, after finishing reactions, the XRD analyses of the products are shown in Figure 9. Figure 8 shows when n(SiO 2 )/n(Al 2 O 3 ) = 1.0, the diffraction peak intensity of the product is very low, this is because the crystallinity and the zeolite type highly depend on the n(SiO 2 )/n(Al 2 O 3 ) ratios [30][31][32][33][34]; when n(SiO 2 )/n(Al 2 O 3 ) = 1.0 or 1.5, they deviate from the target NaA zeolite product n(SiO 2 )/n(Al 2 O 3 ) = 2.0, which is not conducive to the nucleation and growth of zeolite; when n(SiO 2 )/n(Al 2 O 3 ) = 2.0, the diffraction intensity increases. The search result shows that the final product is NaA zeolite (PDF card number: 39-0223), there is a further increase of n(SiO 2 )/n(Al 2 O 3 ) = 2.5, and the diffraction intensity also increases.…”