The methanol-to-olefins reaction is a viable and promising technological route to replace increasingly scarce petroleum resources. SAPO-34 zeolite is an ideal catalyst for the methanol-to-olefins reaction due to its suitable acidity and pore structure. However, a single zeolite catalyst has limited performance, and in this work, metal species were introduced on SAPO-34 molecular sieves to achieve higher low-carbon olefin selectivity through the modulation of acidity. However, since the introduction of metals promotes aromatic cycling, it allows the creation of carbonaceous precursors and reduces the catalyst lifetime. Therefore, the introduction of CO2 into the carrier gas inhibited the generation of carbonaceous precursors and thus prolonged the catalyst life. The presence of the metal species and their effects on SAPO-34's pores and structure were characterized by XPS, the change in acid amount was determined by NH3-TPD, and the adsorption strength of the catalyst for CO2 was determined by CO2-TPD, revealing the active sites of the catalyst. High low-carbon olefin selectivity and long catalyst life were also achieved, with low-carbon olefin selectivity of 88.0%.
Longyu Wang,Na Wang,Suohe Yang,Guangxiang He,Haiyan Liu,Xianghai Meng,Chunming Xu,Zhichang Liu,Haibo Jin
A diverse suite of Zn-SAPO-34 catalysts was synthesized employing three distinct methodologies for the incorporation of zinc species: thermal ion exchange, wet impregnation, and physical mixing. The catalysts were characterized using various analytical techniques including XRD, FT-IR, BET, SEM, XRF, XPS, NH 3 -TPD, and Py-IR, to elucidate the crystal structure, morphology, surface acidity, and the presence of zinc species within the catalysts. The study showed that the method of zinc introduction markedly impacts the physicochemical properties of the catalysts. Different approaches to introducing zinc species significantly influence the acid strength and type on the catalyst surface, with variations in the existing states of zinc across the catalysts. Specifically, zinc species introduced via thermal ion exchange coexist as ZnOH + and ZnO within the catalyst, whereas those from wet impregnation and physical mixing are individually present as either ZnOH + or ZnO. Furthermore, the study examined the catalytic performance of these Zn-SAPO-34 catalysts in the dehydration of fructose to produce 5-hydroxymethylfurfural (HMF). Catalysts prepared via thermal ion exchange exhinited superior performance, achieving an remarkable HMF yield of 94.6 %. Additionally, in situ infrared technology was used to investigate the effect of zinc species introduction on the fructose dehydration process, indicating suggesting that the introduction of zinc species enhances the transformation of fructose molecules.
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