Mechanistic study on the effect of ZnO on methanol conversion over SAPO-34 zeolite

Evaluating the Role of Descriptor- and Spectator-Type Reaction Intermediates During the Early Phases of Zeolite Catalysis

“…105,106 Since the Lewis acid site (LAS) (e.g., CeO 2 , 107 ZnO, 108 TiO 2 109 ) could decompose formaldehyde, utilizing the bifunctional BAS-LAS zeolite system would be an appropriate way to improve the catalyst lifetime (Figure 6c; BAS, Brønsted acid site). 107,108 With this objective, Hwang et al 110 6d). 110 Since HCHO is highly reactive and can rapidly react with hydrocarbons produced during the MTH reaction, an increase in proximity between a BAS and LAS has improved the catalyst lifetime via decomposing HCHO (Figure 6d,e), a promoter for the initiation and termination of chain carriers.…”

“…Besides, formaldehyde could condense with surface acetate and acetic acid to form carboxylic acids, a precursor for olefins via decarboxylation (Figure b) . Additionally, formaldehyde could promote aromatics selectivity, accelerating the deactivation via forming bulky coke species (Figure a). , Since the Lewis acid site (LAS) (e.g., CeO 2 , ZnO, TiO 2 ) could decompose formaldehyde, utilizing the bifunctional BAS-LAS zeolite system would be an appropriate way to improve the catalyst lifetime (Figure c; BAS, Brønsted acid site). , With this objective, Hwang et al evaluated the lifetime of bifunctional catalysts (H-SAPO-34 and Y 2 O 3 ) in different fixed-bed configurations: Y 2 O 3 packed upstream of H-SAPO-34, Y 2 O 3 packed downstream of H-SAPO-34, an interpellet physical mixture of H-SAPO-34 with Y 2 O 3 , and an intrapellet physical mixture of H-SAPO-34 with Y 2 O 3 , in addition to the standalone zeolite. The addition of Y 2 O 3 does not directly influence the MTH reaction, yet it facilitates HCHO decomposition into CO.…”

Maximizing the catalytic performance of FER zeolite in the methanol-to-hydrocarbon process by manipulating the crystal size and constructing a bifunctional system

“…Strangely, this observation is opposite to that of the literature, where an intramixed bifunctional system led to superior performance based on HSAPO-34 catalysts. 46 Since the inter-pellet mixing of Y 2 O 3 with 10-membered ring FER zeolite might lead to diminishing stronger acid strength to some extent (see Table S1 †), we hypothesize that the optimal proximity between the surface of Y 2 O 3 and the zeolite's Brønsted acid sites is crucial to catalyze the decomposition of HCHO, 46,70 which would eventually enhance the catalyst lifetime by decelerating the arene cycle of the dual cycle mechanism.…”

MTO Synthesis and Characterization of ZnAPO-34 and SAPO-34: Effect of Zn on the Acidity and Catalytic Activity in the MTO Reaction

“…Isomorphic substitution of framework Al 3+ and P 5+ ions by metal cations or silicon, respectively, produce the MeAPSO material. Since Zn is an active metal to promote the aromatization of methanol, the physical mixtures of SAPO-34 and ZnO were used for MTO reaction to increasing the ratio of ethene to propene, to gain a deep understanding of the synergetic effect of various catalyst functions [20]. Metal heteroatom modification, through isomorphous substitution (MeAPSO-34) or ion exchange and impregnation (Me/SAPO-34), has been extensively investigated to tune the acidity and local structure of SAPO-34 cavity improving the reaction product and enhance the catalyst lifetime [21].…”

“…Generally, the synthesis of SAPO-34 is performed in the presence of organic templates [23], tetraethylammonium hydroxide (TEAOH), dipropylamine (DPA), diethylamine DEA and tripropylamine (TEA). Several previous reports [18,20] show that using TEA as the structure directing agent (SDA) forms smaller SAPO-34 crystals (200 nm). MTO process is strongly influenced by the crystal size providing catalytic performance and olefins selectivity.…”