Influence of crystal size on the catalytic performance of H-ZSM-5 and Zn/H-ZSM-5 in the conversion of methanol to aromatics

Insight into the Formation of COX By‐Products in Methanol‐to‐Aromatics Reaction over Zn/HZSM‐5: Significantly Affected by the Chemical State of Surface Zn Species

“…This is mainly attributed to a fact that the ZnÀ L acid sites formed can effectively promote the dehydrogenation of intermediates (such as cyclane, cycloolefin) in MTA reaction (the oligomerization and cyclization of light olefins can also be promoted by chemical equilibrium). [16,21,22,26,38] It is in accordance with many previous researches. For example, Niu et al obtained an aromatic selectivity of 46 % over a 1.16 wt %Zn/HZSM-5 (ion exchange method, building new surface-ZnOH + species) at 663 K, 0.5 MPa and 3.2 h À 1 WHSV of methanol, while only 35.6 % over the HZSM-5 without modification.…”

“…As can be seen, AÀ Zn(IM)/HZSM-5 and Zn(IE)/ HZSM-5 showed the very close content of Zn element, about 0.8 wt%. [16,22,26,31,36,38] As can be seen, the distribution of the chemical state of the zinc species on Zn/HZSM-5 are significantly influenced by the preparation method. As can be seen in Table 2, two types of zinc species are discriminated on the Zn-modified HZSM-5 during XPS analysis, with Zn (2p 3/2 ) binding energies around 1023.66 eV and 1022.73 eV respectively.…”

“…Chen and Niu et al attributed this high binding energy peak to ZnOH + species, [31,33] which is Zn-Lewis (ZnÀ L) acid site formed from the strong interaction of the zinc species with Brønsted (B) acid sites. [16,22,26,31,36,38] As can be seen, the distribution of the chemical state of the zinc species on Zn/HZSM-5 are significantly influenced by the preparation method. The majority of zinc species is present as ZnOH + species (91.6 %) for Zn(IE)/ ZSM-5, while that was much lower for Zn(IM)/ZSM-5.…”

High Zn/Al ratios enhance dehydrogenation vs hydrogen transfer reactions of Zn-ZSM-5 catalytic systems in methanol conversion to aromatics

“…Several combinations of zeolites and transition metals have been investigated as MTA catalysts, with ZSM-5 being one of the most interesting topology in terms of stability and selectivity for the process, and Zn the metal that provides the highest yield of BTX products [3,[25][26][27][28]. A full picture of the interplay between acid sites and metal sites is still missing, but it is known that the location of the metal sites (on the external crystal surface or within the micropores) and the nature of the sites formed have a great influence in the catalytic performance of the final material [28][29][30][31][32]. While only few contributions report the stabilization of unusual Zn + species in the zeolitic system [33], metallic Zn, ZnO agglomerates or other Zn 2+ species are generally proposed as the possible Zn sites formed in the zeolite.…”

Dimethyl Ether to Olefins over Modified ZSM-5 Based Catalysts Stabilized by Hydrothermal Treatment

“…HZSM-5 is the general component of catalysts for olefin synthesis from oxygenates (dimethyl ether or methanol) [1]. Investigations of MTH (methanol-to-hydrocarbons) catalysts are focused on studying the effect of crystal size, the module of the HZSM-5 zeolite, binder type, dealumination degree, the presence of mesopores, and the physical chemical properties of catalyst, such as crystallinity, acidity, specific surface area, and the volume of micro-and mesopores [2][3][4][5][6][7][8]. The total number of works in the field of catalysts for propylene synthesis from methanol in the last 5 years has more than 200.…”