Novel OSDA-Synthesized EUO Zeolites with High Catalytic Performance in C8 Aromatic Isomerization

Abstract

EU-1 zeolite exhibits excellent catalytic performance in C8 aromatic isomerization due to its unique pore structure. The traditional synthesis of EU-1 requires alkaline sources such as NaOH, necessitating subsequent multiple ion-exchange steps to obtain the catalytically active H-type zeolite. However, the ion-exchange process is not only tedious and time-consuming but also generates substantial wastewater, contradicting the principles of energy conservation, low carbon emissions, and environmental sustainability. In this work, we synthesized a new methyl carbonate quaternary ammonium salt (HMC) and successfully utilized it as organic structure-directing agent (OSDA) to produce a novel zeolite with EUO topology, designated TYU-1. Extensive characterization has demonstrated that HMC serves not only as an effective OSDA comparable to hexamethonium bromide (HMBr2), but also provides the necessary alkaline medium for synthesis of zeolites. This dual functionality eliminates the requirement for external alkali source, thereby bypassing the tedious and energy-intensive ion-exchange steps. Furthermore, C8 aromatic isomerization is primarily catalyzed by Brønsted acid sites within the zeolite. NH3-TPD and Py-IR characterizations revealed that although the total acid amount of TYU-1 is relatively lower, its external Brønsted acid content are higher than those of conventional EU-1. This unique acidic property endows TYU-1 with superior performance in C8 aromatic isomerization, exhibiting a higher xylene isomerization activity (~25.3%) and a lower C8 aromatic loss rate (~3.03%).