Rational Design of a Novel ETL/OFF Intergrowth Zeolite Using Renewable Silica Resources for Catalytic Cracking of n-Hexane

Abstract

The rational design of a modern zeolite plays a pivotal role in heterogeneous catalysis, in particular, the elaboration of an intergrowth zeolite. In this context, we report the synthesis of a novel ETL/OFF intergrowth zeolite using renewable nanosilica as a starting material. The crystallization profiles show that the formation of the intergrowth zeolite requires a short induction period of less than 48 h. Subsequently, the crystalline phase is developed, eventually forming the ETL/OFF intergrowth structure with a relative crystallinity of 86% and 14% for ETL and OFF-type zeolites, respectively, at a crystallization time of 168 h. In addition, the phase identification of the designer intergrowth zeolite was investigated via single-crystal electron diffraction (SCED) and high-resolution transmission electron microscopy (HRTEM) techniques. The refined structure derived from the SCED measurement exhibited remarkable alignment with the ETL and OFF zeolite databases, confirming the formation of both ETL and OFF frameworks within the intergrowth structure. Furthermore, to validate the precise intergrowth location, we employed fast Fourier transform (FFT) and inverse FFT (iFFT) analyses of the HRTEM images. Our findings revealed that the intergrowth region between the ETL and OFF phases was localized within the innermost regions of the crystals. Conversely, the outermost regions exhibited only the lattice fringe of the ETL framework. Interestingly, the ETL/OFF intergrowth zeolite also illustrated higher product selectivity of light olefins (C2–C3 products) in the catalytic cracking of n-hexane compared to the isolated ETL zeolite at n-hexane conversion in the range of 40–50%. This first example opens up perspectives of the development of the ETL/OFF intergrowth zeolite using renewable silica resources.