Mechanistic insights into structural and surface variations in Y-type zeolites upon interaction with binders

Abstract

Zeolite Y is one of the most important solid acid catalysts that find immense applications in catalytic processes such as fluid catalytic cracking (FCC), acylation and cumene cracking. The technical grades of FCC catalyst require specifications that are met by dispersing the zeolite in amorphous binders. On contact with binders, zeolite properties in composite catalysts alter. This article reports an insight into structural and surface modifications of Y zeolites caused by binders’ incorporation. Experiments employing various characterization techniques, including solid state MAS-NMR and FTIR reveal alumina incorporation adjusts zeolite framework in comparison with silica binder. Incorporation of alumina binder into zeolite Y polarizes the framework by extra-framework alumina species (such as Al3+, AlO+ and Al(OH)2+) coming from the binder. The polarization, apparent with USY and REY, is considered as the operating mechanism for distortion of zeolite framework, involving the attraction of aluminum species from the binder to the framework of zeolite and its subsequent framework structure reorientation. Compensating framework Na+ cations restrain the polarization of NaY framework due to its deficiency of protons, revealing Brönsted acid sites as active centers for the zeolite framework polarization. The resulting alumina bound catalysts are amorphized by layers of alumina materials that implicate the Brönsted acidity as a function of its weight in the catalyst. Catalytic reaction reveals that polarization of the zeolite framework by extra-framework alumina species decreases the transformation of paraffin to carbenium ion, increasing the hydrogen transfer reaction pathway.