Title : Influence of Extra-Framework Aluminum on the lifetime of Faujasite Y zeolite under iso-octan cracking
Abstract:
Zeolite Y with Faujasite structure includes high surface area, high thermal/hydrothermal stability, and large pore volume. Tunable acidity is responsible for its application as an acid catalyst in several crucial industrial chemical processes. The micro-porous structure of zeolite Y limits the accessibility of the large feedstock molecules to pore active sites. Moreover, such mass transfer limitations may cause a fast catalyst deactivation and undesired secondary reactions. To improve the mass transfer limitations, catalytic effectiveness in chemical reactions, and decrease the coke formation several approaches were proposed. synthesis of extra-large pore zeolites, synthesis of zeolite with mesopores, and generated interconnected mesoporous structures with intrinsic micropores have been suggested. Post-synthesis treatment was found to be the most practical method for obtaining hierarchical zeolites by desilication and dealumination methods including steam treatment, leaching methods with acidic or basic media, and chemical templates. It is generally known that the post modification processes especially steaming, generates extra-framework Al (EFAL) species with lewis acidity, which contributes to increased cracking activity. These EF cations play a significant role in determining the catalytic properties of zeolites. The work, described here, introduces lewis acidity by using different concentrations of the aluminum precursor into HY zeolite followed by calcination. The resulting catalysts were characterized by means of XRD, XRF, and nitrogen-physisorption. Catalytic testing was investigated over the HY catalysts for cracking of iso-octan. X-ray diffraction and nitrogen physisorption suggest that the zeolitic framework is retained after these treatments. With an increase in the total extra-framework aluminum in the modified zeolites, there was a considerable increase in the number of Lewis acid sites, which is a synergic effect on the coking rate and rapid deactivation of zeolite, thus the catalytic lifetime decreased after ion exchange.
Audience take-away:
- Faujasite Y zeolite is an applicable catalyst for petrochemical industries that notices the characterization of it results in optimal use with higher efficiency. On the other hand, generated products over these improved catalysts have a significant influence on reducing energy consumption and environmental pollution.
- After treatment of zeolites as catalytic cracking, produced Extra-framework Al should be extracted from the catalyst. If there are EFAl species in the zeolite cages, the catalytic property is affected. Leaching methods are used for the elimination of this species. But, these species, as lewis acid sites, have different roles in different applications. we investigated the influence of EFAl in the lifetime of catalysts that are used for the cracking of alkanes. you can study this kind of lewis acid in the efficiency of other catalysts.
