Hydrothermal synthesis of ZSM‐5 is an often applied but incompletely understood procedure. In comparison to current research efforts that aim to produce complex micro‐mesoporous catalysts for the conversion of biogenic and bulky hydrocarbons, this work focuses on the dependency between Si/Al ratio and zeolite morphology of microporous ZSM‐5 to understand and to control the synthesis process. In two series of time dependent crystallization, kinetics were analyzed at Si/Al ratio 20 and 100 to optimize the crystallization time. Subsequently, zeolites with different Si/Al ratio were obtained and characterized. The results show a transition from a slow dissolution‐recrystallization process to a fast solid‐state‐transformation with increasing Si/Al ratio. This is followed by a switching morphology from clusters of small agglomerates to bigger spherical particles. Respective acid site density and zeolite morphology determine local residence time, hydride transfer behavior and finally selectivity towards aromatics and higher hydrocarbons during methanol conversion. This background should provide control of even more complex syntheses of porous catalysts.

The commercial recycling of spent FCC catalyst typically focuses on recovering only 1–3 % of rare‐earth elements, with the remaining residues often disposed of in landfills. Here, we present a novel method to close a recycling loop for spent FCC catalyst. The method involves a series of leaching steps: Firstly, the spent catalyst material is leached with HNO₃ to remove rare‐earth elements such as La; second, solvothermal leaching with HCl removes most of Al and impurities like Fe, Ni and V; finally, a third leaching with H₂SO₄ removes Ti. The solid residues are then used to synthesize ZSM‐5 without the addition of any extra silicon or aluminum sources after mild activation. The impurities in the synthesis gel strongly modify the properties of the zeolite, with ZSM‐5 crystals containing higher levels of impurities exhibiting lower crystallinities, surface areas, acidities, cracking activities, as well as larger particle sizes.

Significant efforts have been made to partially reuse FCC catalysts, particularly rare earth elements (REE), but only comprehensive recycling strategies can effectively contribute to a sustainable chemical industry. This work presents a novel recycling process for spent FCC catalyst materials, involving pre-treatment, selective separation of silica and alumina species, and synthesis of zeolites or zeolite-like materials. The process exclusively utilizes silicon and aluminum recovered from the spent FCC catalyst to produce high-quality catalyst components and sorbents. Optional rare earth element (REE) leaching, acid treatment after reactivation with sodium hydroxide, precipitation, and filtration yield silicon species (silica). The acidic, aluminum-rich filtrate is processed further by converting it into an alkaline medium with sodium hydroxide, enabling the precipitation and removal of unwanted heavy metals and rare earth elements. Aluminum species are recovered through neutralization of the alkaline solution, followed by precipitation and filtration. Overall, up to 95 % of the silicic acid and aluminum oxide are recovered. Subsequent chemical syntheses yield high-crystalline zeolite Y and ZSM-5 as active zeolites for FCC catalysts, alongside AlPO₄ as an alternative binder. A techno-economic analysis reveals a manageable turnover on industrial scale next to a refinery, while the costs still surpass current market prices, as long they do not care about environmental remediation. Unlike recent studies, no additional silicon and aluminum sources are required, which promotes a more independent local recycling. Furthermore, zeolite A was synthesized as a sorbent using the filtrate solution obtained during the production of zeolite Y, thus nearly completing the recycling loop.

In this study a commercial H‐ZSM‐5 zeolite (Si/Al=11) was post‐synthetically modified by a combined dealumination procedure to adjust its catalytic properties for the selective formation of aromatics from ethanol. The solid‐state properties of original and modified zeolites are determined by structural, textural and acidity analysis. The formation of aromatics and durability of the zeolites were investigated depending on space velocity or contact time in the catalyst bed. In particular, the formation rate and desorption of aromatics from solid‐state surface as well as their tendency to form coke precursors by consecutive build‐up reactions determine the formation of coke. Therefore, the rate of build‐up and finished aromatization by hydride transfer (pre‐determined by the kind, location and geometric arrangement of surface acid sites) and the statistical number of reaction events until final desorption at the specific contact time have to be harmonized to increase aromatics yield and to decrease catalyst decay by coke simultaneously.