Hierarchical Y and USY Zeolites Designed by Post‐Synthetic Strategies

Abstract

Strategic combinations of affordable and scalable post‐synthetic modifications enabled to design a broad family of hierarchical Y and USY zeolites (FAU topology) independent on the Si/Al ratio. Pristine (Y, Si/Al = 2.4), steamed (USY, Si/Al = 2.6), and steamed and dealuminated (USY, Si/Al = 15 and 30) zeolites were exposed to a variety of acid (H4EDTA and Na2H2EDTA) and base (NaOH) treatments, which led to the introduction of mesopore surfaces up to 500 m2 g−1, while preserving the intrinsic zeolite properties. Pristine Y and USY zeolites (Si/Al ∼ 2.5) required mild dealumination (to Si/Al > 4 in the case of Y) to facilitate subsequent efficient desilication. Alkaline treatment of Y and USY zeolites with low Si/Al ratios (∼4–6) led to an abundance of Al‐rich debris, which could be removed by a subsequent mild acid wash. On the other hand, severely steamed and dealuminated, hence Si‐rich, USY zeolites (Si/Al = 15 and 30) proved extremely sensitive to the alkaline solution, displaying facile dissolution and substantial amorphization. For the latter group of ultra‐stable Y zeolites, the presence of TPA+ in the alkaline solution enables to protect the zeolite structures upon the introduction of mesoporosity by desilication, preserving crystallinity and micropore volume. The sorption and catalytic properties of the hierarchical Y and USY zeolites were superior compared to the conventional counterparts.

On the influence of Si:Al ratio and hierarchical porosity of FAU zeolites in solid acid catalysed esterification pretreatment of bio-oil

“…The spent catalyst was washed with 200 ml methanol and 3 Results and discussion 3.1 Catalyst characterisation Figure 2 shows the N 2 adsorption-desorption isotherms for the series of FAU zeolites under investigation, which show a progressive development of the hysteresis loop and intraparticle mesoporosity as the Si:Al ratio of the zeolites increases. A further enhancement in mesoporosity is observed upon alkaline treatment of FAU30 to generate HFAU30, consistent with previous reports [50,51]. XRD shown in Fig.…”

Catalyst Design by NH4OH Treatment of USY Zeolite

“…[19][20][21] Recently, this technique was also applied to create mesopores in USY zeolites (FAU topology). [22][23][24] It was pointed out that siliceous 12-membered ring zeolites, such as highly dealuminated USY, are extremely sensitive to these alkaline treatments, resulting in amorphization and considerable loss of material. To obtain hierarchical zeolites with preserved intrinsic zeolitic properties, Verboekend et al optimized the base leaching procedure for USY zeolites by adding organic pore-directing agents such as tetrapropylammonium cations (TPA + ).…”

“…Although effective, the method involves dissolution of copious amounts of solid (35-50 wt%). [ 15,23,24 ] Moreover, the use of organic pore-directing agents or organic bases should preferably be avoided in order to realize a sustainable and economically attractive manufacture of hierarchical zeolites. Very recently, efforts were made to largely recover the used organic compounds, using the volatile diethylamine (DEA) as an organic leaching agent.…”

Influence of steam-calcination and acid leaching treatment on the VGO hydrocracking performance of faujasite zeolite

“…Chemical modification methods, in turn, are designed to improve zeolite properties such as mesoporosity and acid strength and density. Many modifying agents have been employed for this purpose such as mineral acids, organic acids, (NH 4 ) 2 SiF 6 , NaOH and EDTA [24]. Some of these methods have been employed with success to obtain suitable zeolites as the acidic component in hydrocracking catalysts [8,12,25,26].…”