Micron-Sized Hierarchical Beta Zeolites Templated by Mesoscale Cationic Polymers as Robust Catalysts for Acylation of Anisole with Acetic Anhydride

Abstract

Hierarchical Beta zeolites with interconnected intracrystalline mesopores and high structural stability are highly attractive for catalytic applications involving bulky reactants. Here, by introducing a suitable amount of polydiallyldimethylammonium chloride into the initial synthesis system, micron-sized Beta zeolite crystals with abundant hierarchical porosity (Beta-H) were hydrothermally synthesized. The sample named Beta-H_1 exhibited very high catalytic activity and durability for the Friedel–Crafts acylation of anisole with acetic anhydride. A 92% conversion rate of acetic anhydride could be achieved after 1 h of reaction in a fixed bed reactor, and 71% conversion still remained after 10 h, much better than the rate for conventional Beta zeolite (which decreased rapidly from 85% to 37% within 10 h). The enhanced catalytic performance of Beta-H zeolites could be mainly attributed to the relatively lower strong acid density and the faster transport rate of the hierarchical zeolites. In addition, Beta-H showed high structural stability and could be easily regenerated via high-temperature calcination without obvious loss in catalytic activity, demonstrating its great potential for catalytic applications in the industrially important Friedel–Crafts acylation process.

Fine Tuning of Hierarchical Zeolite Beta Acid Sites Strength

“…The mechanism for the "self-reduction" of Cu 2+ under vacuum or inert flow is thought to start from the dehydration of two [Cu-OH] + ions located close to one framework Al [47]. There is a possibility that Cu + in the samples is formed via autoreduction of [CuOH] + during the vacuum pretreatment [22]. In the literature, the "blocking effect" of the active sites is explained by the formation of a strong complex between the Cu 2+ cation and probe molecule (CD 3 CN) during its introduction into the zeolite framework [47].…”

“…For example, zeolite beta catalyzes different types of reactions, such as (trans)alkylations, acylations, isomerizations, disproportionations, cracking, etc. [18][19][20][21][22][23], while metal exchanged/impregnated beta shows catalytic activity in NOx decomposition [24,25], acetone and methanol conversion to hydrocarbons [26,27] or oxidation of different organic compounds [28,29]. Also, the aim of this research is to shed a light on the structure-reactivity relationship governing the zeolite Beta acid strength, through design and development of efficient and environmentally friendly materials.…”

Morphology and Microstructural Optimization of Zeolite Crystals Utilizing Polymer Growth Modifiers for Enhanced Catalytic Application

“…It is well known that the catalytic properties of zeolite catalysts depend on not only their pore openings and cage/intersection cavities but also their various physicochemical properties, including morphology, crystal size, phase purity, composition, and acidity/redox properties [6][7][8]. Through the optimization of synthesis methods and parameters, these physicochemical properties could be modulated to a certain extent by adjusting the morphology and microstructural characteristics of the zeolite crystals, making them well fit for the requirement of a specific catalytic reaction [9][10][11][12][13][14]. Among the various modulation strategies, the introduction of so-called "zeolite growth modifiers" (ZGMs) has shown great advantages in precisely modulating of the morphology and microstructure of various zeolite crystals, with remarkable effects in terms of enhancing their catalytic activity, selectivity, and/or stability for a broad range of industrially important catalytic processes [10,[15][16][17][18][19][20].…”