A Remarkable Catalytic Activity of Hierarchical Zeolite (ZH‐5) for Tertiary Butylation of Phenol with Enhanced 2,4‐Di‐t‐Butylphenol Selectivity

Abstract

Hierarchical zeolites with the ordered arrangement at the nanoscopic level are of paramount importance in catalysis owing to their remarkable properties. Nevertheless, architecting such structures is extremely difficult owing to their challenging synthesis conditions. In this study, we report a designed synthesis of such a material with MFI topology viz., hierarchical nanoporous ZSM-5 (designated as ZH-5) with unique serrated morphologies. The synthetic approach was envisaged by considering the stable supramolecular aggregation, controlled zeolitization and strong organosilane interactions as the key factors for the hierarchical organization. Furthermore, for the first time, we emphasize the effect of dual-templating nature of organosilanes in stabilizing the crystalline mesophase for the development of a hierarchical pore-architecture. In addition, the catalysts have shown remarkable catalytic activities for the formation of 2,4-di-tert-butylphenol.The breakthrough in the synthesis of high silica zeolites and their innovative applications in petrorefineries has reformed the industrial catalysis. [1] Among the plethora of zeolites, the structures with MFI topology have been phenomenal in refining and fine chemical synthesis owing to their exceptional properties. Nevertheless, the presence of intricate network of micropores can impose severe mass transfer constraints. [2] In this regard, numerous synthetic strategies have been developed in order to induce mesoporosity in to the MFI-type frameworks. [3][4][5][6] Among the various strategies, desilication, nanocasting, dry-gel conversion, recrystallization, etc., are most commonly used to synthesize hierarchical ZSM-5. [5][6][7][8][9][10] In addition, the mesoporosity was also induced by the repetitive branching of MFI/MEL intergrowths caused by the co-templating action of auxiliary templates. [11,12] Although supramolecular templating has been one of the best methods to prepare mesoporous solids, the conventional surfactants have failed to construct such struc-tures of zeolites owing to the phase segregation. [3,13] For an ordered mesoporous zeolite to organize, the supramolecular templates must cooperate with the molecular templates to form a stable crystalline mesophase, which is a difficult task. [3] In addition, the crystal growth of the zeolite must be confined with in the fine pore walls of the self-assembled mesostructure. Despite the numerous efforts, only few have reported the synthesis of such zeolitic structures by employing expensive and complex surfactants viz., multi-quaternary ammonium (MQA) surfactants. [14,15] On the other hand, the surfactants viz., amphiphilic organosilanes were unable to impart similar mesostructures owing to the uncontrolled growth of crystalline phase. [16,17] In the current work, for the first time, we report the successful synthesis of short-range ordered mesoporous structures of MFI-type zeolites with unique serrated morphologies by supramolecular templating of cost-effective organosilanes. The synthetic approach was envisa...

Rational design, synthesis, characterization and catalytic properties of high-quality low-silica hierarchical FAU- and LTA-type zeolites

“…Consequently, the catalytic properties of the synthesized zeolites have been evaluated for industrially important vapor phase tertiary butylation of phenol (Figs 13 and 14 ; Table 3 ). In general, the selectivity of the alkylated products depends on the nature of acid sites, e.g., Brønsted acid sites preferably form 4- t -BP as the major product while Lewis acid sites direct the ortho -alkylation to form 2- t -BP 49 – 54 . Although steamed form of zeolites are the common cracking catalysts in refineries.…”

Overview of Current and Future Perspectives of Saudi Arabian Natural Clinoptilolite Zeolite: A Case Review

“…e fact of the existence of impurities in natural zeolites composition still presents a challenge and has wide implementation for the continuing use of zeolites material employed in industrial applications. Additional investigations focused on designing hierarchical zeolites for petroleum refinery [87][88][89][90][91]. e importance of hierarchical zeolites results from their active acidic sites, which lead to high catalytic activity in the desired reaction [38,83,84].…”

“…erefore, based upon the wider literature review [102,106,[117][118][119], this article also recommends the utilization of a greater variety of characterization techniques on the local materials in Saudi Arabia such as pyrrole adsorption [120], temperature-programmed desorption of ammonia and temperature-programmed desorption of carbon dioxide [102], and isopropanol methyl butynol test reactions [102,118,121]. By employing these additional methods, the details and descriptions of catalytic activity together with the clear demonstration of their acidic or basic properties may be better understood [89,91]. As a result, more efficient methods can be provided in the modification of local Saudi zeolite materials for use in a greater range of industrial production applications such as the coke formation.…”

Nanostructured zeolite with brain-coral morphology and tailored acidity: a self-organized hierarchical porous material with MFI topology

“…Numerous efforts have also been made to alleviate the diffusion limitations by inducing mesoporosity in the zeolite matrix, however, these approaches use various expensive templating strategies and tedious post-synthetic modifications. [14][15][16][17][18][19] In this regard, the development of novel nanostructured materials with unique morphology that exhibit inherent mesoporosity, high external surface area and enhanced diffusivity has gained significant interest owing to their exceptional performance in catalysis. [20][21][22] However, tailoring the crystallization process to achieve the desired morphology and porosity without employing expensive mesoporogens is a major challenge.…”

“…Furthermore, the rate of crystallization process was controlled by employing low-temperature polymerization and two-step variable hydrothermal treatment, i.e., an initial low temperature to promote nucleation followed by hightemperature treatment to complete the crystallization process. 17,25,26 The resulting zeolite, i.e., n-ZSM-5, is consequently evaluated and tested for its catalytic activity in industrially important tertiary butylation reaction (Scheme S1 ‡). 27 A preliminary account of the work is presented elsewhere.…”