IP: 5.8.37.23 On: Tue, 10 Apr 2018 11:00:34 Copyright: American Scientific Publishers Delivered by Ingenta Copyright © 2018 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 18, 5404–5413, 2018 www.aspbs.com/jnn Nanocrystalline Hierarchical ZSM-5: An Efficient Catalyst for the Alkylation of Phenol with Cyclohexene N. P. Radhika 1 , Rosilda Selvin 2 ∗ , Rita Kakkar 1 , and L. Selva Roselin 3 1 Department of Chemistry, University of Delhi, Delhi 110007, India 2 Department of Basic Sciences and Humanities, Don Bosco Institute of Technology, Kurla (W), Mumbai 400070, India 3 Department of Chemistry, Faculty of Sciences and Arts, King Abdulaziz University, Rabigh 21911, Saudi Arabia In this paper, authors report the synthesis of nanocrystalline hierarchical zeolite ZSM-5 and its application as a heterogeneous catalyst in the alkylation of phenol with cyclohexene. The catalyst was synthesized by vacuum-concentration coupled hydrothermal technique in the presence of two templates. This synthetic route could successfully introduce pores of higher hierarchy in the zeolite ZSM-5 structure. Hierarchical ZSM-5 could catalyse effectively the industrially important reaction of cyclohexene with phenol. We ascribe the high efficiency of the catalyst to its conducive structural features such as nanoscale size, high surface area, presence of hierarchy of pores and existence of Lewis sites along with Brønsted acid sites. The effect of various reaction parameters like duration, catalyst amount, reactant mole ratio and temperature were assessed. Under optimum reaction conditions, the catalyst showed up to 65% selectivity towards the major product, cyclohexyl phenyl ether. There was no discernible decline in percent conversion or selectivity even when the catalyst was re-used for up to four runs. Kinetic studies were done through regression analysis and a mechanistic route based on LHHW model was suggested. Keywords: Hierarchical ZSM-5, Alkylation of Phenol, Cyclohexene, Nanozeolite. 1. INTRODUCTION It is beyond doubt that commodities like herbicides, pes- ticides, perfumes, dyes, plastics, soaps and detergents have become an indispensable part of human civilisation. The raw materials for the manufacture of these products are mostly obtained from cyclohexylphenols. 1–4 Thus, the reaction of cyclohexene with phenol is of considerable industrial and academic importance. The reaction of phenol and cyclohexene can lead to many possible products, depending on the site of alkylation and its extent. The O-alkylated prod- uct, cyclohexyl phenyl ether is widely used in the perfume industry. C-alkylation can result in the for- mation of 4-cyclohexylphenol, 2-cyclohexylphenol, 2,4- dicyclohexylphenol or 2,6-dicyclohexylphenol. These are stock materials of many valuable chemicals in agriculture, surfactant, dyestuff and polymer industries. As per the principles of Green Chemistry, intense research is ongoing globally to fabricate heterogeneous ∗ Author to whom correspondence should be addressed. systems that can replace homogeneous catalysts in the alkylation of phenol with cyclohexene. Catalysts investi- gated for this purpose belong to diverse kinds of materials like mesoporous silica, resins, silica-supported BF 3 , sup- ported heteropolyacids, zirconia and zeolites. 5–12 Bulk zeolites offer high diffusional resistance to reagents and products. Consequently, these materials fail to catalyse reactions involving bulky reactants. For such reactions, replacement of bulk zeolites with hierarchical forms as catalysts can prove to be beneficial. Hierarchical zeolites bring together the benefits of pores of diverse size regimes and hold great promise as heterogeneous catalysts. The hierarchical zeolite in the nanocrystalline form further causes an augmentation of the catalytic activity. Given this, we have developed a novel strategy that combines vacuum- concentration coupled hydrothermal synthesis with a dual templating approach to synthesise nanocrystalline hierar- chical ZSM-5. We adopted vacuum-concentration coupled method, as it has been reported to reduce crystallisation time. 13 The cationic polymer, polydiallyldimethylammo- nium chloride (PDDA) was chosen as the soft template to introduce the larger pores. 5404 J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 8 1533-4880/2018/18/5404/010 doi:10.1166/jnn.2018.15390