ORIGINAL PAPER Synthesis of Cost-Effective Hierarchical MFI-Type Mesoporous Zeolite: Introducing Diatomite as Silica Source Morteza Servatan 1 & Mohammad Ghadiri 1 & Mohsen Khodadadi Yazdi 2 & Maryam Jouyandeh 2 & Ghader Mahmodi 3 & Ali Samadi 4 & Payam Zarrintaj 3 & Sajjad Habibzadeh 5,6 & Mohammad Reza Ganjali 2,7 & Mohammad Reza Saeb 2 Received: 25 January 2020 /Revised: 13 October 2020 /Accepted: 14 October 2020 # Springer Nature B.V. 2020 Abstract Zeolite, as an intricate microporous material with redox sites, has been widely examined in many chemical industries. However, zeolite is not available everywhere, and it is expensive considering the price of raw materials from which it can be synthesized. In this study, ZSM-5 zeolite, as a local silica source with the high crystallinity, was synthesized, based on diatomite exploited from a mine in the north-west of Iran. The diatomite was employed as the only source of silica, and underwent hydrothermal transforma- tion in a Teflon-lined autoclave operating at 170 °C without any alkaline post-treatment. The effects of the reaction pH and the reaction time on the properties of the synthesized MFI-type zeolite were monitored. The hydrothermal reaction time was optimized and hierarchical ZSM-5 hexagonal crystals were obtained. Furthermore, the effect of Si/Al ratio on the crystallinity of the resulting zeolite was investigated. The XRD, SEM, TEM, BET, FTIR, TPD, TGA, and DSC analyses were carried out to characterize the synthesized zeolites. The results confirmed the creation of MFI-type zeolites from diatomite applying hydrothermal process at an optimized pH and reaction time. In addition, the synthesized ZSM-5 zeolites exhibited a narrow pore size distribution resembling the mesoporous structure of standard ZSM-5 zeolites. Plenty of regularly arranged pores with diameters of 300–500 nm were observed inside the round circle-like sections of diatomite. For zeolites in which Si/Al ratio was higher (55 compared to 37), a relatively narrower pore size distribution similar to that of the standard ZSM-5 zeolite was detected. Comparably, the synthesized zeolites also contained stronger acid sites, rendering it as an excellent catalyst for the conversion of methanol to gasoline. Keywords ZSM-5 zeolite . Diatomite . Hydrothermal process . Mesoporous structure 1 Introduction Porous-silica-based materials are widely employed in various applications including controlled drug delivery, catalysis, thermal insulators, and bio molecular separation [1–3]. In par- ticular, functionalized mesoporous silica-based products, e.g., zeolites, which encompass organic and inorganic groups to- gether within their mesoporous structures, are promising can- didates for newly-emerged heterogeneous catalysts, adsor- bents, and ion-exchangers [4, 5]. However, relatively small pore size of microporous zeolites may mitigate the diffusion rate of reactants and products into and from the active sites inside the zeolite crystals. Such phenomenon limits the indus- trial application of zeolites [6–10]. Hierarchical zeolites are commonly prepared through a post- treatment or secondary template synthesis method [11, 12]. Notwithstanding, a large number of secondary templates includ- ing carbons [13–15], amines [16, 17], cationic polymers [18, 19], polyvinyl butyral gels [20, 21], amphiphilic organosilanes * Mohammad Ghadiri m.ghadiri@uut.ac.ir * Payam Zarrintaj payam.zarrintaj@gmail.com 1 Department of Chemical Engineering, Urmia University of Technology, P.O. Box 57155-419, Urmia, Iran 2 Center of Excellence in Electrochemistry, School of Chemistry, College of Science, University of Tehran, Tehran, Iran 3 School of Chemical Engineering, Oklahoma State University, 420 Engineering North, Stillwater, OK 74078, USA 4 Department of Polymer Engineering, Faculty of Engineering, Urmia University, Urmia, Iran 5 Department of Petrochemical Engineering, Amirkabir University of Technology, Tehran, Iran 6 Department of Chemical Engineering, Amirkabir University of Technology, Tehran, Iran 7 Biosensor Research Center, Endocrinology and Metabolism Molecular-Cellular Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran Silicon https://doi.org/10.1007/s12633-020-00786-7