Silica Coating of Metal-Loaded H-ZSM-22 to Form the Core-Shell Nanostructures: Characterization, Textural Properties, and Catalytic Potency in the Esterification of Oleic Acid

Maryam Haghighi,Mehranoosh Fereidooni,Prem Kumar Seelam

doi:10.1155/2021/5321383

Abstract

In this study, ZSM-22 was synthesized using N,N-diethylaniline as a template through a hydrothermal method. The proton and various metals such as zirconium, strontium, and iron were immobilized on the surface of obtained zeolites through the ion exchange method. The catalysts were studied by Fourier-Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) adsorption isotherms, Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) elemental analysis, and Temperature-Programmed Desorption of ammonia (TPD-NH3) technique for determining the number of acid sites. In the esterification reaction of oleic acid, the operating conditions such as catalyst dosage, temperature, molar ratio of methanol to oil, and reaction time were optimized and adjusted at 11 wt%, 70°C, 10 : 1, and 48 h subsequently. The maximum yield% of 48.07% was achieved in the presence of Zr-H-ZSM-22 at optimum conditions. In order to improve the efficiency of three zeolites Zr-H-ZSM-22, Fe-H-ZSM-22, and Sr-H-ZSM-22, the core-shell structures with SiO2 coating were prepared. Zr-H-ZSM-22@SiO2 was less active than Zr-H-ZSM-22 due to the SiO2 coverage of Lewis active sites.

Highlights

With the growing trend of fossil fuel consumption, the supply of petrodiesel has currently become a critical issue
It should be noted that the undesirable saponification reaction between free fatty acids (FFAs) and water in basic environments is inevitable
Different metals were exchanged in the structure of zeolite by the hydrothermal method and during synthesis. us, the samples were ion exchanged by impregnation with an aqueous solution of Fe(NO3)2.4H2O, Sr(NO3)2, and ZrCl4 through a hydrothermal method during zeolite synthesis to obtain the M-H-ZSM-22, where M denotes the metal. e ion exchange method for all cases is followed by a similar procedure. 0.2 g of metal salts was solubilized in 20 mL of distilled water along with the 0.39 g of potassium hydroxide, 0.175 g of aluminum sulfate octadecahydrate, and 1 mL of N,N-diethylaniline

Summary

Introduction

With the growing trend of fossil fuel consumption, the supply of petrodiesel has currently become a critical issue. It should be noted that the undesirable saponification reaction between free fatty acids (FFAs) and water in basic environments is inevitable For this purpose, the oil source should be purified by a pretreatment process in order to minimize the FFA content or water removal [29, 30]. The oil source should be purified by a pretreatment process in order to minimize the FFA content or water removal [29, 30] Since this purification process is quite expensive, acids can be considered a potential alternative in biodiesel production in two ways: transesterification and esterification. The external acid sites of the core are surrounded by the shell and may not play a catalytic role in the esterification process. ese studies have reported that the inactive shell (silica) tends to make the external acid sites passive through the coating

Experimental

Results and Discussion

Conclusion