Synthesis and characterization of modified zeolite nanosheets using spectroscopic and chemometric methods

Dissertation for receiving a master's degree in analytical chemistry

Abstract:

Today, modern catalysts are used in the petrochemical industry for various reactions. Zeolites in the more advanced form of "nano zeolite" are very important in this regard due to their high surface area. The purpose of this research is to provide a "spectroscopy-chemimetry" method and provide an optimal method for the preparation of zeolite nanosheets. One of the important components for the synthesis of zeolite nanosheets ZSM-5 [1] with plate morphology is cationic surfactant. For this purpose, symmetrical and asymmetrical surfactants based on DABCO2 were first synthesized and characterized. In the continuation of the work, ZSM-5 nanosheet zeolite synthesized surfactants were synthesized by hydrothermal method with layer thickness between 5.5-10.34 nanometers and the samples were characterized by scanning electron microscope, X-ray diffraction, transmission electron microscope and surface area analysis. To modify the reaction conditions, the partial factorial design method of experiment design was used. According to this method, the lowest layer thickness for zeolite nanosheet is obtained when Template/SiO2 factors should be at the highest level, SiO2/Al2O3 at the lowest level, H2O/SiO2 at the highest level. Finally, the synthesized nanosheet was modified with phosphorus in order to increase its catalytic properties, then reflection-diffusion spectroscopy was used to characterize the zeolite nanosheet, and the spectral data were processed by MCR_ALS. The results show that the use of DBCO-based cationic surfactant in hydrothermal conditions is a successful method for the synthesis of ZSM-5 nanosheet, and the combination of two techniques, infrared spectroscopy and chemimetry, works well. can be used to identify zeolites.

Key words: cationic surfactant, ZSM-5 zeolite nanosheet, chemimetry, infrared spectroscopy, CNMR 13 spectroscopy

Introduction

The familiarity with zeolites as a catalyst in petrochemical reactions, its use in agriculture (as a moisture absorbing material in agriculture, increasing fertility cation exchanges, odor control, animal feed additives, etc.), water and wastewater treatment (removal of heavy metals, swimming pools, removal of ammonia in sludge) goes back centuries. be made The formation of natural zeolites from amorphous volcanic materials and salt water as a reactant takes place at pH values ??between 9 and 10, but it requires long crystallization times of about 50,000 years. Regarding the use of zeolites, zeolite of natural origin is not the answer to the amount of consumption, so in the early 1940s, in order to copy these natural conditions, processes at higher pH and temperatures and finally with shorter reaction times were proposed. The primary variables in this method are the synthesis temperature, pH, reactivity of the silica source, the ratio of silica to alumina in the synthetic mixture and the open nature, in each case a silica-alumina hydrogel is prepared at pH values ??higher than 12. Such a system is always oversaturated with respect to the concentration of its chemical constituents. In hydrothermal conditions (K 473-373), this supersaturation is removed due to the nucleation of semi-stable zeolite phases. After the nucleation of such a phase, the nuclei grow more to form larger crystals, these crystals successively nucleate in the solution source and finally other zeolite phases nucleate from it. As a logical consequence, synthesis time is also a primitive variable. Later, the gel method was slightly modified to add regular silica, alumina, alkali and organic tetravalent cation. This tetravalent organic cation, usually based on aluminum, has a dual role:

They act as a strong base and add more OH- ions to the system. Therefore, it increases the pH, solubility of silica and the degree of supersaturation of the system.

It can clathrate water and possibly silica[1].

Adding these organic ions to the gel used in zeolite synthesis also has two effects:

Always zeolite structures with The content of silicon is increased, or it is obtained with a lower degree of substitution of aluminum instead of silicon.

-Sometimes entirely new sugars are obtained, possibly as a direct result of the arching effect [2] of organic bases.

These organic cations are the most important parameter for the synthesis of zeolites with different morphologies. In 2009, for the first time, these organic cations were used as an arch donor in the synthesis of zeolite nanosheets. The organic cation used in the mentioned research was a diquaternary ammonium with the following structure. rtl;">The use of this cationic surfactant resulted in obtaining a zeolite nanosheet for the first time with a layer thickness of 5.8 nm and a surface area of ??about 558 m2 g-1, which was used as a catalyst in petrochemical reactions due to having active acid sites on its surface.

Our goal in this research is to present a method for the synthesis of zeolite nanosheets based on a A new surfactant and an optimized method have been presented. Also, a new solution is proposed for the characterization of the zeolite nanosheet synthesis process based on this cationic surfactant by spectroscopic and chemometric methods. Material characterization and analysis is one of the main stages of product production or science production. Most of the researches, both in the laboratory and research scale and in the semi-industrial and industrial scales, require the use of analytical tools in order to guide them correctly and reach the desired goal. In fact, material recognition analysis helps us to pave the way to achieve scientific and industrial productions. Among the material characterization methods, we can mention microscopic methods (SEM, TEM, STEM, AFM,...), phase analysis methods (DRX), surface area analysis (BET) and spectroscopic methods (NMR, FTIR, Raman). is Today, obtaining information on chemical systems is much easier than in the past, which is related to the use of computers in chemistry. Using computer, mathematics and statistics, a series of chemical rules called Chemometrics [3] is formed, which helps us in the fields of evaluating and interpreting information, optimizing and modeling processes and experiments, and extracting maximum chemical information from experimental data. Synthesis of scanning electron microscope [4], X-ray diffraction 3, transmission electron microscope 4 and surface area analysis 5 have been used. Then the resulting spectral data has been processed by some chemometric methods

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