Preparation and identification of molybdenum complex stabilized on activated carbon and investigating its catalytic properties

Senior Thesis for Master's Degree

Abstract

Increasing environmental concerns and the progress of green chemistry processes have necessitated the replacement of homogeneous catalysts with heterogeneous ones. In this research, activated carbon was used as a suitable substrate due to its special properties. The most important of these properties are resistance in acidic and alkaline environments, cheapness, porosity and high surface area, and the possibility of recycling metals by burning the substrate. In this research, firstly, activated carbon with carboxylic acid group was replaced with chlorinated thionyl chloride, and then diethylene triamine ligand was substituted for chlorine, and then molybdenum complex was added to activated activated carbon and AC-dien-MoO2 (acac) heterogeneous catalyst was prepared. For the heterogeneous catalyst, AC-Schiff-base-MoO2(acac) after connecting the diethylenetriamine ligand to the acyl chloride activated carbon, in the next step, the amine group was converted to Baschiff by refluxing with salicylaldehyde in ethanol, and then molybdenum complex was added and the heterogeneous catalyst was prepared. These catalysts were investigated by CHN, TG/DTA, FT-IR, SEM and ICP techniques, then they were used in the epoxidation of different alkenes. Also, the catalytic process was optimized for various parameters such as the amount of catalyst, solvent, oxidant, temperature and time, and the efficiency of the reactions was checked with a gas chromatography device. High activity and recovery are among the advantages of these catalysts.

Key words: activated carbon, epoxidation, MoO2(acac)2, alkene

-1 Catalysts

Catalysts play a vital role in improving the quality of human life, especially in the economic process, and catalytic processes account for more than 90% constitute the production processes of chemicals in the world. A catalyst is a substance that increases the speed of a chemical reaction in the form that it initially forms a bond with the raw materials and turns them into a product, and at the end it is restored to its original form. In other words, it opens a new way to perform a reaction and exerts its effect on the reaction rate by reducing the activation energy. Intermediate metals of the periodic table are the most common catalysts [2 and 1].

1-1-1 Types of catalysts

Catalysts are made in different shapes and sizes (microscopic, mesoscopic and macroscopic) depending on the type of process they are used in and can be used in various environments such as liquids, gases or in The surface of solids should be used [3]. Catalysts are divided into homogeneous [1] and heterogeneous [2] categories according to the phase in which it is performed.

1-1-1-1-homogeneous catalyst

A homogeneous catalyst is a single atom, ion or molecule and forms a phase with the reactants. In other words, homogeneous catalyst particles can easily dissolve in the reaction mixture. Very high activity, selectivity and good efficiency are the merits of homogeneous catalysts. In a homogeneous catalyst, the reaction speed is proportional to the concentration of the catalyst in the system, and the temperature control and stirring of the reaction mixture is better compared to the heterogeneous system [4, 5]. The main problem in homogeneous catalyst technology is that after the completion of the reaction, it is not easy to separate the dissolved catalyst from the final mixture. This problem is a big challenge, especially when the catalyst is used in small amounts. Oxidation of an efficient catalyst species during the reaction is also one of the other problems of using homogeneous catalysts [6]. Improvement in the performance of this category of catalysts can be provided by connecting different organic and inorganic groups to the main particle. 1-1-1-2-heterogeneous catalyst The heterogeneous catalyst is not in the same phase as the reactants. The size and characteristics of heterogeneous catalyst particles are so that they are not easily dissolved in the reaction medium. Unlike homogeneous catalysts, they can be easily separated from the reaction mixture (with less cost, time, and materials) and do not cause impurity in the products [7]. In order to compensate for the lack of active surface in such compounds, it is necessary to use a substrate [3] as a support for the catalyst. The substrate is usually a porous structure [4] with a high active surface.. Among the advantages of linking metal complexes on the substrate and preparing heterogeneous catalysts compared to homogeneous systems, it is easy to separate the catalyst from the reaction mixture, reducing volatility and toxicity, especially for toxic metals, easy recovery for reuse, especially for expensive catalysts, and simple maintenance of the catalyst [8].

1-1-2 Methods of increasing the surface of the catalyst

1- Powdering (increasing the surface of the catalyst by physical means)

2- Creating pores and very fine microscopic channels in the body of the catalyst

3- Placing the catalyst on a suitable substrate

1-1-3 Catalyst substrate

Since the performance of a heterogeneous catalytic action is evaluated according to the activity, selectivity and lifetime of the catalyst [9], it is not only important to choose materials that have desirable catalytic properties, but also to make a catalyst with a suitable structure and stability. One of these important tools in controlling the structure and resistance of a catalyst is choosing a suitable substrate] 10. [

The substrate or holder is called a compound that makes the body part of the catalyst and the effective part of the catalyst is attached to it. The catalyst substrate has no catalytic activity and it affects the activity and selectivity of the catalyst based on its area and pores. It is also cheaper than active catalytic materials and has a large surface area [11]. The substrate not only acts as a holder for active catalytic compounds, but also acts as a stabilizer and distributor of active materials and prevents the active metal from clumping due to thermal shocks. Therefore, it increases the stability, physical strength and life of the catalyst. It also helps to spread heat and prevents high temperature in one spot. Among the solid substrates that have been used so far, we can mention zeolite, clay, silica, alumina, polymers and carbon [12]. Among the different types of substrates used by heterogeneous catalysts, carbon materials are of particular importance due to their properties such as resistance in acidic and alkaline environments, the possibility of porosity, high surface area, and the possibility of recycling metals by burning the substrate. Considering the cross-sectional area and high porosity of activated carbon, especially for liquid phase reactions, it is a good choice as a catalytic substrate instead of inorganic oxides [13]. 1-1-3-1 Activated carbon Carbon materials play a major role in nanoscience, electronics industry, electrochemistry, metallurgy, absorption, catalytic processes and so on. They have] 14. [

Active carbon refers to a group of materials that have a carbonaceous texture and are a non-graphite, amorphous solid with high porosity and internal area. Activated carbon pores increase the internal surface and thus increase surface absorption. Activated carbons are known as vital adsorbents in industries and have wide applications due to their ability to absorb gases and disturbing liquids, and they can be used for refining and cleaning and even recycling chemicals [15]. Due to their unique characteristics and low price, activated carbons are of particular importance compared to inorganic adsorbents such as zeolite. Activated carbons are a unique material due to their wide area, porous structure, high adsorption capacity and surface reactivation capability, thermal stability, low reactivity, flexible coordination chemistry and its ability to react with other heteroatoms [16]. Their important and important application is in removing color, unwanted tastes from water in domestic and industrial operations, solvent recycling, air purification, food and chemical industries, and they are also used as catalysts with inorganic materials. In pharmaceuticals, they are used to fight against a specific type of bacteria, and activated carbon can also be used to separate aromatic acids from the solvent inside acetic acid. Activated carbons are complex products and it is difficult to classify them based on their behavior, surface characteristics, and preparation methods, although some classifications have been made based on their physical characteristics.