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  3. Synthesis of silicoaluminophosphate molecular sieves in nano dimensions and its applications (in electrochemistry)

Synthesis of silicoaluminophosphate molecular sieves in nano dimensions and its applications (in electrochemistry)

Number of pages: 66 File Format: word File Code: 31797
Year: Not Specified University Degree: Master's degree Category: Chemical - Petrochemical Engineering
Tags/Keywords: Direct methanol - Electrochemistry - fuel cell - Hydrothermal synthesis - Molecular sieve - Nano Silico Alumino Phosphate - Polymorph - Silicoaluminophosphate
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  • Summary of Synthesis of silicoaluminophosphate molecular sieves in nano dimensions and its applications (in electrochemistry)

    Dissertation

    Master's degree

    Field: Chemical Engineering

    Abstract

    In this project, an attempt was made to take a small step towards molecular sieve synthesis. Silicoaluminophosphate in nano dimensions and its use in fuel cells with methanol fuel. Therefore, in this way, nano silicoaluminophosphate was produced under optimal hydrothermal conditions. Next, XRD, FT-IR, SEM techniques were used to identify molecular sieves. The XRD spectrum results showed that the synthesis of silicoaluminophosphate molecular sieve was successful and the average particle size was estimated to be approximately 35 nm. A synthesized sample was used in direct methanol fuel cells. In the absence of methanol, the value of the electron transfer coefficient (?) was equal to 0.5547, the average charge constant (ks) was equal to 0.023 (1/s), the average electrode surface coverage was equal to 9.89 x 10-7, and in the presence of methanol, the catalytic rate was equal to 4.616.104 and the apparent diffusion coefficient was equal to 4.848.

    Key words: nanosilicoaluminophosphate, hydrothermal synthesis, molecular sieve, cyclic voltammetry, direct methanol fuel cell

    -1- An overview of silicoaluminophosphate molecular sieve[1]

    It has been nearly six decades that Historical advances have been made in molecular sieves. These advances started from aluminosilicate molecular sieves and reached amorphous silicon materials with micron pores [2], polymorphs [3] based on aluminophosphate, metallosilicate and metallophosphate composites, octahedral-tetrahedral frameworks, mesoporous molecular sieves and recently reached hybrid organometallic frameworks [1].

    Today The synthesis of nano-sized zeolite catalysts is of interest to researchers [2-4]. Silicoaluminophosphate (SAPO) is one of the zeolites that can be used as a membrane or absorbent in surface absorption processes [4] or as a template for the production of other nanostructured materials or for petrochemical materials due to its acid catalyst properties [5-7]. Silicoaluminophosphates contain a three-dimensional porous crystal network, which are located in the structural framework of SiO2, AlO2, and PO2 or PO4 in the form of units in the corners of quadrilaterals. Various compounds including phosphoric acid, organic phosphate such as triethylphosphate and aluminophosphate can be used as a source of phosphorus. In AlO2 tetragonal units, various compounds including aluminum alkoxides such as aluminum isopropoxide, aluminum phosphates, aluminum hydroxide, sodium aluminate and pseudoboehmite can be used. As a source of silicon, in SiO2 tetragonal units, various compounds including silica powders and silicon alkoxide such as tetraethyl orthosilicate can be used [8]. Zeolites, with their molecular sieve properties, are widely used in industries such as catalysts, absorbents, and ion exchangers. They are aluminosilicate crystals with a three-dimensional network that have holes in molecular dimensions. These holes are composed of rings connected together in a network of oxygen and tetrahedral atoms such as Si or Al (Figure 1-1). Si and Al in the zeolite network can be replaced by other elements [1]. These elements include iron, germanium and nickel. Each tetrahedral atom is connected to four oxygen atoms and each oxygen atom is connected to two tetrahedral atoms. By adding intermediary elements, things like surface area, BET and acidic properties change.

    For tetravalent tetrahedral atoms such as silicon and germanium, the network structure will be naturally charged, while trivalent tetrahedral atoms such as aluminum need balancing cations such as Na+ or H+. These cations are not members of the zeolite network and are replaced in the channels [9]. The presence of other elements instead of Si and Al elements in the structure of a zeolite will affect the pore size, hydrophilicity or hydrophobicity, chemical resistance to acid and other properties of zeolite [10].

    Figure 1-1 TO4 units in zeolite and aluminophosphate molecular sieve

    Zeolites are known based on their network structure with a three-letter identification code specified by the International Zeolite Association [5] (IZA). All zeolites have holes that have a specific diameter. This diameter varies from 3 angstroms (small cavity zeolites) to greater than 1 nm (large cavity zeolites) [11]. Medium pore zeolites have 10 members in the ring (0.7 to 0.8 nm) and super large zeolites have 14 members in the ring. Examples of these cases are presented in Figure 2-1 and Table 1-1.

    Some zeolites have a 3D channel system, which is spread in all directions of the crystal axes. While other zeolites have a one- or two-dimensional channel system.

    Aluminophosphate (AlPO-n) and silicoaluminophosphate (SAPO-n) molecular sieves are small crystalline materials with cavities [12]. If the tetrahedral structure includes aluminum and phosphorus with a ratio of Al/P=1, the network will be neutral. When a part of P5+ is replaced by Si4-, an anionic network will be obtained and the excess cations of the network must be in charge balance with the network. nano dimension and using it in fuel cells with methanol fuel. Therefore in this way the nano silicoaluminophosphate was produced in optimized and hydrothermal conditions.

    In the following have been used XRD, SEM and FT-IR techniques for the identification of molecular sieve. The result of XRD spectrum showed that the synthesizing of silicoaluminophosphate (SAPO) molecular sieve was successful and the average of particles' size is estimated about 35 nanometers. The synthesized sample was used in the direct methanol fuel cells. The values ??of electron-transfer coefficient, charge-transfer rate constant and electrode surface coverage for the Ni(II)/Ni(III) couple in the surface of Ni–SAPO/CPE were found to be 0.5547, 0.023 s-1 and 9.89× mol cm-2, respectively. Also, the diffusion

    Coefficient and the mean value of catalytic rate constant for Methanol and redox sites of modified electrode were obtained to be 4.848 × cm2 s?1 and 4.616 × 104 cm3 mol?1 s?1, respectively.

  • Contents & References of Synthesis of silicoaluminophosphate molecular sieves in nano dimensions and its applications (in electrochemistry)

    List:

     

    Chapter 1 - Introduction and general research

    Overview of silicoaluminophosphate molecular sieve. 2

    1-1-1.

    Synthesis of molecular sieves. 6

    Modification of silicoaluminophosphate molecular sieves. 9

    Identification of silicoaluminophosphate molecular sieves. 11

    Electron microscope method. 11

    X-ray diffraction (XRD) method. 12

    FTIR method 12

    Introductions to fuel cells. 12

    Modified electrodes and electrocatalyst process 15

    Types of catalysts used in anodic methanol electrooxidation. 18

    Methanol electrocatalysts in acidic environment. 18

    1-7-2. Methanol electrocatalysts in alkaline environment 18

    Electrochemical measurement. 19

    The purpose of the research. 19

    Chapter Two - Literature and Research Background

    The history of fuel cell. 21

    A review of electrocatalytic research. 22

    History of molecular sieve materials. 23

    Aluminosilicate zeolites and silica molecular sieves. 23

    Chapter Three - Research Methodology

    Raw materials and laboratory equipment. 30

    Raw materials 30

    Laboratory equipment. 32

    Potentiostat/Galvanostat device. 32

    Synthesis and construction. 33

    Synthesis of nano silicoaluminophosphate. 33

    Electrocatalyst construction. 34

    Evaluation method of electrocatalytic performance. 35

    Comparison of the corresponding electrode with carbon paste electrode. 36

    Chapter Four - Calculations and research findings

     

    Determining the properties of synthetic catalysts. 39

    XRD analysis 39

    FESEM analysis 40

    FTIR analysis 42

    Evaluation of electrocatalyst performance. 44

    Electrochemical analysis of modified electrodes. 47

    Oxidation of methanol electrolyte on the modified electrode surface. 54

    Evaluation of chronoamperometry. 58

    Evaluation of performance and stability of Ni-SAPO/CPE electrode. 63

    Chapter Five - Conclusions and Suggestions

    Nano silicoaluminophosphate crystal molecular sieve. 66

    Synthesized nanosilicoaluminophosphate modified electrode 66

    Suggestions. 67

    Appendix - sources and sources. 68

    English abstract. 72

     

    Source:

     

     

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Synthesis of silicoaluminophosphate molecular sieves in nano dimensions and its applications (in electrochemistry)
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