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Metal alloy material with different morphologies Synthesis and Catalytic Performance

Author: HuYing
Tutor: LiHui
School: Shanghai Normal University
Course: Physical and chemical
Keywords: microemulsion self-assembly hollow metal alloy maltose hydrogenation
CLC: O643.36
Type: Master's thesis
Year: 2010
Downloads: 132
Quote: 1
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Abstract

Metal catalyst is an important material which is able to improve the rate of chemical reaction and doesn’t minimize the weight of itself in the course of reaction. Catalytic reaction can be divided into two types, Homogeneous and heterogeneous catalytic reaction, the latter dominated. Metal catalyst is very important heterogeneous catalyst. Mainly used for hydrogenation, dehydrogenation, and oxidation reactions can also be used. Transition metals are effective hydrogenation and dehydrogenation catalysts, precious metals can be divided into departments (mainly palladium and platinum, ruthenium, rhodium, iridium, also frequently used) and the department of general metals (iron, cobalt, nickel, copper, zinc, etc.). Metal catalysts is very significant on the development of chemical industry and petroleum chemical industry. For example, carbonyl synthesis, ammonia synthesis, and hydrocarbon hydrogenation use different types of metal catalysts. The main performance indicators of metal catalyst is activity (catalytic activity), selectivity (catalytic specificity) and stability (life). In addition to a particularly active metal group catalyst, but also add a small amount of catalyst (for example, metals B, P, etc.) and carrier to improve the catalytic performance.Preparation is currently very popular but also has a very important role in the catalyst, because the surface atoms occupy a very large volume ratio, coupled with lack of surface atoms and high surface energy, so that these surface atoms are easily reaction with other atoms, so the catalytic activity of nano-catalysts were significantly higher than conventional catalysts, are known as fourth-generation catalyst at home and abroad. Amorphous alloy catalysts in the nano is nano in size, in structure and displays the long-range disorder and short-range order of the structures that the catalyst has excellent catalytic activity, selectivity and resistance to poisoning. But also in the preparation process of environmental pollution, high efficiency catalytic, with the current development trend of chemical production, increasing attention has been paid. However, after decades of research, amorphous alloy catalysts are still some defects, such as uneven distribution of active sites, smaller than the surface area, low dispersion problems affecting the catalytic activity.This paper uses the forefront of the current metal preparation technology, combined with new equipment, explore new catalyst preparation method, try to become easily recovered metal catalyst. All these approaches were employed to prepare metallic catalysts which had high surface area, were able to be recycled easily and convenience for mass transportation of reactants. Furthermore, the relationship between the property and the structure of the catalyst had been studied.1. Catalyst preparation(1) Multi-layer Pd-P Alloy Catalyst: A series of Pd-P alloy catalyst was prepared by the complex system of didodecyldimethylammonium bromide and palladium formed by the special theory of surfactant self-assembly formation of surfactant self-assembly. By adjusting the amount of cyclohexane, can synthesize multi-layer Pd-P alloy catalyst;(2) Preparation of Hollow Ni-based Catalysts: Through displacement reaction with potassium borohydride as reducing agent and adjusting the concentration of solution, uniform hollow Ni-based catalysts with controllable size were obtained and the replacement reaction process were investigated.2. Activity test(1) Hydrogenation performance evaluation: The liquid hydrogenation was carried out in an autoclave containing certain amount of catalyst, solvent for the ultra-pure water and reagent at 3.0 MPa of hydrogen pressure and certain temperature. The activity was measured by monitoring the drop of the hydrogen pressure. The reagent conversion and the selectivity of production were obtained from product analysis by using gas chromatograph. The results showed that ,a. The hollow Ni-Ru catalyst, prepared by chemical replacement ,was superior performance than the commonly used amorphous alloy nanoparticles. This is mainly attributed to its high surface area and specific interface structure. Meanwhile, the material is sub-micron size, making catalyst recovery and processing easy to apply the number greatly increased. Furthermore, this method is of universal significance, it can develop and apply the general approach to other alloys in the synthesis of nanomaterials.(2) Electrocatalytic Performance Evaluation: Take electrocatalytic oxidation of ethanol as a probe reaction to study the different catalytic activity. First pretreated glassy carbon electrodes, glassy carbon electrodes were continuous Al2O3 powder with different size polishing up to produce a smooth, shiny surface. Then use the Multi-layer Pd-P catalyst to modify electrodes, and tests in electrochemical workstation. The results showed that: Compared with a common method of preparation of the Pd-P catalyst, multi-layer Pd-P catalyst prepared by the special theory of surfactant self-assembly shows better catalytic activity in the electrocatalytic oxidation of ethanol.3. The catalytic performance and the structure of the catalystsBy means of XRD, BET, TEM and SEM, the morphology of the as-prepared materials was analysed and characterized in detail, and the formation mechanisms were also discussed. The surface character of these materials was also investigated by XPS and SAED. The results indicated the following points:(1) The multi-layer Pd-P alloy catalyst, through surfactant self-assembly method and chemical reduction method, and applied to electro-catalytic oxidation of ethanol showed higher catalytic activity than the conventional Pd-P catalyst, mainly due to multi-layer structure to send e provides a very conducive environment and means.(2) Through displacement reaction and adjusting the concentration of PVP solution, uniform hollow Ni-Pt spheres were obtained and the relationship between the catalyst property and the structure was also studied. The results showed that the catalytic activity of such hollow catalysts were higher than that of their dense counterparts obtained by normal method. This observation could be attributed to high surface area and special interface structure. In addition, this method has a general meaning, i.e., it can be used to make other alloys with hollow structure.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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