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The Research On Low-temperature CO Catalytic Oxidation Properties Of Cu-Ce-O_x Series Catalysts

Posted on:2017-03-05Degree:MasterType:Thesis
Country:ChinaCandidate:L S XuFull Text:PDF
GTID:2271330488464885Subject:Environmental engineering
Abstract/Summary:PDF Full Text Request
CO catalytic oxidation has wide application and basic theoretical research value in environmental protection, energy, chemical, material, military industry. The materials used for CO catalytic oxidation include transition metal oxides, transition metal nitrides, precious metals and organic skeleton (MOFs). The natural reserves of precious metals are rare, so the precious metals are expensive, and the high activity precious metals are generally poor stability and tend to be CO poisoning. Organic skeleton (MOF) structure is not stable, and the manufacturing cost is too high, so it can not be used for catalytic materials widely and practically. Cu-based catalysts are an arealternative to precious metals used as CO catalytic oxidation at low temperature for their good low temperature activity, inaddition copper has abundant natural reserves and cheap. CeO2 is a new kind of interpretation of the oxygen storage material, and has been widely studied as a carrier and active component in various kinds of catalysts. The price of Cu-Ce-Ox catalysts are low, and can catalytic oxidation CO fully at around 100℃ or even lower temperature, and resist water vapor poisoning, have long service life and good stability. Hence Cu-Ce-Ox catalysts have been widely studied and applied to the low temperature catalytic oxidation of CO.At present, changing the pore structure of catalysts, and the size of the nanoparticles, dispersion of active components and other measures to improve the low temperature catalytic activity of Cu-Ce-Ox catalysts are the key points and difficulties. This article explores the template agent added, different content of Cu, selection of precipitant and transition metal doped on the influence of the composition and structure of Cu-Ce-Ox catalysts, and studies the low-temperature CO catalytic oxidation activity and stability of the catalysts. The concrete research contents are as follows:(1) Cu-Ce-Ox catalysts with different content of Cu (Cu content from 10% to 70%) were prepared by hydrothermal method and P123 as template agent. The effects of the Cu content and preparation methods of Cu-Ce-Ox catalysts on the performance of low temperature CO catalytic oxidation were studied, and characterization methods such as X-ray diffraction (XRD), N2 adsorption-desorption, transmission electron microscopy (TEM), H2 temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the chemical and physical properties of the catalysts. The results showed that the best Cu/Ce mole ratio= 1:1. When Cu content was 50% and air speed was 40000 h-1, the catalyst had the best CO catalytic oxidation activity at 100℃, which can remove more than 90% CO. The Cu content was both too high or too low, were all detrimental to catalytic reaction. When it was too low, the quantities of CuO active species were too little; when it was too high, CuO gathered to form larger particles and doesn’t work to the catalytic reaction. The catalyst prepared by hydrothermal method added P123 showed better CO catalytic oxidation activity than that prepared by coprecipitation with no P123. XRD analysis showed that when the Cu content was low, the catalysts did not contain detectable diffraction peak of CuO species. With the increase of Cu content, the crystalline phase of CuO began to appear. The crystallinity of Cu-Ce-Ox catalysts prepared by hydrothermal method added P123 was higher than that prepared by coprecipitation preparation with no P123. N2 absorption-desorption test results showed, the specific surface area of Cu-Ce-Ox catalysts prepared by hydrothermal method added P123 were greater than that prepared by coprecipitation preparation with no P123. TEM study showed, template agent was introduced in the process of catalysts preparation can form a high degree of crystallinity, morphology, relatively flat Cu-Ce-Ox catalyst particles. H2-TPR results showed, hydrothermal method added P123 was helpful to reduce the reduction temperature of the catalysts, strengthen the strong interaction between CuO and CeO2, this was the reason for its excellent CO catalytic oxidation activity.(2) Cu-Ce-Ox catalysts with Cu content was 20% were prepared by coprecipitation method and different precipitants were used. Also Cu-Ce-Cr-Ox catalysts with different Cr molar content were prepared by coprecipitation method with ammonia as precipitant. The affect of precipitants and Cr mole content on the performance of CO catalytic oxidation of the catalysts were studied. The experimental results showed that among the Cu-Ce-Ox catalysts with different precipitants, when ammonia was precipitant, the catalytic activity was best. Among Cu-Ce-Cr-Ox catalysts doped with different Cr molar content, when Cr molar content was 10%, the activity of the catalyst was best. Compared with the catalysts prepared with the same method and precipitating agent, the catalytic activity of the catalyst contained no Cr at 100℃ was slightly below the catalyst with 10% Cr doping amount, but was higher than other Cu-Ce-Cr-Ox series catalysts. This showed that the addition of suitable amount of Cr can play a role in promoting CO catalytic reaction. No matter the quantity of addition Cr was too high or too low, it would cause a decline in catalytic oxidation performance of the catalysts. XRD results showed that ammonia used as the precipitator was more advantageous to the dispersion of surface active components of the catalysts, the dispersion of active components of the catalyst with 10% Cr doping amount was higher than other catalysts with doping Cr. By XPS analysis, we found that almost all Ce in the catalyst with 10% Cr doping amount was Ce4+, the Ce3+ content of the catalyst prepared by coprecipitation method and ammonia as precipitation agent was highest. The catalyst with 10% Cr doping amount had the most quantity of CuO species, and the catalyst prepared by coprecipitation method and ammonia as precipitation agent was second. Combined with activity test results, it could be concluded that CuO species were contributed to the CO catalytic oxidation, therefore the catalyst with 10% Cr doping amount had better CO catalytic oxidation activity.
Keywords/Search Tags:hydrothermal method, coprecipitation method, Cu-Ce-O_x catalyst, CO catalytic oxidation
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