How to Select Catalyst Carrier

- May 08, 2019 -

Henan Microwave Equipment Network News: catalyst carrier, also known as support, is one of the components of supported catalysts. Catalytic active components are supported on the surface of the carrier. The carrier is mainly used to support the active components, so that the catalyst has specific physical properties, while the carrier itself generally does not have catalytic activity. Most carriers are products of catalyst industry. Alumina carriers, silica gel carriers, activated carbon carriers and some natural products such as pumice and diatomite are commonly used. The composition of supported catalysts, such as nickel-alumina catalysts for hydrogenation and vanadium oxide-diatomite catalysts for oxidation, is usually indicated by the name of active component-carrier.

carrier can make the catalyst have suitable shape, size and mechanical strength to meet the operation requirements of industrial reactor; carrier can disperse active components on the surface of carrier, obtain higher specific surface area, and improve the catalytic efficiency of active components per unit mass. If platinum is loaded on activated carbon. If zeolite is used as carrier, the dispersion of platinum is close to atomic level. The carrier can also prevent the sintering of active components in the use process and improve the heat resistance of the catalyst. For some strong exothermic reactions, the carrier dilutes the active components in the catalyst to meet the requirements of heat balance. Carriers with good thermal conductivity, such as metals and silicon carbide, help to remove the reaction heat and avoid local overheating of the catalyst surface. In addition, some catalysts used in homogeneous reaction can be loaded on solid supports to prepare solid catalysts, such as phosphoric acid adsorbed in diatomite [solid acid catalyst], and enzyme immobilized on the supports. The main functions of

P>titanium dioxide photocatalyst carrier are as follows:

P>P>1) fixing titanium dioxide, preventing loss, easy recovery and improving the utilization ratio of titanium dioxide;

P>2) increasing the specific surface area of the whole titanium dioxide photocatalyst;

P>3) improving the photocatalytic activity. Because some carriers can interact with titanium dioxide, which is conducive to the separation of E-H + and increase the adsorption of reactants, and achieve the regeneration of carriers;

(4) improve the utilization of light sources. For example, the number of catalyst particles irradiated by light on the surface of the chemical agent increases when the titanium dioxide film is prepared;

(5) The catalyst is immobilized on the carrier, which is convenient for making photocatalytic reactors of various shapes. The carrier of

photocatalyst requires to improve the structure of the material (such as increasing the pore size and surface area). At the same time, because the photocatalyst is catalyzed by the combination of light and catalyst, only the photocatalyst activated by light has photocatalytic effect. Therefore, good photocatalyst carriers should have the following characteristics: good light transmittance; without affecting the catalytic activity of titanium dioxide, strong binding force with titanium dioxide particles; large specific surface area; strong adsorption for degraded pollutants; easy solid-liquid separation; conducive to solid-liquid mass transfer; chemical inertia and so on.

At present, there are many catalyst carriers studied at home and abroad: SiO 2, Al2O3, glass fiber mesh (cloth), hollow ceramic ball, sea sand, layered graphite, hollow glass beads, quartz glass tube (sheet), ordinary (conductive) glass sheet, plexiglass, optical fiber, natural clay, foam plastic, resin, wood chips, expanded perlite, activated carbon, etc. Natural minerals: (1) Natural minerals have certain adsorptive and catalytic activity, high temperature resistance, acid and alkali resistance, and are often used as carriers of catalysts. At present, diatomite, kaolin, natural pumice and expanded perlite have been used as carriers of titanium dioxide. Liu Xun et al. studied the compositions of several natural minerals (diatomite, vermiculite, kaolin, bentonite, wollastonite and sepiolite) with nano-titanium dioxide. The results showed that the photocatalytic degradation efficiency of sepiolite was the highest among the six natural minerals. After 6 hours, the photocatalytic degradation rate of methyl orange reached 98%. The second is diatomite and wollastonite, reaching 87% and 85% respectively. Moreover, the photocatalytic degradation efficiency corresponds to the adsorption capacity of natural minerals. Using expanded perlite as carrier, Chen Aiping prepared nano-sized titanium dioxide supported photocatalyst which could float on the water surface for a long time. The photocatalyst was used to photocatalytic degradation of oil slick on the water surface. The photocatalytic degradation of organophosphorus pesticides was studied by using natural pumice supported with titanium dioxide as photocatalyst and high pressure mercury lamp as light source. The results showed that the pesticide with a concentration of 1.2 *10-4 mol L-1 could be completely photocatalytically oxidized to PO4 after 2 hours of illumination.

(2) Adsorbents: These carriers are porous materials with large specific surface area and are the most widely used carriers. Activated carbon, silica gel and porous molecular sieves are the main adsorbent carriers for loading titanium dioxide. Adsorbent carriers can obtain a larger load, which can adsorb organic matter around the particles of titanium dioxide, increase the interfacial concentration, thus speeding up the reaction. Cui Peng et al. carried out photocatalytic degradation experiments on methyl orange aqueous solution using activated carbon supported on titanium dioxide film as photocatalyst. The results show that the degradation rate is higher than that of commercialized titanium dioxide photocatalyst. Because of the good adsorption performance of activated carbon in titanium dioxide/C photocatalyst, the integrated adsorption-reaction-separation behavior is produced in the photocatalytic reaction system and the photocatalytic rate is improved. V.M. GuNk and other foreign studies show that no continuous coating is formed on the surface of silica gel at different loads. The interaction forces between titanium dioxide and SiO 2 include hydrogen bond, electrostatic force and a small amount of Si-O-Ti bond. SiO 2 inhibits the phase transition of titanium dioxide from anatase to rutile. Zheng Guangtao, et al. Used the sol gel method to load the modified TiO2 photocatalyst on the spherical silica gel, and got the nano TiO2 photocatalyst with mixed crystal structure, large specific surface area and high activity. The supported catalyst has strong absorption in the ultraviolet region, and its specific surface area reaches 379.8m.g-1. Zheng Shan et al. synthesized porous molecular sieves MCM-41 with single-layer or double-layer dispersed state of titanium dioxide. The results show that Si-O-Ti bonds are formed on the surface of MCM-41 channel by chemical bonds.

(3) Glass: Glass is cheap, easy to obtain, has good transparency, and is easy to design into various shapes, which attracts the attention of researchers. The carriers used for photocatalyst of titanium dioxide are glass sheet, glass fiber mesh (cloth), hollow glass beads, glass spiral tube, glass cylinder, quartz glass tube (sheet), ordinary (conductive) glass sheet, plexiglass, etc. Zhang Xinying and other hollow glass microspheres were used as carriers, and supported composite photocatalysts were prepared by sol-gel method. The catalyst can float on the water surface and be easy to recycle and reuse. Ceramics

(4): Ceramics are also a porous material with good adhesion to titanium dioxide particles, good acid and alkali resistance and high temperature resistance, and can also be used as catalyst carrier. If titanium dioxide is loaded on ceramics used in daily life, ceramics with good self-cleaning function can be made, which can purify the environment. He Fei and so on used sol gel method to produce TiO2 grain size of 40 ~ 100nm on the surface of the self-made ceramic glaze. It combines tightly to form transparent, homogeneous and non-rainbow effect titanium dioxide photocatalytic thin film self-cleaning functional ceramics with super hydrophilicity and decontamination function.

(5) Organics: Because titanium dioxide can photocatalytically oxidize and degrade organic matter under sunlight, organic materials are generally not used as carriers. Some polymers, such as saturated carbon chain polymers or fluoropolymers, have strong antioxidant capacity, so they can also be used in the study of supported titanium dioxide. However, due to the strong oxidation of OH -, O 2 -, these polymer carriers can only be used in a short time. At present, the polymer carriers used to support titanium dioxide are: polyvinyl pyrrolidone, polyethylene, polypropylene, ABS, NAfiON film, etc. Liu Ping believes that the formation and growth of titanium dioxide particles are confined to the NAfiON micropore cage, and the material transfer required for the formation of particles can only be carried out through small channels. Under the synthetic conditions, the size of titanium dioxide crystals depends only on the diameter of the NAfiON pore cage.

In addition, the efficiency, catalytic activity, stability of catalyst load, service life and price must be considered comprehensively in the selection of carrier.

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