CN101244386A - A monolithic catalyst without coating and its preparation method - Google Patents

Abstract

The invention relates to a monolithic catalyst without coating and a preparation method thereof. The monolithic catalyst uses porous α-alumina ceramic tube or ceramic plate as the carrier, metal as the active component, the loading method is the microemulsion circulation impregnation method, and the calcination temperature is 120-500°C. The monolithic catalyst prepared by the technology of the present invention requires no coating on the selected carrier; the loading amount of the active component is controllable and has high repeatability; the catalyst does not need to be reduced before use. The invention solves the problems of complex preparation process, low controllability, short service life and the like of the current monolithic catalyst.

Description

A monolithic catalyst without coating and its preparation method

[technical field]

The invention relates to a monolithic catalyst without coating and a preparation method thereof. Specifically, it is a monolithic catalyst with metals, especially precious metals, as catalytic active components, and alumina ceramic tube or ceramic plate as carrier and its preparation method.

[Background technique]

Monolithic catalysts are integrated catalysts that are neatly arranged with many narrow parallel channels. The cross-section of the carrier used in the early developed monolithic catalysts is honeycomb, so it is also called honeycomb catalyst. The first industrial application of the monolithic catalyst was in 1966 for the reduction and decolorization of nitrogen oxides in the tail gas of the nitric acid workshop. At present, it is mainly used in gas-solid reaction fields such as automobile exhaust treatment and catalytic combustion of volatile organic compounds (VOC). Compared with the powder catalyst in the traditional slurry bed and the spherical catalyst in the fixed bed, the monolithic catalyst has the advantages of lower bed layer pressure, high catalytic efficiency, low amplification effect, and easy separation and regeneration of the catalyst. Therefore, it is widely used in the fertilizer industry, More fields such as petrochemical industry have shown great application potential.

A monolithic catalyst generally consists of a carrier, a coating and an active component. Commonly used carriers are high temperature resistant ceramics and metal components. The most commonly used ceramic is cordierite (2MgO.2Al ₂ O ₃ .5SiO ₂ ), which has a low specific surface area. Therefore, a layer of coating material with a large specific surface area is generally coated on the carrier to expand the effective catalytic surface of the honeycomb ceramic carrier. Therefore, the coating is also called "secondary carrier". Commonly used coating materials include silica, zeolite, alumina, etc. Among them, γ-Al ₂ O ₃ is the most widely used due to its unique properties and is the most important coating material. The coating methods mainly include: dip coating method (suspension), sol-gel method (sol-gel), PVD, chemical vapor deposition (CVD), etc., the most commonly used is dip coating method (US2742437, US3624196), sol - Gel method (Valerie Meille, Applied Catalysis A: General, 315 (2006): 1-17, CN1171663C). Both methods have advantages and disadvantages. The dip coating method is simple and easy to implement, but the degree of controllability is not high, and the uniformity of the coating is not high. The sol-gel method has strong controllability, but the raw materials are expensive and the preparation time is long. In addition, when cordierite-coated alumina is used as a carrier, the more prominent problem is that the thermal expansion coefficient of the coating is quite different from that of the carrier, so the bonding force is not high and it is easy to fall off; precious metals are buried in the coating, when the coating The specific surface area decreases, precious metals are trapped, and it is difficult to recover. In addition, the coating is the direct carrier of the catalyst components, and its loading capacity, thermal stability, and coating uniformity are all important factors affecting the catalytic activity of the catalyst. Therefore, many articles and patents are dedicated to improving the performance of coatings and developing new coating materials. In coating materials (Jin Lingyun et al., Acta Catalytica Sinica, 2007, 28(7): 635-640), additives and auxiliary agents for dipping liquids (US2007161507, US2007037698, CN1768934A), coating equipment and processes (DE102006027700, EP0327880, CN1954916A, US4631268, CN1652869) have made great progress.

Due to the limitation of coating technology, the coating process is complicated, the repeatability is not high, the uniformity is not high, and the activity of the catalyst cannot be fully exerted. It can be said that the coating technology has become an unfavorable factor affecting the performance of the catalyst. Therefore, the development of a monolithic catalyst with simple preparation process, especially without coating and high repeatability has great industrial application and promotion value. Some researchers have tried to find catalyst loading methods without coating. For example, in Japanese Examined Patent Publication No. 5-50338, acid treatment is performed on the cordierite carrier in an attempt to increase its specific surface area, but the crystal structure of cordierite is destroyed and its strength is reduced. Patent CN1418731A replaces some elements of cordierite, and directly connects the precursors of the catalytic component and the catalytic component with the substituting elements on the carrier, and then obtains a directly supported catalyst through reduction and roasting treatment.

In order to directly support noble metal catalyst components without coating, and at the same time have a relatively high specific surface area, so as to avoid various problems caused by the coating process, the present invention proposes a new monolithic catalyst and its preparation method. The monolithic catalyst uses the α-alumina porous support commonly used in industry as a carrier, and adopts a microemulsion cyclic impregnation method to directly support noble metal catalytic components. The carrier made of alumina, whether it is powder, spherical, or structured, is the most commonly used in the catalyst industry. The production process of alumina porous support body and alumina ceramic membrane is mature, and the pore size range is wide, which is an excellent monolithic catalyst carrier.

[Content of the invention]

The technical problem to be solved by the present invention is to provide a monolithic catalyst without coating and a preparation method thereof, so as to meet the needs of large-scale production of monolithic catalysts.

Method of the present invention comprises the steps:

Selection of carrier, synthesis of active component microemulsion, microemulsion cyclically impregnated carrier, washing, drying at low temperature, and calcination at high temperature.

In the above steps, the porous alumina ceramic carrier is made of α-alumina, with a pore size of several hundred nanometers to tens of microns, which has a higher specific surface area and higher chemical stability than lapis lazuli with a pore size of millimeters. Sex and thermal stability;

The synthesis of active component microemulsion adopts water-in-oil type microemulsion, and the microemulsion is composed of polyoxyethylene nonionic surfactant, organic solvent and aqueous solution. The microemulsion of the metal salt solution is reduced with the microemulsion of the reducing agent to obtain a microemulsion containing active metal particles.

The hydrophilic and lipophilic value of the nonionic surfactant used is 11-13, which can be obtained from a single nonionic surfactant or a compound of two kinds. Organic solvents are alkanes, including aliphatic or cycloalkanes. The aqueous solution is a soluble salt solution of the active metal.

The synthetic steps of active component microemulsion are specifically as follows:

The microemulsion containing the metal salt solution is slowly added dropwise into the microemulsion containing the reducing agent aqueous solution which is stirred at a high speed at 20-30° C. to prepare the microemulsion containing metal particles.

The microemulsion cyclic impregnation process involves the dropwise addition of solvent. The solvent is selected from low-carbon alcohols, such as methanol, ethanol, and isopropanol.

The specific steps of microemulsion circulation impregnation carrier are as follows:

Assemble the alumina ceramic carrier in the container, use a metering pump to circulate the microemulsion containing metal particles through the pores of the ceramic carrier, and slowly add low-carbon alcohol solvents dropwise during the circulation process, so that the metal particles are gradually precipitated and precipitated on the alumina. On the surface of the ceramic carrier and in the pore wall.

The monolithic catalyst loaded with active components was washed with absolute ethanol and water, respectively.

The monolithic catalyst is dried in a vacuum box at 25°C, and the drying time is 18-24 hours.

The monolithic catalyst is calcined in a muffle furnace at 300-500° C. for 2-3 hours.

In the monolithic catalyst prepared by the invention, the active component loading range is 0.065-5%, and the metal active component is directly loaded in the form of simple metal without reduction before use. The α-alumina monolithic catalyst has high thermal and chemical stability, strong binding force between the active component and the carrier, high dispersion, good repeatability, simple process, and is superior to the existing monolithic catalyst preparation methods and processes.

The catalyst carrier and microemulsion cyclic impregnation loading method involved in the present invention are not only applicable to α-alumina tubular and plate-shaped structural carriers and noble metal catalytic components, but also to a wider range of catalyst carriers with larger specific surface areas, and all available Microemulsion Synthesis of Nanoparticles of Metal Catalytic Components.

The present invention will be further described in detail below in combination with specific embodiments.

[Detailed ways]

Example 1

The alumina ceramic tube is 25 cm long, 2.9 mm in outer diameter, 1.9 mm in inner diameter, and has an average pore diameter of 3.0 μm. The microemulsion system is composed of water, fatty alcohol polyoxyethylene ether surfactant Marlipal O13/80 and cyclohexane.

Add the microemulsion of 0.2 mol/L H ₂ PdCl ₄ aqueous solution dropwise to the microemulsion of 0.6 mol/L hydrazine hydrate at a stirring rate of 1600r/min and 25°C to obtain a microemulsion of black palladium particles.

60ml of the microemulsion containing palladium microparticles was circulated through the alumina ceramic carrier, and absolute ethanol was slowly added dropwise during the circulation process. The impregnated catalyst is washed with a large amount of ethanol and water respectively, dried in vacuum at room temperature for 24 hours, and baked in a muffle furnace at 300°C for 2 hours. The obtained monolithic catalyst, the active component palladium is evenly distributed on the surface and pores of the monolithic carrier On the wall, the palladium loading was 4.50 mg.

Example 2

Adopt the preparation method among the embodiment 1. The microemulsion containing 120ml of palladium microparticles is circulated through the alumina ceramic carrier, and the rest of the conditions are the same as in Example 1. The resulting monolithic catalyst, the active component palladium is evenly distributed on the surface and pore walls of the monolithic carrier, and the palladium load is 9.11 mg. .

Example 3

Adopt the preparation method among the embodiment 1. Add dropwise the microemulsion of H ₂ PtCl ₄ aqueous solution with a concentration of 0.2 mol/L to the microemulsion of 0.6 mol/L hydrazine hydrate at a stirring rate of 1600r/min and 25°C to obtain a microemulsion of black platinum particles.

60ml microemulsion containing platinum microparticles was circulated through the alumina ceramic carrier, and absolute ethanol was slowly added dropwise during the circulation process. Washing, drying and roasting steps are the same as in Example 1. In the monolithic catalyst obtained, the active component platinum is evenly distributed on the surface and pore walls of the monolithic carrier, and the platinum loading is 4.50 mg.

Example 4

The palladium monolith catalyst prepared in Example 1 was used to catalyze the selective hydrogenation reaction of 1,5-cyclooctadiene. Add 5.5mL of 1,5-cyclooctadiene and 104.5mL of octane into the gas-liquid mixing tank, start stirring (1200r/min), and circulate through the integral catalyst with a gear pump at a flow rate of 210ml/min. Heat up to 47°C, and adjust the hydrogen pressure in the gas-liquid mixing tank to be constant at 1MPa. The reaction solution was analyzed by a 5710A gas chromatograph. The conversion rate of 1,5-cyclooctadiene, the selectivity of cyclooctene, the stability of monolithic catalysts, and the performance comparison of monolithic catalysts with cordierite coatings supporting noble metal components are shown in Table 1.

               Table 1 Comparison of Catalytic Hydrogenation Performance of Monolithic Catalysts

Palladium load, mg Average catalyst activity, μmolCOD/mgPd.s Cyclooctene selectivity at complete conversion of 1,5-cyclooctadiene, % The average catalyst activity after 5 consecutive uses, μmolCOD/mgPd.s Existing cordierite monolithic catalysts 5.00 10.46 85 10.13 The monolithic catalyst prepared by this patent 4.50 16.44 94 16.38

Claims (5)

1. integral catalyzer, it is characterized in that: carrier is that the aperture is several microns to tens microns a porous Alpha-alumina, need not coating, active component is a metal.

2. according to the described integral catalyzer of claim 1, it is characterized in that: described activity component metal is a precious metals pd, Pt.

3. the preparation method of an integral catalyzer as claimed in claim 1 is characterized in that using the microemulsion circulatory maceration, and step is as follows:

(1) microemulsion that will contain the aqueous solution of metal precursor is added in the microemulsion of the aqueous solution that contains reducing agent, makes the microemulsion that contains the nano metal particulate;

(2) microemulsion that will contain the nano metal particulate cycles through the Alpha-alumina ceramic monolith, and slowly dripping carbon number in cyclic process is the low-carbon alcohols of 1-3, makes the nano metal particulate separate out and be deposited on the surface and hole wall of carrier;

(3) good integral catalyzer be will flood and ethanol and water washing used respectively;

(4) under the vacuum room temperature dry 18-24 hour;

(5) with dried catalyst roasting 2-3 hour, take out, make the integral catalyzer of metal or metal oxide active component.

4. according to the preparation method of the described integral catalyzer of claim 3, it is characterized in that: in the described microemulsion, the surfactant of forming microemulsion is a non-ionic surface active agent, and the hydrophilic and oleophilic value is 11-13.

5. according to the preparation method of the described integral catalyzer of claim 3, it is characterized in that: the calcination atmosphere of step (5) is air or inert gas atmosphere, and sintering temperature is 300-500 ℃.