CN1242844C - Highly specific surface area possessed cerium-zirconium solid solution and its preparing method - Google Patents

Abstract

The present invention relates to a cerium zirconium solid solution with a high specific surface area, which is characterized in that the chemical molecular formula of a cerium zirconium solid solution is Ce<x>Zr<1-x>O<2>, and the molar ratio of cerium and zirconium meets the following requirements of Ce=x, Zr=1-x and x=0.1-1.0. The preparation technology of the cerium zirconium solid solution with a high specific surface area comprises: cerous nitrate (Ce (No3) 3 6H2O) and zirconium nitrate (Zr (NO3) 4 5H2O) are used as raw materials, and a proper amount of distilled water is added in the raw materials; the distilled water is heated for dissolving the cerous nitrate and the zirconium nitrate, and then, a cationic surface active agent of certain proportion is added; an obtained solution is dropped in ammonia water under stirring, and the pH value of obtained deposition liquid is regulated by sodium hydroxide; precipitates are aged, washed, dried and calcined to obtain the cerium zirconium solid solution with a high specific surface area. The present invention has the advantages of simple technological process, homogeneous component and large specific surface area.

Description

Cerium-zirconium solid solution with high specific surface area and preparation method thereof

Technical field

The invention relates to a cerium-zirconium solid solution and a preparation method thereof, in particular to a formula of a high specific surface area cerium-zirconium solid solution and a preparation method thereof.

Background technique

The study of CeO ₂ and its related materials has received great attention. The relevant studies have shown that adding ZrO ₂ to CeO ₂ to form a solid solution can greatly improve its oxygen storage and release performance and high temperature resistance. CeO ₂ is an excellent additive for oxidation-type catalysts with ^a fluorite structure. It has a high ability to store oxygen and release ^oxygen . Acts as a chemical regulator. When _ZrO2 is added, part of Ce in the original lattice is replaced by Zr, and the ion radius of Zr (0.84 Å) is smaller than that of Ce ion (0.97 Å), and the crystal structure of _CeO2 is distorted due to lattice contraction. Face-centered cubic defects are generated, which greatly increases the mobility of oxygen anions in the fluorite lattice, greatly improves the ability to store and release oxygen, and improves the catalytic activity. Single CeO ₂ will sinter itself and reduce the catalytic effect when it experiences high temperature (>1023K), so it is not suitable for use under high temperature conditions. The incorporation of Zr can stabilize the cubic fluorite structure, as a catalyst coating carrier, improve the high temperature stability of the catalyst, and improve the anti-sintering ability of the additive. In addition, different Ce/Zr molar ratios can make _Cex Zr _1-x O ₂ solid solutions have different structures, and different templates can be used for _Cex Zr _1-x O ₂ solid solutions to obtain different high specific surface areas. Although there are some reports, there is no similar research. Such as: references Catalysis Today, 43 (1998) 79-88 is to use CeCl ₃ 7H ₂ O and ZrOCl ₂ 8H ₂ O plus surfactant, the CeZr80 with high specific surface area is roasted at 723K, and the specific surface area is 230m ² /g; after roasting at 1173K, the specific surface area is 40m ² /g.

The significance of preparing _Cex Zr _1-x O ₂ solid solution with high specific surface area is to increase the specific surface area and thermal stability of the _Cex Zr _1-x O ₂ carrier, which is beneficial to the active components in _Cex Zr _1-x O ₂ The loading and dispersion on the carrier is of great significance in the actual green catalytic reaction.

Contents of Invention

The purpose of the present invention is to provide a high specific surface area cerium-zirconium solid solution and a preparation method thereof.

In the high specific surface area cerium-zirconium solid solution provided by the present invention, the cerium-zirconium ratio of the components is Ce=x (x=0.1-1.0), Zr=1-x (molar ratio), wherein C _x Zr _1-x O ₂ ( Molar ratio x=0.5) has the best catalytic performance, and at this ratio, zirconium can maximize the increase of defect space and the mobility of oxygen. for maximum activity of the catalyst.

The high specific surface area cerium-zirconium solid solution provided by the present invention and its preparation method: the precursors of cerium nitrate (Ce(NO ₃ ) ₃ 6H ₂ O) and zirconium nitrate (Zr(NO ₃ ) ₄ 5H ₂ O) are used as raw materials , press, Ce=x (x=0.1～1.0), Zr=1-x, molar ratio preparation cerium, zirconium mixed aqueous solution, add a certain proportion of cationic surfactant, after adding water to dissolve, mix with above-mentioned cerium, zirconium aqueous solution, in Add the mixed solution dropwise to ammonia water at a rate of 60 drops/minute under stirring, and it is very important to control the rate of addition of 60 drops/minute, which can make the precipitation complete (pH ≥ 9.5), and then use sodium hydroxide to adjust the precipitation. pH value = 11.5, in order to increase the degree of combination of Ce+Zr and surfactant; transfer the precipitate to an oil bath at 70-80°C for aging for 132-144h, after the aged product is suction-filtered, heat it with 60-70°C Wash with distilled water, then wash with cold distilled water, then soak with acetone for several times, remove the solution, put it in an oven at 100-120°C for 36 hours, and transfer it to a muffle furnace for 2 hours at 600-650°C.

The present invention controls the dropping speed of the raw material solution by adding cationic surfactants, utilizes the hydrate reaction of cationic surfactants and mixed oxides under alkaline conditions, makes the surfactants form an electric double layer on the surface of the particles, and reduces the The surface energy inhibits the clustering of particles, the surfactant solution and the cerium-zirconium solution are uniformly mixed, and vigorously stirred during the precipitation process, so that the Ce-Zr-O solid solution particles are separated from each other, the grain growth is inhibited, and the particles are hindered during calcination. Between sintering. In addition, the addition of surfactants can reduce the tension of water, and can mix with the liquid in the pores of porous materials, reducing the energy of the interface and the surface tension of water. It reduces the shrinkage and collapse of the mesh during drying and firing, helping to maintain a large specific surface area.

The cerium-zirconium solid solution prepared by the invention has uniform crystal phase and large specific surface area. Through the nitrogen adsorption-desorption experiment, it was found that the adsorption-desorption isotherm belongs to the type IV isotherm in the BDDT classification, which is the adsorption type of mesoporous porous substances; the XRD measurement results show that the 2θ is 29.1°, 34° and The characteristic peak of cerium-zirconium solid solution appears at 485°; SEM measurement also shows that the high specific surface area cerium-zirconium solid solution prepared by co-precipitation-constant temperature aging method has uniform particles, and the particles are not easy to agglomerate under the high temperature condition of 1073K. In addition, the high specific surface area cerium-zirconium solid solution prepared by the present invention is calcined at 973K and 1073K, and its specific surface area is 280.5m ² /g and 232.6m ² /g; after calcination at 1173K, there is still 58.7m ² /g.

Detailed ways

Example 1:

The preparation of high specific surface area cerium-zirconium solid solution comprises the following steps:

(1) Cerium-zirconium solid solution with high specific surface area, the chemical formula of which is _{CexZr1 -xO2 (} where x=0.1-1.0). Calculate the corresponding cerium nitrate (Ce(NO ₃ ) ₃ ·6H ₂ O) and zirconium nitrate (Zr(NO 3 ) ₃ ) ₄ ·5H ₂ O), add water to dissolve.

(2) Weigh a certain amount of cerium nitrate (Ce(NO ₃ ) ₃ 6H ₂ O) and zirconium nitrate (Zr(NO ₃ ) ₄ 5H ₂ O), add appropriate amount of distilled water, heat to dissolve, and then add cationic surface The active agent C ₁₆ alkyltrimethylammonium bromide is used in an amount of 70-80% of the weight of the cerium-zirconium precursor. After being dissolved in water, it is mixed with the aqueous solution of cerium and zirconium, and the mixed liquid is yellow. Add 125ml of ammonia water (25%) and 125ml of distilled water into a 600ml beaker and mix well. Slowly add the mixed solution into ammonia water at a rate of 60 drops/min at a certain speed under stirring, control the rate of 60 drops/min to make the precipitation complete (pH ≥ 9.5), adjust the concentration of the precipitated solution with sodium hydroxide pH value = 115, in order to increase the combination degree of Ce+Zr and surfactant, and obtain a slightly purple precipitate.

(3) Then transfer the precipitate to an oil bath at 70-80°C for aging for 5.5-6 days (132-144h). Wash with distilled water, then soak several times with acetone, remove the solution, put it in an oven at 100-120°C for 36 hours, and transfer it to a muffle furnace for calcination at 600-650°C for 2 hours to obtain a high specific surface area cerium-zirconium solid solution.

Example 2:

(1) Cerium-zirconium solid solution with high specific surface area, the chemical formula of which is _{CexZr1 -xO2 (} where x=0.1-1.0). According to the ratio of Ce:Zr, 9.6867g of cerium nitrate (Ce(NO ₃ ) ₃ 6H ₂ O) and 9.7626g of zirconium nitrate (Zr(NO ₃ ) ₄ . 5H ₂ O), 13.6446-15.5938g surfactant (C ₁₆ alkyltrimethylammonium bromide), add appropriate amount of water to dissolve.

(2) Add 125ml of ammonia water (25%) and 125ml of distilled water into a 600ml beaker, and mix well (pH=9.5). Under fast stirring, the raw material solution that mixes is slowly added dropwise to ammoniacal liquor with the speed of 60 drops/min, controls the rate of addition to make its precipitation complete (pH ≥ 9.5), adjusts the pH value=11.5 of precipitation liquid with sodium hydroxide, A slightly purple precipitate was obtained.

(3) Then transfer the precipitate to an oil bath at 70-80°C for aging for 5.5-6 days (132-144h). Wash with distilled water, then soak several times with acetone, remove the solution, put it in an oven at 100-120°C for 36 hours, and transfer it to a muffle furnace for calcination at 600-650°C for 2 hours to obtain a high specific surface area cerium-zirconium solid solution.

Claims (3)

1. A method for preparing a cerium-zirconium solid solution with a high specific surface area. The chemical molecular formula of the cerium-zirconium solid solution is _Cex Zr _1-x O ₂ , and the molar ratio of the components cerium and zirconium is Ce=x, Zr=1-x , x=0.1～<1.0, characterized in that the preparation method is as follows: the precursors of cerium nitrate Ce(NO ₃ ) ₃ ·6H ₂ O and zirconium nitrate Zr(NO ₃ ) ₄ ·5H ₂ O are used as raw materials, according to Prepare the mixed aqueous solution of cerium and zirconium in the above molar ratio of cerium and zirconium, add a certain proportion of cationic surfactant, add water to dissolve, mix with the above aqueous solution of cerium and zirconium, and add the mixed solution dropwise to ammonia water at a rate of 60 drops/min under stirring , make the precipitation complete, and then use sodium hydroxide to adjust the pH value of the precipitation solution to 11.5, transfer the precipitate to an oil bath at 70-80°C for aging for 132-144 hours, and after suction filtration, first use 60-70°C Wash with hot distilled water, then wash with cold distilled water, then soak with acetone to remove the solution, dry in an oven at 100-120°C for 36 hours, transfer to a muffle furnace for roasting at 600-650°C for 2 hours. 2. The method for preparing a high specific surface area cerium-zirconium solid solution according to claim 1, characterized in that the cationic surfactant is cetyltrimethylammonium bromide, and the dosage is 70% of the weight of the cerium-zirconium precursor. ~80%. 3. The method for preparing a high specific surface area cerium-zirconium solid solution according to claim 1, characterized in that the precipitate is aged in an oil bath at 70-80°C for 132 hours.