CN1102429C - Preparation method of superfine zirconium dioxide with high specific surface area - Google Patents

Abstract

The invention relates to a preparation method of superfine zirconium dioxide with high specific surface area, which comprises the following steps: preparation of Zr (OH)₄/ZrO(OH)₂And (3) gelling, cooking and aging, and performing suction filtration, washing, drying, roasting and the like to obtain the sample. The superfine ZrO with high specific surface area can be prepared by controlling the cooking temperature, time, system pH value, the property of used alkali, the temperature, time, atmosphere and other conditions during drying and roasting₂. ZrO produced by the present invention₂Not only has small crystal grains and large specific surface area; but also shows better catalytic performance and carrier effect in a plurality of catalytic reactions.

Description

A kind of preparation method of ultrafine high specific surface area zirconia

Background technique

The invention relates to a method for preparing ultrafine zirconium dioxide with high specific surface area, belonging to the technical field of chemical catalyst preparation.

technical field

ZrO ₂ is widely used in the field of catalytic technology due to its acidic, basic, oxidizing and reducing properties (Materials Chem.Phys., 1985, 133:47; Catal.Today, 1994, 20:185). As a catalyst alone, _ZrO2 exhibits excellent catalytic performance in reaction systems such as hydrogenation of aromatic carboxylic acids to aldehydes, isomerization of olefins, hydrogenation of dienes, dehydration of alcohols, and preparation of isomeric hydrocarbons from synthesis gas. The reaction has been applied industrially. ZrO ₂ can also be used as a catalyst support and has shown a good support effect in many catalyst systems (Catal. Today, 1994, 20: 199). For example: JP 4,613,700 reports that using ZrO ₂ as a catalyst to prepare the corresponding aldehydes from p-tert-butylbenzoic acid and p-toluic acid hydrogenation has successfully realized industrialization; adding a small amount of SO ₄ ^2- in ZrO ₂ can Obtain a solid strong acid catalyst with super acid properties, which can be used to catalyze the isomerization reaction of alkanes (Topics in Catalysis, 1998, 6: 61); DE 9,400,513 reported that Pt can be supported on ZrO ₂ for the reaction of carbon dioxide reforming methane to synthesis gas , 500 hours of continuous use while maintaining the same activity. In our laboratory, supercritically dried “pure ZrO ₂ ” was used to catalyze the reaction of syngas to isobutene. At 450°C and GHSV=1000 h ^-1 , the conversion rate of CO and the selectivity of isobutene were 29.1% and 35.5% respectively ( Proc. of XII Intern. Symp. Alcohol Fuels, Beijing, China, 1998: 55). When the "pure ZrO ₂ " is used as a catalyst for carbon dioxide reforming methane to synthesis gas, the conversion rate of _methane and carbon dioxide can exceed 15% at 800 ° C; It not only exhibits high activity, but also has strong anti-coking ability of the catalyst. Under the reaction conditions of 1030K, GHSV=2.4×10 ⁴ ml/hg-cat, it has been used continuously for 600 hours without any decline in activity, and has good industrial application Prospect (CN 1,234,366A). In addition, ZrO ₂ supported B ₂ O ₃ has a good catalytic effect on the Beckmann rearrangement reaction of cyclohexanone oxime (Appl. Catal., 1999, 188: 361).

It is well known that the larger the specific surface area of a catalyst, the more catalytic active centers are provided per unit surface, which is beneficial to the conversion of reactants. For some supported catalysts, the more active components are dispersed on the surface of the carrier, the better the catalytic performance (such as high activity and selectivity), and the dispersed amount of active components is closely related to the specific surface area of the carrier; In addition, the support with high specific surface area enhances the carbon capacity of the catalyst. Therefore, the preparation of high specific surface area ZrO ₂ has become one of the ways to improve the performance of such catalysts using ZrO ₂ as catalyst or support. However, so far, there are few preparation methods for high specific surface area ZrO ₂ . CN 90108855.4 once disclosed a kind of preparation ZrO _The method, because this method introduces more anions, the prepared ZrO _The powder is mainly used for optical purposes, and is not suitable for being applied to the technical field of catalysis, because most of the catalysis reaction is to Impurities are very sensitive. GK Chuah et al. have tried to heat and reflux Zr(OH) ₄ hydrogel (ZrCl ₄ as the source of zirconium) in ammonia solution under normal pressure to prepare high specific surface area ZrO ₂ (Appl.Catal., 1996, 145:267), However, the prepared ZrO ₂ precursor Zr(OH) ₄ is prone to agglomeration after high-temperature calcination, resulting in large grains of ZrO ₂ and insufficient specific surface area.

Contents of the invention

The purpose of the present invention is to propose a preparation method of ultra-fine high specific surface area _ZrO2 , using the prepared _ZrO2 as catalyst or catalyst carrier to obtain a novel catalyst with good catalytic effect on certain chemical reactions.

The preparation method of the ultrafine high specific surface area zirconia proposed by the present invention comprises the following steps:

(1) Prepare the water-soluble zirconium salt into an aqueous solution with a concentration of 0.5-4mol/L for later use. The soluble zirconium salt (ie, the raw material of ZrO ₂ ) can be ZrOCl ₂ , ZrO(NO ₃ ) ₂ and various hydrates thereof, It can also be other inorganic salts of zirconium (such as ZrCl ₄ , Zr(NO ₃ ) ₄ ), etc.

(2) prepare an alkali solution for use, and the alkali solution includes NH ₃ , KOH and NaOH aqueous solution or a mixture of two or more alkalis with a concentration of 0.2-2 mol/L.

(3) Under the condition of continuous stirring, drop the prepared zirconium salt solution into the alkali solution or drop the alkali solution into the zirconium salt solution at a speed of 2-3ml/min to obtain Zr(OH) ₄ /ZrO (OH) ₂ hydrogel.

(4) Prepare Zr(OH) ₄ /ZrO(OH) ₂ gel after suction filtration or centrifugal separation, then add a certain amount of lye, or directly add lye to Zr(OH) ₄ /ZrO(OH) _2. In the hydrogel, keep the pH value of the system at 8.5-13.5, and cook for 5-100 hours at a continuous stirring speed of 100-500 rpm, a temperature of 60-150° C. and a pressure of 0.1-0.5 Mpa.

(5) Wash the digested Zr(OH) ₄ /ZrO(OH) ₂ hydrogel with deionized water until no Cl ^- can be detected with 0.1M AgNO ₃ solution, or the specific conductance of the washing solution is <10 ^-5 Ω ^-1 m ^-1 , filtered or centrifugally separated, then dried in static or flowing air or N ₂ at a temperature of 60-150°C for 8-20 hours, and finally calcined to obtain ultra-fine ZrO ₂ with high specific surface area, the roasting conditions are: : Temperature 450-900°C, heating rate 2-20°C/min, constant temperature calcination time 4-15 hours, static or flowing air or N ₂ atmosphere.

By using the method of the invention, ZrO ₂ with the smallest crystal grain and the largest specific surface area can be prepared so far, and the crystal grain size, crystal phase and specific surface area of ZrO ₂ can be controlled as required. The _ZrO2 prepared by the present invention exhibits excellent carrier effect in catalytic reactions such as gas-phase cyclohexanone oxime Beckmann rearrangement to synthesize caprolactam, carbon dioxide reforming methane to synthesis gas, and the like.

Detailed ways

Embodiments of the present invention are described below.

Example 1: Weigh 69.3g ZrOCl ₂ 8H ₂ O to prepare a 0.5M aqueous solution, dilute 50ml of concentrated ammonia water with a mass concentration of 25% to a 0.2M solution, and take 200ml of 0.2M ammonia solution as a precipitating agent and place it in three ports In the bottle, under vigorous stirring, drop ZrOCl ₂ aqueous solution at 0.5ml/min to prepare Zr(OH) ₄ /ZrO(OH) ₂ hydrogel, and then add ammonia solution with a concentration of 0.2M to Zr(OH) ) ₄ /ZrO(OH) ₂ hydrogel to make the PH of the system = 8.5, and cook at a continuous stirring speed of 100 rpm, a pressure of 0.1 MPa and a temperature of 60 ° C for 5 hours, and finally dry at 60 ° C in flowing air for 8 hours, Calcined in flowing air at 450°C for 4 hours, with a rate of 2°C/min, the specific surface area of the obtained ZrO ₂ was 260m ² /g, and the average particle size was 8.3nm.

Example 2: Weigh 69.3g ZrOCl ₂ 8H ₂ O to prepare a 1.0M aqueous solution, dilute 100ml of concentrated ammonia water with a mass concentration of 25% to a 0.6M solution, and take 200ml of 0.6M ammonia solution as a precipitant and place it under high pressure In the kettle, under vigorous stirring, drop ZrOCl ₂ aqueous solution at 1ml/min to prepare Zr(OH) ₄ /ZrO(OH) ₂ hydrogel, and then add ammonia solution with a concentration of 0.6M to Zr(OH) ₄ /ZrO(OH) ₂ hydrogel to make the system PH=9.5, and cook at a continuous stirring speed of 200rpm, a pressure of 0.2MPa and a temperature of 80°C for 15 hours, and finally dry at 80°C in flowing nitrogen for 8 hours, at 500 ℃ in flowing nitrogen for 10 hours, and the heating rate of the calcination is 5°C/min. The obtained ZrO ₂ had a specific surface area of 285 m ² /g and an average particle diameter of 7.8 nm.

Embodiment 3: take by weighing 69.3g ZrO(NO ₃ ) ₂ is formulated into 1.5M aqueous solution, the strong ammonia water of 100ml mass concentration 25% is diluted into 1.0M solution, and mixes with the 1.0M NaOH solution of equal volume, takes 200ml of this mixed solution was placed in an autoclave as a precipitating agent, and under vigorous stirring, ZrO(NO ₃ ) ₂ aqueous solution was dripped at 1.5ml/min to obtain Zr(OH) ₄ /ZrO(OH) ₂ hydrogel, Then add mixed lye to the Zr(OH) ₄ /ZrO(OH) ₂ hydrogel to make the system PH = 10.5, and cook at a continuous stirring speed of 300rpm, a pressure of 0.3MPa and a temperature of 90°C for 30 hours, and finally at 100°C Dry in flowing nitrogen for 13 hours, and bake in flowing air at 600°C for 12 hours, with a heating rate of 10°C/min. The obtained ZrO ₂ had a specific surface area of 325 m ² /g and an average particle diameter of 6.2 nm.

Example 4: Weigh 69.3g Zr(NO ₃ ) ₄ and 40g NaOH respectively to prepare 2.0M Zr(NO ₃ ) ₄ solution and 1.5M NaOH aqueous solution, and dilute 100ml of concentrated ammonia water with a mass concentration of 25% to 1.5M solution, take 200ml of the ammonia water as a precipitant and place it in an autoclave, and under vigorous stirring, drop in a Zr(NO ₃ ) ₄ aqueous solution at 2.0ml/min to obtain Zr(OH) ₄ /ZrO(OH) ₂ water Gel, then add NaOH solution with a concentration of 1.5M to the Zr(OH) ₄ /ZrO(OH) ₂ hydrogel to make the system PH=11.5, and at a continuous stirring speed of 400rpm, a pressure of 0.4MPa and a temperature of 110°C Cook for 50 hours, finally dry at 120°C in static air for 16 hours, and bake at 700°C for 12 hours in flowing air with a heating rate of 14°C/min. The obtained ZrO ₂ had a specific surface area of 295 m ² /g and an average particle diameter of 7.6 nm.

Embodiment 5: Take 69.3g Zr(NO ₃ ) ₄ and be mixed with 2.0M aqueous solution, 40g NaOH is mixed with 2.0M solution, take 200ml of this NaOH solution and place it in the autoclave as a precipitating agent, under vigorous stirring, Add Zr(NO ₃ ) ₄ aqueous solution dropwise at 3.0ml/min to prepare Zr(OH) ₄ /ZrO(OH) ₂ hydrogel, then add NaOH with a concentration of 2.0M to Zr(OH) ₄ /ZrO(OH) _2. Maintain the pH of the hydrogel system at 12.5, cook for 70 hours at a continuous stirring speed of 500 rpm, a pressure of 0.5 MPa, and a temperature of 130°C, and finally dry at 140°C in flowing air for 18 hours, and bake at 800°C in flowing nitrogen for 15 hours. Hours, the rate of calcination heating rate is 20°C/min. The obtained ZrO ₂ had a specific surface area of 250 m ² /g and an average particle diameter of 8.7 nm.

Example 6: Weigh 69.3g ZrOCl ₂ 8H ₂ O to prepare a 0.5M aqueous solution, dilute 80ml of concentrated ammonia water with a mass concentration of 25% to a 2M solution, and mix it with an equal volume of 2M KOH solution, and take 200ml of the Put the mixed lye in a three-necked flask as a precipitant, and under vigorous stirring, drop the ZrOCl ₂ aqueous solution at 3ml/min to obtain a Zr(OH) ₄ /ZrO(OH) ₂ hydrogel, and then add the mixed lye Keep the pH of the Zr(OH) ₄ /ZrO(OH) ₂ hydrogel system at 13.5, and cook for 80 hours at a continuous stirring speed of 500 rpm, a pressure of 0.1 MPa and a temperature of 100°C, and finally dry at 150°C in flowing air After 20 hours, it was calcined at 900°C in flowing air for 15 hours, and the rate of calcination was 20°C/min. The specific surface area of the obtained ZrO ₂ was 200m ² /g, and the average particle size was 9.7nm.

Example 7: Weigh 69.3g ZrOCl ₂ 8H ₂ O to make 4M aqueous solution, make 56g KOH to make 2M, take 200ml as a precipitant and put it in an autoclave, and drop ZrOCl at 3ml/min under vigorous stirring ₂ aqueous solution to prepare Zr(OH) ₄ /ZrO(OH) ₂ hydrogel, and then add KOH solution with a concentration of 2M to Zr(OH) ₄ /ZrO(OH) ₂ hydrogel to maintain the system pH=13.0, And cook at a continuous stirring speed of 400rpm, a pressure of 0.1MPa and a temperature of 150°C for 100 hours, and finally dry at 150°C for 10 hours in flowing air, and bake at 800°C for 15 hours in flowing air, with a heating rate of 20°C/min , the specific surface area of the obtained ZrO ₂ is 210m ² /g, and the average particle diameter is 9.4nm.

Example 8: Take 69.3g ZrCl ₄ and make it into a 2.0M aqueous solution, make 40g NaOH into a 2.0M solution, take 200ml as a precipitant and place it in an autoclave, and drop it in at 1.5ml/min under vigorous stirring Zr(NO ₃ ) ₄ aqueous solution to prepare Zr(OH) ₄ /ZrO(OH) ₂ hydrogel, then add 2.0M NaOH to Zr(OH) ₄ /ZrO(OH) ₂ hydrogel to maintain the system PH=12.5, and cook at a continuous stirring speed of 350rpm, a pressure of 0.2MPa and a temperature of 150°C for 100 hours, and finally dry at 140°C for 20 hours in flowing air, and bake at 500°C for 15 hours in flowing air. 10°C/min. The obtained ZrO ₂ had a specific surface area of 350 m ² /g and an average particle diameter of 6.0 nm.

Example 9: Take 69.3g Zr(NO ₃ ) ₄ and make it into a 4.0M aqueous solution, make 60g KOH into a 1.5M solution, take 200ml as a precipitating agent and place it in a three-necked flask, and stir vigorously with 3ml/ ZrOCl ₂ aqueous solution was dropped into Zr(OH) ₄ /ZrO(OH) ₂ hydrogel for min, and then KOH solution with a concentration of 1.5M was added to Zr(OH) ₂ /ZrO(OH) ₂ hydrogel to make The pH of the system is 13.5, and the continuous stirring speed is 500rpm, 0.1MPa, and the temperature is 100°C, and it is cooked for 80 hours. Finally, it is dried in flowing air at 150°C for 10 hours, and roasted in flowing air at 450°C for 10 hours. 7°C/min, the specific surface area of the obtained ZrO ₂ is 450m ² /g, and the average particle size is 5.0nm.

Example 10: Take a certain amount of 4% boric acid aqueous solution and impregnate 3 g of ZrO ₂ prepared according to the method described in Example 9. After stirring at room temperature for 2 hours, rotary evaporate to dryness, and then bake at 600 ° C in static air After 10 hours, the B ₂ O ₃ /ZrO ₂ catalyst was prepared (the chemical titration method analyzed that the weight percentage of B ₂ O ₃ was 20%, and the specific surface area of the catalyst was 260m ² /g). After the B ₂ O ₃ /ZrO ₂ catalyst was pressed into tablets , broken into 40-80 mesh particles, take 1.6g and place it in a glass reactor with an inner diameter of 10ml, and carry out the Beckmann rearrangement reaction of cyclohexanone oxime on the self-built reaction device _. Pretreat the catalyst under atmosphere for 1.5 hours, then lower the temperature to 300°C, and use CO ₂ to bring 10% cyclohexanone oxime benzene solution into the reactor. The space velocity of the reactant cyclohexanone oxime is WHSV=0.32h ^-1 . The result of the reaction is: the initial conversion rate of cyclohexanone oxime reaches 100%, the selectivity of caprolactam reaches 97%, and the one-way reaction time for maintaining the conversion rate of cyclohexanone oxime not lower than 85% and the selectivity of caprolactam not lower than 95% is not less than After 30 hours, the performance of the deactivated catalyst remained basically unchanged after being regenerated many times, and the cumulative reaction time had exceeded 200 hours.

Example 11: Weigh a certain amount of commercial Ni(NO ₃ ) ₂ ·6H ₂ O, prepare it into a 10% aqueous solution, and use this Ni(NO ₃ ) ₂ solution to impregnate ZrO ₂ prepared according to the method described in Example 9, After the impregnation system was stirred at room temperature for 2 hours, it was rotary evaporated to dryness, and then dried at 110° C. for 12 hours. The dried sample was moved into a muffle furnace and calcined at 650°C for 5 hours to prepare a Ni/ZrO ₂ catalyst with a nickel content (Ni wt%) of 15% and a specific surface area of 210m ² /g. Dilute the catalyst with α-Al ₂ O ₃ at a ratio of 2:5, grind and press into tablets, break into 20-40 mesh particles, take 700 mg and place it in a quartz tube reactor with an inner diameter of 10 ml. Evaluation of the reactivity of carbon dioxide reforming methane to synthesis gas on a pressurized fixed-bed flow reactor. Before the reaction, the catalyst was reduced with a mixed gas of H ₂ /N ₂ (1:9) at 700°C for 3 hours, and then the temperature was raised to 757°C. Under normal pressure, CO ₂ /CH ₄ (1:1) was fed into the reactor at a flow rate of 80 ml/min, the space velocity GHSV=2.4×10 ⁴ ml/h·g-cat, and the tail gas composition was detected by gas chromatography. The reaction result showed that the conversion rate of methane was 90%, and there was no decline after the catalyst was used for 100 hours.

Comparative Example 1: The commercial zirconium oxychloride ZrOCl ₂ 8H ₂ O containing crystal water is prepared into an aqueous solution with a concentration of 0.05 to 0.5 mol/L for subsequent use, and the commercial ammonia water with a concentration of 25% is diluted into a 2M solution, and continuously Under the condition of stirring, the prepared ZrOCl ₂ aqueous solution was added dropwise to the precipitating agent at a speed of 3 ml/min, while controlling the final pH value of the solution at 9.5. Continue to stir for 0.5 hours after the dropwise addition, leave to age for 12 hours, filter with suction, wash with deionized water until there is almost no Cl ^-1 , and obtain Zr(OH) ₄ /ZrO(OH) ₂ hydrogel after suction filtration. Then calcined at 600°C for 10 hours, the obtained ZrO ₂ has a specific surface area of 100m ² /g and a particle size of 80nm.

Comparative Example 2: Take a certain amount of 4% boric acid aqueous solution and impregnate 3 g of ZrO ₂ prepared according to the method described in Comparative Example 1. After stirring at room temperature for 2 hours, rotary evaporate to dryness, and then bake in static air at 600°C After 10 hours, the B ₂ O ₃ /ZrO ₂ catalyst was prepared (the chemical titration method analyzed that the weight percentage of B ₂ O ₃ was 20%, and the specific surface area of the catalyst was 65m ² /g). After the B ₂ O ₃ /ZrO ₂ catalyst was pressed into tablets , broken into 40-80 mesh particles, take 1.6g and place it in a glass reactor with an inner diameter of 10ml, and carry out the Beckmann rearrangement reaction of cyclohexanone oxime on the self-built reaction device _. Pretreat the catalyst under atmosphere for 1.5 hours, then lower the temperature to 300°C, and use CO ₂ to bring 10% cyclohexanone oxime benzene solution into the reactor. The space velocity of the reactant cyclohexanone oxime is WHSV=0.32h ^-1 . Catalyst performance evaluation results are: 1 hour before the reaction, the conversion rate of cyclohexanone oxime is 100%, the selectivity of caprolactam is 90%, and the conversion rate of cyclohexanone oxime is not lower than 85% and the selectivity of caprolactam is not lower than 90%. 6 hours; after regenerating the deactivated catalyst for 3 times, the initial conversion rate of cyclohexanone oxime and the selectivity of caprolactam have dropped to 80% and 85%, and the conversion rate of cyclohexanone oxime is not lower than 80% and the selectivity of caprolactam is not low At 85% only up to 4 hours.

Comparative Example 3: Take a certain amount of commercial Ni(NO ₃ ) ₂ ·6H ₂ O, prepare it into a 10% aqueous solution, use this Ni(NO ₃ ) ₂ solution to impregnate ZrO ₂ prepared by the method described in Comparative Example 1, impregnate After the system was stirred at room temperature for 2 hours, it was rotary evaporated to dryness, and then dried at 110° C. for 12 hours. The dried sample was moved into a muffle furnace and calcined at 650°C for 5 hours to prepare a Ni/ZrO ₂ catalyst with a nickel content (Ni wt%) of 15%, and a specific surface area of the catalyst was 45 m ² /g. Dilute the catalyst with α-Al ₂ O ₃ at a ratio of 2:5, grind and press into tablets, break into 20-40 mesh particles, take 700 mg and place it in a quartz tube reactor with an inner diameter of 10 ml. Evaluation of the reactivity of carbon dioxide reforming methane to synthesis gas on a pressurized fixed-bed flow reactor. Before the reaction, the catalyst was reduced with a mixed gas of H ₂ /N ₂ (1:9) at 700°C for 3 hours, and then the temperature was raised to 757°C. Under normal pressure, CO ₂ /CH ₄ (1:1) was fed into the reactor at a flow rate of 80 ml/min, the space velocity GHSV=2.4×10 ⁴ ml/h·g-cat, and the tail gas composition was detected by gas chromatography. The reaction results showed that the initial conversion rate of methane was 87%, but after 50 hours of use, the conversion rate of methane dropped to 60%.

Claims (1)

1, a kind of preparation method of superfine zirconia with large specific surface area is characterized in that, this method comprises following each step:

(1) water miscible zirconates being mixed with concentration is that the aqueous solution of 0.5～4mol/L is standby;

(2) the preparation aqueous slkali is standby, and aqueous slkali comprises that a kind of concentration is the NH of 0.2-2mol/L ₃, KOH and NaOH the aqueous solution or the mixed liquor of two or more alkali wherein;

(3) under the condition of continuous stirring, drop to the zirconium salt solution for preparing in the aqueous slkali or alkali lye dripped to zirconium salt solution with the speed of 2-3ml/min and make Zr (OH) ₄/ ZrO (OH) ₂Hydrogel;

(4) make Zr (OH) after suction filtration or the centrifugation ₄/ ZrO (OH) ₂Gel adds a certain amount of alkali lye again, or directly alkali lye is added to Zr (OH) ₄/ ZrO (OH) ₂In the hydrogel, the system pH value of making maintains 8.5-13.5, and continuous stirring speed be 100-500rpm, temperature 60-150 ℃ with pressure 0.1-0.5Mpa under boiling 5-100 hour;

(5) spend Zr (OH) after the deionised water boiling ₄/ ZrO (OH) ₂Hydrogel is to using 0.1M AgNO ₃Solution detects less than Cl ^-Till, or the ratio electricity of cleaning solution lead＜10 ^-5Ω ^-1m ^-1, suction filtration or centrifugation, then at temperature 60-150 ℃ in static state or flow air or N ₂In dry 8-20 hour, at last at temperature 450-900 ℃, heating rate 2-20 ℃/min, static state or flow air or N under the constant temperature ₂In the atmosphere roasting 4-15 hour, promptly get the ZrO of ultra-fine high-specific surface area of the present invention ₂