WO2023087412A1

WO2023087412A1 - Preparation method for catalyst having wide temperature window for combustion of non-methane hydrocarbons, product and application thereof

Info

Publication number: WO2023087412A1
Application number: PCT/CN2021/135014
Authority: WO
Inventors: 崔大祥; 赵昆峰; 童琴; 蔡婷; 马玉丽; 陈晓彤; 刘权辉
Original assignee: 上海纳米技术及应用国家工程研究中心有限公司
Priority date: 2021-11-16
Filing date: 2021-12-02
Publication date: 2023-05-25
Also published as: CN114011414B; CN114011414A

Abstract

A preparation method for a catalyst having a wide temperature window for the combustion of non-methane hydrocarbons, a product and an application thereof. The catalyst is a catalyst having a stable Co@Co3O4 core@shell structure. High-crystallinity Co3O4 or CoO is reduced by using a reducing atmosphere, is naturally cooled to a temperature of less than 300°C in the reducing atmosphere, and is directly exposed to the air, so as to obtain the catalyst having a stable Co@Co3O4 core@shell structure. By means of a synergistic of an elemental Co core and a Co3O4shell, the catalyst has a low operating temperature in catalytic combustion of non-methane hydrocarbons, and an operating temperature window of the catalyst for the catalytic combustion of non-methane hydrocarbons is significantly widened. The obtained catalyst having a wide temperature window for the combustion of non-methane hydrocarbons is simple in preparation process and easy for large-scale production, and has good application prospects.

Description

Preparation method, product and application of non-methane total hydrocarbon combustion catalyst with wide temperature window

technical field

The invention relates to the field of environmental protection catalysis, in particular to a preparation method of a non-methane total hydrocarbon combustion catalyst with a wide temperature window and its product and application.

Background technique

Non-methane total hydrocarbons (NMHC) refer to all volatile hydrocarbons (mainly C2-C8) except methane. When the concentration of NMHC in the atmosphere exceeds a certain level, it can directly harm human health. In addition, NMHC can also produce photochemical smog or secondary aerogels to form smog when exposed to light, causing harm to the environment and humans. Therefore, in recent years, the state has continuously increased the supervision of organized and unorganized NMHC emissions in various industries.

Catalytic combustion-hydrogen flame ionization method is an emerging detection technology of NMHC. Only a small amount of catalyst can be used to achieve the selective catalytic combustion removal of NMHC, and then the NMHC content can be calculated according to the difference between THC and NMHC. The structure of the equipment is simple, and it is easy to realize the lightweight and portable detection of the equipment; the catalytic combustion reaction is fast, and real-time online monitoring can be realized, and the detection cycle is as low as a few seconds.

The working temperature window of the catalyst in the detection of catalytic combustion-hydrogen flame ionization method is the key of this technology. Because the NMHC catalytic combustion reaction is an exothermic reaction, the heat released during the reaction will cause the temperature of the catalyst bed to rise, so that part of the methane participates in the reaction and affects the detection results. Therefore, the working temperature window of the catalyst is directly related to the accuracy of the detection method, and the larger the working temperature window, the higher the detection accuracy. Especially when the solubility of NMHC is high, a wider operating temperature window for catalytic combustion is required. Cobalt-based catalysts have good performance in NMHC catalytic combustion reactions, but their working temperature window is only about 50°C (201910471905.X, 202010650947.2). It is urgent to develop a non-methane total hydrocarbon catalytic combustion catalyst with a wide temperature window to meet the detection requirements of various NMHC working conditions.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a non-methane total hydrocarbon combustion catalyst with a wide temperature window.

Another object of the present invention is to provide a non-methane total hydrocarbon combustion catalyst product with a wide temperature window prepared by the above method.

Another object of the present invention is to provide an application of the above product.

The object of the present invention is achieved by the following scheme: a preparation method of a non-methane total hydrocarbon combustion catalyst with a wide temperature window, characterized in that the catalyst is a cobalt catalyst with a stable Co@Co ₃ O ₄ core@shell structure, and the preparation method comprises The following steps:

In the first step, take an appropriate amount of 0.1-0.5mol/L cobalt nitrate aqueous solution, add 1mol/L Na ₂ CO ₃ solution to adjust the system to pH=9, continue stirring for 1 hour, then return to pH=9, and react at 20-80°C 1h, stand at room temperature for 10-30min; filter to obtain a pink solid, wash with deionized water until neutral, dry in an oven at 50-100°C, and bake in a muffle furnace at 800-1000°C for 3-5h to obtain highly crystalline cobalt oxide ;

In the second step, the highly crystalline cobalt oxide _is reduced in a 5% H ₂ /Ar atmosphere at 500°C for 3-5 hours to obtain a highly crystalline cobalt element; the highly crystalline cobalt element is naturally Cool to a temperature of <300°C and directly expose to the air to obtain a stable Co@Co ₃ O ₄ core@shell structure catalyst.

The invention provides a non-methane total hydrocarbon combustion catalyst with a wide temperature window, which is prepared according to the method described above.

The invention provides a non-methane total hydrocarbon combustion catalyst with a wide temperature window, which is used in the portable and continuous detection of non-methane total hydrocarbons by a catalytic combustion-hydrogen flame ionization method.

The test conditions are as follows: Methane/propane mixture gas is used to simulate methane and non-methane total hydrocarbon pollution gas, the concentrations of methane and propane are respectively 1000ppm, air is the balance gas, and the space velocity is 30,000mL/g _cat /h.

The invention utilizes a simple process, does not add any catalyst additives, only through the construction of the Co ₃ O ₄ microstructure, and under the premise of maintaining a low working temperature, significantly widens the non-methane catalytic combustion working temperature window of the catalyst. The invention discloses a non-methane total hydrocarbon combustion catalyst with a wide temperature window and its preparation method and application. Firstly, the nano-Co ₃ O ₄ catalyst is pre-sintered at high temperature to form a highly crystalline cobalt oxide, which avoids sintering in the subsequent application process of the catalyst. Deactivation; then the catalyst is reduced at an appropriate temperature. After reduction, the highly crystalline Co structure allows only the surface of the catalyst to be oxidized to Co ₃ O ₄ , while the internal structure is very stable and maintains Co even under oxygen-rich catalytic combustion reaction conditions. Elementary structure, the catalyst is a stable Co@Co ₃ O ₄ core@shell structure; the synergistic effect of the elemental Co core and Co ₃ O ₄ shell makes the catalyst not only have a lower working temperature of non-methane total hydrocarbons, but also significantly broaden the catalyst The operating temperature window of non-methane catalytic combustion.

The present invention has the following advantages:

(1) The catalyst of the present invention does not add any catalytic promoters, and only through the construction of the Co ₃ O ₄ microstructure, the non-methane catalytic combustion working temperature window of the catalyst is significantly widened under the premise of maintaining a low working temperature, which is innovative .

(2) The catalyst of the present invention has a stable Co@Co ₃ O ₄ core@shell structure, and maintains a stable structure under oxygen-enriched combustion conditions, which is innovative.

(3) The preparation process is simple, easy for large-scale production, and has good application prospects.

Description of drawings

The non-methane total hydrocarbon catalytic combustion performance of 100Co8C5R catalyst in Fig. 1 embodiment 1;

The XRD figure of 100Co8C5R catalyst in Fig. 2 embodiment 1;

The XPS figure of 100Co8C5R catalyst in Fig. 3 embodiment 1;

The non-methane total hydrocarbon catalytic combustion performance of 100Co10C5R catalyst in Fig. 4 embodiment 2.

Detailed ways

The embodiments of the present invention are described in detail below: the present embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation and specific operation process are provided, but the protection scope of the present invention is not limited to the following implementation example.

Example 1:

A non-methane total hydrocarbon combustion catalyst with a wide temperature window is a cobalt catalyst with a stable Co@Co ₃ O ₄ core@shell structure with Co as the core and Co ₃ O ₄ as the shell. It is prepared by the following steps:

In the first step, dissolve 5.44 g of cobalt nitrate hexahydrate in 100 mL of deionized water to obtain an aqueous solution of cobalt nitrate, add 1 mol/L Na ₂ CO ₃ solution dropwise to adjust the system to pH = 9, continue stirring for 1 hour, and return to pH = 9. Reaction at 50°C for 1 hour, standing at room temperature for 30 minutes; suction filtration to obtain a pink solid, washed with deionized water until neutral, oven-dried at 70°C for 24 hours, and calcined in a muffle furnace at 800°C for 3 hours to obtain highly crystalline Co ₃ O ₄ precursors;

In the second step, the highly crystalline Co ₃ O ₄ precursor _is reduced in a 5% H ₂ /Ar atmosphere at 500°C for 3 hours to obtain a highly crystalline cobalt element. Naturally cooled to a temperature <300°C, and directly exposed to the air, a stable Co@Co ₃ O ₄ core@shell structure catalyst was obtained, denoted as 100Co8C5R. XRD results show that the bulk phase structure of the catalyst is Co simple substance, as shown in Figure 2; XPS results show that the surface composition of the catalyst is Co ₃ O ₄ , as shown in Figure 3. Its non-methane total hydrocarbon catalytic combustion performance is shown in Figure 1 and Table 1.

Example 2:

A non-methane total hydrocarbon combustion catalyst with a wide temperature window, similar to the steps of Example 1, is prepared as follows:

In the first step, dissolve 10.88 g of cobalt nitrate hexahydrate in 100 mL of deionized water to obtain a cobalt nitrate aqueous solution, add 1 mol/L Na ₂ CO ₃ solution dropwise to adjust the pH to 9, continue stirring for 1 hour, and return to pH = 9. Reaction at 80°C for 1 hour, standing at room temperature for 10 minutes; suction filtration to obtain a pink solid, washing with deionized water until neutral, oven drying at 100°C for 24 hours, and calcination in a muffle furnace at 1000°C for 5 hours to obtain a highly crystalline CoO precursor;

In the second step, the highly crystalline CoO precursor was reduced in a 5% H ₂ /Ar atmosphere at 500°C for 5 hours to obtain a highly crystalline cobalt element; the highly crystalline cobalt element was naturally cooled in a 5% H ₂ /Ar atmosphere When the temperature is lower than 300°C, it is directly exposed to the air to obtain a stable Co@Co ₃ O ₄ core@shell catalyst, denoted as 100Co10C5R. Its non-methane total hydrocarbon catalytic combustion performance is shown in Figure 4, Table 1.

Comparative example 1:

A kind of cobalt catalyst, is identical with embodiment 1 step one, is prepared according to the following steps:

In the first step, dissolve 5.44g of cobalt nitrate hexahydrate in 100mL of deionized water to obtain a cobalt nitrate solution, add 1mol/L Na ₂ CO ₃ solution dropwise to adjust the pH to 9, continue stirring for 1 hour, and return to pH = 9. Reaction at 50°C for 1h, standing at room temperature for 30min; suction filtration to obtain a pink solid, washed with deionized water until neutral, oven-dried at 70°C for 24h, and calcined in a muffle furnace at 800°C for 3h to obtain highly crystalline Co ₃ O ₄ , record Make 100Co8C. Its non-methane total hydrocarbon catalytic combustion performance is shown in Table 1.

Comparative example 2:

A kind of cobalt catalyst, is identical with embodiment 2 step one, is prepared according to the following steps:

In the first step, dissolve 10.88g of cobalt nitrate hexahydrate in 100mL of deionized water to obtain a cobalt nitrate solution, add 1mol/L Na ₂ CO ₃ solution dropwise to adjust the pH to 9, continue stirring for 1 hour, and adjust the pH to 9. React at 80°C for 1 hour, and let stand at room temperature for 10 minutes. The pink solid was obtained by suction filtration, washed with deionized water until neutral, oven-dried at 100°C for 24 hours, and calcined in a muffle furnace at 1000°C for 5 hours to obtain highly crystalline CoO, denoted as 100Co10C. Its non-methane total hydrocarbon catalytic combustion performance is shown in Table 1.

Comparative example 3:

A kind of cobalt catalyst, compared with embodiment 1, the roasting temperature is changed into 500 ℃ in the step one, and the step two is the same, prepared according to the following steps:

In the first step, dissolve 5.44g of cobalt nitrate hexahydrate in 100mL of deionized water, add 1mol/L Na ₂ CO ₃ solution dropwise to adjust pH=9, continue stirring for 1h, then return to pH=9, and react at 50°C for 1h , stand at room temperature for 30min. The pink solid was obtained by suction filtration, washed with deionized water until neutral, oven-dried at 70°C for 24 hours, and calcined in a muffle furnace at 500°C for 3 hours to obtain the Co ₃ O ₄ precursor;

In the second step, the Co ₃ O ₄ precursor was reduced in a 5% H ₂ /Ar atmosphere at 500°C for 3 hours to obtain highly crystalline CoO, then naturally cooled to a temperature <300°C in a 5% H ₂ /Ar atmosphere, and directly exposed to In the air, it is recorded as 100Co5C5R. Its non-methane total hydrocarbon catalytic combustion performance is shown in Table 1.

Application example:

The catalysts in Examples 1-2 and Comparative Examples 1-3 were respectively used to test the catalytic combustion performance of non-methane total hydrocarbons. The test conditions are as follows: Methane/propane mixture gas is used to simulate methane and non-methane total hydrocarbon pollution gas, the concentrations of methane and propane are respectively 1000ppm, air is the balance gas, and the space velocity is 30,000mL/g _cat /h. The working temperature window refers to the reaction temperature range in which the non-methane total hydrocarbon conversion rate is higher than 95% and the methane conversion rate is lower than 5%. Table 1 shows the working temperature windows of catalytic combustion of non-methane total hydrocarbons for different catalysts.

Table 1 Working temperature window of catalytic combustion of non-methane total hydrocarbons with different catalysts

Find out from table 1: in the embodiment of the present invention, catalyst non-methane total hydrocarbon catalytic combustion operating temperature is obviously lower than comparative example, has lower non-methane total hydrocarbon catalytic combustion operating temperature; Catalyst operating temperature window is obviously wider than in the embodiment comparative example.

Claims

A method for preparing a non-methane total hydrocarbon combustion catalyst with a wide temperature window, characterized in that it is a cobalt catalyst with a stable Co@Co 3 O 4 core@shell structure with Co as the core and Co 3 O 4 as the shell , including the following steps:

In the first step, take an appropriate amount of 0.1-0.5mol/L cobalt nitrate aqueous solution, add 1mol/L Na 2 CO 3 solution to adjust the system to pH=9, continue stirring for 1 hour, then return to pH=9, and react at 20-80°C 1h, stand at room temperature for 10-30min; filter with suction to obtain a pink solid, wash with deionized water until neutral, dry in an oven at 50-100°C, and roast in a muffle furnace at 800-1000°C for 3-5h to obtain highly crystalline cobalt oxide;

In the second step, the highly crystalline cobalt oxide is reduced in a 5% H 2 /Ar atmosphere at 500°C for 3-5 hours to obtain a highly crystalline cobalt element; the highly crystalline cobalt element is naturally Cool to a temperature of <300°C and directly expose to the air to obtain a stable Co@Co 3 O 4 core@shell structure catalyst.
According to the preparation method of the non-methane total hydrocarbon combustion catalyst of the desired wide temperature window of claim 1, it is characterized in that, prepared according to the following steps:

In the first step, dissolve 5.44 g of cobalt nitrate hexahydrate in 100 mL of deionized water to obtain a cobalt nitrate aqueous solution, add 1 mol/L Na 2 CO 3 solution dropwise to adjust the system to pH = 9, continue stirring for 1 hour, and return to pH = 9. Reaction at 50°C for 1 hour, standing at room temperature for 30 minutes; suction filtration to obtain a pink solid, washed with deionized water until neutral, oven-dried at 70°C for 24 hours, and calcined in a muffle furnace at 800°C for 3 hours to obtain highly crystalline Co 3 O 4 precursors;

In the second step, the highly crystalline Co 3 O 4 precursor is reduced in a 5% H 2 /Ar atmosphere at 500°C for 3 hours to obtain a highly crystalline cobalt element. Naturally cooled to a temperature <300°C, and directly exposed to the air, a stable Co@Co 3 O 4 core@shell structure catalyst was obtained, denoted as 100Co8C5R.
According to the preparation method of the non-methane total hydrocarbon combustion catalyst of the desired wide temperature window of claim 1, it is characterized in that, prepared according to the following steps:

In the first step, dissolve 10.88 g of cobalt nitrate hexahydrate in 100 mL of deionized water to obtain a cobalt nitrate aqueous solution, add 1 mol/L Na 2 CO 3 solution dropwise to adjust the pH to 9, continue stirring for 1 hour, and return to pH = 9. Reaction at 80°C for 1 hour, standing at room temperature for 10 minutes; suction filtration to obtain a pink solid, washing with deionized water until neutral, oven drying at 100°C for 24 hours, and calcination in a muffle furnace at 1000°C for 5 hours to obtain a highly crystalline CoO precursor;

In the second step, the highly crystalline CoO precursor was reduced in a 5% H 2 /Ar atmosphere at 500°C for 5 hours to obtain a highly crystalline cobalt element; the highly crystalline cobalt element was naturally cooled in a 5% H 2 /Ar atmosphere When the temperature is lower than 300°C, it is directly exposed to the air to obtain a stable Co@Co 3 O 4 core@shell catalyst, denoted as 100Co10C5R.
A non-methane total hydrocarbon combustion catalyst with a wide temperature window, characterized in that it is prepared according to the method described in any one of claims 1 to 3.
A non-methane total hydrocarbon combustion catalyst with a wide temperature window according to claim 4 is used in the portable and continuous detection of non-methane total hydrocarbons by catalytic combustion-hydrogen flame ionization method.