Cobalt-silver bimetal synergistic VOCs purification catalyst as well as preparation method and application thereof

Abstract

The invention discloses a cobalt-silver bimetallic synergistic VOCs purification catalyst and a preparation method and application thereof, and belongs to the field of VOCs catalysts.The preparation method includes the steps that 1, a certain amount of modifier, a certain amount of dispersing agent, a certain amount of precursor Ag-Co metal salt and a certain amount of deionized water are mixed to be uniform under the stirring condition; 2) stirring the mixed solution at constant temperature to form gel; (3) carrying out temperature programming, heating and roasting, and molding to obtain a cobalt-silver bimetallic catalyst precursor; and 4) putting the formed catalyst into an acid solution, etching, and drying to obtain the required catalyst. Cobalt-silver bimetals can mutually change mutual structures and atomic surface microenvironments, so that the oxidation-reduction capacity of the catalyst is improved, the high-activity effect of the catalyst is fully exerted, and the reaction process for purifying VOCs is accelerated; the prepared catalyst has the characteristics of developed pore structure, excellent activity in catalytic combustion of VOCs (Volatile Organic Compounds) such as propane and the like, is mainly used for purifying the VOCs such as propane and the like, and can remove more than 90% of propane within 240 DEG C.

Description

Technical Field

[0001] The present invention relates to the technical field of VOCs catalysts, and in particular to a VOCs purification catalyst with synergistic enhancement of cobalt-silver bimetals, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of industrialization worldwide and the large-scale consumption of fossil resources, volatile organic compounds (VOCs) have gradually become the main source of air pollution. Many VOCs are not only toxic, carcinogenic, and teratogenic themselves, but also can form ozone (O3) with nitrogen oxides (NOx) under the action of light and heat. At the same time, it is also an important precursor of photochemical smog and fine particulate matter (PM2.5), seriously harming the atmospheric environment and human health. China has successively issued a series of documents such as the "Comprehensive Treatment Plan for Volatile Organic Compounds in Key Industries", comprehensively strengthening the top-level design and management of VOCs treatment.

[0003] Catalytic combustion is an efficient method for deep treatment of VOCs pollution, with advantages such as high treatment efficiency, low operating temperature, clean and pollution-free, and can achieve deep purification treatment of low-concentration VOCs. However, the high price of its key material, noble metal catalysts (platinum, palladium, ruthenium, iridium), limits the popularization and application of this method. Non-noble metal transition metal compounds are widely sourced, low in price, and the prepared catalysts have good high-temperature stability. In particular, cobalt-based catalysts of the same family as noble metals even show better catalytic combustion performance than noble metals in the catalytic combustion of hydrocarbons, esters, etc. Developing cobalt-based catalysts is of great significance for the popularization of catalytic combustion technology and the realization of deep purification treatment of VOCs.

[0004] Cobalt-based catalysts show better performance in alkane treatment. At present, the research on cobalt-based catalysts mainly focuses on improving the low-temperature activity of cobalt-based catalysts through the regulation of preparation methods. Improving the low-temperature activity of catalysts can effectively solve problems such as high ignition temperature and poor stability of non-noble metal catalysts, can effectively reduce energy consumption, improve the reaction speed and efficiency, and reduce the operating cost of catalyst applications.

[0005] For example, a supported cobalt-based catalyst was prepared in Chinese CN110560063A, and the T90 temperature for propane treatment was as high as 400 °C. Chinese patent CN106268814A prepared a flower-like cobalt tetroxide catalyst by using water-soluble amine and cobalt salt in a hydrothermal method, and its T90 temperature for methane treatment was 333 °C. In Chinese patent CN107952441A, a VOCs treatment catalyst was prepared by sol-gel method through drying and two calcination steps of cobalt nitrate and cerium nitrate complexed with citric acid, and its T90 temperature for propane treatment was 310 °C.

[0006] Chinese Patent Application CN117101728A discloses a preparation method and device for a catalyst for VOCs waste gas treatment projects. This patent involves the synergy of Au, Ag, and Co. It uses the noble metal Au, and the experimental results show that at 250°C, the VOCs removal rate of all examples is less than 90%. That is, to achieve 90%, a temperature higher than 250°C is required.

[0007] Chinese Patent Application CN118059930A discloses a catalyst that uses at least one of Pt, Pd, and Ag as the first active component and at least one of Mn, Fe, Co, and Cu as the second active component. However, this catalyst mainly solves the problem of catalytic oxidation of nitrogen-containing VOCs, and moreover, the T90 of this patent is still above 260°C.

[0008] The applicant of this application applied for a cobalt-based related patent CN 114471614 A in 2022, preparing a CoOx mixed-phase cobalt-based catalyst for VOCs catalytic combustion. The optimal temperature for catalytic combustion of propane T90 is around 250°C. There is still room for further reduction of the T90 temperature of this catalyst.

[0009] In summary, the T90 temperature of the existing Co-based catalysts, especially for propane catalytic treatment, is still relatively high, and the low-temperature activity potential of such catalysts remains to be further explored. Summary of the Invention

[0010] One of the objectives of the present invention is to provide a VOCs purification catalyst with synergistic enhancement of cobalt-silver bimetals to solve the above problems.

[0011] To achieve the above objective, the technical solution adopted by the present invention is as follows: A VOCs purification catalyst with synergistic enhancement of cobalt-silver bimetals, wherein the active components of the catalyst are cobalt and silver. Among them, the cobalt exists in the form of a mixed phase of CoO and Co 3 O 4 and the silver exists in the form of elemental Ag, and the molar percentage of Ag / (Ag + Co) is 0.5% - 12%.

[0012] As a preferred technical solution, the molar percentage of Ag / (Ag + Co) is 3.2%. The catalyst with this ratio has better performance.

[0013] The cobalt-silver bimetal of the present invention can mutually change each other's structure and the microscopic environment of the atomic surface, improve the redox ability of the catalyst, give full play to the high activity of the catalyst, and accelerate the reaction process of purifying VOCs; the prepared catalyst has the characteristics of developed pore structure, enhanced redox ability, and good activity for catalytic combustion of VOCs such as propane, and is mainly used for purifying VOCs such as propane, and can remove more than 90% of propane within 240 °C.

[0014] The second object of the present invention is to provide a preparation method of the above-mentioned VOCs purification catalyst with synergistic effect of cobalt-silver bimetal. The technical solution adopted is as follows: It includes the following steps:

[0015] S1. Under stirring, add a modifier to a stoichiometric AgNO 3 and Co(NO 3 )2•6H 2 O mixed solution. After stirring evenly, add a dispersant to obtain a corresponding mixed solution A;

[0016] S2. Continuously stir and evaporate the mixed solution A at 80-120 °C to form a gel, and then dry it at 120-180 °C to obtain a precursor B;

[0017] S3. Calcinate the precursor B in air at 300-600 °C at a heating rate of 2-10 °C / min, and press it into a tablet to obtain a catalyst precursor C;

[0018] S4. Place the catalyst precursor C in an acid solution for etching, and dry it to obtain the required catalyst.

[0019] As a preferred technical solution, in step S1, the modifier is selected from one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and glycerol; the dispersant is selected from one or more of carboxymethyl cellulose, ascorbic acid, citric acid, tartaric acid, sodium citrate, and cetyltrimethylammonium bromide.

[0020] As a preferred technical solution, in step S2, the evaporation time is 60-120 min; the drying time is 5-8 h.

[0021] As a preferred technical solution, in step S3, the calcination time is 1-4 h.

[0022] As a preferred technical solution, in step S4, the acid solution used for etching is one or a mixture of two of nitric acid, oxalic acid, and acetic acid, and the concentration of the acid solution is 0.2-6 mol / L.

[0023] As a preferred technical solution, the acid solution is a mixed solution of 0.5 mol / L nitric acid + 1.5 mol / L oxalic acid.

[0024] A third object of the present invention is to provide an application of the above-mentioned cobalt-silver bimetallic synergistic VOCs purification catalyst for VOCs purification catalytic reaction.

[0025] As a preferred technical solution, the VOCs is propane.

[0026] The catalyst provided by the present invention is mainly used for the purification of VOCs such as propane, and more than 90% of propane can be removed within 240 °C.

[0027] Compared with the prior art, the advantages of the present invention are as follows: by adding silver to the cobalt-based catalyst to form a bimetallic catalyst, the two metals promote and synergistically enhance each other, increasing crystal defects and improving lattice disorder. At the same time, the strong interaction between Ag and Co increases the content of Co2+ and adsorbed oxygen on the catalyst surface, improves the catalyst structure and microenvironment, and promotes the low-temperature reduction performance and catalytic activity of the catalyst; further, the specific surface area and pore volume of the catalyst are optimized by the sol-gel modifier dispersant preparation method, which helps to reduce the particle size of the active component and improves the low-temperature activity of the catalyst for purifying VOCs (such as propane);

[0028] In addition, the present invention also uses an acid etching catalyst post-treatment method to remove the passivation layer on the catalyst surface, improve the mass transfer path by regulating the pore structure of the catalyst, enhance the surface roughness of the catalyst to improve the adsorption capacity for VOCs molecules, and adjust the surface oxidation state of the Co metal catalyst (Co 2+ / Co 3+ ), further improving the degradation performance of the catalyst for VOCs molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the XRD spectrum of the catalysts obtained in some embodiments and comparative examples of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not indicated by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0031] The nouns mentioned in the present invention are described as follows:

[0032] g is the mass unit gram; ml is the volume unit milliliter; °C is the temperature unit degree Celsius; mol is the amount of substance unit mole; h is the time unit hour; min is the time unit minute; vol% is the volume percentage concentration; mol / L is the concentration unit mole per liter; (ml•g-1 •h -1 ) is the airspeed unit, that is, the volume of gas processed per gram of catalyst per hour. Specifically,

[0033] The present invention provides a highly active VOCs purification catalyst with cobalt-silver bimetal synergistic effect and a preparation method thereof, including the following steps: using the sol-gel method to mix metal cobalt nitrate, metal silver nitrate, dispersant, modifier and deionized water and stir evenly at a constant temperature to form a sol-gel, drying at a constant temperature, and calcining with a programmed temperature rise to obtain catalyst powder, pressing and forming to obtain the required catalyst precursor, and etching and drying the precursor with an acid solution to obtain the required catalyst.

[0034] Example 1

[0035] Under stirring, 1.02 mol of 1,3-propanediol (PDO) was added to a mixed solution of 0.53 g of AgNO 3 , 180 g of Co(NO 3 ) 2 •6H 2 O and 618 g of deionized water. After stirring evenly, 0.67 mol of citric acid was added to obtain the corresponding mixed solution; the obtained mixed solution was continuously stirred and evaporated at 80 °C for 90 min to form a gel, and then dried at 120 °C for 6 h to obtain the corresponding precursor; then, the precursor was calcined in air at 300 °C for 1 h at a heating rate of 2 °C / min; finally, it was heated to 400 °C at a heating rate of 2 °C / min and kept at a constant temperature for 2 h to be pressed and formed to obtain the corresponding catalyst precursor. The precursor was etched in a mixed solution of 0.5 mol / L nitric acid + 1.5 mol / L oxalic acid for 30 min and dried at 180 °C for 4 h to obtain the required catalyst.

[0036] The XRD pattern of the obtained catalyst is as Figure 1 shown. It can be seen from Figure 1 that the cobalt in the obtained catalyst exists in the form of a mixed phase of CoO and Co 3 O 4 , and the silver exists in the form of elemental Ag.

[0037] Example 2

[0038] Under stirring, 1.02 mol of 1,3-propanediol (PDO) was added to 10.2 g of AgNO 3 , 158 g of Co(NO 3 ) 2 •6H 2In a mixed solution of 1.02 mol of 1,3 - propanediol (PDO), 2.1 g of AgNO₃, 168 g of Co(NO₃)₂•6H₂O and 618 g of deionized water, after stirring evenly, 0.67 mol of citric acid was added to obtain the corresponding mixed solution; the obtained mixed solution was continuously stirred and evaporated at 80 °C for 90 min to form a gel; then it was dried at 120 °C for 6 h to obtain the corresponding precursor; then, the precursor was calcined in air at 300 °C for 1 h at a heating rate of 2 °C / min; finally, it was heated to 400 °C at a heating rate of 2 °C / min and kept at a constant temperature for 2 h, and then tableted to obtain the corresponding catalyst precursor. The precursor was etched in a mixed solution of 0.5 mol / L nitric acid + 1.5 mol / L oxalic acid for 30 min and dried at 180 °C for 4 h to obtain the required catalyst.

[0039] Example 3

[0040] Under stirring, 1.02 mol of 1,3 - propanediol (PDO) was added to 2.1 g of AgNO₃ 3 , 168 g of Co(NO₃)₂ 3 ) 2 •6H₂O 2 In a mixed solution of 1.02 mol of 1,3 - propanediol (PDO), 2.1 g of AgNO₃, 168 g of Co(NO₃)₂•6H₂O and 618 g of deionized water, after stirring evenly, 0.67 mol of citric acid was added to obtain the corresponding mixed solution; the obtained mixed solution was continuously stirred and evaporated at 80 °C for 90 min to form a gel, then it was dried at 120 °C for 6 h to obtain the corresponding precursor; then, the precursor was calcined in air at 300 °C for 1 h at a heating rate of 2 °C / min; finally, it was heated to 400 °C at a heating rate of 2 °C / min and kept at a constant temperature for 2 h, and then tableted to obtain the corresponding catalyst precursor. The precursor was etched in a mixed solution of 0.5 mol / L nitric acid + 1.5 mol / L oxalic acid for 30 min and dried at 180 °C for 4 h to obtain the required catalyst.

[0041] Example 4

[0042] Under stirring, 1.02 mol of 1,4 - butanediol was added to 2.1 g of AgNO₃ 3 , 168 g of Co(NO₃)₂ 3 ) 2 •6H₂O 2In a mixed solution of 2.1 g AgNO3, 168 g Co(NO3)2•6H2O and 618 g deionized water, after stirring evenly, 0.67 mol tartaric acid was added to obtain the corresponding mixed solution; the obtained mixed solution was continuously stirred and evaporated at 80 °C for 90 min to form a gel, and then dried at 120 °C for 6 h to obtain the corresponding precursor; then, the precursor was calcined in air at 300 °C for 1 h at a heating rate of 2 °C / min. Finally, it was heated to 400 °C at a heating rate of 2 °C / min and kept at a constant temperature for 2 h to be tableted to obtain the corresponding catalyst precursor, and the precursor was etched in a mixed solution of 0.5 mol / L nitric acid + 1.5 mol / L oxalic acid for 30 min and dried at 180 °C for 4 h to obtain the required catalyst.

[0043] Example 5

[0044] Under stirring, 1.02 mol of 1,3 - propanediol (PDO) was added to 2.1 g AgNO3, 168 g Co(NO 3 ) 2 •6H 2 In a mixed solution of 2.1 g AgNO3, 168 g Co(NO3)2•6H2O and 618 g deionized water, after stirring evenly, 0.67 mol tartaric acid was added to obtain the corresponding mixed solution; the obtained mixed solution was continuously stirred and evaporated at 100 °C for 120 min to form a gel, and then dried at 130 °C for 6 h to obtain the corresponding precursor; then, the precursor was calcined in air at 300 °C for 1 h at a heating rate of 5 °C / min; finally, it was heated to 400 °C at a heating rate of 5 °C / min and kept at a constant temperature for 2 h to be tableted to obtain the corresponding catalyst precursor, and the precursor was etched in a mixed solution of 0.5 mol / L nitric acid + 1.5 mol / L oxalic acid for 30 min and dried at 180 °C for 4 h to obtain the required catalyst.

[0045] Example 6

[0046] Under stirring, 1.02 mol of 1,3 - propanediol (PDO) was added to 2.1 g AgNO 3 , 168 g Co(NO 3 ) 2 •6H 2 In a mixed solution of 2.1 g AgNO3, 168 g Co(NO3)2•6H2O and 618 g deionized water, after stirring evenly, 0.67 mol citric acid was added to obtain the corresponding mixed solution; the obtained mixed solution was continuously stirred and evaporated at 80 °C for 90 min to form a gel, and then dried at 120 °C for 6 h to obtain the corresponding precursor; then, the precursor was calcined in air at 300 °C for 1 h at a heating rate of 2 °C / min; finally, it was heated to 400 °C at a heating rate of 2 °C / min and kept at a constant temperature for 2 h to be tableted to obtain the corresponding catalyst precursor, and the precursor was etched in a mixed solution of 0.5 mol / L nitric acid + 2 mol / L acetic acid for 50 min and dried at 180 °C for 4 h to obtain the required catalyst.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that the mixed solution does not contain AgNO 3 , and the rest is the same as Example 1.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 3 is that the modifier 1,3-propanediol (PDO) was not added during the preparation process, and the rest is the same as Example 3.

[0051] Comparative Example 3

[0052] The difference between this comparative example and Example 3 is that the dispersing complexing agent citric acid was not added during the preparation process, and the rest is the same as Example 3.

[0053] Comparative Example 4

[0054] The difference between this comparative example and Example 3 is that the catalyst was not etched with a mixed solution of 0.5 mol / L nitric acid + 1.5 mol / L oxalic acid during the preparation process, and the rest is the same as Example 3.

[0055] The above examples and comparative examples were placed in a fixed bed to evaluate the activity of the catalyst for purifying VOCs (propane). The catalyst activity evaluation conditions were: the composition of the VOCs simulated gas was 0.3 vol% C 3 H 8 ,, 21 vol% O 2 , and the rest was nitrogen. The evaluation space velocity was 30000 (ml•g -1 •h -1 ). The reaction tail gas was detected and analyzed by gas chromatography. The catalytic activity was represented by the operating temperature when the conversion rate of propane was 90%. The evaluation results of the above catalysts are shown in Table 1.

[0056] Table 1 Preparation conditions and corresponding performance evaluation results of each example and comparative example

[0057]

[0058] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A cobalt-silver bimetallic synergistic VOCs purification catalyst, characterized in that: The active components of the catalyst are cobalt and silver, wherein the cobalt exists in the form of a mixed phase of CoO and Co3O4, and the silver exists in the form of a single substance Ag, and the molar percentage of Ag / (Ag+Co) is 0.5% to 12%.

2. The cobalt-silver bimetallic synergistic VOCs purification catalyst according to claim 1, characterized in that: The molar percentage of Ag / (Ag+Co) is 3.2%.

3. The method for preparing the cobalt-silver bimetallic synergistic VOCs purification catalyst according to claim 1 or 2, characterized in that: The steps include: S1. Add the modifier to the mixed solution of AgNO3 and Co(NO3)2•6H2O in stoichiometric amounts under stirring, and after stirring evenly, add the dispersant to obtain the corresponding mixed solution A; S2, continuously stirring and evaporating the mixed solution A at 80-120° C. to form a gel, and then drying at 120-180° C. to obtain a precursor B; S3, calcining the precursor B in air at 300-600°C at a heating rate of 2-10°C / min, and pressing into tablets to obtain a catalyst precursor C; S4, placing the catalyst precursor C in an acid solution for etching, and drying to obtain the desired catalyst.

4. The method according to claim 3, characterized in that In step S1, the modifier is selected from one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, and glycerol; the dispersant is selected from one or more of carboxymethyl cellulose, ascorbic acid, citric acid, tartaric acid, sodium citrate, and hexadecyltrimethylammonium bromide.

5. The method according to claim 3, characterized in that: In step S2, the evaporation time is 60 to 120 minutes; the drying time is 5 to 8 hours.

6. The method according to claim 3, characterized in that: In step S3, the calcination time is 1 to 4 hours.

7. The method according to claim 3, characterized in that In step S4, the etching acid solution is one of nitric acid, oxalic acid and acetic acid or a mixture of two of them, and the concentration of the acid solution is 0.2-6 mol / L.

8. The method according to claim 7, characterized in that The acid solution is a mixed solution of 0.5 mol / L nitric acid and 1.5 mol / L oxalic acid.

9. The use of the cobalt-silver bimetallic synergistic VOCs purification catalyst according to claim 1 or 2, characterized in that: Used for VOCs purification catalytic reaction.

10. The use according to claim 9, characterized in that: The VOCs is propane.

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