CN114471614A

CN114471614A - CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst and preparation method thereof

Info

Publication number: CN114471614A
Application number: CN202210148156.9A
Authority: CN
Inventors: 蒋毅; 张彪; 袁善良; 薄其飞; 刘照
Original assignee: Chengdu Organic Chemicals Co Ltd of CAS
Current assignee: Chengdu Organic Chemicals Co Ltd of CAS
Priority date: 2022-02-17
Filing date: 2022-02-17
Publication date: 2022-05-13

Abstract

The invention relates to the technical field of catalyst preparation, and aims to solve the problems of insufficient low-temperature activity and higher reaction temperature of the current cobalt-based catalytic combustion catalyst, in particular to the problem of lower activity of a supported cobalt-based catalytic combustion catalyst; a CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst is provided, comprising a cobalt oxide, a promoter metal or an oxide thereof, a support and a modifier; the preparation method comprises the following steps: 1) modifying a carrier; 2) dissolving an organic acid complexing agent and an organic acid salt complexing agent in water to form a mixed organic complexing agent aqueous solution, and dissolving a salt solution of a water-soluble cobalt salt and an auxiliary metal component in water to form a mixed metal salt aqueous solution; 3) dropwise adding the mixed metal salt aqueous solution obtained in the step (2) into the mixed organic complexing agent aqueous solution under continuous stirring, keeping the temperature and stirring, and soaking the modified carrier obtained in the step (1) in the solution; 4) and forming and roasting to obtain the CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst. The catalyst prepared by the invention has high catalytic activity and low treatment temperature.

Description

CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst and preparation method thereof

Technical Field

The invention relates to the technical field of catalyst preparation, in particular to a CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst and a preparation method thereof.

Background

Volatile Organic Compounds (VOCs) are one of the major pollutants responsible for atmospheric and ecological deterioration. VOCs are a generic term for organic compounds with a saturated vapor pressure of more than 70Pa at normal temperature and a boiling point of less than 260 ℃ at normal pressure, and include alkanes, aromatics, alcohols, aldehydes, ketones, acids, esters, ethers, halogenated hydrocarbons, and other heteroatom volatile organic compounds. Some VOCs have toxicity, or are disabled and teratogenic, which cause direct harm to human bodies, and some VOCs form acid rain, destroy ozone layers, generate greenhouse effect and the like, which indirectly affect the health of human bodies. The VOCs exist in a gaseous state, a mist state or an organic aerosol state formed by adsorption and concentration of particles in the air under certain environmental conditions, are a main component of inhalable particles (PM2.5), and are a main source of air pollution.

Catalytic combustion is an efficient method for deeply treating VOCs pollution, but the cost of a catalyst and the operation cost are key factors for restricting the development of the catalyst. Although the noble metal type catalyst has better catalytic combustion performance on VOCs such as aromatic hydrocarbon and the like, the noble metal type catalyst has the defects of high cost, poor heat-resistant stability and the like, and has relatively poor activity on alkane volatile organic compounds. The transition metal compound of non-noble metal has wide source and low price, and the prepared catalyst has good high-temperature stability, particularly the transition metal cobalt (Co) and the oxide thereof which belong to the VIII family with the noble metal and have similar electronic structure and a plurality of variable valence states even show catalytic combustion performance superior to the noble metal in the catalytic combustion of alkane, ester and the like, and can obviously reduce the cost of the catalytic combustion catalyst, thereby having important significance for the popularization of the catalytic combustion technology and the realization of deep purification treatment of VOCs.

Although cobalt-based catalysts show better performance in alkane treatment, the cobalt-based catalysts still have the problems of insufficient activity and higher operation temperature. Chinese patent CN106268814A utilizes water-soluble amine and cobalt salt to prepare a flower-like cobaltosic oxide catalyst used for treating T of methane in a hydrothermal method₉₀The temperature was 333 ℃. The alkane has no obvious electron-deficient and electron-rich sites, so the molecular structure is stable, and the treatment difficulty is high. Wherein propaneBecause of its wide range in industrial exhaust gas, it is generally used as a representative of low carbon alkane and probe molecule for evaluation of VOCs catalyst purification treatment. In Chinese patent CN107952441A, a sol-gel method is adopted to prepare a VOCs treatment catalyst by drying and twice roasting cobalt nitrate and cerium nitrate complexed with citric acid, and the catalyst is used for treating T treated by propane₉₀The temperature can reach 310 ℃. A supported cobalt-based catalyst was prepared in chinese CN 110560063A. Silicon, aluminum and titanium oxides are soaked in cobalt nitrate solution, then the cobalt nitrate solution is loaded on a carrier by using a urea uniform precipitation method, a high-temperature stable load type core-shell structure cobaltosic oxide catalyst is prepared by modes of reduction-passivation-in-situ reoxidation and the like after calcination, and the catalyst prepared by loading cobalt on carriers of aluminum, titanium and the like is used for T treatment of propane₉₀The temperature is up to 400 ℃.

The loading of part of the carrier further reduces the catalytic oxidation capacity of the cobalt-based active component. In the actual application of the catalyst for purifying VOCs, active components are usually required to be loaded on a carrier with a certain shape so as to reduce resistance, reduce the cost of the catalyst and improve the specific surface area of the catalyst so as to achieve the purposes of exposing more active centers and improving the catalytic activity. Cobalt still belongs to relatively expensive metal in non-noble metal materials, and the cost of the catalyst can be obviously reduced by loading the cobalt on a carrier. However, when the cobalt-based active component is highly dispersedly supported on the carrier, the catalytic activity is significantly reduced due to the strong interaction with the carrier; when the cobalt-based active component is simply and mechanically mixed in the carrier, the activity is reduced due to the problems of reduced content, smaller specific surface area and the like.

In conclusion, the cobalt-based catalytic combustion catalysts currently used for the purification treatment of VOCs still have the problems of insufficient activity and high cost, and particularly, the activity of the supported cobalt-based catalysts is further limited.

Disclosure of Invention

The invention aims to provide a CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst and a preparation method thereof, and aims to solve the problems that the activity of the conventional cobalt-based VOCs catalytic combustion catalyst is still insufficient, the cost is higher, and the catalytic activity is remarkably reduced particularly when the catalyst is loaded on a carrier.

The embodiment of the invention is realized by the following technical scheme:

a CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst comprises cobalt oxide, auxiliary metal or oxide thereof, a carrier and a modifier, wherein the cobalt oxide accounts for 1-50% of the total amount of the catalyst, the auxiliary metal or oxide thereof accounts for 0-30% of the total amount of the catalyst, the carrier accounts for 0-97% of the total amount of the catalyst, and the modifier accounts for 0-40% of the total amount of the catalyst in percentage by mass.

A preparation method of a CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst comprises the following steps:

(1) modification of a carrier: dissolving a salt solution of a modifier in water, soaking the carrier in the salt solution, and then drying and calcining the carrier to obtain a modified carrier;

(2) pretreatment liquid: dissolving an organic acid complexing agent and an organic acid salt complexing agent in water to form a mixed organic complexing agent aqueous solution, and dissolving a salt solution of a water-soluble cobalt salt and an auxiliary metal component in water to form a mixed metal salt aqueous solution;

(3) pretreatment: dropwise adding the mixed metal salt aqueous solution obtained in the step (2) into the mixed organic complexing agent aqueous solution under continuous stirring, keeping the temperature and stirring, and soaking the modified carrier obtained in the step (1) in the solution;

(4) molding: and drying and roasting the impregnated modified carrier to obtain the VOCs catalytic combustion cobalt-based catalyst.

The technical scheme of the embodiment of the invention at least has the following advantages and beneficial effects:

1. according to the CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst and the preparation method thereof, specific metal ions and a process are selected to modify a carrier, so that adverse effects caused by strong interaction between the carrier and active components are overcome, and the catalytic activity is obviously improved; meanwhile, the CoOx mixed phase catalyst is prepared by adopting a mixed complexing agent consisting of organic acid and organic acid salt, so that the Co-O bond strength of the catalyst is weakened, the lattice disorder degree is improved, the specific surface area is increased, the oxygen adsorption ratio is increased, the catalytic activity is improved, and the treatment temperature is further reduced.

2. According to the catalyst and the preparation method thereof, the auxiliary metal component is added on the basis of taking cobalt as a main active component, so that the crystal defects are further increased, the lattice disorder degree is improved, the synergistic effect is achieved, and the catalytic activity is enhanced.

3. The catalyst improves the content of the carrier, reduces the cost of the catalyst, reduces the interaction between the carrier and the active component, improves the dispersion degree of the active component, and improves the catalytic activity.

Detailed Description

In order to make the objects, 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. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The cobalt-based catalyst for catalytic combustion of CoOx mixed-phase VOCs and the preparation method thereof provided by the embodiment of the invention are specifically described below.

Further, the cobalt oxide and the precursor of the promoter metal or the oxide component thereof are pretreated with an aqueous solution containing an organic complexing agent and a salt solution of the promoter metal.

Further, the auxiliary metal is one or more of copper, manganese, silver, iron and vanadium; the carrier is one or more of titanium oxide, aluminum oxide, silicon oxide, molecular sieve and composite oxide carriers thereof; the modifier is one or more of oxides of magnesium, calcium, barium and zinc.

Furthermore, the molar ratio of the metal cobalt in the cobalt oxide to the auxiliary metal is 1: 1-100000: 1.

(1) modification of a carrier: dissolving a salt solution (such as one or more of nitrate, acetate, chloride or sulfate) of a modifier (magnesium, calcium, barium and zinc) in water, soaking a carrier (one or more of titanium oxide, aluminum oxide, silicon oxide, a molecular sieve and a composite oxide carrier thereof) in the salt solution for 1-10 hours, and then drying and calcining the carrier to obtain the modified carrier, wherein: the drying process condition is that the drying is carried out at 50-150 ℃ until the moisture content is lower than 1%; calcining the mixture for 3 to 5 hours at the temperature of between 300 and 700 ℃;

(2) pretreatment liquid: dissolving organic acid complexing agent and organic acid salt complexing agent in water to form mixed organic complexing agent water solution, and dissolving water soluble cobalt salt and auxiliary metal component salt solution (such as one or more of nitrate, acetate, chloride or sulfate) in water to form mixed metal salt water solution;

(3) pretreatment: dropwise adding the mixed metal salt aqueous solution obtained in the step (2) into a mixed organic complexing agent aqueous solution under continuous stirring, stirring at the temperature of 1-95 ℃ for 0.1-10 hours while keeping the temperature, and soaking the modified carrier obtained in the step (1) in the solution for 1-10 hours;

Further, in the step (2), the organic acid complexing agent is one or more of citric acid, oxalic acid, tartaric acid and malic acid; the organic acid salt complexing agent is one or more of sodium salt, potassium salt, ammonium salt, amine salt and the like of the organic acid.

Further, the sodium salt, potassium salt, ammonium salt and amine salt of the organic acid are one or more of sodium citrate, potassium citrate, ammonium citrate, ethanolamine citrate, sodium oxalate, potassium oxalate, ammonium oxalate, ethanolamine oxalate, sodium malate, potassium malate, ammonium malate, sodium tartrate, potassium tartrate, ammonium tartrate and ammonium tartrate.

Further, in the step (2), the molar ratio of the total organic carboxylate amount of the organic acid complexing agent and the organic acid salt complexing agent to the total amount of active component metal ions in the catalyst is 1: 0.1-1: 10. .

Further, in the step (2), the addition amount of the organic acid complexing agent and the organic acid salt complexing agent is 200: 1-1: 10 according to the molar ratio of the organic acid carboxylate to the organic acid salt carboxylate.

Example 1

(1) Dissolving calcium nitrate used for modifying the carrier in water to form a 2mol/L solution, taking 50ml of the solution, putting 50g of titanium dioxide carrier in the solution, soaking for 8 hours, drying at 120 ℃ until the water content is lower than 1%, and calcining at 600 ℃ for 4 hours to obtain the modified carrier;

(2) dissolving 7.2g of citric acid and 0.4g of ammonium citrate in 15g of water to form a mixed organic complexing agent aqueous solution, and dissolving 60ml of 2mol/L cobalt nitrate solution and 0.2g of silver nitrate to form a mixed metal salt aqueous solution;

(3) dropwise adding the mixed metal salt aqueous solution obtained in the step (2) into the mixed organic complexing agent aqueous solution under continuous stirring, keeping the temperature and stirring at 80 ℃ for 3 hours, and soaking the modified carrier obtained in the step (1) in the solution for 6 hours;

(4) and drying the impregnated modified carrier at 120 ℃ for 4 hours, and roasting at 650 ℃ for 4 hours to obtain the cobalt-based catalyst for catalytic combustion of VOCs.

Example 2

(1) Dissolving magnesium nitrate used for modifying the carrier in water to form a 2mol/L solution, taking 50ml of the solution, putting 50g of titanium dioxide carrier in the solution, soaking for 8 hours, drying at 120 ℃ until the water content is lower than 1%, and calcining at 600 ℃ for 4 hours to obtain the modified carrier;

(2) dissolving 7.2g of oxalic acid and 0.4g of sodium oxalate in 15g of water to form a mixed organic complexing agent aqueous solution, and dissolving 60ml of 2mol/L cobalt nitrate solution and 0.2g of manganese nitrate to form a mixed metal salt aqueous solution;

(3) dropwise adding the mixed metal salt aqueous solution obtained in the step (2) into the mixed organic complexing agent aqueous solution under continuous stirring, keeping the temperature and stirring at 60 ℃ for 5 hours, and soaking the modified carrier obtained in the step (1) in the solution for 8 hours;

(4) and drying the impregnated modified carrier at 100 ℃ for 10 hours, and roasting at 600 ℃ for 3 hours to obtain the cobalt-based catalyst for catalytic combustion of VOCs.

Example 3

(1) Dissolving zinc acetate used for modifying the carrier in water to form a 2mol/L solution, taking 50ml of the solution, putting 50g of titanium dioxide carrier in the solution, soaking for 6 hours, drying at 100 ℃ until the water content is lower than 1%, and calcining at 600 ℃ for 4 hours to obtain the modified carrier;

(2) dissolving 7.2g of malic acid and 0.4g of sodium malate in 15g of water to form a mixed organic complexing agent aqueous solution, and dissolving 60ml of 2mol/L cobalt nitrate solution and 0.2g of vanadium nitrate to form a mixed metal salt aqueous solution;

(3) dropwise adding the mixed metal salt aqueous solution obtained in the step (2) into the mixed organic complexing agent aqueous solution under continuous stirring, keeping the temperature and stirring at 75 ℃ for 7 hours, and soaking the modified carrier obtained in the step (1) in the solution for 7 hours;

(4) and drying the impregnated modified carrier at 100 ℃ for 15 hours, and roasting at 600 ℃ for 3 hours to obtain the cobalt-based catalyst for catalytic combustion of VOCs.

Example 4

(2) dissolving 7.2g of citric acid and 0.4g of ammonium citrate in 15g of water to form a mixed organic complexing agent aqueous solution, and dissolving 60ml of 2mol/L cobalt nitrate solution and 0.15g of silver nitrate to form a mixed metal salt aqueous solution;

Comparative example 1

This comparative example differs from example 1 in that: in the step (1): 50g of deionized water solution is taken, 50g of titanium dioxide carrier is placed in the deionized water solution to be soaked for 8 hours, then the titanium dioxide carrier is dried at 120 ℃ until the water content is lower than 1 percent, and then the titanium dioxide carrier is calcined at 600 ℃ for 4 hours to obtain a comparative blank carrier; in the step (2): without silver nitrate.

Comparative example 2

This comparative example differs from example 1 in that: in the step (1): dissolving calcium nitrate used for modifying the carrier in water to form 1mol/L solution, taking 50ml of the solution, putting 50g of titanium dioxide carrier in the solution, soaking for 8 hours, drying at 120 ℃ until the water content is lower than 1%, and calcining at 600 ℃ for 4 hours to obtain the modified carrier; in the step (2): 7.2g of citric acid and 0.4g of ammonium citrate were dissolved in 15g of water to form a mixed organic complexing agent aqueous solution, free of silver nitrate.

Comparative example 3

This comparative example differs from example 1 in that: in the step (2): without silver nitrate.

Comparative example 4

This comparative example differs from example 1 in that: in the step (2): ammonium citrate 0.2g, and no silver nitrate.

Comparative example 5

This comparative example differs from example 1 in that: in the step (2): no ammonium citrate and no silver nitrate.

Comparative example 6

This comparative example differs from comparative example 1 in that: ammonium citrate was not included.

Comparative example 7

This comparative example differs from comparative example 6 in that: step (1) is not included.

Comparative example 8

This comparative example differs from comparative example 7 in that: the organic complexing agent solution in the step (2) contains ammonium citrate, namely the step is as follows: dissolving 7.2g of citric acid and 0.4g of ammonium citrate in 15g of water to form an organic complexing agent solution, and taking 60ml of 2mol/L cobalt nitrate solution for later use.

Examples of the experiments

The catalytic activity of the catalysts obtained in the above examples and comparative examples was evaluated. The evaluation of the catalyst activity was carried out on a fixed bed reactor using propane as a probe molecule, the amount of the catalyst used was 0.6g, the propane concentration was 0.2 vol%, the remainder was air, and the gas flow rate was 200 mL/min. The reaction off-gas was analyzed by gas chromatography detection, and the catalytic activity was represented by the operating temperature at which the conversion of propane was 90%, and the evaluation results of the above catalyst are shown in table 1. T in examples 2 and 3₉₀248 ℃ and 251 ℃ respectively.

As can be seen from the data in table 1: comparing the data of comparative examples 6 and 7, it is shown that the catalytic activity of the cobalt-based catalyst is significantly reduced when the cobalt-based catalyst is loaded on a carrier, because of the strong interaction between the cobalt-based catalyst and the carrier, the catalytic activity is significantly reduced; the comparison of the data of the comparative examples 1, 2 and 3 shows that the activity of the cobalt-based catalyst on the carrier is obviously improved after the carrier is treated by the modifier; ③ comparative example 6 in comparative examples 1 and 6 No organic acid salt, T₉₀Higher temperature, lower catalytic activity, similar to comparative examples 7 and 8; and comparative example 4 in comparative examples 3 and 4, the amount of organic acid salt in the aqueous solution of the mixed organic complexing agent in comparative example 3 was relatively low compared to that of the organic acid, T₉₀The temperature is high, and the catalytic activity is low; from the two groups of comparative data, it can be shown that after the organic acid salt is added as the mixed complexing agent, the catalytic activity effect is remarkably improved due to the formation of a CoOx mixed phase structure; comparison of examples 1 and 4 with comparative example 3The addition amount of the auxiliary is less than that of example 1, while comparative example 3 does not contain the auxiliary, T of example 4 and comparative example 3₉₀The temperatures were higher than in example 1 and lower than in comparative example 4, which indicates that the synergistic effect between the promoter metal component and the support, modifier and aqueous solution of mixed organic complexing agent and mixed aqueous solution of mixed metal salt has a significant effect on the catalytic activity of the entire catalyst system, and the catalytic activity of the catalyst can be significantly improved.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The CoOx mixed phase VOCs catalytic combustion cobalt-based catalyst is characterized by comprising 1-50% of cobalt oxide, 0-30% of assistant metal or oxide thereof, 0-97% of carrier and 0-40% of modifier by mass.

2. The CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst of claim 1, wherein the cobalt oxide and a precursor of a promoter metal or an oxide component thereof are pretreated with an aqueous solution comprising an organic complexing agent and a salt solution of a promoter metal.

3. The CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst of claim 1, wherein the promoter metal is one or more of copper, manganese, silver, iron, vanadium; the carrier is one or more of titanium oxide, aluminum oxide, silicon oxide, molecular sieve and composite oxide carriers thereof; the modifier is one or more of oxides of magnesium, calcium, barium and zinc.

4. The CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst of claim 1, wherein the molar ratio of metallic cobalt to promoter metal in the cobalt oxide is 1:1 to 100000: 1.

5. A method for preparing a CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst according to any one of claims 1-4, comprising the steps of:

6. The method for preparing a CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst according to claim 5, wherein in the step (2), the organic acid complexing agent is one or more of citric acid, oxalic acid, tartaric acid and malic acid; the organic acid salt complexing agent is one or more of sodium salt, potassium salt, ammonium salt, amine salt and the like of the organic acid.

7. The preparation method of the CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst according to claim 5, wherein in the step (2), the molar ratio of the total organic carboxylate amount of the organic acid complexing agent and the organic acid salt complexing agent to the total amount of active component metal ions in the catalyst is 1: 0.1-1: 10.

8. The preparation method of the CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst according to claim 5, wherein in the step (2), the addition amount of the organic acid complexing agent and the organic acid salt complexing agent is 200: 1-1: 10 according to the molar ratio of the organic acid carboxylate to the organic acid salt carboxylate.

9. The preparation method of the CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst according to claim 5, characterized in that in the step (1), the catalyst is immersed for 1-10 hours; drying process conditions are 50-150 ℃, and drying is carried out until the moisture content is lower than 1%; the calcination process condition is 300-700 ℃ for 3-5 hours.

10. The preparation method of the CoOx mixed-phase VOCs catalytic combustion cobalt-based catalyst according to claim 5, wherein in the step (3), the mixture is stirred at a temperature of 1-95 ℃ for 0.1-10 hours, and is immersed for 1-10 hours.