CN106391009A - Preparation method and application of catalyst for catalytic oxidation of VOCs - Google Patents

Abstract

The invention discloses a method for preparing a catalyst for catalytic oxidation of VOCs. The salt of noble metal Pt is dissolved in water to form a chloroplatinic acid solution; powdered TiO ₂ after washing and drying is used as a carrier; CeO ₂ , lemon Put the acid as an auxiliary agent and TiO ₂ into a beaker, add the chloroplatinic acid solution dropwise, and stir vigorously at the same time, adjust the rotor speed of the stirrer to make it mix evenly, and soak overnight. After impregnation, evaporate to dryness in a constant temperature water bath, dry in an oven, and dry to obtain a precursor for oxidizing VOCs catalyst; place this precursor in a muffle furnace, and roast it for 5 hours at 500°C in an air atmosphere; In a tube furnace at 300°C and H ₂ atmosphere, reduce for 3 hours to obtain a catalyst for catalytic oxidation of VOCs. The catalyst prepared by the invention has the advantages of high selectivity, high activity, high stability, low light-off temperature, long service life and the like, and has good application value and prospect.

Description

A kind of preparation method and application of catalyst for catalytic oxidation of VOCs

technical field

The invention relates to a preparation method and application of a catalyst used for catalytic conversion of VOCs, and belongs to the technical field of catalysts and preparation thereof.

Background technique

Volatile Organic Compounds (Volatile Organic Compounds, referred to as VOCs) refer to organic compounds with a boiling point between 50-260°C under normal pressure. The composition of VOCs is complex, and can be divided into linear alkanes, cycloalkanes, halogenated hydrocarbons, aromatic hydrocarbons, alcohols, ketones, phenols, ethers, esters, etc. according to their functional groups. Many VOCs have neurotoxicity, kidney and liver toxicity, and even carcinogenicity. They can damage blood components and cardiovascular system, cause gastrointestinal disorders, induce immune system, endocrine system and hematopoietic system diseases, and cause metabolic defects. The composition of organic waste gas is extremely complex, and a series of chemical reactions can occur in the atmosphere with other gas pollutants (such as SOx, NOx), particulate matter, etc. under certain conditions, resulting in secondary pollution, resulting in photochemical smog, secondary organic aerosols and Increased concentration of atmospheric organic acids, etc., endanger human health and plant growth; and halogenated hydrocarbons will have a chain reaction with ozone in the stratosphere, destroying the atmospheric ozone layer, and then affecting the global environment. VOCs exhaust gas will seriously pollute the environment and endanger human health. . With the continuous improvement of the degree of industrialization, the pollution of VOCs has a tendency to further expand. Therefore, in-depth research on its pollution control technology is of great significance for the control and treatment of the pollution of VOCs exhaust gas. Due to the different characteristics of various VOCs exhaust gases, targeted treatment methods should be adopted in order to reduce treatment costs and avoid secondary pollution. After years of research, the VOCs purification technologies that have been successfully applied in industry mainly include absorption method, adsorption method, condensation method, membrane separation method, biochemical method, low temperature plasma method, photocatalytic oxidation method and combustion method. Catalytic combustion is currently the most widely used VOCs purification technology in the world. The catalytic combustion method refers to the use of catalysts to reduce the activation energy required for the oxidation reaction of organic matter and increase the reaction rate, so that flameless combustion can be carried out at a lower temperature, and finally converted into harmless substances such as CO ₂ and H ₂ O. Compared with direct combustion and thermal combustion, catalytic combustion not only has a wide range of applications and high purification efficiency, but also has a low combustion temperature (about 200°C-450°C), short residence time (about 0.25s), and avoids high temperature generation. Secondary pollution caused by NOx, etc. High performance oxidation catalyst is the key to catalytic combustion technology.

At present, the active components of oxidation catalysts used for catalytic combustion to remove VOCs mainly include noble metals (mainly Pd, Pt), transition metals (Cu, Mn, Cd, Ni, Co, Cr, etc.) and rare earth metals (Ce, La etc.) oxides, and composite oxides (perovskite, spinel and Cu-Mn-O, etc.). Carriers mainly include oxides (Al ₂ O ₃ , TiO ₂ , SiO ₂ , CeO ₂ , ZrO ₂ , Fe ₂ O ₃ , etc.), zeolites, honeycomb ceramics, metal supports, etc. Loading methods include impregnation method, electrodeposition method, sol-gel method, reverse microemulsion method and precipitation method. These catalyst materials have their own advantages and disadvantages. For example, noble metal catalysts have the best catalytic effect, but they are expensive and have poor poisoning resistance. It is difficult to control the position of precipitation and the repeatability is not good; the nucleation process is more likely to occur in solution rather than On the carrier; the generated metal particles are larger and the uniformity is not good. The exhaust gas generated during roasting will cause environmental pollution, and the active components will migrate during drying. Oxide catalysts have certain selectivity to the treated organic gases and the effect is less stable than that of noble metals. Therefore, reasonable design of catalyst materials, so that the catalyst can play a more effective role, so that the catalytic effect and economic efficiency can be better unified, and increase the stability and adaptability of the catalyst, are currently technical problems that need to be solved urgently.

\Invention content

Aiming at the above existing problems and overcoming the deficiencies of the prior art, the present invention provides a novel VOCs oxidation catalyst with high selectivity, high activity, high stability, low light-off temperature and long service life. The porous material _TiO2 with good thermal stability is used as the carrier, and the noble metal Pt is added as the active component. Rare earth oxides have a catalytic effect and can improve catalytic activity and thermal stability, among which CeO ₂ has an obvious oxygen storage effect. The additive Ce can not only improve the activity of the catalyst, but also improve the anti-aging performance of the catalyst and improve the ability of TiO2 to resist phase change. As a competitive adsorbent, citric acid can effectively change the dispersion state of Pt on the surface and even inside of the carrier, and control the distribution of Pt. Compared with pure noble metal catalysts, the catalyst prepared by this technology can greatly reduce the amount of noble metal used, and through the reasonable distribution of less noble metal, it can catalyze some macromolecules with strong oxidation resistance in VOCs. role, to achieve the effect of rapid oxidation. Reasonable distribution of catalyst materials can not only achieve a good catalytic effect, but also greatly reduce the usage of precious metals and save costs.

In order to solve the above-mentioned technical problems, the present invention proposes a method for preparing a catalyst for the catalytic oxidation of VOCs, using porous material _TiO2 as a carrier, using CeO2 and citric _acid as auxiliary agents, and adding noble metal Pt as Active components, the specific steps are as follows:

Step 1. Dissolving the chloroplatinic acid solid containing crystal water in water to form a 0.049mmol/mL chloroplatinic acid solution, and adding a few drops of 0.1% hydrochloric acid by volume to prevent the chloroplatinic acid solution from decomposing;

Get powdered TiO ₂ wash with deionized water several times, dry for subsequent use;

Step 2. Add appropriate amount of CeO ₂ , citric acid, and TiO ₂ into a glass container, and dropwise add chloroplatinic acid solution into the container, wherein the mass ratio of CeO ₂ : citric acid: TiO ₂ : Pt is 6- 13:1:89～90:1, while adding the chloroplatinic acid solution dropwise, stir vigorously at a constant temperature of 60～80°C for 60～80min, then soak the mixture overnight;

Step 3: Take the impregnated mixed solution, heat and evaporate to dryness in a constant temperature water bath at 80°C, put it in an oven at 80°C for drying for 12 hours, and obtain a solid;

Step 4, placing the above solid in a muffle furnace, and calcining for 5 hours at 500°C in an air atmosphere to obtain a catalyst precursor;

Step 5. Place the above precursor in a tube furnace at 300°C and H ₂ atmosphere, and reduce it for 3 hours to obtain a catalyst for catalytic oxidation of VOCs.

Oxidize the catalyst prepared above for the catalytic oxidation of VOCs, and perform a fixed-bed reaction at a reaction temperature of 70-300° C., so as to oxidize volatile organic compounds into carbon dioxide and water. The volatile organic compound includes one of acetone, ethyl acetate and n-pentane.

Compared with prior art, the beneficial effect of the present invention is:

(1) The inventive method adopts common and economical inorganic salts of precious metals and rare earth oxides to prepare the catalyst for oxidizing VOCs;

(2) The metal particles generated by the catalyst are small, with a particle size ranging from 2 to 10 nm and good uniformity;

(3) Effectively change the dispersion state of Pt on the surface and even inside of the carrier, and control the uniform distribution of precious metal Pt;

(4) The catalyst has good aging resistance and phase change resistance;

(5) The catalyst has high selectivity and purification efficiency for the purification of VOCs, and the operating temperature range can be 70-300°C. As shown in Figure 1, when the conversion rate is 100%, the conversion temperature is only about 250°C. Can.

In summary, the catalyst prepared by the present invention is used to oxidize volatile organic compounds into carbon dioxide and water, has the advantages of high selectivity, high activity, high stability, low light-off temperature, long service life, etc., and has good application value and prospect.

Description of drawings

Fig. 1 is the conversion ratio of the catalyst that the embodiment of the present invention 1 obtains to acetone;

Fig. 2 is the XRD figure of the catalyst that example 1 of the present invention obtains;

Fig. 3 is the XRD figure of the catalyst that example 2 of the present invention obtains;

Figure 4 is the XRD pattern of the catalyst obtained in Example 3 of the present invention.

detailed description

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the described specific embodiments are only for explaining the present invention, and are not intended to limit the present invention.

Example 1

(1) Dissolve the platinum chlorate solid containing crystal water in water to prepare a 0.049mmol/mL chloroplatinic acid solution, and add a few drops of hydrochloric acid, wherein the volume ratio of hydrochloric acid is 0.1%, to prevent its decomposition. Get 2.7259g powdery _TiO Carry out repeatedly cleaning with deionized water, dry for subsequent use;

(2) Add 0.3758g CeO ₂ , 0.0302g citric acid and TiO ₂ into a beaker, add dropwise 4.27ml of chloroplatinic acid solution while vigorously stirring, stir at a constant temperature of 80°C, and adjust the rotor of the stirrer to make it evenly mixed. After about 60 minutes, stop stirring and soak overnight;

(3) Take the impregnated mixed solution, heat and evaporate to dryness in a constant temperature water bath at 80°C, and put it in an oven at 80°C for drying for 12 hours;

(4) Place the above-mentioned solid in a muffle furnace, and roast it for 5 hours at 500° C. under an air atmosphere to obtain a catalyst precursor;

(5) Place the above precursor in a tube furnace at 300°C and _H2 atmosphere, and reduce it for 3 hours to obtain the target product catalyst for VOCs treatment. The XRD pattern of the catalyst is shown in Figure 2, and its catalytic activity is shown in Figure 1 , wherein, the activity test conditions: 1000ppm acetone, O ₂ , N ₂ as the balance gas, the reaction temperature is 70 ~ 300 ℃, the space velocity is 25000h ^-1 , the experimental equipment: VOCs catalytic oxidation evaluation device.

Example 2

(1) Dissolve the platinum chlorate solid containing crystal water in water to prepare a 0.049mmol/mL chloroplatinic acid solution, and add a few drops of hydrochloric acid, wherein the volume ratio of hydrochloric acid is 0.1%, to prevent its decomposition. Get 2.7905g powdery _TiO Carry out repeatedly cleaning with deionized water, dry for subsequent use;

(2) Add 0.1892g CeO ₂ , 0.0340g citric acid and TiO ₂ into a beaker, add dropwise 4.27ml of chloroplatinic acid solution while stirring vigorously, stir at a constant temperature of 60°C, and adjust the rotor of the stirrer to mix evenly. After about 60 minutes, stop stirring and soak overnight;

(3) Take the impregnated mixed solution, heat and evaporate to dryness in a constant temperature water bath at 80°C, and put it in an oven at 80°C for drying for 12 hours;

(4) Place the above-mentioned solid in a muffle furnace, and roast it for 5 hours at 500° C. under an air atmosphere to obtain a catalyst precursor;

(5) Place the above precursor in a tube furnace at 300°C and H ₂ atmosphere, and reduce it for 3 hours to obtain the target catalyst for VOCs treatment. The XRD pattern of the catalyst is shown in Figure 3.

Example 3

(1) Dissolve the platinum chlorate solid containing crystal water in water, prepare 0.049mmol/mL chloroplatinic acid solution, add a few drops of hydrochloric acid, wherein the volume ratio of hydrochloric acid is 0.1%, to prevent its decomposition. Get 2.7581g powdery _TiO Carry out repeatedly cleaning with deionized water, dry for subsequent use;

(2) Add 0.2655g CeO ₂ , 0.0345g citric acid and TiO ₂ into a beaker, add dropwise 4.27ml of chloroplatinic acid solution while vigorously stirring, stir at a constant temperature of 60°C, and adjust the rotor of the stirrer to mix evenly. After about 80 minutes, stop stirring and soak overnight;

(3) Take the impregnated mixed solution, heat and evaporate to dryness in a constant temperature water bath at 80°C, and put it in an oven at 80°C for drying for 12 hours;

(4) Place the above-mentioned solid in a muffle furnace, and roast it for 5 hours at 500° C. under an air atmosphere to obtain a catalyst precursor;

(5) The above precursor was placed in a tube furnace at 300 °C and H ₂ atmosphere, and reduced for 3 hours to obtain the target product catalyst for VOCs treatment. The XRD pattern of the catalyst is shown in Figure 4.

In the preparation method of the present invention, the mass ratio of CeO ₂ : citric acid: TiO ₂ : Pt is 6-13:1:89-90:1. In this ratio, the distribution of Pt can be best promoted. The stirring process Stir vigorously at a constant temperature of 60-80°C for 60-80min, heat and evaporate to dryness in a constant-temperature water bath at 80°C, put it in an oven at 80°C for 12 hours, then place it in a muffle furnace, and bake it at 500°C and an air atmosphere for 5 hours. Place in a tube furnace at 300°C and H ₂ atmosphere, and reduce for 3h.

Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the enlightenment of the present invention, many modifications can be made without departing from the gist of the present invention, and these all belong to the protection of the present invention.

Claims (3)

1. A preparation method for a catalyst used for VOCs catalytic oxidation, characterized in that, use porous material _TiO2 as carrier, with CeO2 and citric _acid as auxiliary agent, add noble metal Pt as active component simultaneously, concrete steps as follows: Step 1. Dissolving the chloroplatinic acid solid containing crystal water in water to form a 0.049mmol/mL chloroplatinic acid solution, and adding a few drops of 0.1% hydrochloric acid by volume to prevent the chloroplatinic acid solution from decomposing; Get powdered TiO ₂ wash with deionized water several times, dry for subsequent use; Step 2. Add appropriate amount of CeO ₂ , citric acid, and TiO ₂ into a glass container, and dropwise add chloroplatinic acid solution into the container, wherein the mass ratio of CeO ₂ : citric acid: TiO ₂ : Pt is 6- 13:1:89～90:1, while adding the chloroplatinic acid solution dropwise, stir vigorously at a constant temperature of 60～80°C for 60～80min, then soak the mixture overnight; Step 3: Take the impregnated mixed solution, heat and evaporate to dryness in a constant temperature water bath at 80°C, put it in an oven at 80°C for drying for 12 hours, and obtain a solid; Step 4, placing the above solid in a muffle furnace, and calcining for 5 hours at 500°C in an air atmosphere to obtain a catalyst precursor; Step 5. Place the above precursor in a tube furnace at 300°C and H ₂ atmosphere, and reduce it for 3 hours to obtain a catalyst for catalytic oxidation of VOCs. 2. An application of a catalyst for catalytic oxidation of VOCs, oxidizing the catalyst for catalytic oxidation of VOCs prepared by the preparation method according to claim 1, and performing a fixed-bed reaction at a reaction temperature of 70 to 300°C , thereby oxidizing volatile organic compounds into carbon dioxide and water. 3. The application of the catalyst for VOCs catalytic oxidation according to claim 2, characterized in that: the volatile organic compound comprises one of acetone, ethyl acetate and n-pentane.