CN118237014A - Preparation method and application of precious metal catalyst - Google Patents

Abstract

The invention provides a preparation method and application of a noble metal catalyst, wherein the preparation method comprises the following steps: step 1, mixing a noble metal precursor aqueous solution, second carrier powder and a reducing agent, and performing ball milling to obtain coated catalyst slurry; and 2, coating the coating type catalyst slurry obtained in the step 1 on a first carrier, and then drying and roasting to obtain the noble metal catalyst. The catalyst obtained by the method has higher noble metal dispersity.

Description

Preparation method and application of precious metal catalyst

Technical Field

The present invention belongs to the field of volatile organic compound treatment, and specifically relates to a method for preparing a noble metal catalyst and application of the noble metal catalyst in volatile organic compound treatment.

Background technique

The main technologies for the treatment of volatile organic compounds (VOCs) include direct combustion, adsorption, absorption, catalytic combustion, and biological methods. Among them, the catalytic combustion method has the advantages of high efficiency, energy saving, low reaction temperature, and no secondary pollution, and is more suitable for the treatment of various VOCs waste gases in petrochemical enterprises. Catalyst research is an important research direction for catalytic combustion technology. So far, VOCs treatment catalysts are mainly Pt, Pd, and Rh precious metal catalysts. Such catalysts are mostly based on cordierite honeycomb ceramics as the first carrier, and a second carrier mainly composed of γ-Al ₂ O ₃ is coated on it to increase the specific surface area and the comprehensive performance of the carrier. Various additives with special functions are usually added to the second carrier to improve the catalyst performance, and finally the precious metal active components are impregnated on the second carrier to obtain the product. Due to the limited impregnation level, the precious metal distribution effect is poor, resulting in a large amount of precious metals and high catalyst costs.

CN105148908A discloses a method for preparing a supported precious metal catalyst, using precious metal as an active component to prepare a precursor solution, and uniformly mixing it with a carrier; adding a liquid reducing agent to reduce the precious metal ions adsorbed or free on the surface or in the pores of the carrier, so that the precious metal is applied to the carrier in a reduced state to obtain a mixed slurry; coating the mixed slurry on a cordierite substrate or a metal substrate, and calcining to obtain a supported precious metal catalyst. In the invention, the reduced component is in an ionic state, and usually does not react with the added reducing agent. However, when ordinary reduction methods such as heating are used, the precious metal reduced state is easily aggregated to form large particles during the reaction process, which affects the dispersibility of the precious metal.

CN 103127936 discloses a method for preparing a catalyst by a liquid phase ball milling partial reduction method, and relates to a method for preparing a copper-based catalyst for dimethyldichlorosilane synthesis reaction by a liquid phase ball milling partial reduction method. The method comprises the following steps: using copper oxide as a raw material, adding a solvent medium containing a reducing substance, and reducing the copper oxide particles by mechanical ball milling, and obtaining a copper-based catalyst containing a ternary component of copper, cuprous oxide and copper oxide after suction filtration, drying and crushing. By adjusting parameters such as the type and concentration of the reducing agent and the ball milling conditions, a ternary copper catalyst with adjustable composition and controllable particle size is obtained. Under the action of high-energy grinding force, the invention continuously grinds and reduces the copper oxide, and while the particles are continuously reduced, the copper oxide is reduced layer by layer from the outside to the inside, forming a multi-phase mosaic structure wrapped layer by layer.

CN 106492795 discloses a DOC oxidation catalyst for diesel engine exhaust emissions and a preparation method, comprising: alumina or silicon-modified alumina with a large specific surface area, cerium zirconium oxide or cerium dioxide with a large specific surface area, sulfur poisoning-resistant materials, and materials with adsorption effects on HC. In the invention, ball milling is used to prepare coating slurry for subsequent coating. This technology only reduces the powder particles by ball milling to improve the performance of the coating slurry.

CN 109093124 discloses a method for preparing metal nanomaterials by high-energy ball milling reduction. After the metal oxide and the reducing agent are evenly mixed, they are placed in a ball milling tank and protected by an inert gas. The metal oxide and the reducing agent are fully reacted by high-energy ball milling to finally obtain metal nanoparticles with uniform crystal grains and a particle size of about 3-10nm. The reducing agent needs to be added during the ball milling process to achieve the reduction of the metal. The ball milling reduction described in the technology is protected by an inert gas so that the metal oxide is gradually reduced during the ball milling process.

CN 102646828 discloses a method for preparing LiMnPO ₄ /C, a positive electrode material for lithium ion batteries, comprising mixing a lithium source, a high-valent manganese source and a phosphorus source in a lithium, manganese and phosphorus element molar ratio of 1:1:1, wherein the valence of manganese ions in the high-valent manganese source should be greater than 2; adding an organic carbon source reducing agent, and performing mechanical activation reduction at 5 to 35° C. for 0.5 to 20 hours, thereby reducing the high-valent manganese to divalent manganese and preparing an amorphous LiMnPO ₄ precursor, and then heating to 400 to 800° C. in a non-oxidizing atmosphere, and maintaining the temperature for 0.5 to 12 hours, to obtain a pure phase LiMnPO ₄ /C material. The ball milling described in the technology realizes mechanical activation, and the ball milling only plays a stirring role.

Therefore, those skilled in the art still need to study the preparation of supported noble metal catalysts to improve the dispersion of noble metals.

Summary of the invention

The main purpose of the present invention is to provide a method for preparing a noble metal catalyst and its application, so as to overcome the defect of poor dispersibility of the noble metal in the noble metal catalyst in the prior art.

In order to achieve the above object, the present invention provides a method for preparing a noble metal catalyst, comprising the following steps:

Step 1, mixing a noble metal precursor aqueous solution, a second carrier powder and a reducing agent, and ball milling to obtain a coated catalyst slurry;

Step 2: coating the coated catalyst slurry of step 1 onto the first carrier, and then drying and calcining to obtain a precious metal catalyst.

In the method for preparing the noble metal catalyst of the present invention, a dispersant and/or a pH buffer is further added in step 1.

The method for preparing a precious metal catalyst described in the present invention, wherein the precious metal precursor aqueous solution is an aqueous solution containing a Pt compound or a Pd compound, and the Pt compound or the Pd compound is soluble in water; the mass concentration of the precious metal precursor aqueous solution is 0.1wt% to 5wt% in terms of the precious metal element.

The method for preparing a noble metal catalyst of the present invention, wherein the second carrier powder is _TiO2 , cerium- _zirconium solid solution, γ- _Al2O3 , ZSM-5 molecular sieve or a mixture thereof; the reducing agent is alcohols, aldehydes, organic acids or sodium borohydride; wherein the noble metal precursor is calculated as a single noble metal, and the mass ratio of the noble metal precursor, the second carrier powder and the reducing agent is 1:20-1000:10-100.

The method for preparing a precious metal catalyst of the present invention comprises the following steps: the dispersant is a non-ionic dispersant, the pH buffer is citric acid-citrate; the precious metal precursor is calculated as a single precious metal, the molar ratio of the precious metal precursor to the pH buffer is 1:6-20, and the mass ratio of the precious metal precursor to the dispersant is 1:5-30.

The method for preparing a precious metal catalyst of the present invention comprises the following steps: the ball milling time is 0.1 to 30 hours, the ball milling speed is 100 to 1000 rpm, and the material particles after ball milling are less than 30 μm; and the solid content of the coated catalyst slurry is 5wt% to 60wt%.

The method for preparing the noble metal catalyst of the present invention, wherein the content of the noble metal in the coated catalyst slurry accounts for 0.1wt% to 5wt% of the solid.

The method for preparing the precious metal catalyst described in the present invention, wherein, after the first carrier is coated with the catalyst slurry in step 2, it also includes the steps of purging the first carrier with gas and aging, the aging temperature is 20°C to 40°C, and the aging time is 6-18h; the coating amount of the coated catalyst slurry is 5g/L to 200g/L.

The method for preparing the precious metal catalyst of the present invention comprises the following steps: the drying temperature is 100° C. to 120° C., and the drying time is 1 to 12 hours; the calcination temperature is 500° C. to 600° C., and the calcination time is 4 to 6 hours.

In order to achieve the above object, the present invention also provides the use of the noble metal catalyst obtained by the above preparation method in the treatment of volatile organic compounds.

Beneficial effects of the present invention:

The present invention mixes the precious metal precursor solution with the reducing agent and the carrier and then performs ball milling. On the one hand, the macroscopic size of the carrier can be reduced. More importantly, during the ball milling process, the mechanical energy of the mechanical friction point can be transmitted to the solution at that part, so that the temperature of the local solution increases, thereby turning the local part into a reaction center. Moreover, these reaction centers are changing at any time, so that the reduction reaction is carried out at a constantly changing new position. The reduced nano-precious metal particles generated by the reaction are directly loaded onto the surface of the carrier. In this way, the aggregation of the precious metal after reduction can be avoided, the dispersion of the precious metal can be improved, and the activity and metal utilization rate of the obtained precious metal catalyst can be improved.

Detailed ways

The technical scheme of the present invention is described in detail below. The following implementation modes are implemented on the premise of the technical scheme of the present invention, and a detailed implementation process is given. However, the protection scope of the present invention is not limited to the following implementation modes. The structures or experimental methods of specific conditions are not specified in the following implementation modes, and generally conventional conditions are followed.

The present invention provides a method for preparing a noble metal catalyst, comprising the following steps:

Step 1, mixing a noble metal precursor aqueous solution, a second carrier powder and a reducing agent, and ball milling to obtain a coated catalyst slurry;

Step 2: coating the coated catalyst slurry of step 1 onto the first carrier, and then drying and calcining to obtain a precious metal catalyst.

The present invention mixes the precious metal precursor solution with the reducing agent and the carrier and then performs ball milling. On the one hand, the macroscopic size of the carrier can be reduced. More importantly, during the ball milling process, the mechanical energy of the mechanical friction point can be transmitted to the solution at that part, so that the temperature of the local solution increases, thereby turning the local part into a reaction center. Moreover, these reaction centers are changing at any time, so that the reduction reaction is carried out at a constantly changing new position. The reduced nano-precious metal particles generated by the reaction are directly loaded onto the surface of the second carrier. In this way, the aggregation of the precious metal after reduction can be avoided, the dispersion of the precious metal can be improved, and the activity and metal utilization rate of the obtained precious metal catalyst can be improved.

In addition, a large number of reaction centers will be generated during the ball milling process, which will promote molecular movement and electron transfer, allowing the precious metal to react with the reducing agent, avoiding the step of re-reduction and activation in the subsequent use of the catalyst, and thus avoiding the growth of particles during the reduction process of the precious metal.

Furthermore, the carrier powder is rich in pores. Since the carrier powder is immersed in the precious metal precursor solution, the solute in the solution is distributed inside and outside the carrier pores. Therefore, the reduction reaction is also distributed inside and outside the carrier pores. The reduced metal particles are distributed on various surfaces inside and outside the carrier pores, further improving the dispersion of the precious metal.

The present invention does not particularly limit the precious metal in the precious metal precursor, which may be Pt or Pd. The precious metal precursor is a Pt-containing compound or a Pd-containing compound, and the precious metal precursor aqueous solution is an aqueous solution of a Pt-containing compound or an aqueous solution of a Pd-containing compound. In one embodiment, the Pt-containing compound and the Pd-containing compound of the present invention are soluble in water. In another embodiment, the Pt-containing compound and the Pd-containing compound of the present invention are soluble salts of Pt, soluble salts of Pd, soluble acids, such as nitrates, chlorides, etc. In yet another embodiment, the mass concentration of the precious metal precursor aqueous solution of the present invention is 0.1wt% to 5wt%, preferably 0.5wt% to 2wt%, based on the precious metal element.

The present invention does not impose any particular limitation on the second carrier powder, and it may be any commonly used catalyst carrier material, preferably TiO ₂ , cerium-zirconium solid solution, γ-Al ₂ O ₃ , ZSM-5 molecular sieve and a mixture thereof.

In one embodiment, the reducing agent of the present invention can be alcohols, aldehydes, organic acids, sodium borohydride, preferably methanol and ethylene glycol.

In another embodiment, the precious metal precursor of the present invention is calculated as a single precious metal, and the mass ratio of the precious metal precursor, the second carrier powder and the reducing agent is 1:20-1000:10-100.

The present invention does not particularly limit the method of ball milling, and ball milling can be performed in a ball mill. The ball milling time is, for example, 0.1 to 30 hours, preferably 0.5 to 3 hours, the ball milling speed is 100 to 1000 rpm, and the material particles after ball milling are less than 30 μm.

In one embodiment, a dispersant and/or a pH buffer and a high molecular weight organic additive for optimizing coating properties are added during the mixing process of the precious metal precursor aqueous solution, the second carrier powder and the reducing agent of the present invention. In another embodiment, the molar ratio of the precious metal precursor to the pH buffer is 1:6-20, and the mass ratio of the precious metal precursor to the dispersant is 1:5-30, based on the precious metal element.

Some of the precious metals formed by the reduction of precious metal ions by the reducing agent of the present invention are directly loaded on the surface of the carrier to form highly dispersed reduced active sites at the nanometer (1-5nm) level. Even if some of them are not attached to the surface of the carrier in time, the collision and aggregation between particles will be reduced under the barrier effect of the dispersant, and they will be gradually loaded on the surface of the carrier in the subsequent ball milling process.

During the reduction process of the precious metals in the present invention, the pH value of the solution will continue to decrease. When it decreases to a certain level, the reduction reaction will no longer occur. Adding a pH buffer can effectively control the pH change rate during the reaction, thereby controlling the degree of the reduction reaction and forming a mixture of reduction products of different valence states to adapt to different reaction scenarios.

The dispersant of the present invention may be a nonionic dispersant, preferably PVP (polyvinyl pyrrolidone); the pH buffer of the present invention may be various pH buffer solutions in the prior art, preferably citric acid-citrate.

In one embodiment, the solid content of the coated catalyst slurry obtained by the present invention is 5wt% to 60wt%, preferably 20wt% to 40wt%; in another embodiment, the content of precious metals in the coated catalyst slurry of the present invention is 0.1wt% to 5wt%, preferably 0.5 to 2wt%.

Step 2 is: coating the coated catalyst slurry of step 1 onto the first carrier, and then drying and calcining to obtain a precious metal catalyst.

The present invention does not specifically limit the first carrier, and it may be, for example, a frame carrier, or more preferably, a honeycomb frame carrier.

In one embodiment, the coating amount of the coated catalyst slurry of the present invention is, for example, 5 g/L to 200 g/L, preferably 25 g/L to 120 g/L, wherein the coating amount refers to: (mass m1 of the catalyst after coating and calcination - mass m0 of the first carrier)/volume of the first carrier, in g/L. After coating the slurry, the first carrier can be purged with a gas, including the internal passage of the first carrier, the gas being, for example, compressed air, and then the first carrier is aged at 20°C to 40°C for 6-18h, dried at 100°C to 120°C for 1-12h, and finally the carrier is calcined at 500°C to 600°C for 4h to 6h to obtain a precious metal catalyst.

Therefore, the present invention provides a method for preparing a precious metal catalyst, specifically, mixing a precious metal precursor solution and a carrier powder evenly, adding a reducing agent and a dispersant, and ball milling on a high-energy ball mill. In the macroscopic aspect, the high-speed friction shear of the ball milling beads breaks the carrier particles and reduces the macroscopic size. At the same time, in the microscopic aspect, the mechanical energy of the mechanical friction point of the ball milling beads is transmitted to the solution at that part, so that the point locally becomes a reaction center. However, such a reaction center is changing at any time, so that the reduction reaction is carried out at a constantly changing new position. The reduced nanoparticles generated by the reaction are directly loaded onto the carrier surface, and highly dispersed reduced active sites at the nanometer (1 to 5 nm) level are formed on the carrier surface. The nanoparticles that are not attached to the carrier surface in time reduce the collision and aggregation between particles under the barrier effect of the dispersant, and are gradually loaded onto the carrier surface in the subsequent ball milling process.

In the ball milling reduction process of the present invention, carrier crushing, metal reduction activation, and reduced nanoparticle loading occur simultaneously, forming a slurry coating with uniformly distributed active sites in one step, and then the slurry is coated on a frame carrier, and anions, excess reducing agents, dispersants, buffers and other substances in the solution are decomposed through drying, evaporation or roasting to finally obtain a precious metal catalyst.

The preparation method of the present invention performs carrier crushing, metal reduction activation and reduced nanoparticle loading simultaneously, has a simple process, is easy to operate, and is convenient for large-scale industrial production and application.

The noble metal catalyst prepared by the method of the present invention has good noble metal dispersibility, and when used for treating volatile organic compounds, the catalyst has high activity and high noble metal utilization rate.

The technical solution of the present invention will be further described in detail below through specific embodiments. Unless otherwise specified, "%" refers to mass percentage.

Catalyst preparation conditions: After the cordierite honeycomb ceramic is coated with the active coating, it is naturally dried for 12 hours, dried at 105°C for 2 hours, and calcined at 500°C for 6 hours to obtain the catalyst.

Coating amount: (mass m1 of the catalyst after coating and calcination - mass m0 of the first carrier)/volume of the first carrier, unit: g/L.

Precious metal loading: mass ratio of precious metal to second carrier × coating amount, unit: g/L.

The active carrier refers to a second carrier to which a precious metal is added.

Catalyst evaluation method: The catalyst matrix used in this test is 16mm×16mm×50mm, 200 mesh cordierite honeycomb ceramic. The catalyst is filled in a fixed bed reactor. The configured reaction raw gas is preheated to a certain temperature and then enters the reaction bed. The reactant concentration in the reaction inlet and outlet gases is analyzed. The conversion rate = (1-outlet concentration/inlet concentration) × 100%. The programmed temperature method is used to examine the conversion rate of the reactants at different temperatures. The catalyst activity is judged by comparing the reaction temperature (T90) when the conversion rate is 90%. The lower the temperature, the higher the activity.

Analytical method: Agilent 8860 gas chromatograph with FID detector was used for quantitative analysis of the reactants.

Reaction conditions: The reaction gas composition is a mixture of 1000 mg/m ³ benzene and air, and the reaction space velocity is 16000 h ^-1 .

Example 1

48g of chloroplatinic acid solution with a platinum content of 0.5% and 12g of _palladium chloride solution with a palladium content of 0.5% were added to a mixed powder of 25g of γ- _Al2O3 and 5g of cerium-zirconium solid solution, and then 12.5ml of methanol, 0.44g of citric acid, 8.5g of PVP and 60ml of deionized water were added, and the mixture was ball-milled at a speed of 400 rpm for 1 hour to form an active slurry with a solid content of 20%. The slurry was then coated on a cordierite honeycomb ceramic carrier with a coating amount of 25g/L, and a VOCs catalytic oxidation catalyst was obtained after drying and calcining.

The precious metal content in the active carrier = the mass of precious metal/the mass of the carrier after calcination = (48+12)*0.5%/(25+5)=1%.

Catalyst precious metal loading = coating amount * precious metal content in active carrier = 25 * 1% = 0.25 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 242°C.

Comparative Example 1

90 ml of deionized water was added to 25 g of γ-Al ₂ O ₃ and 5 g of cerium-zirconium solid solution mixed powder, and ball milled at 400 rpm for 1 hour to form a slurry with a solid content of 20%. The slurry was then coated on a porous honeycomb carrier with a coating amount of 25 g/L. After drying at 105°C for 2 hours and calcining at 500°C for 4 hours, a VOCs catalytic oxidation catalyst carrier was obtained. 10.24 g of chloroplatinic acid solution with a platinum content of 0.1% and 2.56 g of palladium chloride solution with a palladium content of 0.1% were mixed evenly, and loaded onto 4 honeycomb ceramic carriers (volume 51.2 ml) by an equal amount impregnation method, and dried at 105°C for 2 hours and calcined at 500°C for 4 hours to obtain a catalyst. Before the catalyst evaluation, it was reduced with 5% H ₂ +N ₂ by volume at a space velocity of 500 h ^-1 and 200°C for 1 hour.

The catalyst precious metal loading amount = 0.25 g/L, which is the same as that in Example 1.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 334°C.

Compared with Example 1, the catalyst of Comparative Example 1 does not add the precious metal solution to the slurry for ball milling. Instead, the slurry is ball milled, coated, dried, and calcined, and then the precious metal solution is introduced into the catalyst by impregnation. Since the reduction step is not performed, the catalyst needs to be reduced and activated before use. The evaluation results show that under the same precious metal ratio and loading, the catalyst of Example 1 has higher activity, and the benzene T90 is 92°C lower than that of Comparative Example 1.

Example 2

60g of palladium chloride solution with a palladium content of 0.5% is added to 30g of ZSM-5 molecular sieve mixed powder, and then 12.5ml of methanol, 0.44g of citric acid, 8.5g of PVP and 30ml of deionized water are added, and ball milled at a speed of 800 rpm for 0.5 hour to form an active slurry with a solid content of 25%, and then the slurry is coated on a cordierite honeycomb ceramic carrier with a coating amount of 50g/L, and a VOCs catalytic oxidation catalyst is obtained after drying and calcining.

Catalyst noble metal loading = 0.5 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 221°C.

Comparative Example 2

60 ml of deionized water was added to 30 g of ZSM-5 molecular sieve powder, and the mixture was ball-milled at 400 rpm for 1 hour. 30 g of palladium chloride solution with a palladium content of 1.0% was added to the slurry and stirred evenly to form an active slurry with a solid content of 25%. The slurry was then coated on a porous honeycomb carrier in an amount of 50 g/L. The catalyst was formed after drying and calcining. Before the catalyst was evaluated, it was reduced with 5% H ₂ +N ₂ by volume at a space velocity of 500 h ^-1 and 200°C for 1 hour.

The catalyst precious metal loading amount = 0.5 g/L, which is the same as that in Example 2.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 295°C.

Compared with Example 2, in Comparative Example 2, the precious metal solution is not added to the slurry for ball milling. Instead, the precious metal solution is added to the slurry after ball milling, mixed evenly, and then coated, dried, and calcined to form a catalyst. Since the reduction step is not performed, the catalyst needs to be reduced and activated before use. The evaluation results show that under the same precious metal ratio and loading, the catalyst activity of Example 2 is higher, and the benzene T90 is 74°C lower than that of Comparative Example 2.

Example 3

30g of palladium nitrate solution with a palladium content of 1.0% is added to 20g of _TiO2 , 5g of ammonium metatungstate _with a _WO3 content, and 5g of γ- _Al2O3 mixed powder, and then 12.5ml of methanol, 0.44g of citric acid, 8.5g of PVP and 60ml of deionized water are added, and ball milling is performed at a speed of 800 rpm for 1 hour to form an active slurry with a solid content of 25%, and then the slurry is coated on a cordierite honeycomb ceramic carrier with a coating amount of 75g/L, and a VOCs catalytic oxidation catalyst is obtained after drying and calcination.

Catalyst noble metal loading = 0.75 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 195°C.

Comparative Example 3

To 30 g of palladium chloride solution with a palladium content of 1.0%, 12.5 ml of methanol, 0.44 g of citric acid, and 8.5 g of PVP aqueous solution were added, and the mixture was heated under reflux for 2 h to form a reduced noble metal sol.

Add 30 ml of deionized water to 20 g of TiO ₂ , 5 g of ammonium metatungstate with WO ₃ content, and 5 g of γ-Al ₂ O ₃ mixed powder, and ball mill at 400 rpm for 1 hour. Add the precious metal sol to the slurry and stir evenly. Add 30 ml of deionized water to adjust the active slurry to a solid content of 25%. Apply the slurry to a porous honeycomb carrier with a coating amount of 75 g/L. After drying and calcining, a catalyst is formed.

The catalyst precious metal loading amount = 0.75 g/L, which is the same as that in Example 3.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 263°C.

Compared with Example 3, the noble metal solution is hydrothermally reduced in advance, and after slurry ball milling, it is mixed with the noble metal sol, and then coated, dried, and calcined to form a catalyst. Since the noble metal is reduced in advance, it does not need to be reduced again before use. The evaluation results show that under the same ratio and loading of noble metals, the catalyst activity of Example 3 is higher, and the benzene T90 is 68°C lower than that of Comparative Example 3.

Example 4

24g of hydroxyplatinic acid solution with a platinum content of 1.0% and 6g of palladium nitrate solution with a palladium content of 1.0% were added to 25g of _TiO2 and 5g of a cerium-zirconium solid solution mixed powder, and then 12.5ml of methanol and 40ml of deionized water were added. The mixture was ball-milled at a speed of 400 rpm for 2 hours to form an active slurry with a solid content of 40%. The slurry was then coated on a cordierite honeycomb ceramic carrier in an amount of 120g/L. After drying and calcining, a VOCs catalytic oxidation catalyst was obtained.

Catalyst noble metal loading = 1.2 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 216°C.

Comparative Example 4

24g of hydroxyplatinic acid solution with a platinum content of 1.0% and 6g of palladium nitrate solution with a palladium content of 1.0% were added to 25g of _TiO2 and 5g of a cerium-zirconium solid solution mixed powder, and ball-milled at a speed of 400 rpm for 1 hour. Then 12.5ml of methanol and 40ml of deionized water were added to form an active slurry with a solid content of 40%. The slurry was then coated on a cordierite honeycomb ceramic carrier with a coating amount of 120g/L. After drying and calcining, a VOCs catalytic oxidation catalyst was obtained.

Catalyst noble metal loading = 1.2 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 287°C.

Compared with Example 4, in Comparative Example 4, the precious metal solution is not added to the slurry for ball milling. Instead, the precious metal solution is added to the slurry after ball milling, mixed evenly, and then coated, dried, and calcined to form a catalyst. The evaluation results show that under the same precious metal ratio and loading, the catalyst activity of Example 4 is higher, and the benzene T90 is 75°C lower than that of Comparative Example 4.

Example 5

24g of hydroxyplatinic acid solution with a platinum content of 1.0% and 6g of palladium nitrate solution with a palladium content of 1.0% were added to 25g of _TiO2 and 5g of a cerium-zirconium solid solution mixed powder, and then 12.5ml of methanol, 0.44g of citric acid, 8.5g of PVP and 40ml of deionized water were added, and the mixture was ball-milled at a speed of 400 rpm for 2 hours to form an active slurry with a solid content of 40%. The slurry was then coated on a cordierite honeycomb ceramic carrier in a coating amount of 120g/L, and a VOCs catalytic oxidation catalyst was obtained after drying and calcining.

Catalyst noble metal loading = 1.2 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 188°C.

Example 6

15g of platinum nitrate solution with a platinum content of 2.0% is added to 25g of _TiO2 , 4g of ammonium metatungstate with a _WO3 content, 1g of ammonium metavanadate with a _V2O5 content, and _5g of a mixed powder of γ- _Al2O3 , and then 12.5ml of methanol, 0.44g of citric acid, 8.5g of PVP and 40ml of deionized water are added, and the mixture is ball-milled at a speed of 100 rpm for 2 hours to form an active slurry with a solid content of 35%. _The slurry is then coated on a cordierite honeycomb ceramic carrier with a coating amount of 100g/L, and a VOCs catalytic oxidation catalyst is obtained after drying and calcining.

Catalyst noble metal loading = 1.0 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 193°C.

Example 7

12g of chloroplatinic acid solution with a platinum content of 2.0% and 3g of palladium chloride solution with a palladium content of 2.0% were added to 25g of _TiO2 and 5g of cerium-zirconium solid solution mixed powder, and then 12.5ml of methanol, 0.44g of citric acid, 8.5g of PVP and 40ml of deionized water were added, and the mixture was ball-milled at a speed of 1000 rpm for 3 hours to form an active slurry with a solid content of 35%. The slurry was then coated on a cordierite honeycomb ceramic carrier with a coating amount of 100g/L, and a VOCs catalytic oxidation catalyst was obtained after drying and calcining.

Catalyst noble metal loading = 1.0 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 190°C.

Example 8

60g of palladium nitrate solution with a palladium content of 0.5% was added to 25g of _γ - _Al2O3 and 5g of cerium-zirconium solid solution mixed powder, and then 12.5ml of methanol, 0.44g of citric acid, 8.5g of PVP and 30ml of deionized water were added, and ball milling was carried out at a speed of 100 rpm for 10 hours to form an active slurry with a solid content of 25%. The slurry was then coated on a porous honeycomb carrier with a coating amount of 75g/L. After drying and calcination, a VOCs catalytic oxidation catalyst was obtained.

Catalyst noble metal loading = 0.75 g/L.

The obtained catalyst was evaluated according to the above evaluation method. The evaluation result showed that benzene T90 = 212°C.

Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims (10)

1. The preparation method of the noble metal catalyst is characterized by comprising the following steps:

step 1, mixing a noble metal precursor aqueous solution, second carrier powder and a reducing agent, and performing ball milling to obtain coated catalyst slurry;

and 2, coating the coating type catalyst slurry obtained in the step 1 on a first carrier, and then drying and roasting to obtain the noble metal catalyst.

2. The method for preparing a noble metal catalyst according to claim 1, wherein a dispersing agent and/or a pH buffer is further added in step 1.

3. The method for producing a noble metal catalyst according to claim 1, wherein the noble metal precursor aqueous solution is an aqueous solution of a Pt-containing compound or a Pd-containing compound, which is soluble in water; the mass concentration of the noble metal precursor aqueous solution is 0.1-5 wt% based on the noble metal simple substance.

4. The method of preparing a noble metal catalyst according to claim 1, wherein the second carrier powder is TiO ₂, a solid solution of cerium zirconium, γ -Al ₂O₃, ZSM-5 molecular sieve, ammonium metatungstate, ammonium metavanadate or a mixture thereof; the reducing agent is alcohols, aldehydes, organic acids or sodium borohydride; wherein, the noble metal precursor is calculated by noble metal simple substance, the mass ratio of the noble metal precursor, the second carrier powder and the reducing agent is 1: 20-1000: 10 to 100.

5. The method for preparing a noble metal catalyst according to claim 2, wherein the dispersant is a nonionic dispersant, and the pH buffer is citric acid-citrate; the noble metal precursor is calculated by noble metal simple substance, and the molar ratio of the noble metal precursor to the pH buffer is 1: 6-20, wherein the mass ratio of the noble metal precursor to the dispersing agent is 1:5 to 30.

6. The method for preparing a noble metal catalyst according to claim 1, wherein the ball milling time is 0.1-30 hours, the ball milling rotating speed is 100-1000 rpm, and the material particles are <30 μm after ball milling; the solid content of the coating catalyst slurry is 5-60 wt%.

7. The method for preparing a noble metal catalyst according to claim 1, wherein the noble metal content of the coated catalyst slurry is 0.1wt% to 5wt%.

8. The method for preparing a noble metal catalyst according to claim 1, wherein after the first carrier is coated with the catalyst slurry in step 2, the method further comprises the steps of purging the first carrier with a gas and aging, wherein the aging temperature is 20 ℃ to 40 ℃ and the aging time is 6 to 18 hours; the coating amount of the coating catalyst slurry is 5g/L to 200g/L.

9. The method for preparing a noble metal catalyst according to claim 1, wherein the drying temperature is 100 ℃ to 120 ℃ and the drying time is 1 to 12 hours; the roasting temperature is 500-600 ℃, and the roasting time is 4-6 h.

10. Use of the noble metal catalyst obtained by the preparation method of any one of claims 1 to 9 in the treatment of volatile organic compounds.