Coating type honeycomb noble metal reduction catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the field of noble metal catalysts, and relates to a coating type honeycomb noble metal reduction catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: coating alumina slurry into pore channels of an acid-etched honeycomb ceramic carrier, and drying and roasting to obtain a carrier containing a transition coating; the preparation method comprises the following steps: mixing and stirring a Pt precursor, a Pd precursor, gamma-Al2O3, titanium oxide, a transition metal oxide and a binder in water, fully mixing, and carrying out ball milling to obtain precious metal precursor slurry; uniformly mixing the noble metal precursor slurry with organic acid and an additive to obtain modified slurry; and coating a carrier containing a transition coating with the modified slurry, and drying and roasting to obtain the coating type honeycomb noble metal reduction catalyst. The catalyst can achieve high loading and high dispersion, the low-temperature catalytic activity of the catalyst is remarkably improved, water resistance and chlorine poisoning resistance can be achieved, the loading amount of precious metal is remarkably reduced, and the catalyst is suitable for industrial production of the precious metal catalyst.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of noble metal catalysts, and particularly relates to a coated honeycomb noble metal reduced catalyst, a preparation method thereof and application thereof. BACKGROUND

[0002] Volatile organic compounds (VOCs) and carbon monoxide (CO) are important components of atmospheric pollutants, have a wide range of sources and cause great harm. Among the many technologies for treating VOCs and CO pollution, catalytic oxidation has become one of the most widely used and most promising methods due to its high efficiency, energy saving and other significant advantages. In the catalytic oxidation system, noble metal catalysts have always been dominant due to their excellent catalytic activity, good stability and wide applicable temperature range. Noble metals such as palladium (Pd) and platinum (Pt) can promote the oxidation of VOCs and CO at relatively low temperatures, converting them into harmless substances such as carbon dioxide and water, greatly improving the purification efficiency.

[0003] However, with the large-scale application of noble metal catalysts, its inherent drawbacks have become increasingly prominent. On the one hand, noble metals are extremely scarce, with limited reserves on Earth and extremely uneven distribution. This has caused the price of noble metals to remain high for a long time and has shown a continuous upward trend, significantly increasing the cost of catalyst preparation. On the other hand, in the preparation process of the catalyst, in order to achieve high catalytic activity, a high content of noble metal is often required, which further exacerbates resource consumption and cost burden. At the same time, during the preparation process, noble metal particles are unevenly distributed on the carrier (such as alumina or titanium dioxide) (such as due to immature preparation process or insufficient surface treatment of the carrier), resulting in inconsistent active sites, reducing catalytic efficiency and selectivity; during use (such as high temperature reaction or under mechanical stress), particles are prone to fall off, causing activity loss, resource waste, and possibly causing secondary pollution (such as metal particles falling off into the environment). In view of this, developing a preparation method that can achieve noble metal reduction while maintaining or even improving catalyst performance has become a key problem to be solved in the current environmental protection field. SUMMARY

[0004] To solve the above problems, the application provides a coated honeycomb noble metal reduced catalyst and a preparation method thereof, which improves the adhesion of slurry and cordierite carrier by composite layered coating (i.e. carrier pretreatment + pre-coating), increases the loading on the coating while maintaining a low shedding rate; by transition metal protection site strategy, the catalyst is added with transition metal and organic acid regulating aid in the slurry preparation process to control the crystal structure, morphology, oxygen vacancy number and surface acid site of the catalyst, while improving the uniform dispersion and stability of the catalytically active component, and enhancing the synergistic interaction of the carrier interface metal multi-site, so as to significantly improve the low-temperature activity, chlorine resistance and water resistance while reducing the content of noble metal.

[0005] The application adopts the following technical scheme:

[0006] A preparation method of a coated honeycomb noble metal reduced catalyst, comprising the following steps: placing a honeycomb ceramic carrier into an acid solution for ultrasonic treatment, and drying to obtain an acid-etched honeycomb ceramic carrier; adding γ-Al2O3 and a binder into deionized water, fully stirring and then ball milling to obtain an alumina slurry; coating the alumina slurry into the pores of the acid-etched honeycomb ceramic carrier, and drying and calcining to obtain a carrier containing a transition coating; mixing Pt precursor, Pd precursor, γ-Al2O3, titanium oxide, transition metal oxide and a binder in water, fully mixing and then ball milling to obtain a noble metal precursor slurry; uniformly mixing the noble metal precursor slurry with organic acid and an additive to obtain a modified slurry; coating the modified slurry onto the carrier containing the transition coating, and drying and calcining to obtain the coated honeycomb noble metal reduced catalyst.

[0007] Further, the organic acid is one or more of citric acid, tartaric acid and oxalic acid; the amount of the organic acid is 10-20% of the total mass of γ-Al2O3 and titanium oxide.

[0008] Further, the additive comprises one or more of carboxymethyl cellulose, polyvinyl alcohol and polyethylene glycol; the amount of the additive is 0.5-1% of the total mass of the noble metal precursor slurry; the acid solution is one of sulfuric acid, nitric acid and hydrochloric acid, and the mass concentration is 10-20%.

[0009] Further, in the alumina slurry, the mass percentages of the raw materials are respectively: γ-Al2O3 30-45%, binder 3-5%, and the rest is water; in the modified slurry, the mass percentages of the raw materials are respectively: Pt precursor 0.05-0.1%, Pd precursor 0.05-0.1%, γ-Al2O3 5-10%, titanium oxide 10-20%, transition metal oxide 5-8%, binder 3-5%, and the rest is water.

[0010] Further, the transition metal oxide is a mixture of iron oxide and cerium oxide, the mass ratio of iron oxide to cerium oxide is 1-3:1; the Pt precursor is one of platinum nitrate, chloroplatinic acid and platinum chloride, the Pd precursor is one of palladium chloride, palladium nitrate, palladium acetate and potassium tetrachloropalladate; the binder is aluminum sol or silicon sol; and the carrier is cordierite honeycomb ceramic carrier.

[0011] Further, the preparation method of the alumina slurry comprises: adding γ-Al2O3 and a binder into deionized water, fully stirring and then ball milling, the ball milling temperature is room temperature, the rotating speed is 500-1000 r / min, and the ball milling time is 1-10 h, so that the particle size D90 of the obtained alumina slurry is 10-50 μm, and the viscosity is 30-300 mPa·s.

[0012] Further, the preparation method of the noble metal precursor slurry comprises: mixing and stirring Pt precursor, Pd precursor, γ-Al2O3, titanium oxide, transition metal oxide and a binder in water, fully mixing and then ball milling, the ball milling temperature is room temperature, the rotating speed is 500-1000 r / min, and the ball milling time is 1-10 h, so that the particle size D90 of the obtained noble metal precursor slurry is 1-5 μm, and the viscosity is 80-200 mPa·s.

[0013] Further, the drying temperature is 90-130℃, the drying time is 1-2 h, the calcination temperature is 450-600℃, and the calcination time is 2-5 h.

[0014] In a first aspect, the application provides a preparation method of a coated honeycomb noble metal reduced catalyst, comprising:

[0015] ①First, the honeycomb ceramic carrier is put into an acid solution for ultrasonic treatment, and then taken out and dried for standby use;

[0016] ②γ-Al2O3 and a binder are added into deionized water, fully stirred and then ball milled to obtain alumina slurry for standby use;

[0017] ③The alumina slurry is coated into the pore channels of the honeycomb carrier, dried and calcined to obtain a carrier containing an overplated coating layer;

[0018] ④Pt precursor, Pd precursor, γ-Al2O3, titanium oxide, transition metal oxide and a binder are mixed and stirred in water, fully mixed and ball milled to obtain a noble metal precursor slurry;

[0019] ⑤The noble metal precursor slurry is added into an organic acid and an additive, the organic acid is one or more of citric acid, tartaric acid and oxalic acid, to obtain a modified slurry;

[0020] ⑥ The modified slurry is coated onto a carrier containing a transition coating, and then dried and calcined to obtain a coated honeycomb catalyst.

[0021] Preferably, the solid content of the precious metal precursor slurry is 25%-45%.

[0022] Preferably, the alumina slurry is ground using a ball mill at room temperature, with a rotation speed of 500-1000 r / min and a ball milling time of 1-10 h, to obtain a slurry particle size D90 (i.e., the particle size corresponding to the cumulative particle size distribution number of a sample reaching 90%) of 10-50 μm and a viscosity of 30-300 mPa·s.

[0023] Preferably, the precious metal precursor slurry is ground using a ball mill at room temperature, with a rotation speed of 500-1000 r / min and a ball milling time of 1-10 h, to obtain a slurry particle size D90 (i.e., the particle size corresponding to the cumulative particle size distribution number of a sample reaching 90%) of 1-5 μm and a viscosity of 80-200 mPa·s.

[0024] Preferably, the additive is used at 0.5-1% of the total mass of the precious metal precursor slurry. It is used to improve the dispersibility of the catalytically active components, regulate the pore structure of the catalyst, and enhance adhesion.

[0025] Preferably, the coating is performed using a vacuum coating machine, and the coating is applied 1-4 times.

[0026] In a second aspect, the present invention provides a coated honeycomb noble metal reduction catalyst prepared by the method described above.

[0027] Preferably, the catalyst comprises a support, a transition layer, and a catalytic coating. The loading of the transition layer (calculated as coating mass g / support volume L) is 10-30 g / L, and the loading of the catalytic coating is 50-180 g / L. This invention improves the coating's peeling rate while increasing the coating loading and reducing infiltration loss within the coating.

[0028] More preferably, the precious metal loading (expressed as the total mass of precious metals Pt and Pd in ​​g / carrier volume in m³) 3 (Calculated) 400-800g / m 3 .

[0029] Preferably, the catalytic coating is composed of the following components in the indicated mass percentages: Pt 0.1-5%, Pd 0.1-5%, γ-Al2O3 5-10%, TiO2 10-20%, and transition metal oxides 5%-8%.

[0030] The present invention also provides a coated honeycomb noble metal reduction catalyst, which is prepared by the above-described preparation method.

[0031] The application also provides application of the coated honeycomb noble metal reduced amount catalyst in pollution gas treatment, the pollution gas including one or more of VOCs and CO.

[0032] The application is that the noble metal reduced amount catalyst is applied to treat chlorobenzene gas and CO. Complete chlorobenzene oxidation is achieved within 120 minutes under the atmosphere of 400 DEG C, 1000 ppm chlorobenzene and 10% H2O, excellent chlorine and water resistance is shown; complete CO oxidation is achieved at 240 DEG C under the atmosphere of 5000 ppm CO, excellent catalytic oxidation performance is shown.

[0033] Beneficial effects

[0034] The catalyst of the application can realize high loading and high dispersion through composite layer coating and transition metal protection site strategy, significantly improve low-temperature catalytic activity and water and chlorine resistance of the catalyst, reduce noble metal loading by 20-60%, greatly reduce catalyst cost, can realize 99% conversion of 1000 ppm toluene and 5% water vapor at 300 DEG C, the temperature required for conversion of 90% chlorobenzene under the working condition of 500 ppm chlorobenzene and 5% water vapor is 367 DEG C, and the noble metal Pt content is only 189 g / m 3 , and 100% CO conversion is achieved at 240 DEG C under the working condition of 5000 ppm carbon monoxide. The catalyst is suitable for industrialized production and application of noble metal catalyst. Through carrier acid etching and pre-coating, the adhesion of slurry to the carrier is improved, slurry penetration on the carrier surface is reduced, coating loading rate is increased, and powder shedding rate is reduced.

[0035] Through transition metal oxide modification and surfactant addition, the transition metal oxide additive provides more oxygen vacancies, improves the redox capacity of the catalyst, increases the surface acid sites of the catalyst, improves the strong interaction with noble metals, significantly improves the low-temperature activity and high-temperature thermal stability of the catalyst, and improves the water and chlorine resistance.

[0036] Compared with the noble metal catalyst with the same performance, the noble metal content of the catalyst of the application is reduced by 20-60%, the production cost is lower, and the catalyst is suitable for industrialized production and application. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 SEM spectrum of blank honeycomb cordierite;

[0038] Figure 2 SEM spectrum of coated honeycomb cordierite;

[0039] Figure 3 Chlorobenzene oxidation performance spectrum of examples 1-7;

[0040] Figure 4 The CO oxidation performance spectrum of Comparative Examples 1-10;

[0041] Figure 5 The CO oxidation performance spectrum of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0042] In the following examples, the mass concentration of palladium nitrate and platinum nitrate solution is 15%;

[0043] The solid content of the binder aluminum sol and silica sol is 30%;

[0044] The calculation formula of the solid content of the mixed solution is (m a +m b +m c x 30%) / M 总 x 100%, wherein the mass of γ-Al2O3 and TiO2 is denoted as m a ; the total mass of the transition metal composite oxide is denoted as m b ; the mass of the silica sol / aluminum sol is denoted as m c ; and the total mass of the mixed solution is denoted as M 总 .

[0045] Example 1

[0046] Step 1: Take 100x100x50mm honeycomb cordierite carrier, immerse in 10% HNO3 solution for ultrasonic soaking for 30min, take out and dry, to obtain the acid-etched honeycomb ceramic carrier;

[0047] Step 2: Take 300g γ-Al2O3, 30g aluminum sol, and stir in 670g water to obtain a mixed solution with a solid content of 31.2%, transfer to a ball mill and grind at 500r / min for 1h, the grinding temperature is room temperature, to obtain an alumina slurry with a particle size D90 of 10-50μm and a viscosity of 61.5mPa·s;

[0048] Step 3, coat the alumina slurry of step 2 onto the acid-etched 100x100x50mm honeycomb cordierite carrier by vacuum coating machine, the coating times is 1, the coating amount is 100g / L, after drying at 120℃ for 1h, calcining at 500℃ for 2h, to obtain a carrier containing a transition coating layer;

[0049] Step 4: 1 g of platinum nitrate, 1 g of palladium nitrate, 100 g of γ-Al2O3, 200 g of TiO2, 80 g of transition metal oxide (40 g of cerium oxide, 40 g of iron oxide), and 50 g of aluminum sol binder were stirred in 570 g of water to obtain a mixed solution with a solid content of 40%, which was then transferred to a ball mill for grinding at 500 r / min for 1 h at room temperature to obtain a noble metal precursor slurry with a particle size D90 of 1-5 μm and a viscosity of 95.3 mPa·s;

[0050] Step 5: 50 g of citric acid and 10 g of polyethylene glycol were added to the noble metal precursor slurry and mixed uniformly to obtain a modified slurry.

[0051] Step 6: The modified slurry was coated onto the cordierite honeycomb carrier containing the transition coating layer by a vacuum coating machine, with a coating frequency of 1 time, dried at 100°C for 1 h, and calcined at 500°C for 2 h to obtain a coated noble metal reduction catalyst.

[0052] Example 2

[0053] Step 1: A 100x100x50 mm honeycomb cordierite carrier (300 mesh) was placed in a 10% HNO3 solution and ultrasonically soaked for 30 min, then taken out and dried to obtain an acid-etched honeycomb ceramic carrier.

[0054] Step 2: 300 g of γ-Al2O3 and 30 g of aluminum sol were stirred in 670 g of water to obtain a mixed solution with a solid content of 31.2%, which was then transferred to a ball mill for grinding at 500 r / min for 1 h at room temperature to obtain an alumina slurry with a particle size D90 of 10-50 μm and a viscosity of 61.5 mPa·s.

[0055] Step 3: The alumina slurry of Step 2 was coated onto the acid-etched 100x100x50 mm honeycomb cordierite carrier by a vacuum coating machine, with a coating frequency of 1 time and a coating amount of 100 g / L, and then dried at 120°C for 1 h and calcined at 500°C for 2 h to obtain a carrier containing a transition coating layer.

[0056] Step 4: 0.8 g of platinum nitrate, 0.8 g of palladium nitrate, 100 g of γ-Al2O3, 200 g of TiO2, 80 g of transition metal oxide (40 g of cerium oxide, 40 g of iron oxide), and 50 g of aluminum sol binder were stirred in 570 g of water to obtain a mixed solution with a solid content of 40%, which was then transferred to a ball mill for grinding at 500 r / min for 1 h at room temperature to obtain a noble metal precursor slurry with a particle size D90 of 1-5 μm and a viscosity of 94.6 mPa·s.

[0057] Step 5: 50 g of citric acid and 10 g of polyethylene glycol were added to the noble metal precursor slurry and mixed uniformly to obtain a modified slurry.

[0058] Step 6, the modified slurry was coated on the cordierite honeycomb carrier containing the transition coating by a vacuum coater, the coating times was 1, dried at 100℃ for 1h, and calcined at 500℃ for 2h to prepare the coated noble metal reduction catalyst.

[0059] Example 3

[0060] In step 5, 50g tartaric acid and 10g polyethylene glycol were added into the noble metal precursor slurry and mixed uniformly to obtain the modified slurry;

[0061] The other preparation steps and raw material compositions were consistent with those of Example 1.

[0062] Example 4

[0063] In step 5, 50g oxalic acid and 10g polyethylene glycol were added into the noble metal precursor slurry and mixed uniformly to obtain the modified slurry;

[0064] The other preparation steps and raw material compositions were consistent with those of Example 1.

[0065] Example 5

[0066] In step 5, 50g citric acid and 10g polyvinyl alcohol were added into the noble metal precursor slurry and mixed uniformly to obtain the modified slurry;

[0067] The other preparation steps and raw material compositions were consistent with those of Example 1.

[0068] Example 6

[0069] In step 5, 50g citric acid and 10g carboxymethyl cellulose were added into the noble metal precursor slurry and mixed uniformly to obtain the modified slurry;

[0070] The other preparation steps and raw material compositions were consistent with those of Example 1.

[0071] Example 7

[0072] In step 4, 1g platinum nitrate, 1g palladium nitrate, 100g γ-Al2O 、 100g TiO2, 80g transition metal oxide (40g cerium oxide, 40g iron oxide), 50g aluminum sol were placed in 670g water and stirred to obtain a mixed solution with a solid content of 30%, which was transferred to a ball mill and ground at 500r / min for 1h at room temperature to obtain a slurry with a particle size D90 of 1-5μm and a viscosity of 85.2 mPa·s, thereby obtaining the noble metal precursor slurry;

[0073] The other preparation steps and raw material compositions were consistent with those of Example 1.

[0074] Comparative Example 1

[0075] Steps 1-3 are cancelled, no pretreatment of the support is performed;

[0076] The other preparation steps are consistent with the raw material composition and example 1.

[0077] Comparative Example 2

[0078] Step 4, take 1 g of platinum nitrate, 1 g of palladium nitrate, 300 g of γ-Al2O3, 80 g of transition metal oxide (40 g of cerium oxide, 40 g of iron oxide), 50 g of aluminum sol in 670 g of water, stirring to obtain a mixed solution with a solid content of 40%, transfer to a ball mill, 500 r / min, grinding for 1 h, grinding temperature room temperature, to obtain a noble metal precursor slurry, the particle size D90 of the slurry is 1-5 μm, the viscosity is 90.1 mPa·s.

[0079] The other preparation steps are consistent with the raw material composition and example 1.

[0080] Comparative Example 3

[0081] Step 4, take 1 g of platinum nitrate, 1 g of palladium nitrate, 300 g of TiO2, 80 g of transition metal oxide (40 g of cerium oxide, 40 g of iron oxide), 50 g of aluminum sol in 670 g of water, stirring to obtain a mixed solution with a solid content of 40%, transfer to a ball mill, 500 r / min, grinding for 1 h, grinding temperature room temperature, to obtain a noble metal precursor slurry, the particle size D90 of the slurry is 1-5 μm, the viscosity is 90.1 mPa·s.

[0082] The other preparation steps are consistent with the raw material composition and example 1.

[0083] Comparative Example 4

[0084] Step 4, take 1 g of platinum nitrate, 1 g of palladium nitrate, 100 g of γ-Al2O3, 100 g of TiO2, 50 g of aluminum sol in 750 g of water, stirring to obtain a mixed solution with a solid content of 22%, transfer to a ball mill, 500 r / min, grinding for 1 h, grinding temperature room temperature, to obtain a noble metal precursor slurry, the particle size D90 of the slurry is 1-5 μm, the viscosity is 80.2 mPa·s.

[0085] The other preparation steps are consistent with the raw material composition and example 1.

[0086] Comparative Example 5

[0087] Step 4, 1 g of platinum nitrate, 1 g of palladium nitrate, 100 g of γ-Al2O3, 200 g of TiO2, 80 g of transition metal oxide (manganese oxide), 50 g of aluminum sol were stirred in 570 g of water to obtain a mixed solution with a solid content of 40%, and then transferred to a ball mill for grinding at 500 r / min for 1 h at room temperature to obtain a noble metal precursor slurry, wherein the particle size D90 of the slurry was 1-5 μm, and the viscosity was 94.6 mPa·s.

[0088] The other preparation steps, raw material compositions and preparation methods were the same as in Example 1.

[0089] Comparative Example 6

[0090] Step 5, 50 g of citric acid was added to the noble metal precursor slurry and mixed uniformly to obtain a modified slurry.

[0091] The other preparation steps, raw material compositions and preparation methods were the same as in Example 1.

[0092] Comparative Example 7

[0093] Step 5, 10 g of polyethylene glycol was added to the noble metal precursor slurry and mixed uniformly to obtain a modified slurry.

[0094] The other preparation steps, raw material compositions and preparation methods were the same as in Example 1.

[0095] Comparative Example 8

[0096] Step 5 was not used.

[0097] The other preparation steps, raw material compositions and preparation methods were the same as in Example 1.

[0098] Comparative Example 9

[0099] A Pt-based catalyst of a certain catalyst manufacturer was purchased, and the model was Pt-5511, and the measured noble metal content was 392 g / m 3 The catalyst was first prepared into a slurry containing Pt precursor, aluminum sol, alumina carrier powder, metal oxide additive and water, and then the slurry was coated onto the cordierite carrier by manual immersion or vacuum coating equipment, and the honeycomb catalyst was obtained after drying and calcination.

[0100] Comparative Example 10

[0101] A PtPd double noble metal-based catalyst of a certain catalyst manufacturer was purchased, and the model was PtPd-6551, and the measured noble metal content was 686 g / m 3 The catalyst was first prepared into a slurry containing Pt, Pd precursor, aluminum sol, alumina carrier powder, metal oxide additive and water, and then the slurry was coated onto the cordierite carrier by manual immersion or vacuum coating equipment, and the honeycomb catalyst was obtained after drying and calcination.

[0102] Comparative Example 11

[0103] Step 1 does not include an ultrasonic step; the honeycomb cordierite carrier is simply immersed in a 10% HNO3 solution for 30 minutes. Other preparation steps and raw material composition are consistent with Example 1.

[0104] Comparative Example 12

[0105] The acid etching step in step 1 is excluded; the other preparation steps and raw material composition are the same as in Example 1.

[0106] The catalysts prepared in Examples 1-7 and Comparative Examples 1-7 were subjected to toluene and chlorobenzene catalytic oxidation activity tests and catalyst shedding rate tests.

[0107] The catalytic efficiency test method is as follows: A columnar catalyst sample with a diameter of 15 mm and a height of 30 mm is taken using a drilling machine and placed in a fixed-bed reactor. Simulated gas is introduced into the reaction system by bubbling organic matter through compressed air. The concentrations of toluene and chlorobenzene are controlled at 1000±10 ppm, and the volume hourly space velocity is 20000 h⁻¹. -1 The concentrations of toluene, chlorobenzene, and CO2 were monitored in real time by online chromatography, and the reaction temperature when the catalytic efficiency reached 90% was recorded as T90.

[0108] The method for testing the shedding rate is as follows: the catalyst is dried at 120℃ for 1 hour and weighed, recorded as m1. After cooling to room temperature, it is sonicated for 1 hour. After sonication, it is dried at 120℃ for 1 hour and weighed, recorded as m2. The mass of the catalyst coating is recorded as m3. The formula for calculating the shedding rate is (m1-m2) / m3x100%.

[0109] The results are shown in the table below.

[0110] Table 1. Noble metal, transition layer, coating loading, peeling rate, and VOCsT90 in the catalyst.

[0111]

[0112] The results of Examples 1-6 and Comparative Examples 1-10 show that when the catalytic coating loading is 100 g / L, the detachment rate is 0.15-0.21%, with the catalyst prepared in Example 1 having a detachment rate of only 0.15%, far lower than that of the catalysts in Comparative Examples 1 / 6 / 7 / 8 / 9 / 10. This indicates that layered coating and the effects of organic acids and additives can effectively improve the adhesion of the slurry and enhance the bonding between the slurry and the ceramic carrier.

[0113] The catalysts prepared in Examples 1-6 all exhibited higher catalytic activity than those in Comparative Examples 1-8. Specifically, the catalyst prepared in Example 1 had T90 values ​​of 278°C for toluene and 373°C for chlorobenzene. Compared to the catalyst prepared in Example 2, the precious metal content was reduced by 20%, the T90 of toluene decreased by 13%, and the T90 of chlorobenzene decreased by 12.1%. Compared to the commercially available catalyst purchased in Comparative Example 10, the precious metal content was reduced by 27.1%, the T90 of toluene decreased by 7.9%, and the T90 of chlorobenzene decreased by 5.8%. This indicates that the coated honeycomb precious metal reduction catalyst prepared by this invention can effectively maintain or even improve the catalytic activity of the catalyst while reducing the precious metal content.

[0114] Long-term stability tests were conducted on the catalysts prepared in Examples 1-7 and Comparative Examples 4 and 8. The test conditions were a volume hourly space velocity (VHSV) of 20,000 h⁻¹. -1 The long-term performance evaluation was conducted under an air atmosphere with a chlorobenzene concentration of 1000 ppm and a water vapor concentration of 10%, as shown in the figure. The results indicate that the long-term stability and resistance to moisture and chlorine poisoning of the catalysts prepared in Examples 1-7 are superior to those in Comparative Example 4 / 8. In particular, the catalyst prepared in Example 1 can completely convert chlorobenzene (T98) at 350℃, a decrease of more than 10℃ compared to Comparative Example 4 / 8. This demonstrates that the coated honeycomb precious metal reduction catalyst prepared by this invention can effectively maintain or even improve the catalytic activity of the catalyst while reducing the precious metal content, and exhibits excellent resistance to water and chlorine poisoning and long-term stability.

[0115] The difference in chlorobenzene and CO oxidation performance between Example 1 and Comparative Example 1 indicates that support pretreatment can effectively improve the surface properties of the cordierite support, while also allowing the active components to be fully and uniformly coated on the cordierite surface, thereby enhancing the monolithic catalyst's oxidation capacity for VOCs and CO. The difference in chlorobenzene and CO performance between Example 1 and Example 3 indicates that using different organic acids can alter the binding form of noble metals on the support surface, leading to changes in the distribution, valence state, and electronic structure of the active components, thus improving the catalyst's VOCs and CO oxidation performance.

Claims

1. A method for preparing a coated honeycomb noble metal reduction catalyst, characterized in that, Includes the following steps: The honeycomb ceramic carrier is placed in an acid solution and ultrasonically cleaned. After drying, the acid-etched honeycomb ceramic carrier is obtained. γ-Al2O3 and binder are added to deionized water, stirred thoroughly, and then ball-milled to obtain an alumina slurry. The alumina slurry is coated into the channels of the acid-etched honeycomb ceramic carrier, and after drying and calcination, a carrier containing a transition coating is obtained. Pt precursor, Pd precursor, γ-Al2O3, titanium dioxide, transition metal oxide and binder are mixed and stirred in water, and then ball-milled after thorough mixing to obtain a noble metal precursor slurry; the noble metal precursor slurry is then mixed evenly with organic acid and additives to obtain a modified slurry. The modified slurry was coated onto a carrier containing a transition coating, and then dried and calcined to obtain a coated honeycomb noble metal reduction catalyst.

2. The preparation method of the coated honeycomb noble metal reduction catalyst according to claim 1, characterized in that, The organic acid is one or more of citric acid, tartaric acid, and oxalic acid; the amount of the organic acid used is 10-20% of the total mass of γ-Al2O3 and titanium dioxide.

3. The preparation method of the coated honeycomb noble metal reduction catalyst according to claim 1, characterized in that, The additives include one or more of carboxymethyl cellulose, polyvinyl alcohol, and polyethylene glycol; the amount of the additives used is 0.5-1% of the total mass of the precious metal precursor slurry; the acid solution is one of sulfuric acid, nitric acid, and hydrochloric acid, with a mass concentration of 10-20%.

4. The preparation method of the coated honeycomb noble metal reduction catalyst according to claim 1, characterized in that, In the alumina slurry, the mass percentages of each raw material are as follows: γ-Al2O3 30~45%, binder 3~5%, and the remainder is water; The modified slurry contains the following mass percentages of raw materials: 0.05-0.1% Pt precursor, 0.05-0.1% Pd precursor, 5-10% γ-Al2O3, 10-20% titanium oxide, 5-8% transition metal oxide, 3-5% binder, and the remainder is water.

5. The preparation method of the coated honeycomb noble metal reduction catalyst according to claim 1, characterized in that, The transition metal oxide is a mixture of iron oxide and cerium oxide, with a mass ratio of iron oxide to cerium oxide of 1 to 3:1; the Pt precursor is one of platinum nitrate, chloroplatinic acid, and platinum chloride; the Pd precursor is one of palladium chloride, palladium nitrate, palladium acetate, and potassium tetrachloropalladate; the binder is aluminum sol or silica sol; and the carrier is a cordierite honeycomb ceramic carrier.

6. The preparation method of the coated honeycomb noble metal reduction catalyst according to claim 1, characterized in that, The preparation method of the alumina slurry includes: adding γ-Al2O3 and binder to deionized water, stirring thoroughly, and then ball milling. The ball milling temperature is room temperature, the rotation speed is 500~1000 r / min, and the ball milling time is 1~10 h. The resulting alumina slurry has a particle size D90 of 10~50 μm and a viscosity of 30~300 mPa·s.

7. The preparation method of the coated honeycomb noble metal reduction catalyst according to claim 1, characterized in that, The method for preparing the noble metal precursor slurry includes: mixing and stirring Pt precursor, Pd precursor, γ-Al2O3, titanium oxide, transition metal oxide and binder in water, and ball milling after thorough mixing. The ball milling temperature is room temperature, the rotation speed is 500~1000 r / min, and the ball milling time is 1~10 h. The resulting noble metal precursor slurry has a particle size D90 of 1~5 μm and a viscosity of 80~200 mPa·s.

8. The preparation method of the coated honeycomb noble metal reduction catalyst according to claim 1, characterized in that, The drying temperature is 90~130℃, the drying time is 1~2h, and the calcination temperature is 450~600℃, the calcination time is 2~5h.

9. A coated honeycomb precious metal reduction catalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. The application of the coated honeycomb precious metal reduction catalyst according to claim 9 in the treatment of polluted gas, wherein the polluted gas includes one or more of VOCs and CO.

Images