A composite catalyst for degrading nitrogen oxide compounds and a method for preparing the same

Abstract

The present application relates to a kind of composite catalysts for degrading nitrogen oxide compounds and its preparation method, with diamond micro powder as carrier and play the reduction and catalysis, simultaneously with one or more metal or metal oxide as catalytic active component.The metal oxide is the mixture of 1-2 kinds of V2O5, Co3O4, CuO, ZrO2, NiO, Fe2O3, Al2O3, TiO2, WO3, M O3, CeO2, Rh2O3 Or Sm2O3;Or one of ternary metal oxide V2O5-M O3-TiO2, CeO2-ZrO2-WO3.The catalyst of the present application has good degradation NO x Activity, degradation efficiency can reach more than 80% in 200-700 ℃ temperature range, suitable for the requirement of degradation in different temperature range.The composite catalyst has high activity and strong resistance to oxygen inhibition, which is conducive to long-term use.The preparation method provided by the present application is reasonable and suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of catalytic degradation of air pollutants, specifically to a method for the direct catalytic degradation of nitrogen oxides by mixing diamond powder with a metal catalyst or a metal oxide catalyst. Background Technology

[0002] Nitrogen oxides (NO) x NO is one of the major pollutants in the atmospheric environment. It is mainly emitted in large quantities during the operation of coal-fired power plants and steel mills, as well as in vehicle exhaust emissions. x The harmless treatment of [the pollutants] is generally referred to as denitrification treatment, and the state has formulated relevant policies, emission standards, and requirements. Currently, the main denitrification technology and process utilizes selective catalytic reduction (SCR) denitrification, which involves the combined action of a reducing agent and a catalyst (including metal catalysts, such as precious metals or metal oxide catalysts), and has been widely applied industrially. Within a certain temperature range, NOx in flue gas is converted into nitrogen and water through spraying with an amino-containing reducing agent (such as ammonia water, urea solution, etc.) under the synergistic effect of the catalyst.

[0003] Metals (such as noble metals Pt, Pd, Rh, Ir, Au, Ag, Pt-Rh, Pt-Pd, etc.) or metal oxides (such as V2O5, Co3O4, CuO, ZrO2, NiO, Fe2O3, Al2O3, Rh2O3, Sm2O3, etc.) are commonly used as catalysts, or supported on other materials such as Al2O3, TiO2, ZrO2, SiO2, ZnO, etc., to further improve catalytic efficiency and timeliness. Among them, noble metals are the earliest catalysts used in SCR catalysis because they readily adsorb reactants on their surfaces, which is conducive to the formation of intermediate active compounds. However, noble metal catalysts are expensive, prone to oxygen inhibition, and easily aggregate, resulting in agglomeration and deactivation.

[0004] Currently, the mature and industrially applied catalysts in the SCR method are V₂O₅ / TiO₂ system catalysts, with V₂O₅ as the active component and TiO₂ as the support. However, they also suffer from oxygen inhibition and deactivation. In recent years, MnO₂ has also been developed. x FeO x CuO x CeO x MnO x Catalysts using metal oxides such as CeO2 as active components are commonly used. However, these metal and metal oxide catalysts are prone to deactivation with long-term use, resulting in a significant reduction in catalytic efficiency. Therefore, frequent replacements are necessary (an average of every two years), leading to high replacement costs and requiring system shutdowns that disrupt overall unit operation. Furthermore, current SCR methods require the use of large quantities of ammonia or urea as reducing agents, increasing both cost and process complexity.

[0005] Carbon-based catalysts are widely used. Common carbon-based materials include activated carbon, biochar, pyrolysis semi-coke, and graphite carbon. Carbon-based catalysts can lower reaction temperatures, are abundant in sources, and are inexpensive. Ye et al. reported in Fullernes, Nanotubes and Carbon Nanostructures, 2021, 30(2):297 that they modified activated carbon with HNO3 and H2SO4, prepared a series of supported Mn catalysts by impregnation, and tested their denitrification performance. The results showed that the catalyst prepared by HNO3-modified activated carbon had the highest NO conversion rate. Yang et al. reported in Chemical Engineering Journal, 2020, 379:122398 that they prepared Fe-modified carbon-based supported MnOx / CeOy catalysts by inserting metal ions into the graphite microcrystalline structure. The activity test results showed that when the reaction temperature was 125℃ and the space velocity was 12000h, the catalysts were effective. -1 At that time, the denitrification efficiency was 90%, indicating that the carbon-based catalyst has good low-temperature denitrification activity. Nevertheless, carbon-based catalysts have the drawback of poor water resistance, and carbon materials are highly flammable when in contact with oxygen, posing a certain risk and making them unsuitable for industrial applications. The catalysts mentioned above, as SCR catalysts, all play a catalytic role in denitrification processes using ammonia or urea water as reducing agents. Summary of the Invention

[0006] To address the above problems, the present invention provides a method for degrading nitrogen oxides NO. x The composite catalyst and its preparation method are described in detail below.

[0007] The composite catalyst for degrading nitrogen oxides in this invention is composed of micro / nano diamond particles and metal or metal oxide powder.

[0008] The metal is one or a combination of two or more of Al, Cu, Fe, V, Co, Cr, Mo, Mn, Ni, Pt, Ce, Pd, Rh, Ir, Au or Ag;

[0009] The metal oxide is a mixture of one or two of the following: V2O5, Co3O4, CuO, ZrO2, NiO, Fe2O3, Al2O3, TiO2, WO3, MoO3, CeO2, Rh2O3, or Sm2O3; or one of the following: V2O5-MoO3-TiO2, CeO2-ZrO2-WO3.

[0010] The mass ratio of metal or metal oxide to micro / nano diamond particles is (0.01–10):1; the particle size of the micro / nano diamond particles and the metal or metal oxide powder is 0.1–10 micrometers.

[0011] Preferably, the catalytic degradation efficiency is better in the particle size range of 500 nanometers to 5 micrometers, and the mass ratio of metal oxide powder to diamond powder is (1~2):1.

[0012] The preparation method of a composite catalyst for degrading nitrogen oxides in this invention includes the following steps:

[0013] High-purity commercial diamond powder and metal powder or metal oxide powder are selected and screened to obtain powder particles with an average size of 1 to 10 micrometers. Diamond and metal powder with a narrow particle size distribution are mixed at a mass ratio of (0.01 to 10):1 and then mixed by ultrasonic vibration to obtain a composite catalyst for degrading nitrogen oxides.

[0014] Preferably, the composite catalyst obtained after ultrasonic vibration mixing is further ground and ultrasonically treated to further improve the mixing effect.

[0015] Preferably, a method for preparing a composite catalyst for degrading nitrogen oxides further includes the following step: combining the composite catalyst for degrading nitrogen oxides with a binder or support to form a catalyst module for use.

[0016] Furthermore, the bonding of the composite catalyst with the binder is accomplished through mixing, extrusion, and molding steps. The composite catalyst is bonded to the support through mixing, coating onto the support surface, drying, and calcination.

[0017] Furthermore, the catalyst module is honeycomb, plate, or corrugated plate type.

[0018] The beneficial effects of this invention are:

[0019] 1. Diamond is an allotrope of carbon, possessing many unique properties compared to other carbon materials, such as high hardness, high-temperature physicochemical stability, and abundant surface active sites. Mixing diamond powder with traditional metal or metal oxide catalysts can disperse the original catalyst, prevent agglomeration, and increase the specific surface area. Simultaneously, diamond participates in reduction and catalysis. Introducing micro / nano diamonds into traditional catalysts can synergistically improve NO... x The effect of degradation.

[0020] 2. This invention can achieve NO reduction without adding reducing agents such as ammonia or urea. x This degradation method avoids the need for additional reducing agents in existing SCR methods to perform NO degradation. x The problem of catalytic degradation reduces the cost of use.

[0021] 3. The method for preparing nitrogen oxides by diamond-supported catalyst of the present invention has the advantages of simple process, low cost, easy implementation and easy scale-up, and is expected to be used in large-scale production and practical application in the future. Attached Figure Description

[0022] Figure 1 This invention relates to a method for degrading nitrogen oxides (NO). x Schematic diagram of the catalytic degradation principle of composite catalyst. Detailed Implementation

[0023] The technical solution of the present invention will be further explained and described below with reference to specific embodiments. The embodiments described below are intended to facilitate the understanding of the technical solution of the present invention and do not constitute any limitation thereof. Unless otherwise specified, all raw materials used in the present invention are commercially available materials.

[0024] Example 1: Metal (Cu)-Diamond Hybrid

[0025] Diamond powder and Cu metal powder are first screened with a certain mesh to obtain powder particles with an average size of 1-10 micrometers. The diamond and metal powders with a narrow particle size distribution are mixed at a mass ratio of 1:1 and further mixed by ultrasonic vibration. The mixture is then ground and ultrasonically treated to make the diamond and metal particles more fully bonded together and reduce particle agglomeration, thus obtaining a fully mixed diamond-metal composite catalyst.

[0026] Example 2: Metal (Ce)-Diamond Hybrid

[0027] The difference between this embodiment and Embodiment 1 is that Ce metal powder is used instead of Cu metal powder in this embodiment.

[0028] Example 3: Metal oxide (CuO)-diamond mixture

[0029] Diamond powder and CuO metal oxide powder are first screened with a certain mesh to obtain powder particles with an average size of 1-10 micrometers. The diamond and metal oxide powders with narrow particle size distribution are mixed at a mass ratio of 1:1 and further mixed by ultrasonic vibration. The mixture is then ground and ultrasonically treated to make the diamond and metal oxide particles more fully bonded together and reduce particle agglomeration, thus obtaining a fully mixed diamond-metal oxide composite catalyst.

[0030] Example 4: Metal oxide (V2O5)-diamond mixture

[0031] The difference between this embodiment and embodiment 3 is that V2O5 metal oxide powder is used instead of CuO metal oxide powder in this embodiment.

[0032] Example 5: Composite of multiple metals (Ag / Cu composite metal)-diamond mixture

[0033] The difference between this embodiment and Embodiment 1 is that Ag / Cu composite metal powder is used instead of Cu metal powder in this embodiment to obtain a composite multi-metal-diamond catalyst. The mass ratio of Ag to Cu in this embodiment is 1:1, but other ratios can be used in actual applications.

[0034] Example 6: Composite of multiple metals (Ce / La / Cu composite metal) - diamond mixture

[0035] The difference between this embodiment and Embodiment 5 is that Ce / La / Cu composite metal powder is used instead of Ag / Cu composite metal powder in this embodiment. The mass ratio of Ce, La, and Cu in this embodiment is 1:1:1, but other ratios can be used in actual applications.

[0036] Example 7: Composite of multiple metal oxides (V2O5 / MoO3)-diamond mixture

[0037] The difference between this embodiment and Embodiment 3 is that V2O5 / MoO3 composite metal oxide powder is used instead of CuO metal oxide powder in this embodiment. The mass ratio of V2O5 to MoO3 in this embodiment is 1:1, but other ratios can also be used in actual use.

[0038] Example 8: Composite of multiple metal oxides (V2O5 / MoO3 / CuO)-diamond mixture

[0039] The difference between this embodiment and Embodiment 7 is that V2O5 / MoO3 / CuO composite metal oxide powder is used instead of V2O5 / MoO3 composite metal oxide powder in this embodiment. The mass ratio of V2O5, MoO3, and CuO in this embodiment is 1:1:1, but other ratios can be used in actual applications.

[0040] Effect verification section:

[0041] Experiment 1: Degradation of Nitric Oxide (NO) Gas by Metal-Diamond Catalyst

[0042] The test gas (pure NO) was introduced into the reactor at a flow rate of 100 mL / min. The reactor contained the diamond-metal composite catalyst prepared in Example 1, and the temperature was above 300°C. After treatment, the discharged gas showed no oxidation of NO to produce brownish-red NO2 or a pungent odor, indicating that NO was effectively degraded. At a temperature of 450-650°C, the mass ratio of metal powder to diamond powder was 3:1, the average size of the metal powder was 500 nm, and the average size of the diamond powder was 1 μm.

[0043] NO degradation rate = ([NO])in -[NO] out ) / [NO] in ×100%, of which [NO] in [NO] out The figures represent the NO concentrations at the reactor inlet and outlet, respectively. The results measured by the flue gas analyzer show that the NO degradation rate can be greater than 90%.

[0044] Experiment 2: Degradation of NO gas using a metal oxide-diamond catalyst

[0045] The test gas (i.e., pure NO) was introduced into the reactor at a flow rate of 100 mL / min. The reactor was filled with the metal oxide-diamond composite catalyst prepared in Example 3, and the temperature was greater than 300°C. After treatment, the discharged gas did not undergo oxidation of NO to produce brownish-red NO2 or produce an irritating odor, indicating that NO was effectively degraded.

[0046] By optimizing the catalyst ratio, size, and processing temperature, NO degradation efficiency can exceed 85%. Generally, catalyst particle sizes in the range of 500 nm to 5 μm show good catalytic degradation efficiency. The mass ratio of metal oxide powder to diamond powder is 1–2:1.

[0047] Experiment 3: Degradation of NO gas using composite metal-diamond catalysts

[0048] The test gas (i.e., pure NO) was introduced into the reactor at a flow rate of 100 mL / min. The reactor was filled with the composite catalyst of metal powder and diamond powder prepared in Example 5. The temperature was greater than 300°C. After treatment, the discharged gas did not undergo oxidation of NO to produce brownish-red NO2 or produce an irritating odor, indicating that NO was effectively degraded.

[0049] By optimizing the catalyst ratio and treatment temperature, NO degradation efficiency can exceed 85%. Generally, catalyst particles with a size of 500 nm to 5 μm exhibit good catalytic degradation efficiency. The mass ratio of composite metal powder to diamond powder is 1–2:1.

[0050] Experiment 4: Degradation of NO gas using a composite multi-metal oxide-diamond catalyst

[0051] The test gas (i.e., pure NO) was introduced into the reactor at a flow rate of 100 mL / min. The reactor contained a composite catalyst prepared in Example 7, which consisted of multiple metal oxide powders and diamond powder. The temperature was greater than 300°C. After treatment, the discharged gas did not show any oxidation of NO to produce brownish-red NO2 or any pungent odor, indicating that NO was effectively degraded.

[0052] By optimizing the catalyst ratio and treatment temperature, NO degradation efficiency can exceed 85%. Generally, catalyst particles with a size of 500 nm to 5 μm exhibit good catalytic degradation efficiency. The mass ratio of composite metal oxide powder to diamond powder is 1–2:1.

[0053] In addition to the above embodiments, in other embodiments of the present invention, the composite catalyst described above can be used in combination with binders and supports to form catalyst modules such as honeycomb, plate, or corrugated plate.

[0054] The catalyst powders from Examples 1-4 are combined with binders and supports, and through processes such as mixing, extrusion, and molding, the diamond-supported metal or metal oxide catalysts are fabricated into honeycomb, plate, or corrugated plate catalyst modules for catalytic degradation of NO. x Polluting gases.

[0055] like Figure 1 As shown, this invention uses diamond powder mixed with traditional metal or metal oxide catalysts, which can disperse the original catalyst, avoid agglomeration and clumping, and increase the specific surface area. Simultaneously, diamond also participates in the reduction catalysis, reducing the NO to be treated. x When the exhaust gas passes through the catalyst, the combined action of the composite catalyst results in a gas-solid catalytic reaction at high temperature and humidity, where most of the NO is eliminated. x It directly catalyzes the decomposition of nitrogen and oxygen, and the introduction of micro / nano diamonds into traditional catalysts can synergistically improve NO content. x The effect of degradation.

[0056] Different metal or metal oxide mixed catalysts with diamond exhibit varying optimal catalytic temperatures, ranging from 200 to 800°C. After the experiments, no metal or metal oxide agglomeration or clumping was observed, demonstrating that the metal or metal oxide particles and diamond particles can achieve effective dispersion through physical or chemical adsorption, maintaining good dispersibility even under operating conditions of 200–800°C. The introduction of diamond into the composite catalyst effectively reduces catalyst agglomeration and oxygen inhibition, improving decomposition activity and efficiency, which is beneficial for practical applications.

Claims

1. A composite catalyst for degrading nitrogen oxides, characterized in that, The composite catalyst is composed of micro / nano diamond particles and metal or metal oxide powder. The metal is one or a combination of two or more of Cu, Fe, V, Co, Mo, Mn, Ni, Pt, Ce, Pd, Rh, Ir, Au or Ag; The metal oxide is one or a mixture of two of the following: V2O5, Co3O4, CuO, NiO, Fe2O3, WO3, MoO3, CeO2, Rh2O3, or Sm2O3; or one of the following ternary metal oxides: V2O5-MoO3-TiO2, CeO2-ZrO2-WO3. The mass ratio of metal or metal oxide powder to nanodiamond particles is (1-2):1; the particle size of micro / nanodiamond particles and metal or metal oxide powder is 500 nanometers to 5 micrometers.

2. A method for preparing a composite catalyst for degrading nitrogen oxides as described in claim 1, characterized in that, The specific steps of this method are as follows: Diamond powder and metal powder are first screened to obtain powder particles with an average size of 500 nanometers to 5 micrometers. The diamond and metal powder with a narrow particle size distribution are mixed at a mass ratio of (1 to 2): 1 and then mixed by ultrasonic vibration to obtain a composite catalyst for degrading nitrogen oxides.

3. The method for preparing the composite catalyst for degrading nitrogen oxides according to claim 2, characterized in that, The composite catalyst obtained after ultrasonic vibration mixing is then ground and ultrasonically dispersed again.

4. The method for preparing the composite catalyst for degrading nitrogen oxides according to claim 2 or 3, characterized in that, The method also includes the following step: combining the composite catalyst for degrading nitrogen oxides with a binder or support to form a catalyst module for use.

5. The method for preparing the composite catalyst for degrading nitrogen oxides according to claim 4, characterized in that, The combination of composite catalyst and binder is accomplished through mixing, extrusion and molding steps.

6. The method for preparing the composite catalyst for degrading nitrogen oxides according to claim 4, characterized in that, The composite catalyst is bonded to the support through a series of steps including mixing, coating on the surface of the support, drying, and calcination.

7. The method for preparing the composite catalyst for degrading nitrogen oxides according to claim 4, characterized in that, The catalyst module is honeycomb, plate, or corrugated plate type.

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