A multi-effect catalyst for exhaust gas purification and exhaust gas purification method

Abstract

The present invention discloses a multi-effect catalyst for exhaust gas purification, comprising: a substrate, a co-catalyst layer located on and / or in the substrate, and a main catalyst layer located on the co-catalyst layer; the co-catalyst comprises a carrier and a precious metal loaded on the carrier; the main catalyst comprises a metal-modified molecular sieve and / or CeO2-ZrO2-TiO2 oxide. The catalyst is particularly effective when used to purify exhaust gas containing one or more of hydrocarbons and nitrogen oxides. The multi-effect catalyst can directly use the hydrocarbons in the exhaust gas as a reducing agent to reduce nitrogen oxides to harmless N2, while effectively reducing the concentration of excess hydrocarbons in the exhaust gas. Compared with conventional methods for treating exhaust gas streams containing hydrocarbons and nitrogen oxides, there is no need to additionally introduce NH3 to reduce nitrogen oxides.

Description

Technical Field

[0001] The invention relates to a waste gas purification multi-effect catalyst and a preparation method thereof, as well as a method for purifying waste gas using the catalyst, and belongs to the field of catalysts. Background Art

[0002] Using catalysts to purify waste gas from different sources is already one of the more mature technical means. Among them, catalytic oxidation (CO) and selective catalytic reduction (SCR) technologies can basically meet the purification requirements of most waste gases, especially industrial waste gas. The catalytic oxidation process uses a high proportion of oxygen in the waste gas and a suitable catalyst to efficiently remove a variety of VOCs including hydrocarbons, alcohols, esters, acids, benzene series, etc.; and selective catalytic reduction, especially selective catalytic reduction using NH3 as a reducing agent, is widely used in NO in waste gas from fixed and mobile sources. x Purification. Whether it is a catalytic oxidation catalyst or a selective catalytic reduction catalyst, there are many reports in the existing public literature or patents (Hao et al., Chemical Reviews, 119, 4471 (2019), Kamal et al., Atmospheric Environment, 140, 117 (2016), Beale et al., Chemical Society Reviews, 44, 7371 (2015)). CN 107952441A discloses a preparation method and application of a propane catalytic combustion composite oxide catalyst. The method described uses cerium cobalt composite oxide as a propane catalytic combustion catalyst, which has the advantages of high activity, good stability, low ignition temperature and low cost. CN 106475128A provides a method for preparing an industrial waste gas purification catalyst. The method improves the anti-sintering performance of the catalyst, improves the stability of the catalyst, and exhibits excellent catalytic activity and stability in the purification process of benzene series. US 8715618B2 discloses a Cu-doped CHA-type molecular sieve catalyst with high efficiency NO x Removal efficiency. CN 105032387A discloses a low-temperature denitration catalyst, which solves the problem that the catalyst in the prior art has poor chemical adsorption capacity for NH3 under low temperature conditions.

[0003] According to the existing public technologies and literature, when the exhaust gas contains complex components, especially when it contains both components that need to be removed by oxidation, such as hydrocarbons, esters, benzene series, etc., and NO that needs to be reduced, xWhen the CO catalyst and the SCR catalyst are used, due to the large differences in composition, any single type of catalyst cannot achieve the purpose of purifying the above components at the same time. This requires that CO and SCR technologies (different reaction processes, reactors and reaction conditions) are often used simultaneously to achieve the requirements of exhaust gas purification, resulting in high environmental protection costs for enterprises. In view of this, the ideal solution is to design a catalyst that has the ability to purify different components at the same time, simplify the process and save costs. The present invention meets this need. Summary of the invention

[0004] The purpose of the present invention is to provide a multi-effect catalyst for exhaust gas purification and a preparation method thereof in view of the problems of the prior art. The catalyst is particularly effective when used to purify exhaust gas containing one or more of hydrocarbons and nitrogen oxides. The multi-effect catalyst can directly use the hydrocarbons in the exhaust gas as a reducing agent to reduce the nitrogen oxides to harmless N2, while effectively reducing the concentration of excess hydrocarbons in the exhaust gas. Compared with the conventional method of treating the exhaust gas flow containing hydrocarbons and nitrogen oxides, there is no need to additionally introduce NH3 to reduce the nitrogen oxides.

[0005] According to one aspect of the present invention, there is provided an exhaust gas purification multi-effect catalyst, comprising:

[0006] Substrate, main catalyst and co-catalyst;

[0007] A substrate, a co-catalyst layer located on and / or in the substrate, and a main catalyst layer located on the co-catalyst layer;

[0008] The co-catalyst includes a carrier and a noble metal supported on the carrier;

[0009] The main catalyst includes metal-modified molecular sieves and / or CeO2-ZrO2-TiO2 oxides.

[0010] According to a preferred embodiment of the present invention, the co-catalyst layer is located on and / or within the substrate, and the main catalyst layer is located on the co-catalyst layer.

[0011] In the present invention, the precious metal catalyst plays the role of a co-catalyst. The use of the precious metal catalyst in the catalyst of the present invention can not only reduce the usage of the precious metal and reduce the cost, but also achieve the purpose of multiple-effect purification of exhaust gas.

[0012] In the present invention, the structural characteristics between different components and coating catalysts can bring about particularly good catalytic effects. The main catalyst on the upper layer of the co-catalyst can ensure that the exhaust gas will eventually leave the main catalyst layer when it contacts the catalyst (the exhaust gas passes in the order: enters from the main catalyst layer, passes through the co-catalyst layer, and then leaves from the main catalyst layer), while other combinations may cause the exhaust gas to leave from the co-catalyst layer, so that the exhaust gas purification effect will be poor.

[0013] According to some embodiments of the present invention, the carrier of the co-catalyst includes an oxide carrier, and preferably the oxide includes at least one of aluminum oxide, zirconium oxide, silicon oxide, titanium oxide, and cerium oxide.

[0014] According to a preferred embodiment of the present invention, the noble metal of the promoter includes Pt and / or Pd; preferably, the weight ratio of the noble metal element to the carrier is (0.05-5):100.

[0015] According to some embodiments of the present invention, the metal-modified molecular sieve in the main catalyst includes a ZSM-5 molecular sieve modified with Cu and / or Fe; and / or, the weight ratio of the metal element to the molecular sieve is (1-5):100.

[0016] According to a preferred embodiment of the present invention, the main catalyst comprises a metal-modified molecular sieve and a CeO2-ZrO2-TiO2 oxide, and the weight ratio of the metal-modified molecular sieve and the CeO2-ZrO2-TiO2 oxide is (50-90): (10-50).

[0017] According to a preferred embodiment of the present invention, the CeO2-ZrO2-TiO2 oxide is a mixture of a solid solution formed by CeO2 and ZrO2 and TiO2.

[0018] According to some embodiments of the present invention, the loading ratio of the co-catalyst layer and the main catalyst layer is (1-5): (5-1).

[0019] According to a preferred embodiment of the present invention, the loading amount refers to the mass content of the co-catalyst layer or the main catalyst layer based on the volume of the substrate.

[0020] According to a preferred embodiment of the present invention, the substrate is a honeycomb integral flow substrate; the honeycomb pore density is 200-650 cpsi.

[0021] According to a preferred embodiment of the present invention, the co-catalyst layer acts on the interior and / or surface of the substrate wall; the main catalyst layer acts on the surface of the co-catalyst layer. The main catalyst layer does not contact the interior and / or surface of the substrate material. If the main catalyst contacts the surface of the substrate material but not the co-catalyst, the effect achieved by the catalyst will be slightly reduced. In addition, the inventors have found in their research that contact between the main catalyst and the co-catalyst can reduce the shedding rate of the main catalyst and improve its strength.

[0022] According to another aspect of the present invention, there is provided a method for preparing the above catalyst, comprising the following steps:

[0023] S1. preparing co-catalyst and main catalyst slurries respectively;

[0024] S2. The promoter slurry is coated on the substrate to form a promoter layer;

[0025] S3. Coat the main catalyst slurry on the co-catalyst layer to form the main catalyst layer.

[0026] According to some embodiments of the present invention, step S1 comprises:

[0027] 1A. Loading a noble metal compound onto an oxide carrier and calcining to obtain a promoter slurry;

[0028] 1B. Loading the metal onto the molecular sieve and calcining to obtain the metal-modified molecular sieve;

[0029] 1C. Mix the metal-modified molecular sieve with CeO2-ZrO2-TiO2 oxide to obtain a main catalyst slurry.

[0030] According to a preferred embodiment of the present invention, the step 1A can be performed as follows: a noble metal compound, an oxide carrier and water are mixed to obtain a promoter slurry.

[0031] According to some embodiments of the present invention, the noble metal compound comprises a compound of a soluble salt of a noble metal, preferably comprising chloroplatinic acid and / or palladium nitrate.

[0032] According to a preferred embodiment of the present invention, the step 1B can be performed as follows: adding the molecular sieve into the metal compound solution for impregnation, drying and calcining to obtain the molecular sieve.

[0033] According to some embodiments of the present invention, the metal compound comprises a compound of a soluble metal salt, preferably comprising iron nitrate and / or copper sulfate.

[0034] According to a preferred embodiment of the present invention, step 1C can be performed as follows: the metal-modified molecular sieve obtained in step 1B is mixed with powders of CeO2, ZrO2 and TiO2, and water, a surfactant, a styrene-acrylic emulsion and an aluminum sol are added to obtain a main catalyst slurry.

[0035] According to some embodiments of the present invention, step S2 includes: coating the promoter slurry on the substrate, drying and calcining to form a promoter layer on the substrate.

[0036] According to some embodiments of the present invention, step S3 includes: coating the main catalyst slurry on the co-catalyst layer, drying and calcining, and forming the main catalyst layer on the co-catalyst layer.

[0037] According to a preferred embodiment of the present invention, the calcination temperature in step S3 is 400-600° C., and the calcination time is 2-8 hours.

[0038] According to another aspect of the present invention, a method for purifying waste gas is provided, comprising: contacting waste gas with the above-mentioned catalyst. The waste gas may be waste gas discharged from a variety of chemical production processes, wherein the waste gas contains hydrocarbons and nitrogen oxides. After the catalyst treatment, at least a portion of the components contained in the waste gas can be purified to form N2, CO2 and H2O. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram showing the structure of a multi-effect catalyst for exhaust gas purification according to an embodiment of the present invention:

[0040] Figure 2 A schematic diagram showing the structure of a multi-effect catalyst for exhaust gas purification according to an embodiment of the present invention;

[0041] Figure 3 A graph showing the C3H8 conversion performance results of the catalyst according to Example 1 of the present invention and the catalyst of Comparative Example 1;

[0042] Figure 4 A graph showing the NO conversion performance results of the catalyst according to Example 1 of the present invention and the catalyst of Comparative Example 1;

[0043] Explanation of the reference numerals: 11, substrate; 12, co-catalyst layer; 13, main catalyst layer; 14, co-catalyst layer infiltrated into the substrate; 15, main catalyst layer. DETAILED DESCRIPTION

[0044] The present invention will be further described below by way of examples, but are not limited thereto.

[0045] Examples 1-6

[0046] (1) Preparation of the co-catalyst layer: Alumina (d 50 at 2-3 μm) and cerium oxide (d 50 About 2.6μm) powder (the mass ratio of aluminum oxide and cerium oxide is 2:1) and a certain amount of deionized water are mixed in a container. A certain amount of chloroplatinic acid and (or) palladium nitrate solution is slowly added to the above container under stirring conditions, and after continuing to stir for 30 minutes, the pH is adjusted to about 10 with ammonia water and stirred for 60 minutes. Then, acidic aluminum sol is added, and the pH is adjusted to 4-5 with nitric acid, and then transferred to a ball mill for 2 hours to obtain a promoter slurry. The cordierite honeycomb substrate with a pore density of 300cpsi is completely immersed in the obtained slurry, and it is taken out after standing for a period of time. The excess slurry in the substrate pores is blown off with compressed air, and it is dried and calcined at 450°C for 4 hours. The content of Pt and Pd in ​​the obtained sample (calculated based on the entire substrate volume) is shown in Table 1.

[0047] (2) Preparation of the main catalyst layer: Dry ZSM-5 powder (d 50 The Fe-ZSM-5 molecular sieve powder is prepared by mixing the powder with cerium oxide, zirconium oxide and titanium dioxide, and adding deionized water, surfactant Tween-80, styrene-acrylic emulsion and neutral aluminum sol. The main catalyst slurry is obtained after ball milling for 2 hours. The sample in step (1) is completely immersed in the obtained main catalyst slurry, taken out after standing for a period of time, and the excess slurry in the substrate pores is blown off by compressed air. After drying, the catalyst is obtained by calcining at 550°C for 4 hours. The content of Fe-ZSM-5 and CeO2-ZrO2-TiO2 in the catalyst (calculated based on the entire substrate volume) is shown in Table 1.

[0048] In Examples 1-4, the loading of the main catalyst layer is 80 g / L, including about 10-30 g / L of CeO2-ZrO2-TiO2 oxide and 50-70 g / L of Fe-ZSM5 molecular sieve; the loading of the co-catalyst layer is about 30 g / L. In Example 5, the loading of the co-catalyst layer is 30 g / L, and the loading of the main catalyst layer is 96 g / L, including about 12 g / L of CeO2-ZrO2-TiO2 oxide and 84 g / L of Fe-ZSM5 molecular sieve. In Example 6, the loading of the co-catalyst layer is 24 g / L, and the loading of the main catalyst layer is 120 g / L, including about 15 g / L of CeO2-ZrO2-TiO2 oxide and 105 g / L of Fe-ZSM5 molecular sieve.

[0049] Comparative Example 1

[0050] The same as Example 1, except that chloroplatinic acid and palladium nitrate are not added in step (1), that is, the content of Pt and Pd in ​​the sample is 0.

[0051] Comparative Example 2

[0052] Same as Example 1-6, except that the loading amount of the co-catalyst layer is 90 g / L, and the loading amount of the main catalyst layer is 40 g / L, including about 5 g / L of CeO2-ZrO2-TiO2 oxide and 35 g / L of Fe-ZSM5 molecular sieve.

[0053] Comparative Example 3

[0054] Same as Example 1-6, except that the loading amount of the co-catalyst layer is 120 g / L, and the loading amount of the main catalyst layer is 24 g / L, including about 3 g / L of CeO2-ZrO2-TiO2 oxide and 21 g / L of Fe-ZSM5 molecular sieve.

[0055] Comparative Example 4

[0056] The main catalyst and the co-catalyst were prepared according to the method and formula in Example 1. Unlike Example 1, in this comparative example, two layers were not coated. Instead, the main catalyst and the co-catalyst were mixed and coated once to obtain a single-layer coating, which contained both the main catalyst and the co-catalyst.

[0057] Table 1

[0058]

[0059] Table 2

[0060]

[0061]

[0062] Exhaust gas purification

[0063] The exhaust gas containing hydrocarbons (taking propane C3H8 as an example) and nitrogen oxides (taking NO as an example) was contacted with the catalysts prepared in Example 1 and Comparative Example 1 respectively. The test conditions were: space velocity 8800h -1 The inlet concentration of the exhaust gas was [C3H8] = 1500 ppm, [NO] = 300 ppm, [O2] = 8 vol%, and [N2] was the balance gas. The conversion rate of C3H8 and the conversion rate of NO were measured respectively.

[0064] Depend on Figure 3 It can be seen that the catalyst of Example 1 having a noble metal promoter layer exhibits better C3H8 conversion performance; Figure 4It can be seen that under the conditions of 400°C and 450°C, the NO conversion rates of the catalyst of Example 1 and the catalyst of Comparative Example 1 are almost the same, showing similar performances.

[0065] Any numerical value mentioned in the present invention, if there is only an interval of two units between any minimum value and any maximum value, includes all values ​​from the minimum value to the maximum value each time increasing by one unit. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is declared to be 50-90, in this specification it means that 51-89, 52-88... and 69-71 and 70-71 are specifically listed. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 can be appropriately considered as a unit. These are just some specially specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0066] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. An application of a catalyst in exhaust gas purification, wherein the exhaust gas is contacted with the catalyst, characterized in that: The catalyst comprises: Substrate, main catalyst and co-catalyst; The main catalyst comprises a molecular sieve modified with Cu and / or Fe and a CeO2-ZrO2-TiO2 oxide; the co-catalyst comprises a carrier and a precious metal supported on the carrier; the co-catalyst layer is located on and / or within a substrate, and the main catalyst layer is located on the co-catalyst layer; The ratio of the loading amount of the co-catalyst layer to the loading amount of the main catalyst layer is (1-5):5; The noble metal of the promoter includes Pt and / or Pd; The weight ratio of the noble metal element to the carrier is (0.05-5):100; The weight ratio of the Cu and / or Fe element to the molecular sieve is (1-5):100; The weight ratio of the Cu and / or Fe modified molecular sieve to CeO2-ZrO2-TiO2 oxide is (50-90):(10-50).

2. The use according to claim 1, characterized in that: The support of the co-catalyst includes an oxide support.

3. The use according to claim 2, characterized in that: The oxide includes at least one of aluminum oxide, zirconium oxide, silicon oxide, titanium oxide, and cerium oxide.

4. The use according to any one of claims 1 to 3, characterized in that: The preparation method of the catalyst comprises the following steps: S1. Prepare the co-catalyst and the main catalyst respectively; S2. coating the promoter on the substrate to form a promoter layer; S3. Coating the main catalyst on the co-catalyst layer to form a main catalyst layer.

5. The use according to claim 4, characterized in that: The step S1 comprises: 1A. Loading a noble metal compound onto an oxide carrier and calcining to obtain a promoter; 1B. Loading Cu and / or Fe onto a molecular sieve and calcining to obtain a Cu and / or Fe-modified molecular sieve; 1C. Mixing Cu and / or Fe modified molecular sieve with CeO2-ZrO2-TiO2 oxide to obtain a main catalyst.

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