Supported catalyst and method for preparing catalyst based on laser etching

Abstract

The invention discloses a supported catalyst and a method for preparing the catalyst based on laser etching, and the method comprises the following steps: 1, adding manganese acetate and one or more transition metal salts into water, and fully stirring and mixing to obtain a transition metal mixed solution A; 2, a chelating agent is added into the transition metal mixed solution A, the pH value of the mixed solution is adjusted, and a mixed solution B with the pH being 7-8 is obtained; 3, foamed nickel is placed in a reactor, the mixed solution B is added to immerse the foamed nickel, a water bath reaction is conducted till jelly is formed on the surface of the foamed nickel, then the foamed nickel and the jelly are dried together, and a precursor C is obtained; and 4, performing laser etching on the precursor C by using CO2 to obtain the catalyst MnO2 / MxOy (at) NF. The catalyst is simple in preparation process and low in price, and the prepared catalyst has high catalytic activity for oxidizing NO and has excellent thermal stability and long service life.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst materials, and particularly relates to a supported catalyst and a method for preparing the catalyst based on laser etching. Background Art

[0002] Nitrogen oxides include NO, NO 2 , N 2 O, etc., which can cause various environmental problems, such as photochemical smog, acid rain and haze. The emission of nitrogen oxides will also promote the generation of secondary aerosols and fine particulate matter, especially the formation of PM2.5. In view of this, work is being actively carried out globally to reduce the emission of nitrogen oxides.

[0003] In order to reduce the emission of nitrogen oxides, researchers have deeply explored various emission reduction technologies, including NO x storage reduction technology, three-way catalytic conversion technology, continuous regeneration capture technology, and selective catalytic reduction technology (SCR), etc. Among them, SCR is to selectively oxidize and reduce ammonia or urea solution with NO in flue gas through the action of a catalyst at medium and high temperatures, and finally generate harmless N x and H 2 O. Among them, the reduction of NO to form N 2 is the decisive step in the SCR reaction process. 2 is the decisive step in the SCR reaction process.

[0004] Currently, the catalysts for oxidizing NO are mainly supported noble metal catalysts and metal oxide catalysts, etc. Although noble metal catalysts have high activity, their high cost limits their wide application. Non-noble metal oxide catalysts, on the other hand, provide a more cost-effective solution. Sun et al. studied the promotion effect of rare earth metal (cerium, lanthanum or praseodymium) doped manganese-based catalysts on NO oxidation (Catal. Commun., 2016, 77, 94 - 97). Wang et al. studied the NO oxidation performance on cerium oxide modified by doping with cobalt, manganese, iron, chromium and nickel (Fuel, 2016, 166, 352 - 360). The catalyst modified by cobalt has high catalytic activity for NO oxidation, showing the great potential of non-noble metal oxides in the field of catalyzing NO.

[0005] For another example, Chinese Patent with Publication No. CN108355647A discloses a preparation method of a manganese-based oxide catalyst. An R source and a manganese source are mixed in a solution in a certain proportion, where R is lanthanide elements such as Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Bi, etc. An alkali solution is added to the mixed solution; after the obtained solution undergoes a hydrothermal synthesis reaction at a certain temperature, a mullite-type oxide catalyst is obtained. At 200 °C, the catalytic NO oxidation conversion efficiency is about 50%.

[0006] In view of this, the present invention provides a supported catalyst and a method for preparing the catalyst by laser etching. Summary of the Invention

[0007] In order to overcome the above-mentioned deficiencies in the technology, the present invention provides a supported catalyst, which is inexpensive, has high catalytic activity for NO oxidation, and has excellent thermal stability and service life.

[0008] A supported catalyst includes nickel foam and active components supported on the nickel foam. The active components include manganese oxide and one or more transition metal oxides.

[0009] Preferably, the particle size of the active components is 10 - 50 μm.

[0010] Preferably, the space group of the active components is C2 / m.

[0011] In order to overcome the above-mentioned deficiencies in the technology, the present invention also provides a method for preparing a supported catalyst by laser etching, which is simple to operate. The prepared catalyst has multiple defect structures on its surface, which helps to activate oxygen molecules and improve the rate of the catalytic NO oxidation reaction.

[0012] The present invention provides a method for preparing a supported catalyst by laser etching, including the following steps:

[0013] Step 1: Add manganese acetate and one or more transition metal salts into water, and stir well to obtain a transition metal mixed solution A;

[0014] Step 2: Add a chelating agent to the transition metal mixed solution A, and adjust the pH value of the mixed solution to obtain a mixed solution B with a pH of 7 - 8;

[0015] Step 3: Place the nickel foam in a reactor, add the mixed solution B to submerge the nickel foam, and carry out a water bath reaction until a gel-like substance forms on the surface of the nickel foam. Then, dry the nickel foam and the gel-like substance together to obtain a precursor C;

[0016] Step 4: Use CO 2 to laser etch the precursor C to obtain the catalyst MnO 2 / M x O y @NF.

[0017] Preferably, the transition metal M in the transition metal salt is at least one of Zn, Co, Fe, Ce, Cd, and Ce.

[0018] Preferably, the transition metal soluble salt is a chloride or / and a nitrate.

[0019] Preferably, in the transition metal mixture A, n(Mn):n(M) = 7 - 10:1 - 2.

[0020] Preferably, the chelating agent is citric acid, where n(Mn):n(chelating agent) = 1:1.3 - 1.7.

[0021] Preferably, the CO 2 The laser power is 10 - 20 W, and the scanning rate is 20 - 40 mm / s.

[0022] Preferably, in the third step, the water bath reaction temperature is 80 - 90 °C, and the drying temperature is 70 - 80 °C.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The present invention uses nickel foam as a carrier, and Mn and other transition metals are doped on the nickel foam by the sol - gel method, so that the catalytic active components can be uniformly dispersed on the surface of the nickel foam, providing a large number of active sites for the catalytic reaction and improving the catalytic efficiency.

[0025] 2. The precursor C prepared by the sol - gel method is subjected to CO 2 laser etching. Since the wavelength of the CO 2 laser is mid - infrared light with a wavelength of 9.0 - 11.0 μm (preferably 10.6 μm), which matches the fundamental frequencies of molecular vibration and rotation of the precursor C, the precursor C can effectively absorb photon energy during the etching process and convert it into thermal motion. Different grain boundaries, surface ions with coordination unsaturation, vacancies and other defect structures are further formed on the surface of the nickel foam, which can enhance the oxygen mobility, contribute to the activation of oxygen molecules, and improve the rate of the catalytic NO oxidation reaction.

[0026] 3. The preparation method of the present invention has a simple operation process, and uses transition metals and nickel foam, with a low cost and is easy to achieve large - scale application. The present invention preferably uses nickel foam as a carrier, which is adapted to the laser etching process, and has good mechanical strength and thermal stability, ensuring that the catalyst can be applied in practice for a long time.

[0027] 4. The present invention prepares the precursor C by the sol - gel method, and can accurately select the composite ratio of Mn and the transition metal element M. Brief Description of the Drawings

[0028] Figure 1 is the SEM image of the catalyst prepared in Example 1 of the present invention;

[0029] Figure 2 is a schematic diagram of the mass change during the heating process in a nitrogen environment of the gel substance on the precursor C and the catalytic active substance converted by laser etching in Example 1 of the present invention;

[0030] Figure 3 It is the XPS spectrum of the catalyst prepared in Example 1;

[0031] Figure 4 It is a schematic diagram of the mechanism for the catalyst prepared in Example 1 to oxidize NO;

[0032] The implementation, functional features and advantages of the present invention will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific Embodiments

[0033] The features of the present invention and other related features will be further described in detail through the following embodiments for the understanding of those skilled in the same industry:

[0034] The embodiment of the present invention provides a supported catalyst, including nickel foam and an active component supported on the nickel foam, wherein the active component includes manganese oxide and one or more transition metal oxides.

[0035] In some embodiments, the particle size of the active component is 10 - 50 μm.

[0036] In some embodiments, the space group of the active component is C2 / m.

[0037] The embodiment of the present invention provides a method for preparing a supported oxidation catalyst based on laser etching, including the following steps:

[0038] Step 1: Add manganese acetate and one or more transition metal salts into water, and fully stir and mix to obtain a transition metal mixed solution A;

[0039] Step 2: Add a chelating agent to the transition metal mixed solution A and adjust the pH value of the mixed solution to obtain a mixed solution B with a pH of 7 - 8;

[0040] Step 3: Place the nickel foam in a reactor, add the mixed solution B to submerge the nickel foam, and react in a water bath until a gel-like substance is formed on the surface of the nickel foam, and then dry the nickel foam and the gel-like substance together to obtain a precursor C;

[0041] Step 4: Use CO 2 Laser etch the precursor C to obtain the catalyst MnO 2 / M x O y @NF.

[0042] In some embodiments, the transition metal M in the transition metal salt is at least one of Zn, Co, Fe, Ce, Cd, and Ce.

[0043] In some embodiments, the transition metal soluble salt is a chloride or / and a nitrate.

[0044] In some embodiments, in the transition metal mixture A, n(Mn):n(M) = 7 - 10:1 - 2.

[0045] In some embodiments, the chelating agent is citric acid, which can evenly disperse metal ions and avoid agglomeration.

[0046] In some embodiments, n(Mn):n(chelating agent) = 1:1.3 - 1.7.

[0047] In some embodiments, in the third step, the water bath reaction temperature is 80 - 90 °C, and the drying temperature is 70 - 80 °C.

[0048] In some embodiments, the catalyst MnO 2 / M x O y @NF has an active component particle size of 10 - 50 μm.

[0049] In some embodiments, the catalyst MnO 2 / M x O y @NF has a space group of C2 / m for the active component.

[0050] In some embodiments, the catalyst MnO 2 / M x O y @NF is used for catalyzing NO oxidation.

[0051] Example 1

[0052] A method for preparing a supported catalyst based on laser etching, which comprises the following steps:

[0053] Step 1: Configure metal ion salt solutions with a concentration of 2 mol / L from Mn(CH 3 CO 2 ) 2 ·4H 2 O and Ce(NO 3 ) 3 ·6H 2 O, and mix them in a ratio of n(Mn):n(Ce) = 9:1 to form a transition metal mixture A.

[0054] Step 2: Slowly drop the transition metal mixture A into a 2.5 mol / L citric acid solution to make n(Mn):n(CA) = 1:1.5. After the dropping is completed, use ammonia water to adjust the pH to 7.5. During the dropping process of the solution, continuously stir to form a mixture B.

[0055] Step 3: Place a piece of nickel foam with dimensions of 2×2×0.2 cm at the bottom of a beaker, and slowly pour the mixed solution B to ensure that the nickel foam is completely submerged in the liquid. Heat it in a water bath at 85 °C to evaporate the solvent, and a uniform purple colloidal substance will form on the nickel foam. Put the nickel foam and the colloidal substance into an oven and dry them at 70 °C to obtain the precursor C.

[0056] Step 4: Place the precursor C in a CO 2 laser etching machine, and select a scanning rate of 30 mm / s and a CO 2 laser with a power of 15 W for laser etching, and finally obtain the catalyst MnO 2 / CeO 2 @NF.

[0057] The characterization of the catalyst MnO 2 / CeO 2 @NF is as shown in Figure 1 the figure. It can be seen that flaky oxides are formed on the surface of the nickel foam, and primary particles with a size of about 20 μm are aggregated together.

[0058] As shown in Figure 2 the figure, after the gel material loaded on the surface of the precursor C is treated by laser etching, its thermal stability and component transformation characteristics are significantly improved. Specifically: 1. The original gel without laser treatment shows a significant weight loss curve in the thermogravimetric test, which is attributed to the intense evaporation of water inside the gel material. 2. Under the same test conditions, the mass retention rate of the precursor C after being irradiated by high-energy CO 2 laser is about 80%, which proves that laser treatment can effectively promote the thermal decomposition and dehydration reaction of the active components on the surface of the precursor C. Further, the thermogravimetric experimental data show that the laser etching process realizes the controllable reconstruction of the material structure through the localized high-temperature effect. Specifically, high-energy CO 2 laser treatment effectively induces the lattice distortion of the transition metal oxide on the surface of the precursor C, forming a composite structure with a high density of oxygen vacancy defects, resulting in a higher mass retention rate of the precursor C than that of the precursor C without laser treatment.

[0059] As shown in Figure 3 the figure, in the catalyst MnO 2 / CeO 2 @NF, the Mn element exists in two different oxidation states of +3 and +4.

[0060] As shown in Figure 4 the figure, the NO oxidation mechanism of MnO 2 / CeO 2 @NF: The oxygen vacancies on the surface of CeO 2 can capture oxygen to form superoxide anions (O 2 -) These strong interactions between superoxide anions and NO promote the formation of free nitrate, which further reacts to generate NO 2 . NO 2 After release, the oxygen vacancies are reversibly restored. On MnO 2 , NO is first adsorbed at the metal sites, and then the nitrosyl formed based on the reactive oxygen species is unstable and is oxidized to nitrate; finally, the decomposition of nitrate produces NO 2 . Generally speaking, dispersed MnO 2 and CeO 2 act as different active sites and may play their unique roles in the catalytic oxidation process of NO.

[0061] Example 2

[0062] Compared with Example 1, in the transition metal mixture A of Example 2, the ratio of n(Mn):n(Ce) is 8:2, and other conditions are the same. The catalyst MnO 2 / CeO 2 @NF-1 is prepared.

[0063] Example 3

[0064] Compared with Example 1, in Example 3, element M is selected as Fe, and FeCl 3 ·6H 2 O is used to prepare a transition metal mixture A with a concentration of 2 mol / L. The ratio of n(Mn):n(Fe) in the transition metal mixture A is 9:1, and other conditions are the same. The MnO2 / Fe 3 O 4 @NF catalyst is obtained.

[0065] Example 4

[0066] Compared with Example 1, in Example 4, element M is selected as Co, and CoCl 2 is used to prepare a metal ion salt solution with a concentration of 2 mol / L. The ratio of n(Mn):n(Co) in the transition metal mixture solution A is kept at 9:1, and other conditions are the same. The MnO 2 / Co 2 O 3 @NF catalyst is obtained.

[0067] Comparative example

[0068] Take 2 g of γ-Al 2 O 3 powder, impregnate and stir it with a certain concentration of chloroplatinic acid solution for 3 h, then add sodium borohydride solution, stir overnight, wash it with deionized water, and then dry it at 100 °C to obtain the catalyst Pt / Al 2 O 3, the content of noble metal platinum is 2%.

[0069] Catalytic performance test

[0070] The catalytic activity of the catalytic material prepared by the above method was evaluated in a fixed-bed reactor under atmospheric pressure. Test conditions: the space velocity was 24000 h -1 , the gas composition was 0.05% NO and 10% O 2 (volume fraction), and the rest was the balance gas N 2 , and the reaction temperature was 200 °C. (NO in -NO out ) / NO in was used to calculate the conversion rate of NO.

[0071] Table 1 Catalytic performance test results

[0072] Example NO conversion rate (%) <![CDATA[MnO 2 / CeO 2 @NF]]> 77.4 <![CDATA[MnO 2 / CeO 2 @NF-1]]> 64.5 <![CDATA[MnO 2 / Fe 3 O 4 > 55.3 <![CDATA[MnO 2 / Co 2 O 3 > 60.3 <![CDATA[Pt / Al 2 O 3 > 21.7

[0073] (1) The catalyst prepared by the present invention has a NO conversion rate of at least 55.3% at a high oxygen content and 200 °C, while the supported noble metal catalyst in the comparative example has a NO conversion rate of 21.7% under the same catalytic oxidation conditions.

[0074] This is because the present invention preferably uses nickel foam as the carrier, which has a large specific surface area, and Mn and other transition metals are doped on the nickel foam by the sol-gel method, so that the catalytic active components can be uniformly dispersed on the surface of the nickel foam, providing a large number of active sites for the catalytic reaction and improving the catalytic efficiency. Moreover, the precursor C prepared by the sol-gel method is subjected to CO 2 laser etching. Since the wavelength of the CO 2 laser is mid-infrared light with a wavelength of 9.0 - 11.0 μm (preferably 10.6 μm), which matches the fundamental frequencies of molecular vibration and rotation of the precursor C, the precursor C can effectively absorb photon energy during the etching process and convert it into thermal motion, further forming defect structures such as different grain boundaries, surface ions with coordination unsaturation, and vacancies on the surface of the nickel foam, which can enhance the oxygen mobility, contribute to the activation of oxygen molecules, and improve the rate of the catalytic NO oxidation reaction, so that the catalyst of the present invention can achieve a high NO conversion rate even at 200 °C.

[0075] The NO conversion rate of the catalyst in the comparative example can reach 55% at 275 °C. However, the required reaction temperature is relatively high, and ultimately the NO treatment cost is relatively high.

[0076] (2) It can be seen from the comparison of Examples 1 - 4 that the catalyst using Ce transition metal has a NO conversion rate of 64.5% - 77.4%, which is superior to other selected transition metals.

Claims

1. A method for preparing a supported catalyst based on laser etching, characterized in that: The following steps are involved: Step 1: adding manganese acetate and one or more transition metal salts into water, and stirring and mixing them thoroughly to obtain a transition metal mixed solution A; Step 2: adding a chelating agent to the transition metal mixed solution A and adjusting the pH value of the mixed solution to obtain a mixed solution B with a pH of 7 to 8; Step 3: placing the nickel foam in a reactor, adding the mixed solution B to immerse the nickel foam, reacting in a water bath until a colloid is formed on the surface of the nickel foam, and then drying the nickel foam and the colloid together to obtain a precursor C; Step 4: Use CO2 laser to etch the precursor C to obtain the catalyst MnO2 / M x O y @NF.

2. The method for preparing a supported catalyst based on laser etching according to claim 1, characterized in that: The transition metal M in the transition metal salt is at least one of Zn, Co, Fe, Ce, Cd, and Ce.

3. The method for preparing a supported catalyst based on laser etching according to claim 2, characterized in that: The soluble transition metal salt is chloride and / or nitrate.

4. The method for preparing a supported catalyst based on laser etching according to claim 2, characterized in that: In the transition metal mixed solution A, n(Mn):n(M)=7-10:1-2.

5. The method for preparing a supported catalyst based on laser etching according to claim 1, characterized in that: The chelating agent is citric acid, wherein n(Mn):n(chelating agent)=1:1.3-1.

7.

6. The method for preparing a supported catalyst based on laser etching according to claim 1, characterized in that: The CO2 laser power is 10-20W, and the scanning rate is 20-40mm / s.

7. The method for preparing a supported catalyst based on laser etching according to claim 1, characterized in that: In the step 3, the water bath reaction temperature is 80-90°C, and the drying temperature is 70-80°C.

8. A supported catalyst, prepared by the method for preparing supported catalyst based on laser etching according to claims 1 to 7, characterized in that: The invention comprises nickel foam and active components loaded on the nickel foam, wherein the active components comprise manganese oxide and one or more transition metal oxides.

9. A supported catalyst according to claim 8, characterized in that: The particle size of the active component is 10-50 μm.

10. A supported catalyst according to claim 8, characterized in that: The space group of the active component is C2 / m.

Images