Catalyst for removing non-methane hydrocarbon as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for removing non-methane hydrocarbon as well as a preparation method and application thereof, and relates to the technical field of catalytic environmental protection. Comprising the following steps: synthesizing chromium and / or cobalt-doped two-dimensional carbon nitride through a thermal polycondensation method, and synthesizing cerium oxide through a hydrothermal method; mixing two-dimensional carbon nitride and cerium oxide, dissolving in a solvent, and sequentially carrying out ultrasonic treatment, stirring, drying and calcining treatment to obtain a composite carrier; platinum and / or palladium single atoms are adsorbed on the composite carrier through an impregnation method to obtain a composite catalyst; precious metal monomers platinum and / or palladium are used as high-activity sites to efficiently activate oxygen and accelerate C-H bond breakage of hydrocarbon molecules, the oxidation efficiency under the low-temperature condition of 180 DEG C or below can be remarkably improved, the electronic structure of g-C3N4 can be adjusted through doping of Cr and Co, Cr-N-Co active sites are formed, and the adsorption and activation capacity on intermediate products is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of catalytic environmental protection technology, and in particular to a catalyst for removing non-methane total hydrocarbons, a preparation method and application thereof. Background Art

[0002] Non-methane hydrocarbons (NMHC) refer to all volatile hydrocarbons (mainly C2-C8) except methane. When NMHC in the atmosphere exceeds a certain concentration, it can form ozone and fine particulate matter, which has an adverse effect on the environment and human health. Therefore, in industries such as petroleum and chemical industries where NMHC is easily contained in waste gas, NMHC needs to be treated to meet waste gas emission requirements.

[0003] In the prior art, one of the common methods is to treat non-methane total hydrocarbons by oxidation catalysts. However, the existing oxidation catalysts generally have a narrow operating temperature window and a short service life when treating non-methane total hydrocarbons. Summary of the invention

[0004] The object of the present invention is to provide a catalyst for removing non-methane total hydrocarbons, a preparation method and application thereof, so as to solve the above technical problems.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a catalyst for removing non-methane total hydrocarbons, comprising the following steps: The chromium and / or cobalt doped two-dimensional carbon nitride was synthesized by a thermal shrinkage polymerization method, and the cerium oxide was synthesized by a hydrothermal method; The two-dimensional carbon nitride and cerium oxide are mixed and dissolved in a solvent, and then subjected to ultrasonic, stirring, drying and calcination treatments in sequence to obtain a composite carrier; The composite catalyst is obtained by adsorbing platinum and / or palladium single atoms on the composite carrier through an impregnation method.

[0006] Further, urea and chromium salt and / or cobalt salt are dissolved in water and stirred until completely dissolved, and then placed in a water bath for evaporation and drying to obtain a mixed precursor powder; The precursor powder is subjected to a heating polymerization reaction in a high temperature environment and then ground to obtain a chromium and / or cobalt-doped two-dimensional carbon nitride sheet layer.

[0007] Furthermore, the chromium and / or cobalt doped two-dimensional carbon nitride and cerium oxide are mixed in a mass ratio of (4-8):3, and then the solvent is heated for ultrasonic treatment, and then stirred and evaporated at 60-70°C, and then calcined in an air atmosphere at 280-330°C to form a composite carrier.

[0008] Furthermore, the mass percentages of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride are 0-1wt% of the chromium salt and 0-1wt% of the cobalt salt, respectively, wherein the total mass percentage of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride is 0.8-1wt%.

[0009] Further, the platinum salt and / or palladium salt are dissolved in water respectively, the composite carrier is added for ultrasonic dispersion, and then stirred and evaporated to dryness at 60-65° C. to obtain a precursor powder; The precursor powder is subjected to a high-temperature reduction reaction in a hydrogen and argon atmosphere to reduce the platinum salt and / or palladium salt to metal monomer platinum and / or metal monomer palladium to obtain a composite catalyst.

[0010] Furthermore, the mass percentage of the metal monomer platinum in the composite catalyst is 0-1wt%, the mass percentage of the metal monomer palladium in the composite catalyst is 0-1wt%, and the total mass percentage of the metal monomer platinum and metal monomer palladium in the composite catalyst is 1-1.2wt%.

[0011] Further, the chromium salt is one of chromium nitrate, chromium sulfate, chromium acetate and chromium oxalate; The cobalt salt is one of cobalt nitrate, cobalt sulfate, cobalt oxalate and cobalt citrate.

[0012] Furthermore, the platinum salt is platinum nitrate or chloroplatinic acid; the palladium salt is palladium nitrate or chloropalladic acid.

[0013] Furthermore, the present invention also provides a catalyst for removing non-methane total hydrocarbons prepared by the above method.

[0014] Furthermore, the present invention also provides a catalyst for removing non-methane total hydrocarbons prepared by the above method, which is applied to the detection field of removing non-methane total hydrocarbons and non-methane total hydrocarbons.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses precious metal monomers platinum and / or palladium as high-activity sites to efficiently activate oxygen and accelerate the breaking of CH bonds of hydrocarbon molecules, which can significantly improve the oxidation efficiency under low-temperature conditions below 180°C. The doping of Cr and Co can adjust the electronic structure of g-C3N4, forming Cr-N-Co active sites and enhancing the adsorption and activation capabilities of intermediate products.

[0016] The composite catalyst of the present invention has extremely strong stability and anti-poisoning performance. During use, it only needs to remove particulate impurities in the exhaust gas through a spray tower, and does not require supporting special equipment and facilities, thereby reducing the difficulty and cost of the process. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0018] The present invention provides a technical solution: a method for preparing a catalyst for removing non-methane total hydrocarbons, comprising the following steps: The chromium and / or cobalt doped two-dimensional carbon nitride was synthesized by a thermal shrinkage polymerization method, and the cerium oxide was synthesized by a hydrothermal method; The two-dimensional carbon nitride and cerium oxide are mixed and dissolved in a solvent, and then subjected to ultrasonic, stirring, drying and calcination treatments in sequence to obtain a composite carrier; The composite catalyst is obtained by adsorbing platinum and / or palladium single atoms on the composite carrier through an impregnation method.

[0019] In a further embodiment of this example, urea and chromium salt and / or cobalt salt are dissolved in water and stirred until completely dissolved and then placed in a water bath for evaporation and drying to obtain a mixed precursor powder; The precursor powder is subjected to a heating polymerization reaction in a high temperature environment and then ground to obtain a chromium and / or cobalt-doped two-dimensional carbon nitride sheet.

[0020] In a further implementation of this example, chromium and / or cobalt doped two-dimensional carbon nitride and cerium oxide are mixed in a mass ratio of (4-8):3, the solvent is heated for ultrasonic treatment, and then the mixture is stirred and evaporated to dryness at 60-70°C and calcined in an air atmosphere at 280-330°C to form a composite carrier.

[0021] In a further implementation of this example, the mass percentages of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride are 0-1wt% of the chromium salt and 0-1wt% of the cobalt salt, respectively, wherein the total mass percentage of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride is 0.8-1wt%.

[0022] In a further implementation of this embodiment, platinum salt and / or palladium salt are dissolved in water, respectively, a composite carrier is added for ultrasonic dispersion, and then stirred and evaporated to dryness at 60-65° C. to obtain a precursor powder; The precursor powder is subjected to a high-temperature reduction reaction in a hydrogen and argon atmosphere to reduce the platinum salt and / or palladium salt to metal monomer platinum and / or metal monomer palladium to obtain a composite catalyst.

[0023] In a further implementation of this example, the mass percentage of the metal monomer platinum in the composite catalyst is 0-1wt%, the mass percentage of the metal monomer palladium in the composite catalyst is 0-1wt%, and the total mass percentage of the metal monomer platinum and metal monomer palladium in the composite catalyst is 1-1.2wt%.

[0024] In a further embodiment of this example, the chromium salt is one of chromium nitrate, chromium sulfate, chromium acetate and chromium oxalate; The cobalt salt is one of cobalt nitrate, cobalt sulfate, cobalt oxalate and cobalt citrate.

[0025] In a further embodiment of this example, the platinum salt is platinum nitrate or chloroplatinic acid; the palladium salt is palladium nitrate or chloropalladic acid.

[0026] It should be noted that: by using precious metal monomers platinum and / or palladium as highly active sites to efficiently activate oxygen and accelerate the breaking of the CH bonds of hydrocarbon molecules, the oxidation efficiency under low temperature conditions below 180°C can be significantly improved.

[0027] The electronic structure of g-C3N4 can be adjusted by doping with Cr and Co, forming Cr-N-Co active sites and enhancing the adsorption and activation ability of intermediate products, e.g., Co 3+ / Co 2+ and Cr 3+ / Cr 6+ Redox pairs can promote free radicals (such as OH, O2 - ) formation, strengthening the deep oxidation path.

[0028] The oxygen vacancies in ceria can serve as active oxygen (O - ) storage reservoir, releasing oxygen to participate in the reaction under oxygen-deficient conditions and dynamically maintaining catalytic activity. The heterojunction formed by cerium oxide and two-dimensional carbon nitride can promote the separation of photogenerated carriers (such as photocatalytic scenarios) or thermally excited electrons, inhibit electron-hole recombination, and improve energy utilization efficiency.

[0029] The alkaline sites on the surface of cerium oxide can preferentially adsorb acidic poisons (such as SO2 and HCl) in the exhaust gas, reducing their toxicity to the active sites of precious metals. Cr and Co doping can form a stable metal-nitrogen coordination structure (such as Co-N-Cr), inhibiting the sintering or loss of precious metal particles at high temperatures.

[0030] The two-dimensional sheet structure can limit the excessive adsorption of reaction intermediates (such as tar and polycyclic aromatic hydrocarbons) and reduce the formation of carbon deposits. The active oxygen on the surface of cerium oxide can oxidize the deposited carbonaceous species and keep the catalyst surface clean.

[0031] Embodiment 1: 10 g of urea, 0.01 mmol of chromium nitrate and 0.09 mmol of cobalt nitrate were dissolved in 50 ml of deionized water respectively, stirred until completely dissolved, and then evaporated to dryness in a water bath at 80° C. to obtain a mixed precursor powder.

[0032] The mixed precursor powder was placed in a crucible, heated to 600°C at 3°C / min, kept warm for 4 hours in a nitrogen atmosphere, cooled naturally to room temperature, and then ground to obtain Cr / Co-doped g-C3N4 sheets.

[0033] 0.1 g of cerium nitrate hexahydrate is dissolved in 50 ml of ethanol, and 0.1 g of a dispersant (eg, PVP) is added for ultrasonic dispersion for 36 minutes, and then the mixture is transferred to a high-pressure reactor for hydrothermal reaction at 200° C. for 12 hours. The mixture is centrifugally washed and dried to obtain cerium oxide nanoparticles.

[0034] Cr / Co doped g-C3N4 sheets and cerium oxide nanoparticles were mixed in a mass ratio of 4:3 and added with 50 ml of ethanol for ultrasonic treatment for 3 hours. After stirring and evaporating at 60°C, they were calcined at 300°C in an air atmosphere for 2 hours to form a composite carrier of g-C3N-CeO2 heterojunction.

[0035] 0.05 mmol of chloroplatinic acid was dissolved in 20 ml of deionized water, 1.0 g of the composite carrier was added and ultrasonically dispersed for 1 hour, then stirred and evaporated at 60°C to obtain a precursor powder. The precursor powder was placed in a tubular furnace, and the temperature was increased to 300°C at 4°C / min in a 5% H2 / Ar atmosphere, and kept warm for 2 hours to reduce the platinum in the platinum salt to a metal monomer to obtain a composite catalyst.

[0036] Example 2 The difference from Example 1 is that 10 g of urea, 0.03 mmol of chromium nitrate and 0.07 mmol of cobalt nitrate are dissolved in 50 ml of deionized water respectively.

[0037] Example 3 The difference from Example 1 is that 10 g of urea, 0.05 mmol of chromium nitrate and 0.05 mmol of cobalt nitrate are dissolved in 50 ml of deionized water respectively.

[0038] Example 4 The difference from Example 1 is that 10 g of urea, 0.07 mmol of chromium nitrate and 0.03 mmol of cobalt nitrate are dissolved in 50 ml of deionized water respectively.

[0039] Example 5 The difference from Example 1 is that 10 g of urea, 0.09 mmol of chromium nitrate and 0.01 mmol of cobalt nitrate are dissolved in 50 ml of deionized water respectively.

[0040] Example 6 The difference from Example 3 is that the Cr / Co doped g-C3N4 sheets and cerium oxide nanoparticles are mixed in a mass ratio of 5:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0041] Example 7 The difference from Example 3 is that the Cr / Co doped g-C3N4 sheets and cerium oxide nanoparticles are mixed in a mass ratio of 6:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0042] Example 8 The difference from Example 3 is that the Cr / Co doped g-C3N4 sheets and cerium oxide nanoparticles are mixed in a mass ratio of 7:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0043] Example 9 The difference from Example 3 is that the Cr / Co doped g-C3N4 sheets and cerium oxide nanoparticles are mixed in a mass ratio of 8:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0044] Example 10 The difference from Example 8 is that 0.04 mmol of chloroplatinic acid and 0.01 mmol of palladium nitrate are dissolved in 20 ml of deionized water.

[0045] Embodiment 11 The difference from Example 8 is that 0.03 mmol of chloroplatinic acid and 0.02 mmol of palladium nitrate are dissolved in 20 ml of deionized water.

[0046] Example 12 The difference from Example 8 is that 0.025 mmol of chloroplatinic acid and 0.025 mmol of palladium nitrate are dissolved in 20 ml of deionized water.

[0047] Embodiment 13 The difference from Example 8 is that 0.02 mmol of chloroplatinic acid and 0.03 mmol of palladium nitrate are dissolved in 20 ml of deionized water.

[0048] Embodiment 14 The difference from Example 8 is that 0.01 mmol of chloroplatinic acid and 0.04 mmol of palladium nitrate are dissolved in 20 ml of deionized water.

[0049] Embodiment 15 The difference from Example 8 is that 0.05 mmol of palladium nitrate is dissolved in 20 ml of deionized water.

[0050] Comparative Example 1 10 g of urea, 0.01 mmol of chromium nitrate and 0.09 mmol of cobalt nitrate were dissolved in 50 ml of deionized water respectively, stirred until completely dissolved, and then evaporated to dryness in a water bath at 80° C. to obtain a mixed precursor powder.

[0051] The mixed precursor powder was placed in a crucible, heated to 600°C at 3°C / min, kept warm for 4 hours in a nitrogen atmosphere, cooled naturally to room temperature, and then ground to obtain Cr / Co-doped g-C3N4 sheets.

[0052] 0.1 g of cerium nitrate hexahydrate is dissolved in 50 ml of ethanol, and 0.1 g of a dispersant (eg, PVP) is added for ultrasonic dispersion for 36 minutes, and then the mixture is transferred to a high-pressure reactor for hydrothermal reaction at 200° C. for 12 hours. The mixture is centrifugally washed and dried to obtain cerium oxide nanoparticles.

[0053] Cr / Co doped g-C3N4 sheets and cerium oxide nanoparticles were mixed in a mass ratio of 7:3 and added with 50 ml of ethanol for ultrasonic treatment for 3 hours. After stirring and evaporating at 60°C, they were calcined at 300°C in an air atmosphere for 2 hours to form a composite carrier of g-C3N-CeO2 heterojunction.

[0054] Comparative Example 2 Dissolve 10 g of urea in 50 ml of deionized water, stir until completely dissolved, evaporate to dryness in a water bath at 80°C to obtain a mixed precursor powder, place the mixed precursor powder in a crucible, heat to 600°C at 3°C / min, and keep warm for 4 hours in a nitrogen atmosphere. After naturally cooling to room temperature, grind to obtain g-C3N4 flakes.

[0055] 0.1 g of cerium nitrate hexahydrate is dissolved in 50 ml of ethanol, and 0.1 g of a dispersant (eg, PVP) is added for ultrasonic dispersion for 36 minutes, and then the mixture is transferred to a high-pressure reactor for hydrothermal reaction at 200° C. for 12 hours. The mixture is centrifugally washed and dried to obtain cerium oxide nanoparticles.

[0056] The g-C3N4 sheets and cerium oxide nanoparticles were mixed in a mass ratio of 7:3 and 50 ml of ethanol was added for ultrasonic treatment for 3 hours. After stirring and evaporating at 60°C, they were calcined at 300°C in an air atmosphere for 2 hours to form a composite carrier.

[0057] Comparative Example 3 YX-12-01 non-methane total hydrocarbon catalyst from Yaxuan Environmental Technology (Shanghai) Co., Ltd.

[0058] The activity and stability of the catalysts of Examples 1 to 15 and Comparative Examples 1 to 3 were tested respectively, and the results are shown in Table 1 below.

[0059] Table 1

[0060] The specific method for testing the activity of the catalyst is as follows: The catalyst was reduced at 300 °C for 2 h in a 5% H2 / N2 atmosphere to remove surface impurities and stabilize active sites, then switched to a N2 atmosphere and cooled to room temperature to avoid oxidation due to exposure to air.

[0061] The simulated exhaust gas configuration is composed according to Table 2 below, and the air speed is controlled to be 20000h -1 .

[0062] Table 2

[0063] N2 was introduced to check the sealing of the gas line. After the pressure stabilized, the experiment was started without passing the catalyst. The simulated exhaust gas was operated at 250°C, and the initial NMHCs concentration (C0) was recorded. The catalyst was loaded and the temperature was raised to 180°C (heating rate 5°C / min). The temperature was stabilized for 30 minutes, and the simulated exhaust gas was introduced. The outlet gas samples were collected every 15 minutes, and the residual NMHCs concentration (C) was analyzed by GC. The reaction was continued for 24-100 hours to monitor the conversion rate decay trend.

[0064] Calculate the conversion rate through data analysis: Conversion rate X (%) is calculated through the formula Calculated.

[0065] Selectivity S (with CO2 as the target product) is given by the formula Calculated.

[0066] The reaction rate constants at different temperatures were fitted using the Arrhenius formula to obtain the decay rate after 100 h of continuous operation.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing a catalyst for removing non-methane total hydrocarbons, characterized in that: The following steps are involved: The chromium and / or cobalt doped two-dimensional carbon nitride was synthesized by a thermal shrinkage polymerization method, and the cerium oxide was synthesized by a hydrothermal method; The two-dimensional carbon nitride and cerium oxide are mixed and dissolved in a solvent, and then subjected to ultrasonic, stirring, drying and calcination treatments in sequence to obtain a composite carrier; The composite catalyst is obtained by adsorbing platinum and / or palladium single atoms on the composite carrier through an impregnation method.

2. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 1, characterized in that: Dissolving urea and chromium salt and / or cobalt salt in water and stirring until completely dissolved, and then placing in a water bath for evaporation and drying to obtain a mixed precursor powder; The precursor powder is subjected to a heating polymerization reaction in a high temperature environment and then ground to obtain a chromium and / or cobalt-doped two-dimensional carbon nitride sheet layer.

3. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 1, characterized in that: The chromium and / or cobalt doped two-dimensional carbon nitride and cerium oxide are mixed in a mass ratio of (4-8):3, and then the solvent is heated for ultrasonic treatment, and then stirred and evaporated to dryness at 60-70°C, and then calcined in an air atmosphere at 280-330°C to form a composite carrier.

4. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 2, characterized in that: The mass percentages of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride are 0-1wt% of the chromium salt and 0-1wt% of the cobalt salt, respectively, wherein the total mass percentage of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride is 0.8-1wt%.

5. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 1, characterized in that: The platinum salt and / or palladium salt are dissolved in water respectively, the composite carrier is added for ultrasonic dispersion, and then stirred and evaporated to dryness at 60-65° C. to obtain a precursor powder; The precursor powder is subjected to a high-temperature reduction reaction in a hydrogen and argon atmosphere to reduce the platinum salt and / or palladium salt to metal monomer platinum and / or metal monomer palladium to obtain a composite catalyst.

6. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 5, characterized in that: The mass percentage of the metal monomer platinum in the composite catalyst is 0-1wt%, the mass percentage of the metal monomer palladium in the composite catalyst is 0-1wt%, and the total mass percentage of the metal monomer platinum and metal monomer palladium in the composite catalyst is 1-1.2wt%.

7. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 2, characterized in that: The chromium salt is one of chromium nitrate, chromium sulfate, chromium acetate and chromium oxalate; The cobalt salt is one of cobalt nitrate, cobalt sulfate, cobalt oxalate and cobalt citrate.

8. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 5, characterized in that: The platinum salt is platinum nitrate or chloroplatinic acid; the palladium salt is palladium nitrate or chloropalladic acid.

9. A catalyst for removing non-methane total hydrocarbons, characterized in that: A composite catalyst obtained according to the catalyst preparation method according to any one of claims 1 to 8.

10. An application of a catalyst for removing non-methane total hydrocarbons, characterized in that: The composite catalyst obtained by the catalyst preparation method according to any one of claims 1 to 8 is applied to the field of removing non-methane total hydrocarbons and detecting non-methane total hydrocarbons.

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