A catalyst for removing total non-methane hydrocarbons, a preparation method thereof and an application thereof

Abstract

The present invention discloses a catalyst for removing non-methane total hydrocarbons, a preparation method thereof and an application thereof, relating to the technical field of catalytic environmental protection; the method comprises the following steps: synthesizing chromium- and cobalt-doped two-dimensional carbon nitride by a thermal polycondensation method, and synthesizing cerium oxide by a hydrothermal method; mixing the two-dimensional carbon nitride and the cerium oxide, dissolving the mixture in a solvent, and successively performing ultrasonic treatment, stirring, drying and calcination treatment to obtain a composite support; adsorbing platinum and / or palladium single atoms on the composite support by an impregnation method to obtain a composite catalyst; using noble metal monomers platinum and / or palladium as highly active sites to efficiently activate oxygen and accelerate the cleavage of C-H 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 to form Cr-N-Co active sites and enhance the adsorption and activation ability of intermediate products.

Description

Technical Field

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

[0002] Non-methane total hydrocarbons (NMHC) refer to the general term for all volatile hydrocarbons except methane (mainly referring to C2-C8). Exceeding a certain concentration of NMHC in the atmosphere can form ozone and fine particulate matter, causing adverse effects on the environment and human health. Therefore, in industries such as petroleum and chemical industries where waste gas is prone to contain NMHC, it is necessary to treat NMHC to meet the waste gas emission requirements.

[0003] In the prior art, treating non-methane total hydrocarbons through an oxidation catalyst is one of the common methods. However, the existing oxidation catalysts generally have a narrow operable temperature window and a short service life when treating non-methane total hydrocarbons. Summary of the Invention

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

[0005] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of a catalyst for removing non-methane total hydrocarbons, comprising the following steps:

[0006] Synthesize chromium and cobalt-doped two-dimensional carbon nitride by thermal polycondensation method, and synthesize cerium oxide by hydrothermal method;

[0007] Mix two-dimensional carbon nitride and cerium oxide and dissolve them in a solvent, and then perform ultrasonic treatment, stirring, drying and calcination treatments in sequence to obtain a composite support;

[0008] Adsorb platinum and / or palladium single atoms on the composite support by impregnation method to obtain a composite catalyst.

[0009] Further, dissolve urea, chromium salt and cobalt salt in water, stir until completely dissolved, and then place it in a water bath for evaporation and drying to obtain a mixed precursor powder;

[0010] Heat and polymerize the precursor powder in a high-temperature environment and then grind it to obtain chromium and cobalt-doped two-dimensional carbon nitride sheets.

[0011] Further, mix chromium and cobalt-doped two-dimensional carbon nitride and cerium oxide in a mass ratio of (4-8):3, add a solvent for ultrasonic treatment, then stir and evaporate to dryness at 60-70 °C, and calcine in an air atmosphere at 280-330 °C to form a composite support.

[0012] Further, the mass percentages of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride are 0-1 wt% of the chromium salt and 0-1 wt% of the cobalt salt respectively, and the total mass percentage of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride is 0.8-1 wt%.

[0013] Further, dissolve the platinum salt and / or palladium salt in water respectively, add the composite support and carry out ultrasonic dispersion, and then stir and evaporate to dryness at 60-65 °C to obtain the precursor powder;

[0014] Carry out a high-temperature reduction reaction on the precursor powder in an atmosphere of hydrogen and argon to reduce the platinum salt and / or palladium salt to metallic monomer platinum and / or metallic monomer palladium, and obtain the composite catalyst.

[0015] Further, the mass percentage of the metallic monomer platinum in the composite catalyst is 0-1 wt%, the mass percentage of the metallic monomer palladium in the composite catalyst is 0-1 wt%, and the total mass percentage of the metallic monomer platinum and the metallic monomer palladium in the composite catalyst is 1-1.2 wt%.

[0016] Further, the chromium salt is one of chromium nitrate, chromium sulfate, chromium acetate and chromium oxalate;

[0017] The cobalt salt is one of cobalt nitrate, cobalt sulfate, cobalt oxalate and cobalt citrate.

[0018] Further, the platinum salt is platinum nitrate or chloroplatinic acid; the palladium salt is palladium nitrate or palladium chloride.

[0019] Further, the present invention also provides a catalyst for removing non-methane total hydrocarbons prepared by the above method.

[0020] Furthermore, the present invention also provides an application of the catalyst for removing non-methane total hydrocarbons prepared by the above method in the fields of removing non-methane total hydrocarbons and detecting non-methane total hydrocarbons.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] In the present invention, the noble metal monomers platinum and / or palladium are used as high-activity sites to efficiently activate oxygen and accelerate the cleavage of the C-H bond 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 to form Cr-N-Co active sites, enhancing the adsorption and activation ability of intermediate products.

[0023] The composite catalyst of the present invention has extremely strong stability and anti-poisoning performance. During use, only the particulate impurities in the waste gas need to be removed through a spray tower, and there is no need to be equipped with special equipment facilities, reducing the process difficulty and cost. Specific Embodiments

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0025] The present invention provides a technical solution: a method for preparing a catalyst for removing non-methane total hydrocarbons, comprising the following steps:

[0026] Synthesize chromium- and cobalt-doped two-dimensional carbon nitride by thermal polycondensation method, and synthesize cerium oxide by hydrothermal method;

[0027] Mix two-dimensional carbon nitride and cerium oxide, dissolve them in a solvent, and then perform ultrasonic treatment, stirring, drying and calcination in sequence to obtain a composite support;

[0028] Adsorb platinum and / or palladium single atoms on the composite support by impregnation method to obtain a composite catalyst.

[0029] In a further embodiment of this embodiment, dissolve urea, chromium salt and cobalt salt in water, stir until completely dissolved, then place it in a water bath for evaporation and drying to obtain a mixed precursor powder;

[0030] Heat and polymerize the precursor powder in a high-temperature environment and then grind it to obtain chromium- and cobalt-doped two-dimensional carbon nitride sheets.

[0031] In a further embodiment of this embodiment, mix chromium- and cobalt-doped two-dimensional carbon nitride and cerium oxide in a mass ratio of (4-8):3, add a solvent for ultrasonic treatment, then stir and evaporate to dryness at 60-70 °C, and calcine in an air atmosphere at 280-330 °C to form a composite support.

[0032] In a further embodiment of this embodiment, the mass percentages of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride are 0-1 wt% of the chromium salt and 0-1 wt% of the cobalt salt respectively, and the total mass percentage of the chromium salt and the cobalt salt in the doped two-dimensional carbon nitride is 0.8-1 wt%.

[0033] In a further embodiment of this embodiment, dissolve platinum salt and / or palladium salt in water respectively, add the composite support for ultrasonic dispersion, and then stir and evaporate to dryness at 60-65 °C to obtain a precursor powder;

[0034] Perform a high-temperature reduction reaction on the precursor powder in an atmosphere of hydrogen and argon to reduce the platinum salt and / or palladium salt to metal monomer platinum and / or metal monomer palladium to obtain a composite catalyst.

[0035] In a further embodiment of the present embodiment, the mass percentage of the metal monomer platinum in the composite catalyst is 0-1 wt%, the mass percentage of the metal monomer palladium in the composite catalyst is 0-1 wt%, and the total mass percentage of the metal monomer platinum and the metal monomer palladium in the composite catalyst is 1-1.2 wt%.

[0036] In a further embodiment of the present embodiment, the chromium salt is one of chromium nitrate, chromium sulfate, chromium acetate and chromium oxalate;

[0037] The cobalt salt is one of cobalt nitrate, cobalt sulfate, cobalt oxalate and cobalt citrate.

[0038] In a further embodiment of the present embodiment, the platinum salt is platinum nitrate or chloroplatinic acid; the palladium salt is palladium nitrate or palladium chlorate.

[0039] It should be noted that: by using the noble metal monomers platinum and / or palladium as highly active sites to efficiently activate oxygen and accelerate the cleavage of the C-H bond of hydrocarbon molecules, the oxidation efficiency under low-temperature conditions below 180 °C can be significantly improved.

[0040] By doping with Cr and Co, the electronic structure of g-C3N4 can be adjusted to form Cr-N-Co active sites, enhancing the adsorption and activation ability of intermediate products. For example, Co 3+ / Co 2+ and Cr 3+ / Cr 6+ redox pairs can promote the generation of free radicals (such as ·OH, O2 - ), strengthening the deep oxidation path.

[0041] The oxygen vacancies of cerium oxide can serve as a reservoir for active oxygen (O - ), releasing oxygen to participate in the reaction under oxygen-deficient conditions and dynamically maintaining the catalytic activity. The heterojunction formed by cerium oxide and two-dimensional carbon nitride can promote the separation of photo-generated carriers (such as in the photocatalytic scenario) or thermally excited electrons, inhibit electron-hole recombination, and improve the energy utilization efficiency.

[0042] The surface basic sites of cerium oxide can preferentially adsorb acidic poisons (such as SO2, HCl) in the waste gas, reducing their poisoning of the noble metal active sites. The doping of Cr and Co can form a stable metal-nitrogen coordination structure (such as Co-N-Cr), inhibiting the sintering or loss of noble metal particles at high temperatures.

[0043] The two-dimensional sheet structure can limit the excessive adsorption of reaction intermediates (such as tar, polycyclic aromatic hydrocarbons), reducing carbon deposition. The active oxygen on the surface of cerium oxide can oxidize the deposited carbonaceous species, maintaining the surface cleanliness of the catalyst.

[0044] Example 1:

[0045] Dissolve 10 g of urea, 0.01 mmol of chromium nitrate, and 0.09 mmol of cobalt nitrate in 50 ml of deionized water respectively. After stirring until completely dissolved, evaporate to dryness under a water bath condition of 80 °C to obtain a mixed precursor powder.

[0046] Place the mixed precursor powder in a crucible, heat it up to 600 °C at a rate of 3 °C / min, carry out a heat preservation reaction for 4 h under a nitrogen atmosphere, and grind it after natural cooling to room temperature to obtain Cr / Co-doped g-C3N4 sheets.

[0047] Dissolve 0.1 g of cerium nitrate hexahydrate in 50 ml of ethanol, add 0.1 g of a dispersant (e.g., PVP), ultrasonically disperse for 36 min, transfer it to a high-pressure reaction kettle, carry out a hydrothermal reaction at 200 °C for 12 h, and dry it after centrifugal washing to obtain cerium oxide nanoparticles.

[0048] Mix the Cr / Co-doped g-C3N4 sheets and cerium oxide nanoparticles in a mass ratio of 4:3, add 50 ml of ethanol, ultrasonically treat for 3 h, stir and evaporate to dryness at 60 °C, and then calcine for 2 h under an air atmosphere at 300 °C to form a composite support of g-C3N-CeO2 heterojunction.

[0049] Dissolve 0.05 mmol of chloroplatinic acid in 20 ml of deionized water, add 1.0 g of the composite support, ultrasonically disperse for 1 h, stir and evaporate to dryness at 60 °C to obtain a precursor powder. Place the precursor powder in a tube furnace, heat it up to 300 °C at a rate of 4 °C / min under a 5% H2 / Ar atmosphere, keep it warm for 2 h, and reduce the platinum in the platinum salt to metallic monomers to obtain a composite catalyst.

[0050] Example 2

[0051] 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.

[0052] Example 3

[0053] 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.

[0054] Example 4

[0055] 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.

[0056] Example 5

[0057] 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 respectively dissolved in 50 ml of deionized water.

[0058] Example 6

[0059] The difference from Example 3 is that the Cr / Co-doped g-C3N4 sheets and cerium oxide nanoparticles are mixed at a mass ratio of 5:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0060] Example 7

[0061] The difference from Example 3 is that the Cr / Co-doped g-C3N4 sheets and cerium oxide nanoparticles are mixed at a mass ratio of 6:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0062] Example 8

[0063] The difference from Example 3 is that the Cr / Co-doped g-C3N4 sheets and cerium oxide nanoparticles are mixed at a mass ratio of 7:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0064] Example 9

[0065] The difference from Example 3 is that the Cr / Co-doped g-C3N4 sheets and cerium oxide nanoparticles are mixed at a mass ratio of 8:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h.

[0066] Example 10

[0067] 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.

[0068] Example 11

[0069] 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.

[0070] Example 12

[0071] 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.

[0072] Example 13

[0073] 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.

[0074] Example 14

[0075] 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.

[0076] Example 15

[0077] The difference from Example 8 is that 0.05 mmol of palladium nitrate is dissolved in 20 ml of deionized water.

[0078] Comparative Example 1

[0079] 10 g of urea, 0.01 mmol of chromium nitrate and 0.09 mmol of cobalt nitrate are respectively dissolved in 50 ml of deionized water. After stirring until completely dissolved, it is evaporated to dryness under a water bath condition of 80 °C to obtain a mixed precursor powder.

[0080] The mixed precursor powder is placed in a crucible and heated to 600 °C at a rate of 3 °C / min. A heat preservation reaction is carried out for 4 h under a nitrogen atmosphere. After naturally cooling to room temperature, it is ground to obtain Cr / Co-doped g-C3N4 sheets.

[0081] 0.1 g of cerium nitrate hexahydrate is dissolved in 50 ml of ethanol, and 0.1 g of a dispersant (for example: PVP) is added and ultrasonically dispersed for 36 min. It is transferred to a high-pressure reaction kettle and a hydrothermal reaction is carried out at 200 °C for 12 h. After centrifugal washing and drying, cerium oxide nanoparticles are obtained.

[0082] The Cr / Co-doped g-C3N4 sheets and cerium oxide nanoparticles are mixed at a mass ratio of 7:3 and 50 ml of ethanol is added for ultrasonic treatment for 3 h. After stirring and evaporating to dryness at 60 °C, it is calcined in an air atmosphere at 300 °C for 2 h to form a composite support of g-C3N-CeO2 heterojunction.

[0083] Comparative Example 2

[0084] 10 g of urea is dissolved in 50 ml of deionized water. After stirring until completely dissolved, it is evaporated to dryness under a water bath condition of 80 °C to obtain a mixed precursor powder. The mixed precursor powder is placed in a crucible and heated to 600 °C at a rate of 3 °C / min. A heat preservation reaction is carried out for 4 h under a nitrogen atmosphere. After naturally cooling to room temperature, it is ground to obtain g-C3N4 sheets.

[0085] 0.1 g of cerium nitrate hexahydrate is dissolved in 50 ml of ethanol, and 0.1 g of a dispersant (for example: PVP) is added and ultrasonically dispersed for 36 min. It is transferred to a high-pressure reaction kettle and a hydrothermal reaction is carried out at 200 °C for 12 h. After centrifugal washing and drying, cerium oxide nanoparticles are obtained.

[0086] Mix g-C3N4 sheets and cerium oxide nanoparticles in a mass ratio of 7:3, add 50 ml of ethanol, and ultrasonically treat for 3 h. After stirring and evaporating to dryness at 60 °C, calcine in an air atmosphere at 300 °C for 2 h to form a composite support.

[0087] Comparative Example 3

[0088] YX-12-01 Non-Methane Total Hydrocarbon Catalyst of Yaxuan Environmental Protection Technology (Shanghai) Co., Ltd.

[0089] Test the activity and stability of the catalysts in Examples 1 - 15 and Comparative Examples 1 - 3 respectively. The results are shown in Table 1 below.

[0090] Table 1

[0091]

[0092] Among them, the specific method for testing the activity of the catalyst is as follows:

[0093] Reduce the catalyst in a 5% H2 / N2 atmosphere at 300 °C for 2 hours to remove surface impurities and stabilize the active sites. Switch to an N2 atmosphere and cool to room temperature to avoid oxidation caused by exposure to air.

[0094] Configure the simulated waste gas according to Table 2 below, and control the space velocity to be 20000 h -1 .

[0095] Table 2

[0096]

[0097] Introduce N2 to check the airtightness of the gas path. After the pressure is stable, start the experiment. Without the catalyst, run the simulated waste gas at 250 °C, record the initial NMHCs concentration (C0), load the catalyst, heat up to 180 °C (heating rate 5 °C / min), stabilize for 30 minutes, introduce the simulated waste gas, collect the outlet gas samples every 15 minutes, analyze the residual concentration of NMHCs (C) by GC, and continuously run for 24 - 100 hours to monitor the decay trend of the conversion rate.

[0098] Calculate the conversion rate through data analysis: The conversion rate X (%) is calculated by the formula and obtained.

[0099] The selectivity S (target product is CO2) is calculated by the formula and obtained.

[0100] Fit the reaction rate constants at different temperatures through the Arrhenius formula to obtain the decay rate after continuous operation for 100 h.

[0101] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within 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: Chromium and cobalt-doped two-dimensional carbon nitride were synthesized by thermal polymerization, and cerium oxide was synthesized by 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, chromium salt and 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 two-dimensional carbon nitride sheet doped with chromium and cobalt.

3. The method for preparing a catalyst for removing non-methane total hydrocarbons according to claim 1, characterized in that: The chromium and cobalt doped two-dimensional carbon nitride and cerium oxide are mixed in a mass ratio of (4-8):3, and then a solvent is added for ultrasonic treatment. Then, the mixture is 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 in the field of removing non-methane total hydrocarbons.

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