A Cr 0.7 Ce 0.3 -MWCNTs x Catalyst, method for preparing the same, and use thereof

Abstract

The application discloses a Cr 0.7 Ce 0.3 -MWCNTs x catalyst, a preparation method and application thereof. The Cr 0.7 Ce 0.3 -MWCNTs x catalyst is a composite metal oxide synthesized by a citric acid method with a carrier being a chromium salt and a cerium salt with a Cr:Ce molar ratio of 7:3, and a loading material being multi-walled carbon nanotubes (MWCNTs) with a loading amount of 0.5% to 2% of the total mass of the chromium salt and the cerium salt. The catalyst prepared by the application has high catalytic activity in catalytic combustion of low-concentration solvent oil, has high selectivity of CO at a low temperature, and can selectively generate a target product CO2 at a high temperature.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a Cr 0.7 Ce 0.3 -MWCNTs x catalyst, a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the continuous development of industrial production level in China, the types and quantities of atmospheric pollutants are also increasing, and air pollution has become one of the most important environmental problems in China. Industrial waste gas, as the main source of atmospheric pollutants, especially volatile organic pollutants (VOCs), has attracted much attention due to its harm to health. VOCs are generally defined as gases with a vapor pressure higher than 0.5 kPa at 25 DEG C, including aromatic hydrocarbons, chlorine-containing hydrocarbons, alcohols, fats, ketones, straight-chain hydrocarbons, etc. Many VOCs can cause photochemical reactions, producing haze and other serious pollution in the urban atmosphere, which seriously threatens human health, can cause allergies, serious respiratory and metabolic diseases, and even can cause cancer. Due to the rapid development of industrial economy, the number of large storage tanks in petrochemical plants is increasing rapidly. When the large storage tanks are close to empty each time, the upper part is full of oil and gas vapor, and when the storage tanks are refilled, the oil and gas vapor above is released into the atmosphere. This not only causes loss of product quantity, but also affects the safety of the plant and pollutes the environment.

[0003] At present, the main methods for recovering and treating VOCs and oil gas at home and abroad include catalytic combustion method, adsorption method, absorption method, membrane separation method, condensation method, and combination of these methods. Among them, the catalytic combustion method has the advantages of simple operation, high catalytic efficiency, no flame combustion, high product selectivity, etc., and has good application prospect. SUMMARY

[0004] To solve the above problems, the application provides a Cr 0.7 Ce 0.3 -MWCNTs x catalyst, a preparation method and application thereof.

[0005] The technical scheme adopted by the application is as follows: a Cr 0.7 Ce 0.3 -MWCNTs x catalyst, a preparation method and application thereof.

[0006] A Cr 0.7 Ce 0.3MWCNTs x The preparation method of the catalyst comprises the following steps:

[0007] 1) purifying the multi-walled carbon nanotubes (MWCNTs) ;

[0008] 2) adding chromium salt and cerium salt into deionized water according to the molar ratio of Cr:Ce of 7:3 with anhydrous citric acid as a complexing agent of sol method, and stirring at 40 DEG C until the solid melts;

[0009] 3) adding ammonia water drop by drop, then increasing the temperature of the system to 80 DEG C, adding the purified multi-walled carbon nanotubes (MWCNTs) when the water in the solution is evaporated to present a colloidal substance, continuing to stir for 10 min, and then placing in an ultrasonic cleaner for ultrasonic treatment for 3 h;

[0010] 4) placing the sample after ultrasonic treatment in a blast drying oven for drying overnight at 130 DEG C, transferring the honeycomb coal-like solid obtained after drying to a porcelain boat, placing in a muffle furnace for calcination at 450 DEG C for 3 h, and then taking out, to obtain Cr 0.7 Ce 0.3 MWCNTs x .

[0011] Further, step 1), purifying the multi-walled carbon nanotubes (MWCNTs), specifically:

[0012] 1.1) placing the MWCNTs in a centrifugal tube, adding concentrated sulfuric acid and concentrated nitric acid after sealing, and placing in an ultrasonic cleaner for ultrasonic treatment for 3 h;

[0013] 1.2) placing in a centrifuge for centrifugal treatment for 5 min after ultrasonic treatment at a speed of 12000 r / min, and washing the MWCNTs after centrifugal treatment with deionized water;

[0014] 1.3) repeating step 1.2) for centrifugal treatment for 2-3 times, and placing the MWCNTs after the last centrifugal treatment in a blast drying oven for drying overnight at 80 DEG C.

[0015] Further, the volume ratio of the concentrated sulfuric acid and the concentrated nitric acid is 1:3.

[0016] Further, the chromium salt is Ce(NO3)3·6H2O, the cerium salt is Cr(NO3)3·9H2O, and the added amount of the purified multi-walled carbon nanotubes (MWCNTs) is 0.5-2% of the total mass of Ce(NO3)3·6H2O and Cr(NO3)3·9H2O.

[0017] The Cr 0.7 Ce 0.3 MWCNTs x application of the catalyst in catalytic combustion of low-concentration aromatic solvent oil.

[0018] The method is as follows: the aromatic hydrocarbon solvent oil is catalytically combusted in a fixed bed tube reactor; in the fixed bed tube reactor, the Cr 0.7 Ce 0.3 -MWCNTs x The catalyst is prepared into a fixed bed catalyst.

[0019] Further, the diameter of the fixed bed tube reactor is 10-20 mm. The gas flow rate is set to 1 L / min.

[0020] Further, the catalytic combustion is, the reaction temperature range is 80-380 DEG C, and the reaction time is 3-5 h.

[0021] Further, the solvent oil is an aromatic hydrocarbon solvent oil.

[0022] The present application has the following beneficial effects:

[0023] 1. The present application prepares a series of chromium-cerium composite oxide catalysts doped with different mass percentage of multi-walled carbon nanotubes (MWCNTs) by a citric acid sol-gel method and an air pyrolysis method. 0.7 Ce 0.3 -MWCNTs x The catalyst can present obvious pore structure in a scanning electron microscope image, the catalyst preparation method is simple, and the physical and chemical properties are stable.

[0024] 2. The catalyst prepared in the present application has high catalytic activity in catalytic combustion of low-concentration aromatic hydrocarbon solvent oil, has high selectivity of CO at a lower temperature (below 280 DEG C), and can selectively generate target product CO2 at a higher temperature (280 DEG C).

[0025] 3. The catalyst prepared in the present application has excellent stability, and the results of three times of continuous stability tests under the same conditions show that the experiment has good repeatability and good stability. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a scanning electron microscope image of the Cr 0.7 Ce 0.3 -MWCNTs 1.5wt％ catalyst.

[0027] Figure 2 is an XRD image of the Cr 0.7 Ce 0.3 -MWCNTs 0.5wt％-2wt％ catalyst.

[0028] Figure 3 is an XRD image of the Cr 0.7 Ce 0.3MWCNTs 0.5wt％-2wt％ FTIR spectra of catalysts.

[0029] Figure 4 Cr 0.7 Ce 0.3 MWCNTs 0.5wt％-2wt％ Catalytic efficiency graph of catalysts for catalytic combustion of solvent oil.

[0030] Figure 5 Cr 0.7 Ce 0.3 MWCNTs 1.5wt％ Catalyst stability test graph.

[0031] Figure 6 Cr 0.7 Ce 0.3 MWCNTs 1.5wt％ Catalyst life test graph. DETAILED DESCRIPTION

[0032] Example 1 Cr 0.7 Ce 0.3 MWCNTs x Catalyst

[0033] (I) Preparation method as follows:

[0034] 1) Multi-walled carbon nanotubes MWCNTs were purified

[0035] 1.1) 2g of MWCNTs was weighed and placed in a 50mL centrifuge tube, 8ml of concentrated sulfuric acid and 24ml of concentrated nitric acid were added, and then sealed, placed in an ultrasonic cleaner, and ultrasonically treated for 3h.

[0036] 1.2) After ultrasonic treatment, centrifuge for 5min at 12000r / min, and the MWCNTs after centrifugation were washed with deionized water for 3 times.

[0037] 1.3) Repeat the centrifugation process of step 1.2) for 3 times, and the MWCNTs after the last centrifugation were placed in a blast drying oven at 80℃ and dried overnight, ready for use.

[0038] 2) 7.68g of anhydrous citric acid was weighed as a complexing agent for sol method. According to the Cr:Ce molar ratio of 7:3, 2.6053g of Ce(NO3)3·6H2O and 5.6021g of Cr(NO3)3·9H2O were accurately weighed and added to 100mL of deionized water, and stirred at 40℃ until the solid melted.

[0039] 3) dropwise add 10 mL of 25 wt% ammonia water, raise the temperature to 80°C, evaporate the water in the solution until it presents a gel, according to the proportion of 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt% of Ce(NO3)3·6H2O and Cr(NO3)3·9H2O in the total mass of the catalyst, add the purified MWCNTs, continue stirring for 10 min, and then place it in an ultrasonic cleaner for 3 h;

[0040] 4) After ultrasonic treatment, the sample is placed in a blast drying oven at 130°C overnight. The honeycomb coal-like solid obtained after drying is transferred to a porcelain boat and placed in a muffle furnace at 450°C for 3 h. Then it is taken out and the Cr 0.7 Ce 0.3 -MWCNTs x catalyst is obtained, respectively, and marked as Cr 0.7 Ce 0.3 -MWCNTs 0.5 , Cr 0.7 Ce 0.3 -MWCNTs1, Cr 0.7 Ce 0.3 -MWCNTs 1.5 and Cr 0.7 Ce 0.3 -MWCNTs2.

[0041] (B) Characterization

[0042] Take a little prepared Cr 0.7 Ce 0.3 -MWCNTs 1.5 catalyst and disperse it in ethanol. After ultrasonic treatment for 10 min, the dispersed sample is dropped on a conductive silicon wafer for scanning electron microscopy test. The scanning results are shown in Figure 1 From Figure 1 it can be clearly observed that there are obvious pore structures.

[0043] Take the prepared Cr 0.7 Ce 0.3 -MWCNTs x catalyst for XRD test. The test results are shown in Figure 2 From Figure 2 it can be seen that the characteristic peaks of all samples are in the range of 20°-80°, and the peak positions are similar. Except for the catalyst with the lowest doping level, the other three catalyst samples all present characteristic peaks of cubic fluorite type CeO2 at 28.54°, 33.08°, 47.48° and 56.29°; Cr2O3 characteristic peaks appear at 24.498°, 36.192°, 41.478° and 65.094°.

[0044] Take the prepared Cr 0.7 Ce0.3 -MWCNTs x The catalyst was subjected to Fourier transform infrared spectroscopy, and the test results are as follows: Figure 3 As shown. By Figure 3 As can be seen, the four catalysts exhibit similar characteristic spectral peaks. (779 cm⁻¹) -1 The peak at 1367, 1581, and 1595 cm⁻¹ corresponds to the out-of-plane vibration of the Cr(Ce)-O bond, and the peak at 2832 cm⁻¹ corresponds to the stretching vibration of the carbon-hydrogen bond. -1 The peak value at that point can be attributed to C=O tensile vibration.

[0045] Example 2 Cr 0.7 Ce 0.3 -MWCNTs x Application of catalysts in the catalytic combustion of low-concentration solvent oils

[0046] A fixed-bed tubular reactor is used for the catalytic combustion reaction of solvent oil. In this embodiment, aromatic solvent oil is used as an example for illustration.

[0047] 1) Accurately weigh 0.5g of Cr 0.7 Ce 0.3 -MWCNTs x The catalyst is placed inside a straight glass tube in a fixed-bed tubular reactor, with quartz wool attached to both ends to prevent catalyst powder from entering the pipe with the airflow.

[0048] 2) Mix aromatic solvent oil and air into a container containing Cr 0.7 Ce 0.3 -MWCNTs x In the tubular reactor, the inlet flow rate is controlled within 1L / min. Before the reaction starts, a handheld VOCs detector is used to detect the VOCs concentration at the inlet. The VOCs concentration at the inlet is controlled at around 120ppm. After the inlet concentration stabilizes, the catalytic combustion reaction begins. The reaction is carried out at 80-380℃ for 3-5 hours. After the temperature reaches the detection point and stabilizes for 10 minutes, the gas concentration at the outlet is detected. After the gas concentration stabilizes, the detection is carried out for more than 10 minutes.

[0049] 3) Calculate the catalytic efficiency using the CO, CO2, and VOCs concentrations detected at the gas outlet.

[0050] 4) Cr 0.7 Ce 0.3 -MWCNTs x Catalyst stability testing: Three consecutive stability tests were conducted under the same temperature and pressure conditions. The catalytic combustion efficiency was calculated and expressed as conversion rate.

[0051]

[0052] In the formula, C in VOCs concentration at the air inlet, in ppm;

[0053] C out The concentration of VOCs at the outlet is expressed in ppm.

[0054] Figure 4 It can be seen that Cr 0.7 Ce 0.3 -MWCNTs x The catalyst exhibits high activity, Cr 0.7 Ce 0.3 -MWCNTs 1.5wt％ The catalyst works best, Cr 0.7 Ce 0.3 -MWCNTs 0.5wt％ The worst effect.

[0055] With the best effect Cr 0.7 Ce 0.3 -MWCNTs 1.5wt％ The catalyst underwent stability testing, and the results are as follows: Figure 5 As shown in the figure, under the same temperature and pressure conditions, the repeatability experiment showed good stability after three consecutive cycles.

[0056] With the best effect Cr 0.7 Ce 0.3 -MWCNTs 1.5wt％ Catalyst lifetime testing was performed, and the results are as follows: Figure 6 As shown, from Figure 6 Cr can be seen from 0.7 Ce 0.3 -MWCNTs 1.5wt％ The catalyst did not decrease in catalytic activity after working continuously for 30 hours, indicating that the catalyst has a long lifespan.

Claims

1. A Cr 0.7 Ce 0.3 -MWCNTs x application of the catalyst in catalytic combustion of low concentration solvent oil, characterized in that, The solvent oil is aromatic hydrocarbon solvent oil; the Cr 0.7 Ce 0.3 -MWCNTs x The catalyst is a composite metal oxide synthesized by citric acid method with a Cr:Ce molar ratio of 7:3 of chromium salt and cerium salt, and the support material is multi-walled carbon nanotubes MWCNTs, and the loading amount is 0.5-2 % of the total mass of the chromium salt and the cerium salt.

2. Use according to claim 1, characterized in that, The Cr 0.7 Ce 0.3 -MWCNTs x The method for preparing the catalyst comprises the following steps: 1) purifying multi-walled carbon nanotubes (MWCNTs); 2) adding chromium salt and cerium salt into deionized water with anhydrous citric acid as a complexing agent of sol method, the molar ratio of Cr:Ce is 7:3, and stirring at 40 ℃ until the solid melts; 3) adding ammonia water drop by drop, then increasing the temperature of the system to 80 ℃, evaporating the water in the solution until it becomes a gel, adding purified MWCNTs, continuing to stir for 10 min, and then placing in an ultrasonic cleaner for 3 h; 4) The sample after ultrasonic treatment was placed in a blast drying oven at 130 °C and dried overnight. The honeycomb coal-like solid obtained after drying was transferred to a porcelain boat and placed in a muffle furnace at 450 °C for 3 h. Then, the porcelain boat was taken out, and Cr 0.7 Ce 0.3 -MWCNTs x .

3. Use according to claim 2, characterized in that, Step 1), purifying MWCNTs, specifically: 1.1) placing MWCNTs in a centrifuge tube, adding concentrated sulfuric acid and concentrated nitric acid, sealing, and placing in an ultrasonic cleaner for 3 h of ultrasonic treatment; 1.2) after ultrasonic treatment, centrifuging for 5 min at 12000 r / min, and washing the MWCNTs after centrifugation with deionized water; 1.3) repeating step 1.2) for 2-3 times, and drying the MWCNTs after the last centrifugation in a blast drying oven at 80 ℃ overnight.

4. Use according to claim 3, characterized in that, The volume ratio of concentrated sulfuric acid to concentrated nitric acid is 1:

3.

5. Use according to claim 2, characterized in that, The cerium salt is Ce(NO3)3·6H2O, and the chromium salt is Cr(NO3)3·9H2O; the amount of purified MWCNTs added is 0.5-2 % of the total mass of Ce(NO3)3·6H2O and Cr(NO3)3·9H2O.

6. Use according to claim 1, characterized in that, The process is as follows: catalytic combustion of solvent oil in a fixed bed tube reactor; in the fixed bed tube reactor, Cr 0.7 Ce 0.3 -MWCNTs x The catalyst is made into a fixed bed catalyst.

7. Use according to claim 6, characterized in that, The diameter of the fixed bed tubular reactor is φ=2.2 cm, and the gas flow rate is set to 1 L / min.

8. Use according to claim 6, characterized in that, The catalytic combustion is at a reaction temperature range of 80-380 ℃ and a reaction time of 3-5 h.

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