Monolithic cerium modified foamed nickel catalyst and preparation method and application thereof

Abstract

The invention discloses a monolithic cerium modified foamed nickel catalyst, a preparation method thereof and application of the monolithic cerium modified foamed nickel catalyst in catalytic oxidation of methane or methane-containing gas, and the preparation method comprises the following steps: adding clean foamed nickel into a cerium salt / precipitator mixed solution, so that the foamed nickel is completely immersed in the mixed solution; performing hydrothermal reaction for 1 to 10 hours under the condition of 120 to 180 DEG C; and after the reaction is finished, cooling, taking out the foamed nickel, cleaning with water, drying, and calcining at 300-800 DEG C for 1-10 hours to obtain the integral cerium modified foamed nickel catalyst. According to the present invention, the foamed nickel is adopted as the monolithic catalyst carrier and the nickel source, such that the cost is extremely low, the activity of the catalyst is substantially improved due to the good thermal conductivity and the good thermal stability, and the uniformly distributed space is provided for the surface deposition of the Ce / Ni solid solution so as to provide the good stability;

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to an integral cerium-modified nickel foam catalyst and a preparation method and application thereof. Background Art

[0002] Fossil energy accompanies human production activities and the development of human society. As fossil energy is increasingly depleted, energy issues are gradually restricting human development. How to use it efficiently and how to develop clean energy have become important issues faced by scholars at home and abroad. Coal mine gas is an unconventional natural gas that is discharged along with coal mining. In recent years, it has been regarded as a clean energy with application potential and an important chemical raw material. Among them, air-deficient gas accounts for about 64% of the total coal mine gas, but because it only contains 0-0.75Vol.% CH 4 Therefore, it is often directly emptied from the coal mine ventilation system and is difficult to utilize.

[0003] According to a report by the International Energy Agency (IEA), my country directly released about 2,428 tons of methane into the atmosphere in 2021, ranking first in the world. As a potent greenhouse gas, methane has a 100-year greenhouse effect that is about 21-23 times that of carbon dioxide, and its ability to destroy the ozone layer is 7 times that of carbon dioxide. The direct discharge of a large amount of lack of wind methane will further aggravate climate deterioration. Global warming, as a common environmental problem currently faced by mankind, seriously endangers the ecological balance of nature, leads to frequent severe weather, and seriously threatens the living environment of mankind. To this end, the rational use of lack of wind methane can not only effectively respond to global warming, but also help improve my country's energy structure and promote sustainable economic development.

[0004] Catalytic oxidation is considered the most promising measure for reducing exhaust gas emissions. By adding certain catalysts, catalytic oxidation of methane at a lower temperature can be achieved, and the reaction heat can be collected for industrial production. Since coal mine exhaust gas contains a variety of impurities such as dust, water vapor and sulfur compounds, the catalysts for them should have high activity, durability and the ability to reduce energy consumption. Currently, many studies are mainly focused on the development of granular precious metal or transition metal oxide catalysts. Among them, although precious metal catalysts have excellent catalytic performance, they are difficult to apply in industrial production due to their economy. Nickel, as a transition metal, has attracted much attention due to its low price and strong performance. For the catalytic combustion of exhaust gas, current catalyst research mainly focuses on granular catalysts. Although they have excellent catalytic performance, the granular packed bed faces problems such as high pressure drop and decreased catalytic bed activity in exhaust gas environments with large flow and possible dust. Summary of the invention

[0005] The purpose of the present invention is to provide a monolithic cerium-modified nickel foam catalyst and a preparation method and application thereof in view of the above problems.

[0006] In order to achieve its purpose, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a method for preparing a monolithic cerium-modified nickel foam catalyst, comprising the following steps:

[0008] Add clean nickel foam to a cerium salt / precipitant mixed solution, fully immerse the nickel foam in the mixed solution, and perform a hydrothermal reaction at 120-180° C. for 1-10 h (preferably 1-8 h or 4-8 h); after the reaction is completed, cool the nickel foam and take it out, wash it with water, dry it, and calcine it at 300-800° C. (preferably 400-600° C.) for 1-10 h (preferably 3-7 h) to obtain the integral modified nickel foam catalyst.

[0009] The cerium salt is selected from cerium nitrate and cerium carbonate;

[0010] The precipitant is selected from urea, hexamethylenetetramine, and ethylenediamine;

[0011] The mixed solution is prepared according to the following raw material dosages: 0.5-5 mmol (preferably 0.5-3.0 mmol or 0.5-1.5 mmol) of cerium salt and 10-100 mmol (preferably 10-60 mmol or 10-30 mmol) of precipitant are dissolved in 50-80 mL of deionized water;

[0012] Preferably, the pore size of the nickel foam is 5 to 120 ppi and the thickness is 0.8 to 1.2 mm.

[0013] The clean nickel foam is obtained by treating the nickel foam according to the following method:

[0014] The nickel foam is placed in an acetone solution for ultrasonic treatment for 10-30 minutes to remove oil stains, and then the nickel foam after ultrasonic treatment is cleaned with deionized water. The nickel foam is then placed in a 0.2-1M hydrochloric acid solution for ultrasonic removal of impurities for 2-10 minutes, and then cleaned with deionized water to prevent residual hydrochloric acid on the surface. Finally, the nickel foam after degreasing and impurity removal is placed in an anhydrous ethanol solution for ultrasonic treatment for 10-30 minutes, and dried for use after the ultrasonic treatment.

[0015] The ultrasonic treatment conditions are: at room temperature, the ultrasonic power is set to 120W, the frequency is set to 40KHz, and the ultrasonic treatment is carried out for 30 minutes.

[0016] The preparation method of the mixed solution is: add 0.5-5 mmol (preferably 0.5-3.0 mmol or 0.5-1.5 mmol) of cerium salt and 10-100 mmol (preferably 10-60 mmol or 10-30 mmol) of precipitant into 50-80 mL of deionized water, stir vigorously for 10-60 min, and perform ultrasonic treatment for 10-60 min;

[0017] The temperature of the hydrothermal reaction is 140-170°C (preferably 150-170°C or 155-165°C), and the reaction time is 6-8h;

[0018] The calcination is carried out in a muffle furnace after the temperature is raised to a set temperature at a speed of 2-5°C / min.

[0019] A second aspect of the present invention provides a monolithic cerium-modified nickel foam catalyst, which is prepared by any of the preparation methods described above.

[0020] The third aspect of the present invention provides the use of the above-mentioned integral cerium-modified nickel foam catalyst in catalytic oxidation of methane in a catalytic oxidation reaction of methane or a gas containing methane, and preferably the methane-containing gas includes natural gas and exhaust gas.

[0021] The application, the catalytic oxidation reaction refers to the conversion of methane into carbon dioxide through a combustion reaction under the catalytic action of the catalyst.

[0022] The application is to add a catalyst in a fixed bed reactor; the conditions of the combustion reaction are: the methane content in the gas is 0.75-1.5 Vol.%, the total gas flow rate is 100-200 ml / min, and the space velocity is 6000-12000 mL / min. -1 h -1 In the case of, the reaction temperature is 450-550°C.

[0023] The conditions of the combustion reaction are: the methane content in the gas is 1 Vol.%, the total flow rate is 200 ml / min, and the air velocity is 12000 mL / min. -1 h -1 In this case, the reaction temperature is 470°C.

[0024] The beneficial effects of the present invention are:

[0025] 1. Using nickel foam as a monolithic catalyst carrier and nickel source has extremely low cost, and due to good thermal conductivity, thermal stability and providing a uniformly distributed space for surface deposition of Ce / Ni solid solution, the surface of nickel foam is modified by Ce. On the one hand, Ce / Ni-NF catalyzes CH 4 Combustion follows the Mvk mechanism, in which CH 4The breaking of the first CH bond is the key to the reaction rate. By introducing Ce into nickel foam, due to CeO 2 Excellent oxygen storage capacity, high oxygen mobility and unique redox properties The dehydrogenation ability of the catalyst surface is greatly improved, which helps CH 4 The dehydrogenation process of Ni is improved, and it is helpful for efficient catalytic oxidation in a water-containing environment, which helps the catalyst to continue to work in a high-humidity environment of wind-deficient gas. On the other hand, the introduction of Ce improves the dispersibility of Ni, and due to the strong interaction between Ce and Ni, the sintering and peeling of Ni are inhibited, which significantly improves the stability of the catalyst, thereby helping to improve the atomic utilization efficiency of the active components and achieve continuous catalytic oxidation of methane at a low preparation cost. By optimizing the hydrothermal conditions, the crystallization degree of the catalyst can be promoted, and while improving the dispersibility of the catalyst, the activity of the catalyst is greatly improved, and it has good stability.

[0026] 2. Ce provides oxygen vacancies, improves electron transfer effect, and improves catalyst activity. Without Ce, there is no activity or very low activity.

[0027] 2. This catalyst is used for catalytic oxidation of exhaust gas and can achieve complete conversion of methane at 470°C.

[0028] 3. The catalyst preparation process of the present invention is simple, low-cost, highly repeatable, and has great potential for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a physical picture of nickel foam and the catalyst prepared in Examples 1-3.

[0030] Figure 2 It is a comparative curve diagram of the conversion rates of the catalysts and NF of Examples 1-3 at different preparation temperatures at the same methane concentration.

[0031] Figure 3 It is a comparison curve of different conversion rates of catalysts prepared at different hydrothermal growth times in Examples 1 and 4-5 at the same methane concentration.

[0032] Figure 4 This is a stability test chart of the catalyst in Example 1.

[0033] Figure 5 This is a water resistance test chart of the catalyst in Example 1.

[0034] Figure 6 is a SEM image of the catalyst of Example 1-3.

[0035] Figure 1-2, 6, 160-8 represents the catalyst of Example 1, 140-8 represents the catalyst of Example 2, and 120-8 represents the catalyst of Example 3.

[0036] Figure 3 160-4 represents the catalyst of Example 4, 160-6 represents the catalyst of Example 5, and 160-8 represents the catalyst of Example 1. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0038] The information of reagents, instruments and equipment used in the following examples is shown in Table 1 and Table 2. Reagents or instruments without indicating the manufacturer are all conventional products that can be purchased commercially.

[0039] Table 1 Information of reagents used

[0040]

[0041] Table 2 Information of instruments and equipment used

[0042]

[0043]

[0044] Example 1

[0045] A method for preparing a monolithic supported palladium-based catalyst comprises the following steps:

[0046] S1. NF carrier pretreatment:

[0047] A regular circular nickel foam (NF) with a diameter of 32 mm, a thickness of 1 mm, and a pore size of 5-120 ppi was selected, immersed in an acetone solution for ultrasonic treatment for 30 min to remove surface oil stains, then taken out and rinsed with deionized water for 5-6 times, and then the NF was placed in a 1M hydrochloric acid solution for ultrasonic treatment for 5 min to remove organic impurities and metal impurities attached to the surface, and then repeatedly rinsed with a large amount of deionized water to prevent hydrochloric acid residues. Finally, the NF was placed in an anhydrous ethanol solution for ultrasonic treatment for 30 min to remove residual hydrochloric acid and attached impurities on the surface, and then naturally dried for use.

[0048] S2, Ce / Ni-NF preparation:

[0049] Prepare a mixed solution of metal Ce salt and urea: Take 1 mmol of Ce(NO 3 ) 3 6H 2 O and 30 mmol of urea were added into 75 mL of deionized water, stirred vigorously for 20 min, and then subjected to ultrasonic treatment (ultrasonic power 120 W, frequency 40 kHz) for 30 min to disperse the solute and obtain a mixed solution.

[0050] Take 5 pieces of the cleaned NF obtained in step S1 and place them in a hydrothermal reactor with a volume of 100 ml, introduce the prepared mixed solution into the hydrothermal reactor containing NF, and then place the hydrothermal reactor in an oven at 160°C (hydrothermal growth temperature) for reaction for 8 hours. After the reaction is completed, rinse the surface of the crystallized NF with deionized water after natural cooling, repeatedly rinse the surface 3-5 times, remove the surface suspension, dry at room temperature, place in a muffle furnace, heat to 500°C at 2°C / min, and calcine for 4 hours to obtain a modified nickel foam catalyst Ce / Ni-NF.

[0051] Example 2-3

[0052] The modified nickel foam catalyst Ce / Ni-NF was prepared according to the method of Example 1. Except for the hydrothermal growth temperature, the other experimental conditions were the same as those of Example 1. The hydrothermal growth temperature of Example 2 was 140°C, and the hydrothermal growth temperature of Example 3 was 120°C. Figure 1 shown.

[0053] Embodiment 4-5

[0054] The modified nickel foam catalyst Ce / Ni-NF was prepared according to the method of Example 1. Except for the hydrothermal growth time, the other experimental conditions were the same as those of Example 1. The hydrothermal growth time of Example 4 was 4 h, and the hydrothermal growth time of Example 5 was 6 h.

[0055] Performance test experiments and results

[0056] The methane catalytic combustion reaction activity test was performed on the NF without hydrothermal growth (i.e., the control without Ce loading) and the catalysts obtained in Examples 1-3, respectively. The test method is as follows:

[0057] The test was conducted using a fixed bed reactor. The catalyst size was cut to be consistent with the size of the fixed bed opening, and the catalyst was arranged vertically along the gas flow direction. 4A mixed gas of +99vol% air was introduced into a fixed bed reactor containing the catalyst of the present invention at a total flow rate of 200ml / min. The test temperature range was 250-600°C. Under normal pressure conditions, an online methane detector was connected to the gas outlet to calculate the conversion rate.

[0058] CH 4 The conversion rate is calculated as follows:

[0059] CH 4 Conversion rate (%) = {([CH 4 ] 进 –[CH 4 ] 出 ) / [CH 4 ] 进}×100%

[0060] Among them: [CH 4 ] 进 ,[CH 4 ] 出 are the methane concentrations at the feed and reactor outlet, respectively.

[0061] When the catalysts obtained in Examples 1-3 were used for methane combustion reaction, complete conversion of methane was achieved at below 600°C. The conversion rate curve of methane at the same concentration is shown in the figure below: Figure 2 As shown, the catalytic activity is positively correlated with the hydrothermal growth temperature. Example 1 can completely convert methane at 470°C, which is the best example. Therefore, the Ce / Ni-NF catalyst obtained in Example 1 was subsequently tested.

[0062] When the catalysts of other batches prepared in Example 1 and Example 4-5 are used in the methane combustion reaction, the conversion rate curve of methane at the same concentration is as follows: Figure 3 As shown, at the same hydrothermal growth temperature (160°C), the catalytic activity is positively correlated with the hydrothermal growth time. Example 1 can almost completely convert methane at 470°C, and the effect is better than that of Examples 4 and 5.

[0063] In order to test the stability of the catalyst, Example 1 was subjected to continuous methane (content of 1 Vol.% CH 4 ) Catalytic experiments such as Figure 4 As shown, in the experiment lasting up to 50 hours, the catalyst of Example 1 maintained 90% of its catalytic activity and there was almost no activity decline.

[0064] The water poisoning resistance of the catalyst of Example 1 was tested: a fixed bed reactor was used to test the water poisoning resistance of Example 1 at 500°C, and a gas flow rate of 10 Vol% H was directly added into the reactor by a peristaltic pump. 2O vapor to simulate the sustained catalytic ability of the catalyst in the harsh high humidity environment of the lack of air gas. Figure 5 As shown: The catalyst exhibits 10 Vol%.H 2 0, the conversion rate can still be maintained above 90%, and after the water is stopped, the activity of the catalyst can be restored, and no permanent poisoning occurs.

[0065] In summary, through the activity test of the catalyst, it was found that the modified monolithic nickel foam catalyst prepared by adding Ce had excellent catalytic activity when the methane content was 1 Vol.%, the total flow rate was 200 ml / min, and the space velocity was 12000 mL / g -1 h -1 Under the condition of low temperature, it can achieve complete conversion of methane at 470℃, and has extremely strong stability and resistance to water poisoning.

[0066] The microstructure of the surface of Examples 1-3 was photographed using SEM. Figure 6 ) It can be seen from the hydrothermal growth temperature that the nanostructure of the catalyst has a significant effect. When the temperature is at a low level of 120°C, Ni and Ce do not form a specific microstructure, but agglomerate in large quantities. As the temperature rises to 140°C, under the influence of the ambient temperature, Ni and Ce gradually nucleate and form a large number of nanorod-like structures on the surface, which are stacked together. When the temperature reaches 160°C, the high temperature environment makes it difficult to form large-scale nanorod clusters on the surface, and instead begins to disperse to form independent regular spheres. The nanostructure of the catalyst has a significant effect on the activity of the catalyst. At 160°C, the catalyst is mainly composed of a large number of regular nanospheres generated on the NF surface. Compared with unshaped agglomerates or larger nanorods, smaller nanospheres have a higher specific surface area for the catalyst, exposing a large number of active sites, which supports the excellent activity of the 160-8 sample (i.e., the sample prepared in Example 1). At the same time, since the catalyst sintering is mainly dominated by two mechanisms, particle migration and Oswald ripening, the larger distance between the two nanospheres on the sample surface can effectively inhibit the reduction of active sites caused by particle agglomeration, and the regular shape of the nanospheres reduces the chemical potential difference between each other, hindering Oswald ripening. The above two pathways jointly support the excellent activity of the 160-8 sample on a long time scale.

[0067] The present invention uses nickel foam as a catalyst carrier and nickel source, and utilizes its good thermal conductivity and thermal stability to prepare a low-pressure drop monolithic catalyst different from a granular catalyst. By introducing Ce to modify the surface of nickel foam, part of Ni enters CeO during the hydrothermal growth process. 2The CeO2 crystal lattice forms a solid solution with Ni, which improves the dispersion of Ni on the catalyst surface and improves its thermal stability. 2 The abundant oxygen vacancies provided and the electron transfer promoted improve the catalytic activity of Ni. The present invention has low preparation cost, excellent activity and stability; and the preparation method is simple, the conditions are mild and controllable, and the repeatability is strong, and it has strong industrial application value and application potential.

Claims

1. A method for preparing a monolithic cerium-modified nickel foam catalyst, characterized in that: The steps include: The clean nickel foam is added into the cerium salt / precipitant mixed solution, so that the nickel foam is completely immersed in the mixed solution, and a hydrothermal reaction is carried out at 120-180° C. for 1-10 hours; after the reaction is completed, the nickel foam is taken out and washed with water after cooling, dried, and calcined at 300-800° C. for 1-10 hours to obtain the integral modified nickel foam catalyst.

2. The preparation method according to claim 1, characterized in that: The cerium salt is selected from cerium nitrate and cerium carbonate; The precipitant is selected from urea, hexamethylenetetramine, and ethylenediamine; The mixed solution is prepared according to the following raw material dosages: 0.5-5 mmol of cerium salt and 10-100 mmol of precipitant are dissolved in 50-80 mL of deionized water; Preferably, the pore size of the nickel foam is 5 to 120 ppi and the thickness is 0.8 to 1.2 mm.

3. The preparation method according to claim 1, characterized in that: The clean nickel foam is obtained by treating the nickel foam according to the following method: The nickel foam is placed in an acetone solution for ultrasonic treatment for 10-30 minutes to remove oil stains, and then the nickel foam after ultrasonic treatment is cleaned with deionized water. The nickel foam is then placed in a 0.2-1M hydrochloric acid solution for ultrasonic removal of impurities for 2-10 minutes, and then cleaned with deionized water to prevent residual hydrochloric acid on the surface. Finally, the nickel foam after degreasing and impurity removal is placed in an anhydrous ethanol solution for ultrasonic treatment for 10-30 minutes, and dried for use after the ultrasonic treatment.

4. The preparation method according to claim 3, characterized in that: The ultrasonic treatment conditions are: at room temperature, the ultrasonic power is set to 120W, the frequency is set to 40KHz, and the ultrasonic treatment is carried out for 30 minutes.

5. The preparation method according to claim 1, characterized in that: The mixed solution is prepared by adding 0.5 to 5 mmol of cerium salt and 10 to 100 mmol of precipitant into 50 to 80 mL of deionized water, stirring vigorously for 10 to 60 minutes, and ultrasonically treating for 10 to 60 minutes; The temperature of the hydrothermal reaction is 140-170°C, and the reaction time is 6-8h; The calcination is carried out in a muffle furnace after the temperature is raised to a set temperature at a speed of 2-5°C / min.

6. A monolithic cerium-modified nickel foam catalyst, characterized in that: The preparation method is described in any one of claims 1 to 5.

7. Use of the integral cerium-modified nickel foam catalyst according to claim 6 in catalyzing methane oxidation in a catalytic oxidation reaction of methane or a gas containing methane, wherein the methane-containing gas preferably comprises natural gas or exhaust gas.

8. The use according to claim 7, characterized in that: The catalytic oxidation reaction refers to the conversion of methane into carbon dioxide through a combustion reaction under the catalytic action of the catalyst.

9. The use according to claim 8, characterized in that: The catalyst is added to the fixed bed reactor; the combustion reaction conditions are: the methane content in the gas is 0.75-1.5 Vol.%, the total gas flow rate is 100-200 ml / min, and the space velocity is 6000-12000 mL / min. -1 h -1 In the case of, the reaction temperature is 450-550°C.

10. The use according to claim 9, characterized in that: The conditions of the combustion reaction are: methane content in the gas is 1 Vol.%, total flow rate is 200 ml / min, and space velocity is 12000 mL / min. -1 h -1 In this case, the reaction temperature is 470°C.

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