Preparation method and application of carrier-loaded platinum-palladium diatomic methane combustion catalyst

Abstract

The invention discloses a carrier-loaded platinum-palladium diatom methane combustion catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) placing a carrier in a palladium source solution, fully and uniformly mixing, standing and aging to uniformly disperse palladium species on the carrier, then carrying out solid-liquid separation, taking a solid, washing, drying and calcining to obtain a first intermediate product; (2) placing the first intermediate product in an imidazole organic ligand solution, stirring and heating, carrying out a coordination reaction between a palladium metal site and an imidazole organic ligand, then carrying out solid-liquid separation, taking a solid, washing, and drying to obtain a second intermediate product; and (3) putting the second intermediate product into a platinum source solution, stirring and heating to enable platinum species and imidazole organic ligands coordinated on palladium metal sites to be subjected to coordination reaction, then carrying out solid-liquid separation, taking solids, washing, drying and calcining to obtain the carrier-loaded platinum-palladium diatomic methane combustion catalyst.

Description

Technical Field

[0001] The present invention relates to the field of environmental catalysis, and particularly to a preparation method and application of a supported platinum-palladium dual-atom methane combustion catalyst on a carrier. Background Art

[0002] As a clean energy source, the main component of natural gas is methane with high energy content, clean combustion products, and low carbon dioxide (CO2) emissions. These characteristics make methane more advantageous than other fossil fuels. However, directly discharging unburned methane gas into the air will cause serious environmental pollution because it is a powerful greenhouse gas with a global warming potential approximately 25 times that of carbon dioxide. Therefore, it is necessary to completely combust low-concentration methane that is difficult to collect and utilize before emission.

[0003] Currently, the main treatment method for low-concentration methane is thermal oxidation technology, which is a method of premixing methane and air and then entering a high-temperature countercurrent reactor (>1000 °C), and completely oxidizing it into CO2 and water (H2O) before discharging. However, since the working temperature is usually above 1000 °C, this method has high requirements for equipment, increasing the design and construction costs of the equipment, and the high temperature will inevitably produce harmful substances such as nitrogen oxides (NO x ) and carbon monoxide (CO), causing environmental damage. Therefore, the research on developing an efficient and low-cost catalyst for low-concentration methane catalytic combustion has important theoretical and practical significance.

[0004] At the present stage, the catalysts applied to methane catalytic combustion are mainly divided into noble metal catalysts and non-noble metal catalysts. Palladium (Pd) is the most studied and most active noble metal methane catalytic combustion catalyst so far. Compared with non-noble metal catalysts, it has a lower ignition temperature and better stability. However, the high preparation cost of a single Pd catalyst and its characteristics of being easily deactivated due to sintering and poisoning by water vapor and sulfides during use have greatly limited its practical application. Therefore, reducing the preparation cost of the noble metal Pd catalyst and extending its service life are problems that must be overcome to make it truly put into application.

[0005] Active palladium species are usually loaded onto metal or non-metal oxide supports by traditional methods such as deposition precipitation and impregnation. Generally, active palladium species mainly exist in the form of nanoparticles or clusters, which is disadvantageous for the methane catalytic combustion reaction that usually occurs at the catalyst interface because in the form of nanoclusters or particles, only the palladium atoms on the surface can participate in the reaction. To improve the utilization rate of palladium atoms, atomic palladium as an active site loaded on the support has received extensive attention. At the same time, the synergistic effect between metals has been proven to improve the catalytic performance and the sulfur and water resistance of Pd.

[0006] Therefore, designing and preparing a dual-atom catalyst with both atomic-level and metal synergy is an important research direction in this field.

[0007] The patent specification with the publication number CN110433798A discloses a preparation method of a single-atom palladium-based catalyst, including the following steps: adding a silicon source and zirconia into an organic solvent for reflux reaction, drying to obtain zirconia modified with amorphous silica; mixing a palladium source and zirconia modified with amorphous silica in an organic solvent and impregnating them, so that the palladium source is loaded on the zirconia modified with amorphous silica, and then drying and calcining to obtain a single-atom Pd / SiO2-ZrO2 catalyst. The catalyst of this patented technology can be used in catalytic combustion reactions of hydrocarbons such as low-concentration methane, but the anti-water and anti-sulfur performance of this patented technology has not been studied.

[0008] The patent specification with the publication number CN114177903A discloses a method for preparing a microporous material-supported single-atom and dual-atom catalyst. The preparation method includes the following steps: using a porous material with a size less than 2 nm as the substrate and an organometallic compound as the metal precursor, dissolving the organometallic compound in supercritical CO2 fluid and uniformly dispersing it into micropores and mesopores, and then performing heat treatment and reduction to obtain a single-atom or dual-atom catalyst. This patented technology does not disclose the specific reactions that the prepared catalyst can be applied to. Summary of the Invention

[0009] In view of the above technical problems and the deficiencies in this field, the present invention provides a support-supported platinum-palladium dual-atom methane combustion catalyst, its preparation method and application. The catalyst of the present invention has high catalytic activity for methane combustion and excellent anti-water and anti-sulfur poisoning performance, and can maintain high catalytic activity for methane combustion in a water- and sulfur-containing environment. The present invention overcomes the problem that it is difficult to balance the stability and catalytic activity of methane catalytic combustion catalysts in the prior art.

[0010] The specific technical solution is as follows:

[0011] [1] A preparation method of a support-supported platinum-palladium dual-atom methane combustion catalyst, including the steps:

[0012] (1) Placing the support in a palladium source solution, fully mixing and then standing for aging to uniformly disperse palladium species on the support, and then separating the solid and liquid, washing, drying and calcining the solid to obtain a first intermediate product;

[0013] (2) Placing the first intermediate product in an imidazole-based organic ligand solution, stirring and heating to carry out the coordination reaction between palladium metal sites and imidazole-based organic ligands, and then separating the solid and liquid, washing and drying the solid to obtain a second intermediate product;

[0014] (3) Place the second intermediate product in a solution of a platinum source (which may include, for example, PtCl2, etc.), stir and heat it to cause a coordination reaction between the platinum species and the imidazole-based organic ligand coordinated to the palladium metal sites. Then, perform solid-liquid separation, take the solid, wash, dry, and calcine it to obtain the supported platinum-palladium dual-atom methane combustion catalyst.

[0015] In the preparation process of the catalyst of the present invention, the imidazole-based organic ligand coordinates with the palladium metal sites through one N in its imidazole structure, and the remaining one N in the imidazole structure coordinates with the platinum species subsequently. That is, in the present invention, two Ns on the imidazole structure of the imidazole-based organic ligand coordinate and connect palladium and platinum respectively to form a local bimetallic system. In this local bimetallic system, palladium atoms and platinum atoms correspond one by one and have an electronic interaction through the imidazole-based organic ligand. Finally, the imidazole-based organic ligand is burned off by calcination to form a platinum-palladium dual-atom structure with strong interaction, which can exhibit amazing synergistic effects in the application of catalytic methane combustion.

[0016] It is found that in the above preparation process, if the loading order of palladium and platinum is reversed, that is, platinum is loaded first and then palladium, the activity and the stability against water and sulfur exhibited by the obtained catalyst in the catalytic methane combustion reaction will be significantly deteriorated.

[0017] In step (1), the carrier may include at least one of metal oxides, non-metal oxides, ZSM-5 zeolite, Y-type zeolite, β-zeolite, etc. Preferably, it includes a zeolite carrier, such as H-USY zeolite, etc. The preferred carrier has characteristics such as a high specific surface area and rich oxygen, which can increase the contact area with methane gas and improve the catalytic performance.

[0018] In step (1), the palladium source may include at least one of palladium nitrate, palladium acetate, palladium acetylacetonate, tetraamminepalladium nitrate (CAS No.: 13601-08-6).

[0019] In step (1), the method of stirring can be used to fully mix them evenly. The stirring time can be 1 to 3 hours, such as 2 hours, etc.

[0020] In step (1), the aging time can be 2 to 4 hours.

[0021] In step (1), the calcination atmosphere can be air, the calcination temperature can be 300 to 700 °C, preferably 500 °C, and the calcination time can be 4 to 8 hours.

[0022] In step (2), the imidazole-based organic ligand may include at least one of imidazole, 2-methylimidazole, benzimidazole.

[0023] In step (2), the mass ratio of the imidazole-based organic ligand to the first intermediate product can be 0.2 to 0.3:1.

[0024] In step (2), the heating temperature can be 60-90°C, such as 80°C, etc., and the reaction time can be 19-24h, such as 20h, etc.

[0025] In step (3), the heating temperature can be 60-90°C, such as 80°C, etc., and the reaction time can be 19-24h, such as 20h, etc.

[0026] In step (3), the calcination atmosphere can be air, the calcination temperature can be 300-700°C, preferably 500°C, and the calcination time can be 4-8 hours, such as 5 hours, etc.

[0027] In the supported platinum-palladium dual-atom methane combustion catalyst, the molar ratio of palladium to platinum can be 1:0.5-2, preferably 1:1-1.2.

[0028] In the supported platinum-palladium dual-atom methane combustion catalyst, the total mass percentage of palladium and platinum can be 0.04%-0.6%.

[0029] [2] The supported platinum-palladium dual-atom methane combustion catalyst prepared by the preparation method described in [1].

[0030] In the supported platinum-palladium dual-atom methane combustion catalyst, when introducing 5 vol% water vapor and 20 ppm sulfur dioxide gas, the decrease in methane catalytic efficiency is within 5%, and the initial conversion rate can be restored after removing the water vapor and sulfur dioxide gas.

[0031] [3] The application of the supported platinum-palladium dual-atom methane combustion catalyst described in [2] in catalytic methane combustion.

[0032] [4] A method for catalytic methane combustion, comprising: using the supported platinum-palladium dual-atom methane combustion catalyst described in [2] to catalyze methane combustion.

[0033] In the application described in [3] and the method for catalytic methane combustion described in [4], the supported platinum-palladium dual-atom methane combustion catalyst can be used to catalyze the combustion reaction of methane and oxygen, and the reaction temperature can be 200-800°C.

[0034] In the application described in [3] and the method for catalytic methane combustion described in [4], the methane concentration in the methane combustion reaction can be 0.2 vol%-5 vol%.

[0035] [3] In the described application and [4] the described method for catalytic combustion of methane, before the supported platinum-palladium dual-atom methane combustion catalyst is used for catalytic combustion of methane, it can be preheated by heating in a nitrogen atmosphere. The temperature of the heating pretreatment can be 200-300 °C, the time of the heating pretreatment can be 1-2 hours, and the heating rate of the heating pretreatment can be 10-20 °C / min.

[0036] The present invention provides a supported platinum-palladium dual-atom methane catalytic combustion catalyst with high methane catalytic combustion activity and excellent water and sulfur poisoning resistance performance, its preparation method and application. The catalyst has a uniform morphology, the noble metals are atomically dispersed, the preparation cost is low, and the catalytic efficiency for low-concentration methane is high. At the same time, due to the synergistic effect of the bimetal, the catalytic performance and water and sulfur resistance performance of the catalyst are further improved.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. Using platinum-palladium dual atoms as reaction sites increases the utilization rate of reaction sites, reduces the amount of noble metals used while improving catalytic performance, and thus reduces the cost of the catalyst.

[0039] 2. Through coordination chemistry, the agglomeration that may be caused by the high surface energy of single atoms is improved, making the platinum and palladium atoms more dispersed.

[0040] 3. Utilizing the interaction between platinum and palladium bimetals improves the resistance of the catalyst to water vapor and sulfur-containing gases, and extends the service life of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a graph showing the change of methane conversion rate with reaction temperature in the catalytic combustion of methane by the catalyst of Example 1 and the catalysts of Comparative Examples 1-3.

[0042] Figure 2 It is a graph showing the influence results of 5 vol% water vapor on the catalytic combustion of methane by the catalyst of Example 1 and the catalysts of Comparative Examples 1-2.

[0043] Figure 3 It is a graph showing the influence results of 20 ppm sulfur dioxide on the catalytic combustion of methane by the catalyst of Example 1 and the catalysts of Comparative Examples 1-2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operation methods without specific conditions noted in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0045] Example 1:

[0046] 1 g of H-USY zeolite (SiO2:Al2O3 molar ratio = 12:1) was suspended in 10 mL of 0.05 wt% palladium tetraammine nitrate aqueous deionized solution, stirred at room temperature for 2 h, and then left to age for 2 h. Then, the reacted sample was washed and dried overnight at 110 °C and calcined at 500 °C for 4 h to collect the first intermediate product, denoted as 0.05Pd1-Y.

[0047] 1 g of the 0.05Pd1-Y sample was suspended in 60 mL of deionized water and 0.2 g of 2-methylimidazole was mixed. The resulting suspension was stirred and reacted at 80 °C for 20 h. The obtained sample was washed extensively and dried overnight at 70 °C and then collected to obtain the second intermediate product, denoted as 0.05Pd1-M-Y.

[0048] 1 g of 0.05Pd1-M-Y was suspended in 10 mL of 0.05 wt% PtCl2 aqueous deionized solution, and the suspension was stirred and reacted at 80 °C for 20 h. The obtained sample was washed extensively and dried overnight at 70 °C, and then calcined at 500 °C for 4 h to collect the supported platinum-palladium dual-atom methane combustion catalyst, denoted as 0.05Pd1-0.05Pt1-Y.

[0049] Example 2:

[0050] 1 g of H-USY zeolite (SiO2:Al2O3 molar ratio = 12:1) was suspended in 10 mL of 0.02 wt% palladium nitrate aqueous deionized solution, stirred at room temperature for 2 h, and then left to age for 2 h. Then, the reacted sample was washed and dried overnight at 110 °C and calcined at 500 °C for 5 h to collect the first intermediate product, denoted as 0.02Pd1-Y.

[0051] 1 g of the 0.02Pd1-Y sample was suspended in 60 mL of deionized water and 0.2 g of 2-methylimidazole was mixed. The resulting suspension was stirred and reacted at 80 °C for 20 h. The obtained sample was washed extensively and dried overnight at 70 °C and then collected to obtain the second intermediate product, denoted as 0.02Pd1-M-Y.

[0052] 1 g of 0.02Pd1-M-Y was suspended in 10 mL of 0.02 wt% PtCl2 aqueous deionized solution, and the suspension was stirred and reacted at 80 °C for 20 h. The obtained sample was washed extensively and dried overnight at 70 °C, and then calcined at 500 °C for 5 h to collect the supported platinum-palladium dual-atom methane combustion catalyst, denoted as 0.02Pd1-0.02Pt1-Y.

[0053] Example 3:

[0054] Take 1 g of H-USY zeolite (SiO2:Al2O3 molar ratio = 12:1) and suspend it in 10 mL of 0.3 wt% palladium acetate deionized aqueous solution. Stir for 2 h at room temperature, and then let it stand for aging for 2 h. Then, wash the reacted sample and dry it overnight at 110 °C, and then calcine it at 500 °C for 5 h to collect the first intermediate product, denoted as 0.3Pd1-Y.

[0055] Suspend 1 g of 0.3Pd1-Y sample in 60 mL of deionized water and mix with 0.2 g of imidazole. Stir and react the obtained suspension at 80 °C for 20 h. Wash the obtained sample extensively and dry it overnight at 70 °C, and then collect the second intermediate product, denoted as 0.3Pd1-M-Y.

[0056] Suspend 1 g of 0.3Pd1-M-Y in 10 mL of 0.3 wt% PtCl2 deionized aqueous solution, and stir and react the suspension at 80 °C for 20 h. Wash the obtained sample extensively and dry it overnight at 70 °C, and then calcine it at 500 °C for 5 h to collect the supported platinum-palladium dual-atom methane combustion catalyst, denoted as 0.3Pd1-0.3Pt1-Y.

[0057] Comparative Example 1: Without coordination of imidazole-based organic ligands.

[0058] Suspend 1 g of the first intermediate product 0.05Pd1-Y in Example 1 in 10 mL of 0.05 wt% PtCl2 deionized aqueous solution, and stir the suspension at 80 °C for 20 h. Wash the obtained sample extensively and dry it overnight at 70 °C, and then calcine it at 500 °C for 4 h to collect the catalyst, denoted as 0.05Pd1-0.05Pt1-Y-U.

[0059] Comparative Example 2: Namely, the first intermediate product 0.05Pd1-Y in Example 1.

[0060] Comparative Example 3:

[0061] Take 1 g of H-USY zeolite (SiO2:Al2O3 molar ratio = 12:1) and suspend it in 10 mL of 0.05 wt% PtCl2 deionized aqueous solution. Stir for 2 h at room temperature, and then let it stand for aging for 2 h. Then, wash the reacted sample and dry it overnight at 110 °C, and then calcine it at 500 °C for 4 h to collect the catalyst, denoted as 0.05Pt1-Y.

[0062] The test conditions of the catalysts prepared in the examples and comparative examples are introduced as follows:

[0063] For the methane combustion reaction, a monolithic catalyst was formed by coating a catalyst with 5 wt% of the cordierite support mass as the active ingredient onto the cordierite support under atmospheric pressure. Before the reaction, the monolithic catalyst was preheated at 300 °C for 1 h in a nitrogen atmosphere, and the heating rate was 10 °C / min. After the pretreatment, the reaction apparatus was cooled to 200 °C for a temperature-programmed reaction. The temperature-programmed reaction temperature was 200 - 600 °C, and the heating rate was 5 °C / min. -1 The gas hourly space velocity (GHSV) for each test was 30000 mL / h -1 g 活性成分 -1 Gas analysis was carried out using an online GC1690 gas chromatograph equipped with a Hayesep Q chromatographic column and a thermal conductivity detector. The conversion rates of low-concentration methane mixtures composed of 0.5 vol% methane and 99.5 vol% air combustion were measured for different samples at different temperatures.

[0064] For the sulfur and water resistance performance of the catalyst, when the temperature was maintained at 400 °C during the above reaction, at 20 minutes of the reaction, 5 vol% of water vapor and 20 ppm of sulfur dioxide gas were respectively introduced based on the original gas composition, and the water vapor and sulfur dioxide gas were removed at 40 minutes of the reaction. The conversion rate of low-concentration methane combustion was measured by the same method.

[0065] As shown in the appendix Figure 1 The measured complete combustion temperatures of methane for the catalyst of Example 1 and the catalysts of Comparative Examples 1 - 3 were 400 °C, 475 °C, 500 °C, and 600 °C respectively. According to the above results, it is shown that the supported platinum-palladium bimetallic methane combustion catalyst of the present invention can significantly reduce the reaction temperature required for catalytic methane combustion.

[0066] From the trend of the conversion rate change in the appendix Figure 2 It can be seen that for the bimetallic catalyst 0.05Pd1-0.05Pt1-Y of Example 1, the conversion rate decreased slightly after introducing 5 vol% of water vapor and quickly recovered after removing the water vapor, indicating that the catalyst has good water resistance performance; the conversion rate of the catalyst of Comparative Example 1 also decreased slightly after contacting water vapor, but the conversion rate was still lower than the initial conversion rate after removing the water vapor; the conversion rate of the catalyst of Comparative Example 2 decreased significantly after contacting water vapor and the conversion rate could not be restored to the initial conversion rate after removing the water vapor. The above results show that the bimetallic synergistic effect between platinum and palladium bimetallic atoms formed by imidazole-based organic ligands and the high dispersion degree of metal atoms in the present invention have a significant effect on improving the overall water resistance performance of the catalyst.

[0067] From the appendix Figure 3From the conversion rate change trend, it can be seen that for the dual-atom catalyst 0.05Pd1-0.05Pt1-Y in Example 1, the conversion rate hardly changes after introducing 20 ppm sulfur dioxide, indicating that the catalyst has excellent resistance to sulfur dioxide gas; while for the catalysts in Comparative Example 1 and Comparative Example 2, the conversion rates both decrease significantly after contacting sulfur dioxide and do not recover after removing sulfur dioxide, indicating that some active sites in the catalysts of Comparative Example 1 and Comparative Example 2 have been poisoned. This proves that the dual-metal synergistic effect between platinum and palladium dual atoms formed by imidazole-based organic ligands and the high dispersion degree of metal atoms in the present invention play an important role in improving the overall sulfur resistance performance of the catalyst.

[0068] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for preparing a carrier-supported platinum-palladium diatomic methane combustion catalyst, characterized in that: Includes steps: (1) placing the carrier in a palladium source solution, mixing it thoroughly and then allowing it to stand for aging so that the palladium species is evenly dispersed on the carrier, and then separating the solid from the liquid, washing, drying, and calcining the solid to obtain a first intermediate product; (2) placing the first intermediate product in an imidazole organic ligand solution, stirring and heating, causing a coordination reaction between the palladium metal site and the imidazole organic ligand, and then performing solid-liquid separation, washing, and drying the solid to obtain a second intermediate product; (3) placing the second intermediate product in a platinum source solution, stirring and heating, so that the platinum species reacts with the imidazole organic ligand coordinated to the palladium metal site, and then separating the solid from the liquid, washing, drying, and calcining the solid to obtain the carrier-supported platinum-palladium diatomic methane combustion catalyst.

2. The preparation method according to claim 1, characterized in that: In step (1): The carrier comprises at least one of metal oxide, non-metal oxide, ZSM-5 molecular sieve, Y-type molecular sieve, and β molecular sieve, and preferably comprises a molecular sieve carrier; The palladium source includes at least one of palladium nitrate, palladium acetate, palladium acetylacetonate, and tetraammine palladium nitrate; The mixture is mixed thoroughly by stirring for 1 to 3 hours; The aging time is 2 to 4 hours; The calcination atmosphere is air, the calcination temperature is 300 to 700° C., preferably 500° C., and the calcination time is 4 to 8 hours.

3. The preparation method according to claim 1, characterized in that: In step (2): The imidazole organic ligand includes at least one of imidazole, 2-methylimidazole and benzimidazole; The mass ratio of the imidazole organic ligand to the first intermediate product is 0.2-0.3:1; The heating temperature is 60-90° C., and the reaction time is 19-24 hours.

4. The preparation method according to claim 1, characterized in that: In step (3): The heating temperature is 60-90°C, and the reaction time is 19-24h; The calcination atmosphere is air, the calcination temperature is 300 to 700° C., preferably 500° C., and the calcination time is 4 to 8 hours.

5. The preparation method according to claim 1, characterized in that: In the carrier-supported platinum-palladium diatomic methane combustion catalyst, the molar ratio of palladium to platinum is 1:0.5-2, preferably 1:1-1.2; In the carrier-supported platinum-palladium diatomic methane combustion catalyst, the total mass percentage of palladium and platinum is 0.04% to 0.6%.

6. A carrier-supported platinum-palladium diatomic methane combustion catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. The carrier-supported platinum-palladium diatomic methane combustion catalyst according to claim 6, characterized in that: The carrier-supported platinum-palladium diatomic methane combustion catalyst can reduce the catalytic efficiency of methane to within 5% when 5 vol% water vapor and 20 ppm sulfur dioxide gas are introduced, and can restore the initial conversion rate after the water vapor and sulfur dioxide gas are removed.

8. Use of the carrier-supported platinum-palladium diatomic methane combustion catalyst according to claim 6 or 7 in catalytic methane combustion.

9. A method for catalyzing methane combustion, characterized in that: include: The carrier-supported platinum-palladium diatomic methane combustion catalyst according to claim 6 or 7 is used to catalyze methane combustion.

10. The method for catalytic combustion of methane according to claim 9, characterized in that: The carrier-supported platinum-palladium diatomic methane combustion catalyst is first subjected to heating pretreatment in a nitrogen atmosphere before being used to catalyze methane combustion. The heating pretreatment temperature is 200 to 300° C., the heating pretreatment time is 1 to 2 hours, and the heating rate of the heating pretreatment is 10 to 20° C. / min.

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