A method for preparing and using a supported platinum-palladium diatomic methane combustion catalyst

Abstract

The application discloses a carrier-supported platinum-palladium bimetallic atom methane combustion catalyst and a preparation method and application thereof. The preparation method comprises the following steps: (1) placing a carrier in a palladium source solution, uniformly mixing, and then aging to make palladium species uniformly dispersed on the carrier, and then performing solid-liquid separation to obtain a solid, and then 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 to make a coordination reaction of palladium metal sites and the imidazole organic ligand occur, and then performing solid-liquid separation to obtain a solid, and then washing and drying the solid to obtain a second intermediate product; and (3) placing the second intermediate product in a platinum source solution, stirring and heating to make a coordination reaction of platinum species and the imidazole organic ligand coordinated on the palladium metal sites occur, and then performing solid-liquid separation to obtain a solid, and then washing, drying, and calcining the solid to obtain the carrier-supported platinum-palladium bimetallic atom methane combustion catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental catalysis, in particular to a preparation method and application of a carrier-supported platinum-palladium bimetallic methane combustion catalyst. BACKGROUND

[0002] Natural gas, as a clean energy, is mainly composed of methane, which has high energy content, clean combustion products and low carbon dioxide (CO2) emissions. These characteristics make methane more advantageous than other fossil fuels. However, direct emission of unburned methane gas into the air will cause serious environmental pollution because it is a powerful greenhouse gas with a global warming potential of about 25 times that of carbon dioxide. Therefore, it is necessary to completely burn 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 completely oxidizing methane and air into CO2 and H2O after pre-mixing and entering a high-temperature counter-flow reactor (> 1000℃). However, due to the working temperature usually above 1000℃, this method has high requirements for equipment, increasing the design and construction cost of equipment, and the high temperature inevitably produces harmful substances such as nitrogen oxides (NO x ) and carbon monoxide (CO) to cause environmental damage. Therefore, it is of great theoretical and practical significance to develop a high-efficiency and low-cost catalyst for catalytic combustion of low-concentration methane.

[0004] At present, 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 has the highest activity among noble metal methane catalytic combustion catalysts. Compared with non-noble metal catalysts, it has a lower light-off temperature and better stability. However, the high preparation cost of single Pd catalyst and the characteristics of easy sintering and deactivation due to water vapor and sulfide poisoning during use greatly limit its practical application. Therefore, reducing the preparation cost of noble metal Pd catalyst and prolonging its service life are the problems that must be overcome to make it truly applied.

[0005] Active palladium species is usually loaded on metal or non-metal oxide carriers by traditional methods such as deposition, precipitation and impregnation. Generally, active palladium species mainly exists in the form of nanoparticles or clusters, which is not conducive to the methane catalytic combustion reaction usually occurring at the catalyst interface, because only the palladium atoms on the surface can participate in the reaction in the form of nanoclusters or particles. In order to improve the utilization rate of palladium atoms, atomic palladium as an active site supported on the carrier has attracted widespread attention. At the same time, the synergistic effect between metals has been proved to improve the catalytic performance and improve the sulfur and water resistance of Pd.

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

[0007] The patent specification with publication number CN110433798A discloses a preparation method of a single-atomic palladium-based catalyst, which includes the following steps: adding a silicon source and zirconium dioxide to an organic solvent for reflux reaction, drying to obtain amorphous silica-modified zirconium dioxide; mixing a palladium source and the amorphous silica-modified zirconium dioxide in an organic solvent, then impregnating, loading the palladium source on the amorphous silica-modified zirconium dioxide, drying, and calcining to obtain a single-atomic Pd / SiO2-ZrO2 catalyst. The catalyst of the patent technology can be used for catalytic combustion reaction of low-concentration hydrocarbons such as methane, but the patent technology does not study the water and sulfur resistance of the catalyst.

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

[0009] In view of the above technical problems and the deficiencies in the field, the present application provides a carrier-supported platinum-palladium dual-atomic methane combustion catalyst, as well as a preparation method and application thereof. The catalyst of the present application has high catalytic activity for methane combustion and excellent water and sulfur resistance, and can maintain high catalytic activity for methane combustion in a water and sulfur-containing environment. The present application overcomes the problem that the stability and catalytic activity of the existing methane catalytic combustion catalyst are difficult to balance.

[0010] The specific technical solutions are as follows:

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

[0012] (1) placing the carrier in a palladium source solution, thoroughly mixing and then standing for aging, so that the palladium species are uniformly dispersed on the carrier, then solid-liquid separation, washing, drying, and calcining to obtain a first intermediate product;

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

[0014] (3) placing the second intermediate product into a solution of a platinum source (for example, which can include PtCl2, etc.), stirring and heating to allow coordination of the platinum species with the imidazole organic ligand coordinated on the palladium metal site, and then solid-liquid separation to obtain the solid, washing, drying, and calcining to obtain the carrier-supported platinum-palladium bimetallic methane combustion catalyst.

[0015] In the preparation process of the catalyst of the present application, the imidazole organic ligand is coordinated to the palladium metal site through one N in the imidazole structure, and the remaining one N in the imidazole structure is subsequently coordinated to the platinum species. That is, the two Ns in the imidazole structure of the imidazole organic ligand are respectively coordinated to palladium and platinum to form a local bimetallic system, in which the palladium atom and the platinum atom are one-to-one and interact with each other through the imidazole organic ligand. Finally, the imidazole organic ligand is burned off by calcination to form a platinum-palladium bimetallic structure with strong interaction, which can exhibit surprising synergistic effect in the application of catalytic methane combustion.

[0016] It is found that if the loading order of palladium and platinum is changed, i.e., platinum is loaded first and then palladium is loaded, the activity and water and sulfur resistance stability of the obtained catalyst in the catalytic methane combustion reaction will be significantly deteriorated.

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

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

[0019] In step (1), stirring can be used to mix thoroughly, and the stirring time can be 1-3 hours, for example, 2 hours, etc.

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

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

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

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

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

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

[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 4-8h, for example 5h.

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

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

[0029] [2] The carrier-supported platinum-palladium bimetallic methane combustion catalyst prepared by the preparation method of [1].

[0030] The carrier-supported platinum-palladium bimetallic methane combustion catalyst can reduce the catalytic efficiency of methane to within 5% when 5vol% water vapor and 20ppm sulfur dioxide gas are introduced, and can restore the initial conversion rate after removing the water vapor and sulfur dioxide gas.

[0031] [3] The application of the carrier-supported platinum-palladium bimetallic methane combustion catalyst of [2] in catalyzing methane combustion.

[0032] [4] A method for catalyzing methane combustion, comprising: using the carrier-supported platinum-palladium bimetallic methane combustion catalyst of [2] to catalyze methane combustion.

[0033] In the application of [3] and the method for catalyzing methane combustion of [4], the carrier-supported platinum-palladium bimetallic 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 of [3] and the method for catalyzing methane combustion of [4], the concentration of methane in the methane combustion reaction can be 0.2vol%-5vol%.

[0035] [3] The application, [4] The method for catalyzing methane combustion, wherein the carrier-supported platinum-palladium bimetallic methane combustion catalyst is subjected to a heating pretreatment in a nitrogen atmosphere before being used to catalyze methane combustion, the heating pretreatment temperature is 200-300 DEG C, the heating pretreatment time is 1-2 hours, and the heating pretreatment temperature rising rate is 10-20 DEG C / min.

[0036] The application provides a carrier-supported platinum-palladium bimetallic methane combustion catalyst with high methane catalytic combustion activity and excellent water and sulfur resistance, a preparation method and application thereof.

[0037] Compared with the prior art, the application has the following beneficial effects:

[0038] 1. The platinum-palladium bimetallic atom is used as a reaction site, the reaction site utilization rate is increased, the catalytic performance is improved, the noble metal consumption is reduced, and thus the catalyst cost is reduced.

[0039] 2. The single atom aggregation caused by high surface energy is improved through coordination chemistry, and thus the platinum-palladium atom dispersity is better.

[0040] 3. The resistance of the catalyst to water vapor and sulfurized gas is improved through the interaction between the platinum and palladium bimetals, and the service life of the catalyst is prolonged. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0043] Figure 3 Figure 3 is a graph of the influence of 20ppm sulfur dioxide on the catalytic methane combustion of the catalysts of Example 1 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0044] The application will be further described below in combination with the drawings and specific examples. It should be understood that the examples are only used to illustrate the application and not used to limit the scope of the application. The operation methods not specified in the following examples are usually carried out according to the conventional conditions or the conditions suggested by the manufacturers.

[0045] Example 1:

[0046] Take 1 g of H-USY zeolite (Si02:Al203 molar ratio = 12:1) and suspend in 10 mL of 0.05 wt% palladium nitrate in deionized water and stir for 2 h at room temperature followed by a 2 h rest period for aging. The reacted sample is then washed and dried at 110 °C overnight followed by calcination at 500 °C for 4 h to collect the first intermediate product, noted as 0.05Pd1-Y.

[0047] Take 1 g of 0.05Pd1-Y sample and suspend in 60 mL of deionized water and mix in 0.2 g of 2-methylimidazole. The resulting suspension is stirred for 20 h at 80 °C. The resulting sample is washed extensively and dried at 70 °C overnight to collect the second intermediate product, noted as 0.05Pd1-M-Y.

[0048] Take 1 g of 0.05Pd1-M-Y and suspend in 10 mL of 0.05 wt% PtCl2 in deionized water and stir the suspension for 20 h at 80 °C. The resulting sample is washed extensively and dried at 70 °C overnight followed by calcination at 500 °C for 4 h to collect the support- loaded platinum-palladium diatomic methane combustion catalyst, noted as 0.05Pd1-0.05Pt1-Y.

[0049] Example 2:

[0050] Take 1 g of H-USY zeolite (Si02:Al203 molar ratio = 12:1) and suspend in 10 mL of 0.02 wt% palladium nitrate in deionized water and stir for 2 h at room temperature followed by a 2 h rest period for aging. The reacted sample is then washed and dried at 110 °C overnight followed by calcination at 500 °C for 5 h to collect the first intermediate product, noted as 0.02Pd1-Y.

[0051] Take 1 g of 0.02Pd1-Y sample and suspend in 60 mL of deionized water and mix in 0.2 g of 2-methylimidazole. The resulting suspension is stirred for 20 h at 80 °C. The resulting sample is washed extensively and dried at 70 °C overnight to collect the second intermediate product, noted as 0.02Pd1-M-Y.

[0052] Take 1 g of 0.02Pd1-M-Y and suspend in 10 mL of 0.02 wt% PtCl2 in deionized water and stir the suspension for 20 h at 80 °C. The resulting sample is washed extensively and dried at 70 °C overnight followed by calcination at 500 °C for 5 h to collect the support- loaded platinum-palladium diatomic methane combustion catalyst, noted 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 in 10 mL of 0.3 wt% palladium acetate aqueous solution, stir at room temperature for 2 h, then let it stand for 2 h of aging. The reacted sample is then washed and dried at 110 °C overnight before calcination at 500 °C for 5 h to collect the first intermediate product, noted 0.3Pd1-Y.

[0055] Suspend 1 g of 0.3Pd1-Y sample in 60 mL of deionized water and mix 0.2 g of imidazole. The resulting suspension is stirred at 80 °C for 20 hours of reaction. The resulting sample is washed extensively and dried at 70 °C overnight to collect the second intermediate product, noted 0.3Pd1-M-Y.

[0056] Suspend 1 g of 0.3Pd1-M-Y in 10 mL of 0.3 wt% PtCl2 aqueous solution, and stir the suspension at 80 °C for 20 hours of reaction. The resulting sample is washed extensively and dried at 70 °C overnight before calcination at 500 °C for 5 h to collect the support loaded platinum-palladium bimetallic methane combustion catalyst, noted 0.3Pd1-0.3Pt1-Y.

[0057] Comparative Example 1 : No imidazole organic ligand coordination.

[0058] Suspend 1 g of the first intermediate product 0.05Pd1-Y in Example 1 in 10 mL of 0.05 wt% PtCl2 aqueous solution, and stir the suspension at 80 °C for 20 hours. The resulting sample is washed extensively and dried at 70 °C overnight before calcination at 500 °C for 4 h to collect the catalyst, noted 0.05Pd1-0.05Pt1-Y-U.

[0059] Comparative Example 2: 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 in 10 mL of 0.05 wt% PtCl2 aqueous solution, stir at room temperature for 2 h, then let it stand for 2 h of aging. The reacted sample is then washed and dried at 110 °C overnight before calcination at 500 °C for 4 h to collect the catalyst, noted 0.05Pt1-Y.

[0062] The catalysts prepared in the Examples and Comparative Examples are tested under the following conditions:

[0063] For the methane combustion reaction, the catalyst with 5wt% of the active component was coated into the cordierite carrier to form a monolithic catalyst under normal pressure. Before the reaction, the monolithic catalyst was preheated at 300°C for 1h under nitrogen atmosphere at a heating rate of 10°C / min. After the pre-treatment, the reaction device was cooled to 200°C for the temperature programmed reaction, the temperature programmed reaction temperature was 200-600°C at a heating rate of 5°C / min -1 . The gas hourly space velocity (GHSV) of each test was 30000 mL / h -1 g 活性成分 -1 An online GC1690 gas chromatograph equipped with a Hayesep Q chromatographic column and a thermal conductivity detector was used for gas analysis. The conversion rate of the low concentration methane mixture consisting of 0.5vol% methane and 99.5vol% air at different temperatures was measured.

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

[0065] As shown in the accompanying Figure 1 , the measured complete combustion temperature of the catalysts of Example 1, Comparative Examples 1-3 for methane was 400°C, 475°C, 500°C and 600°C, respectively. According to the above results, it is shown that the carrier loaded platinum-palladium diatomic methane combustion catalyst of the present application can significantly reduce the reaction temperature required for catalytic methane combustion.

[0066] From the conversion rate change trend in the accompanying Figure 2 , it can be seen that the conversion rate of the diatomic catalyst 0.05Pd1-0.05Pt1-Y of Example 1 slightly decreased after the introduction of 5vol% water vapor, and quickly recovered after the removal of the water vapor, indicating that the catalyst has good water resistance; the conversion rate of the catalyst of Comparative Example 1 also slightly decreased after contacting with water vapor, but the conversion rate was still lower than the initial conversion rate after the removal of the water vapor; the conversion rate of the catalyst of Comparative Example 2 greatly decreased after contacting with water vapor and the conversion rate could not recover to the initial conversion rate after the removal of the water vapor. The above results show that the double metal synergistic effect between the platinum-palladium diatomics formed by the imidazole organic ligand and the high dispersion degree of the metal atoms have a significant effect on the improvement of the water resistance of the catalyst as a whole.

[0067] From the accompanying Figure 3From the change trend of the conversion rate, it can be seen that the diatomic catalyst 0.05Pd1-0.05Pt1-Y of Example 1 has almost no change in the conversion rate after the introduction of 20 ppm of sulfur dioxide, indicating that the catalyst has excellent resistance to sulfur dioxide gas; the conversion rates of the catalysts of Comparative Example 1 and Comparative Example 2 both decrease significantly after contacting with sulfur dioxide, and the conversion rates do not recover after the removal of sulfur dioxide, indicating that part of the active sites in the catalysts of Comparative Example 1 and Comparative Example 2 have been poisoned, which proves that the bimetallic synergistic effect between the platinum and palladium diatoms formed by the imidazole organic ligand and the high dispersion degree of the metal atoms play an important role in improving the sulfur resistance of the catalyst as a whole.

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

Claims

1. A method for the preparation of a support-supported platinum-palladium diatomic methane combustion catalyst, characterized by, The preparation method comprises the following steps: (1) placing a carrier in a palladium source solution, fully mixing and then standing for aging, so that palladium species are uniformly dispersed on the carrier, and then solid-liquid separation is performed to obtain a solid which is washed, dried and calcined to obtain a first intermediate product; the carrier is H-USY zeolite; (2) placing the first intermediate product in an imidazole organic ligand solution, stirring and heating, so that a coordination reaction between palladium metal sites and imidazole organic ligands occurs, and then solid-liquid separation is performed to obtain a solid which is washed and dried to obtain a second intermediate product; (3) placing the second intermediate product in a platinum source solution, stirring and heating, so that a coordination reaction between platinum species and imidazole organic ligands coordinated on the palladium metal sites occurs, and then solid-liquid separation is performed to obtain a solid which is washed, dried and calcined to obtain the carrier-supported platinum-palladium diatomic methane combustion catalyst; in the carrier-supported platinum-palladium diatomic methane combustion catalyst, the total mass percentage of palladium and platinum is 0.04% to 0.6%.

2. The production method according to claim 1, characterized by, In step (1): the palladium source comprises at least one of palladium nitrate, palladium acetate, palladium acetylacetonate and tetraammine palladium nitrate; the mixing is performed by stirring, and the stirring time is 1 to 3 hours; the aging time is 2 to 4 hours; the calcination atmosphere is air, the calcination temperature is 300 to 700 DEG C, and the calcination time is 4 to 8 hours.

3. The production method according to claim 2, characterized by, In step (1), the calcination temperature is 500 DEG C.

4. The method of claim 1, wherein, In step (2): the imidazole organic ligand comprises at least one of imidazole, 2-methyl imidazole and benzimidazole; the mass ratio of the imidazole organic ligand to the first intermediate product is 0.2 to 0.3:1; the heating temperature is 60 to 90 DEG C, and the reaction time is 19 to 24 hours.

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

6. The preparation method according to claim 5, characterized in that In step (3), the calcination temperature is 500 DEG C.

7. 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 to 2.

8. The preparation method according to claim 7, characterized in that In the carrier-supported platinum-palladium diatomic methane combustion catalyst, the molar ratio of palladium to platinum is 1:1 to 1.

2.

9. The carrier-supported platinum-palladium diatomic methane combustion catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. The support-supported platinum-palladium dual atomic methane combustion catalyst of claim 9, wherein, After the carrier-supported platinum-palladium diatomic methane combustion catalyst is introduced into 5vol% water vapor and 20 ppm sulfur dioxide gas, the catalytic efficiency for methane is reduced by less than 5%, and the initial conversion rate can be restored after the water vapor and the sulfur dioxide gas are removed.

11. A method of catalyzing the combustion of methane, characterized by, The preparation method comprises: using the carrier-supported platinum-palladium diatomic methane combustion catalyst according to claim 9 or 10 to catalyze methane combustion.

12. The method of catalytic methane combustion according to claim 11, characterized in that, Before the carrier-supported platinum-palladium diatomic methane combustion catalyst is used to catalyze methane combustion, the catalyst is subjected to heating pretreatment in a nitrogen atmosphere, the heating pretreatment temperature is 200 to 300 DEG C, the heating pretreatment time is 1 to 2 hours, and the heating pretreatment temperature rising rate is 10 to 20 DEG C / min.

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