PdO-coated TS-1 molecular sieve back-loading type core-shell catalyst as well as preparation method and application thereof

Abstract

The invention discloses a PdO at TS-1 molecular sieve back-loading type core-shell catalyst as well as a preparation method and application thereof, and belongs to the technical field of methane catalytic combustion. The preparation method comprises the following steps: S1, mixing a soluble palladium source, ethylenediamine and water to obtain a palladium precursor solution; s2, mixing a quaternary ammonium base template agent, a silicon source, an organic titanium source and water, and carrying out alcohol removal treatment to obtain a first mixed solution; and S3, mixing the palladium precursor solution with the first mixed solution, carrying out hydrothermal crystallization, and roasting to obtain the PdO-coated TS-1 back-loading type core-shell catalyst. According to the invention, an in-situ packaging method is adopted to obtain the PdO-TS-1 molecular sieve back-loading catalyst with a core-shell structure, PdO nanoclusters and Ti sites on a TS-1 titanium silicalite molecular sieve generate a strongly-bonded Pd-O-Ti structure which can inhibit decomposition and migration of the PdO nanoclusters at high temperature, and the PdO-Ti structure and hydrophobic pore channels of the TS-1 titanium silicalite molecular sieve generate a synergistic confinement effect, so that the PdO-TS-1 molecular sieve back-loading catalyst can be used for preparing a high-temperature-resistant catalyst. The catalyst has excellent low-temperature catalytic activity, high-temperature sintering resistance, water resistance and operation stability.

Description

Technical Field

[0001] This invention relates to the field of methane catalytic combustion technology, specifically to a PdO@TS-1 molecular sieve inverted core-shell catalyst, its preparation method, and its application. Background Technology

[0002] Methane (CH4), a significant greenhouse gas, has a global greenhouse potential (GWP) 28-36 times that of carbon dioxide, posing a serious threat to global climate change. Simultaneously, unburned methane emissions from vehicle exhaust directly exacerbate near-surface ozone pollution, harming the human respiratory system. However, in vehicles fueled by compressed natural gas (CNG), the high ignition temperature (typically >400℃) of traditional three-way catalytic converters for methane during cold starts and idling significantly limits their low-temperature catalytic efficiency, resulting in large amounts of unburned methane being directly released into the atmosphere during the initial stages of vehicle operation.

[0003] Current improvements mainly focus on two pathways: one is to use an integrated methane adsorption-catalysis system, which enriches methane at low temperatures using adsorption materials such as molecular sieves, and then releases and catalytically oxidizes it at high temperatures; the other is to develop dedicated methane oxidation catalysts (MOCs) to achieve deep conversion in the 350-550℃ range. However, the above approaches still have significant drawbacks: the adsorption-desorption process requires a regeneration heat source and piping system, which significantly increases energy consumption and space occupation; and high-temperature MOCs cannot effectively cope with low-temperature emissions during the cold start-up phase, and high-temperature operation accelerates catalyst sintering and deactivation.

[0004] CN116371449 A discloses an encapsulated Pd-based catalyst for methane catalytic combustion with controllable particle size and its preparation method. A series of catalysts with different particle sizes are obtained by controlling the molar ratio between ethylenediamine and metallic Pd. However, this prior art only achieves complete methane conversion at 360℃. Furthermore, palladium oxide in the catalyst is easily decomposed into Pd and oxygen at 800℃, reducing the catalytic activity of the catalyst after high-temperature treatment at 800℃. Therefore, the low-temperature activity and anti-sintering performance of the catalyst need further improvement. Summary of the Invention

[0005] To address the problems existing in the prior art, the primary objective of this invention is to provide a PdO@TS-1 molecular sieve-inverted core-shell catalyst.

[0006] Another object of the present invention is to provide the application of the above-mentioned PdO@TS-1 molecular sieve catalyst in the catalytic combustion of methane.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A PdO@TS-1 molecular sieve inverted core-shell catalyst is prepared by the following steps: S1. Mix a soluble palladium source, ethylenediamine, and water to obtain a palladium precursor solution; S2. Mix the quaternary ammonium base template agent, silicon source, organotitanium source and water, and perform alcohol removal treatment to obtain the first mixture; S3. The palladium precursor solution is mixed with the first mixture, hydrothermally crystallized, and calcined to obtain the PdO@TS-1 molecular sieve inverted core-shell catalyst.

[0008] This invention uses ethylenediamine as the active component, encapsulating palladium oxide within a TS-1 titanium-silicon molecular sieve. The resulting PdO@TS-1 molecular sieve catalyst possesses a reverse-loaded confined core-shell structure with PdO nanoclusters as the core and hydrophobic TS-1 titanium-silicon molecular sieve as the shell. Strongly electron-coupled Pd-O-Ti chemical bonds are formed between the PdO nanoclusters and the Ti sites in the TS-1 titanium-silicon molecular sieve framework, enhancing the stability of the PdO nanoclusters. These directionally bridged Pd-O-Ti chemical bonds at the internal interfaces synergistically confine the catalyst with the pores of the TS-1 titanium-silicon molecular sieve, significantly enhancing the catalyst's anti-sintering and water-resistant properties, optimizing the redox cycle of methane catalytic combustion, and achieving efficient adsorption and low-temperature catalytic combustion of methane under cold-start conditions. This inverted core-shell structure can enhance interfacial oxygen mobility and reduce the energy barrier for breaking the CH bond in methane by storing and releasing oxygen through the Pd-O-Ti chemical bond, thus enabling the catalyst to activate methane at low temperatures and efficiently.

[0009] The Si and Ti framework structures of the TS-1 titanium-silicon molecular sieve used in this invention give the catalyst excellent water resistance, effectively blocking the competitive adsorption of water molecules and enhancing the catalyst's ability to enrich low concentrations of methane.

[0010] Preferably, the molar ratio of the soluble palladium source to ethylenediamine is (1~1.2):(130~170).

[0011] More preferably, the molar ratio of the soluble palladium source to ethylenediamine is (1~1.2):(140~160).

[0012] Preferably, the soluble palladium source is at least one of palladium nitrate, palladium chloride, palladium acetate, palladium tetraamine nitrate, palladium acetylacetone, and palladium chloroacetic acid.

[0013] Preferably, in S1, the mixing time is 0.5~2h.

[0014] Preferably, the molar ratio of the silicon source (calculated as SiO2), the quaternary ammonium base template agent, water, and the organic titanium source (calculated as TiO2) is (30~150):(45~50):(2100~2200):1.

[0015] More preferably, the molar ratio of the silicon source (calculated as SiO2), the quaternary ammonium base template agent, water, and the organic titanium source (calculated as TiO2) is (50~150):(45~50):(2100~2200):1.

[0016] Preferably, the quaternary ammonium base template agent is at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, ethyltrimethylammonium hydroxide, and diethyldimethylammonium hydroxide.

[0017] Preferably, the silicon source is at least one of tetramethyl silicate, tetraethyl orthosilicate, propyl orthosilicate, and isopropyl silicate.

[0018] Preferably, the organic titanium source is at least one selected from methyl titanate, ethyl titanate, isopropyl titanate, and tetrabutyl titanate.

[0019] Preferably, the temperature of the alcohol removal treatment is 70~90℃.

[0020] Preferably, the alcohol removal treatment time is 0.5~1.5h.

[0021] Preferably, the molar ratio of the silicon source (calculated as SiO2), the organotitanium source (calculated as TiO2), and the soluble palladium source (calculated as PdO) is (30~150):1:(0.5~0.6).

[0022] More preferably, the molar ratio of the silicon source (calculated as SiO2), the organotitanium source (calculated as TiO2), and the soluble palladium source (calculated as PdO) is (50~150):1:(0.5~0.6).

[0023] Preferably, in step S3, the mixing time is 0.5 to 1.5 hours.

[0024] Preferably, the temperature of the hydrothermal crystallization is 160~180℃.

[0025] Preferably, the hydrothermal crystallization time is 70-74 hours.

[0026] Preferably, the calcination temperature is 450~650℃.

[0027] Preferably, the roasting time is 5-7 hours.

[0028] Preferably, in the PdO@TS-1 molecular sieve inverted core-shell catalyst, the average particle size of the PdO clusters is 1.9~2nm.

[0029] This invention also protects the application of the above-mentioned PdO@TS-1 molecular sieve inverted core-shell catalyst in the catalytic combustion of methane.

[0030] Compared with the prior art, the present invention has the following beneficial effects: This invention employs an in-situ encapsulation method to encapsulate PdO nanoclusters within TS-1 titanium-silicon molecular sieves, yielding a core-shell structured PdO@TS-1 molecular sieve-supported catalyst. The PdO nanoclusters and Ti sites on the TS-1 titanium-silicon molecular sieve form a strongly bonded Pd-O-Ti structure. This structure inhibits the decomposition and migration of PdO nanoclusters at high temperatures. The directionally bridged Pd-O-Ti chemical bonds and the hydrophobic channels of the TS-1 titanium-silicon molecular sieve create a synergistic confinement effect, effectively preventing water vapor erosion of the catalyst. This results in a catalyst with excellent high-temperature anti-sintering properties, water resistance, and operational stability.

[0031] This invention combines low-temperature adsorption with catalysis. The prepared PdO@TS-1 molecular sieve-supported catalyst utilizes the hydrophobic channels of the TS-1 molecular sieve to efficiently enrich low concentrations of methane during the cold start phase (<300℃). The Pd-O-Ti interfacial chemical bonds facilitate in-situ low-temperature catalytic conversion of methane through directional oxygen migration. The synergistic effect of these two processes enhances the catalyst's low-temperature catalytic activity. This invention overcomes the shortcomings of traditional three-way catalytic (TWC) catalysts in terms of insufficient low-temperature activity and eliminates the need for an additional adsorption-desorption regeneration system.

[0032] The PdO@TS-1 molecular sieve reverse-supported catalyst prepared in this invention can achieve complete catalytic combustion of low-concentration propane below 350℃, maintain long-term stable catalytic activity at 330℃ for 100 hours, and still have good catalytic activity after high-temperature sintering at 800℃. Attached Figure Description

[0033] Figure 1 The graph shows the methane catalytic combustion performance of TS-1 molecular sieve in Examples 1, Comparative Examples 1-2, and Comparative Example 2.

[0034] Figure 2 The graphs show the heating-cooling activity test results for Example 1 and Comparative Example 1.

[0035] Figure 3 This is a graph showing the long-term stability test results for Example 1.

[0036] Figure 4 The figures show the water resistance test results for Example 1 and Comparative Example 1.

[0037] Figure 5 The figures (a) and (b) show the catalytic performance test results of Example 1 and Comparative Example 1 before and after high-temperature anti-sintering, respectively.

[0038] Figure 6 This is an AC-HAADF-STEM image from Example 1.

[0039] Figure 7 This is the AC-EDX-MAPPING image of Example 1.

[0040] Figure 8 The image is an EXAFS and wavelet transform image from Example 1.

[0041] Figure 9 The graphs show the methane catalytic combustion performance of Examples 1-4. Detailed Implementation

[0042] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0043] Example 1 This embodiment provides a PdO@TS-1 molecular sieve catalyst, the preparation method of which includes the following steps: S1. Dissolve 0.02 g of PdCl2 in 4 mL of deionized water. After complete dissolution, add 1 mL of ethylenediamine solution and sonicate for 30 min to obtain a palladium precursor solution. The molar ratio of PdCl2 to ethylenediamine is 1.13:150.

[0044] S2. Mix 7.50 g TPAOH solution (25 wt.%) and 7.75 g deionized water in a beaker and stir until homogeneous at 30 °C. Add 4.375 g TEOS (98 wt.%) dropwise, followed by 0.07 g tetrabutyl titanate (TBOT) solution (98 wt.%), and perform alcohol removal treatment at 80 °C for 1 h to obtain the first mixture. The molar ratio of silicon source (SiO2), quaternary ammonium base template agent, water, and organic titanium source (TiO2) is 100:46:2152.5:1.

[0045] S3. Add palladium precursor solution to the first mixture. The molar ratio of silicon source (SiO2), organic titanium source (TiO2), and soluble palladium source (PdO) is 100:1:0.57. After stirring for 1 hour, place the mixture in a stainless steel reactor with a polytetrafluoroethylene liner and perform static hydrothermal crystallization at 170°C for 72 hours. Wash the solid product by centrifugation with water and ethanol, place it in a forced-air drying oven, dry for 12 hours, grind it, and then place it in a muffle furnace under air atmosphere. Heat the mixture to 550°C at a heating rate of 2°C / min and calcine it at this temperature for 6 hours to obtain the PdO@TS-1 molecular sieve catalyst.

[0046] Example 2 This embodiment provides a PdO@TS-1 molecular sieve catalyst, which differs from Example 1 in that the molar ratio of silicon source (calculated as SiO2) to organotitanium source (calculated as TiO2) in the raw materials is 30:1. The rest is the same as in Example 1.

[0047] Example 3 This embodiment provides a PdO@TS-1 molecular sieve catalyst, which differs from Example 1 in that the molar ratio of silicon source (calculated as SiO2) to organotitanium source (calculated as TiO2) in the raw materials is 50:1. The rest is the same as in Example 1.

[0048] Example 4 This embodiment provides a PdO@TS-1 molecular sieve catalyst, which differs from Example 1 in that the molar ratio of silicon source (calculated as SiO2) to organotitanium source (calculated as TiO2) in the raw materials is 150:1. The rest is the same as in Example 1.

[0049] Comparative Example 1 This comparative example provides a PdO@S-1 molecular sieve catalyst, which differs from Example 1 in that no titanate ester is added in S2, and the first mixture is obtained after magnetic stirring for 4 hours.

[0050] Comparative Example 2 This comparative example provides a PdO / TS-1 molecular sieve catalyst, prepared by an impregnation method, which includes the following steps: Preparation of TS-1 molecular sieve: The difference from Example 1 is that S1 is not present, but otherwise it is the same as Example 1.

[0051] Impregnation and loading: Dissolve 0.02 g of PdCl2 in 4 mL of deionized water, weigh 0.5 g of the above-mentioned TS-1 molecular sieve with a silicon-to-titanium ratio of 100, add it to 5 mL of water and stir. While stirring, add the prepared palladium-containing solution and continue stirring for 6 h. After evaporating to dryness in an 80 °C water bath, dry in a forced-air drying oven for 12 h. After the sample is dried, place it in a high-temperature muffle furnace and heat it to 550 °C at a heating rate of 2 °C / min. Calcinate at this temperature for 6 h to finally obtain the PdO / TS-1 supported catalyst.

[0052] Performance testing 1g of sample was weighed and compressed into tablets. 0.05g of sample (40-60 mesh) was sieved out and placed into a reaction tube filled with quartz wool. The tablets were then placed in a thermocatalytic evaluation reaction bed for catalytic activity evaluation. The feed gas consisted of 1000ppm methane, 22% O2 (v / v), 78% N2 (v / v), and high-purity air as a balance gas, with a flow rate of 60mL / min. 1 (The corresponding mass hourly space velocity (WHSV) is 72,000 h) 1 The concentration of methane was measured using a flame ionization detector (FID), and data were recorded after the reaction reached steady state at each target temperature. The methane conversion was calculated using the following equation:

[0053] Figure 1 The graphs show the methane catalytic combustion performance of the TS-1 molecular sieve in Examples 1, Comparative Examples 1-2, and Comparative Example 2. As can be seen from the graphs, the TS-1 molecular sieve in Example 1 exhibits... 10 T 50 T 90 The T values ​​were 262℃, 300℃, and 329℃, respectively, which are far superior to the T values ​​of the catalyst in Comparative Example 1. 10 (283℃), T 50 (330℃), T 90 (365℃), indicating that the catalyst of Example 1 exhibits superior CH4 degradation performance compared to Comparative Example 1. This demonstrates that introducing Ti into the molecular sieve framework can enhance the catalytic activity of the catalyst. Compared to Comparative Example 2 prepared by the impregnation method, the catalyst prepared by the in-situ encapsulation method of this invention exhibits superior catalytic activity.

[0054] Figure 2 The graphs show the heating-cooling activity test results for Example 1 and Comparative Example 1. The test conditions were: 5℃·min 1 The temperature was increased from 100°C to 800°C, then the heating was stopped and cooling began. The methane conversion rate was calculated for each temperature range. As shown in the figure, the catalytic activity of Example 1 was consistently higher than that of Comparative Example 1 during both the heating and cooling phases. During the heating phase (200→800°C), the Tconversion of the catalyst in Example 1 was... 90 It is not much different from before, but when the temperature drops, its T 90 Instead of showing any decline, the activity actually increased compared to the initial activity. This is mainly due to the partial reduction of PdO induced by high temperature, and the confinement effect of the molecular sieve effectively inhibited the migration and aggregation of Pd species. This indicates that the PdO@TS-1 molecular sieve catalyst provided by this invention has excellent anti-sintering performance.

[0055] Figure 3 The figure shows the long-term stability test results for Example 1. As can be seen from the figure, at a reaction temperature of 330°C, the methane conversion rate of Example 1 remained unchanged within 100 h, indicating that the PdO@TS-1 molecular sieve catalyst prepared in this invention has excellent long-term stability.

[0056] Figure 4The graph shows the water resistance test results for Example 1 and Comparative Example 1. The reaction conditions were as follows: air containing 5% water vapor (by volume) was introduced at 200 min of reaction time; the water vapor was stopped at 400 min of reaction time, and methane gas was simultaneously introduced, maintained for 100 h, and data were recorded. As shown in the graph, at 330°C, after the introduction of water vapor, the methane conversion rate of Example 1 decreased by only 18%, and after the water vapor was stopped, its methane conversion rate recovered to the level before the water vapor introduction. In contrast, after the introduction of water vapor, the methane conversion rate of Comparative Example 1 decreased from 51% to 9%, and after the water vapor was stopped, its methane conversion rate was 33%, a decrease of 18% compared to the level before the water vapor introduction. This demonstrates that the PdO@TS-1 molecular sieve catalyst prepared in this invention has excellent water resistance.

[0057] Figure 5 a shows the catalytic performance test results of Example 1 and Comparative Example 1 before and after high-temperature anti-sintering. The test conditions were as follows: the catalyst of Comparative Example 1 and the sample of Example 1 were calcined at 800°C in air for 2 hours (heating rate 5°C / min). 1 The obtained thermally aged samples were labeled as Comparative Example 1-800 and Example 1-800, respectively. Figure 5 As can be seen from a, the T of the fresh sample from Example 1... 90 The temperature was 329℃, while after thermal aging, T... 90 The temperature only rose to 344°C; in contrast, the T of the catalyst in Comparative Example 1 was much higher. 90 Increasing the temperature from the initial 365℃ to 390℃, the catalytic activity of Comparative Example 1 decreased more significantly, indicating that the PdO@TS-1 molecular sieve catalyst prepared in this invention has excellent anti-sintering properties.

[0058] Combination Figure 5 b, Figure 5 b shows the O2-TPO spectra of Example 1 and Comparative Example 1, with test conditions of 5°C·min from 150°C. 1 The temperature was increased to 900℃ at a heating rate and then decreased to 150℃. Within the temperature range of 600℃ to 750℃, during the high-temperature heating process, PdO in the catalyst of Comparative Example 1 may decompose into Pd, leading to a sharp decrease in oxygen signal during the cooling process, suggesting that Pd was re-oxidized to PdO. However, the sample of Example 1 did not decompose, which can be attributed to the fact that the Pd-O-Ti chemical bond anchoring effect on PdO significantly improves the catalyst's thermal stability and anti-sintering properties.

[0059] Figure 6The image shows an AC-HAADF-STEM image of Example 1. As can be clearly seen from the image, the catalyst exhibits typical MFI-type topological characteristics, with a periodic arrangement of ten-membered ring straight channels, indicating that the integrity of the TS-1 molecular sieve framework was not disrupted by the introduction of Pd. Notably, uniformly distributed bright spots are observed inside the molecular sieve channels. These spots are attributed to PdO nanoclusters with an average particle size of approximately 1.97 nm, demonstrating that Pd species are precisely confined within the molecular sieve channels in the form of PdO nanoclusters by Pd-O-Ti chemical bonds. In Comparative Example 1, the average particle size of the PdO nanoclusters is approximately 2.4 nm. This comparison shows that the Pd-O-Ti chemical bonds can anchor the PdO clusters, and their confinement effect results in a smaller average particle size for the PdO clusters.

[0060] Figure 7 The image shows the AC-EDX-MAPPING image of Example 1. As can be seen from the figure, the spatial distribution of Pd element signals and Ti elements highly overlaps, the Ti element is uniformly distributed, and the Pd element line scan signal overlaps with Ti, indicating that Pd species may achieve inverted anchoring within the molecular sieve framework through Pd-O-Ti.

[0061] Figure 8 The images show the EXAFS and wavelet transform results for Example 1. As can be seen from the figures, the Pd K-edge XANES near-edge absorption energies show that the absorption threshold of Pd@TS-1(100) is located at 24350 eV, close to that of standard PdO (24352 eV) but shifted towards lower energies, indicating that the Pd species is in a partially oxidized state (Pd δ+ (0 < δ < 2), this mixed valence state characteristic enhances the covalent nature of the metal-oxygen bond, which is more conducive to the cleavage and activation of the CH bond in the methane molecule. EXAFS spectroscopy shows that ( Figure 8 (b) The coordinates at R=1.7Å belong to Pd-O coordination, at R=2.3Å to Pd-Pd coordination, and at R=2.9Å to Pd-O-Pd (Ti) interface coordination. To intuitively analyze the interface coordination characteristics, wavelet transform (WT) analysis was performed. The results ( Figure 8 c) This further demonstrates the interfacial coordination of Pd-O-Ti, confirming the formation of a strong metal-support interaction (EMSI). Furthermore, the anchoring effect of Ti on Pd species allows the formed Pd-O-Ti interface to better stabilize PdO within the molecular sieve.

[0062] Figure 9 The figures show the methane catalytic combustion performance of Examples 1, 2, 3, and 4. As can be seen from the figures, the methane catalytic activity first increases and then decreases with the increase of the titanium-silicon ratio in the TS-1 molecular sieve, with the catalyst exhibiting the best activity when the Si:Ti ratio is 100.

[0063] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A PdO@TS-1 molecular sieve inverted core-shell catalyst, characterized in that, Its preparation method includes the following steps: S1. Mix a soluble palladium source, ethylenediamine, and water to obtain a palladium precursor solution; S2. Mix the quaternary ammonium base template agent, silicon source, organotitanium source and water, and perform alcohol removal treatment to obtain the first mixture; S3. The palladium precursor solution is mixed with the first mixture, hydrothermally crystallized, and calcined to obtain the PdO@TS-1 molecular sieve inverted core-shell catalyst.

2. The catalyst according to claim 1, characterized in that, The molar ratio of the soluble palladium source to ethylenediamine is (1~1.2):(130~170).

3. The catalyst according to claim 1, characterized in that, The molar ratio of silicon source (calculated as SiO2), quaternary ammonium base template agent, water, and organic titanium source (calculated as TiO2) is (30~150):(45~50):(2100~2200):

1.

4. The catalyst according to claim 1, characterized in that, The quaternary ammonium base template agent is at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, ethyltrimethylammonium hydroxide, and diethyldimethylammonium hydroxide.

5. The catalyst according to claim 1, characterized in that, The temperature for the alcohol removal treatment is 70~90℃.

6. The catalyst according to claim 1, characterized in that, The molar ratio of the silicon source (calculated as SiO2), the organotitanium source (calculated as TiO2), and the soluble palladium source (calculated as PdO) is (30~150):1:(0.5~0.6).

7. The catalyst according to claim 1, characterized in that, The hydrothermal crystallization temperature is 160~180℃.

8. The catalyst according to claim 1, characterized in that, The hydrothermal crystallization time is 70~74h.

9. The catalyst according to claim 1, characterized in that, The roasting temperature is 450~650℃.

10. The application of the PdO@TS-1 molecular sieve inverted core-shell catalyst according to any one of claims 1 to 9 in the catalytic combustion of methane.

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