A methane combustion catalyst with improved sulfur resistance

Abstract

The present invention provides a methane combustion catalyst with improved sulfur resistance. The methane combustion catalyst includes a substrate and a coating coated on the substrate. The coating includes a bottom coating and an upper coating. The bottom coating is a methane oxidation active layer, and the components of the bottom coating include precious metals Pt and Pd, a cerium-aluminum composite oxide, and a binder. The upper coating is an active component protective layer, and the components of the upper coating include Al2O3 or ZrO2, and pseudo-boehmite. The methane combustion catalyst of the present invention improves the methane oxidation activity of the catalyst by high-temperature calcination of the cerium-aluminum composite oxide, improves the sulfur resistance of the catalyst by coating the active protective layer, and can significantly extend the catalyst's efficient methane conversion time under natural gas lean burn conditions. Compared with existing methane combustion catalysts, the catalyst of the present invention has a low methane ignition temperature, high methane conversion activity, can delay the poisoning effect of sulfur dioxide on the catalyst, and has good sulfur resistance.

Description

Technical Field

[0001] The present invention belongs to the field of catalysis technology, and in particular relates to a methane combustion catalyst with improved sulfur resistance, which is applied to an exhaust gas purification system of a lean-burn natural gas engine. Background Art

[0002] Lean-burn natural gas vehicles (NGVs) are emerging as an alternative to gasoline and diesel vehicles due to their high energy density and low emissions of hydrocarbons, nitrogen oxides, and nitrogen oxides during combustion. However, methane has a global warming potential approximately 25 times greater than carbon dioxide, so unburned methane emissions from NGV engines pose potential environmental concerns. High methane oxidation activity is crucial for methane oxidation catalysts used in engine exhaust treatment. Precious metal palladium-based catalysts are considered the most promising for industrial applications due to their low light-off temperature and high stability.

[0003] In addition to low concentrations of CH₄ (400-1500 ppm), lean-burn natural gas engine exhaust also contains significant amounts of water vapor (10-15%). This can severely interfere with CH₄ oxidation on Pd catalysts. This is because adsorption of OH / H₂O species onto the active component, PdO, reduces the number of active sites available for CH₄ activation. The accumulation of OH / H₂O species on the catalyst support can also impair the oxygen supply between the Pd and support. Furthermore, during the catalytic reaction, sulfur compounds in natural gas compete with reactants for adsorption onto active sites, causing a temporary decrease in activity or even reacting with active species or the support, leading to irreversible chemical deactivation. For example, Pd-based precious metal catalysts are susceptible to sulfur poisoning. In an atmosphere containing SO₂, Pd reacts with SO₂ to form PdSO₄, which deactivates the catalyst.

[0004] Patent CN105833897B discloses a double-layered catalyst for catalytic combustion of methane, comprising a rare earth composite molecular sieve-loaded Pt coating and a rare earth composite alumina-loaded Pd coating. While the catalyst exhibits high activity, performance testing was conducted in a water-free, sulfur-free reaction atmosphere, which does not fully reflect its practical application value. Patent CN 114258322A discloses a RuPt / ZrO2 sulfur-tolerant methane oxidation catalyst. While this catalyst exhibits excellent sulfur tolerance, it requires a high noble metal content, resulting in a high methane oxidation ignition temperature. Furthermore, Ru slowly oxidizes when heated above 450°C in air, generating slightly volatile ruthenium dioxide, which significantly impacts the catalyst's durability. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art by providing a methane combustion catalyst with improved sulfur tolerance. The methane combustion catalyst of the present invention enhances its methane oxidation activity by high-temperature calcination of a cerium-aluminum composite oxide, and enhances its sulfur tolerance by coating it with an active protective layer. This catalyst can significantly extend the catalyst's efficient methane conversion time under natural gas lean-burn conditions. Compared to existing methane combustion catalysts, the catalyst of the present invention has a lower methane ignition temperature, higher methane conversion activity, and the ability to delay the poisoning of the catalyst by sulfur dioxide, resulting in excellent sulfur tolerance.

[0006] To achieve the above technical objectives, the technical solutions adopted in the embodiments of the present invention are:

[0007] A methane combustion catalyst with improved sulfur resistance comprises a substrate and a coating applied on the substrate, wherein the coating comprises a bottom coating and an upper coating, wherein the bottom coating is a methane oxidation active layer, and the components of the bottom coating include precious metals Pt and Pd, a cerium-aluminum composite oxide, and a binder; and the upper coating is an active component protective layer, and the components of the upper coating include Al2O3 or ZrO2, and pseudo-boehmite.

[0008] Furthermore, the coating amount of the bottom coating is 80-120 g / L, and the coating amount of the upper coating is 30-50 g / L.

[0009] Furthermore, the mass fraction of the precious metals Pt and Pd in ​​the base coating is 2%-5%, the mass fraction of the cerium-aluminum composite oxide is 92%-96%, and the mass fraction of the binder is 2%-3% based on the mass of the oxides.

[0010] Furthermore, the mass ratio of Pt to Pd is 1:5-1:9.

[0011] Furthermore, the mass fraction of CeO2 in the cerium-aluminum composite oxide is 5%-10%.

[0012] Furthermore, the cerium-aluminum composite oxide is subjected to a high-temperature calcination treatment at 1000-1200° C. for 3-6 hours.

[0013] Furthermore, the D90 particle size range of the bottom coating layer is 10-15 μm; the D90 particle size range of the upper coating layer is 2-5 μm.

[0014] Furthermore, the binder is aluminum sol.

[0015] Furthermore, the mass fraction of Al2O3 or ZrO2 in the upper coating layer is 98%-99%, and the mass fraction of pseudo-boehmite is 1%-2% calculated on the basis of the mass of the oxides.

[0016] Furthermore, the reaction temperature of the methane combustion catalyst when catalyzing the combustion of methane is 250-550°C.

[0017] The technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0018] The methane combustion catalyst of the present invention improves the methane oxidation activity of the catalyst by high-temperature calcination of cerium-aluminum composite oxide, and improves the sulfur resistance of the catalyst by coating an active protective layer. Compared with existing methane combustion catalysts, the catalyst of the present invention has a low methane ignition temperature, high methane conversion activity and can delay the poisoning effect of sulfur dioxide on the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 These are the test results of sulfur resistance of the catalysts prepared in Examples 1-3 of the present invention and the comparative example. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. 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.

[0021] Example 1

[0022] A methane combustion catalyst with improved sulfur resistance comprises a substrate and a coating coated on the substrate, wherein the substrate is a 400-mesh cordierite ceramic carrier with a carrier volume of 1.65 L; the coating comprises a bottom coating and an upper coating, wherein the bottom coating is a methane oxidation active layer, and the components of the bottom coating include precious metals Pt and Pd, a cerium-aluminum composite oxide, and a binder aluminum sol, wherein the mass fraction of the precious metals Pt and Pd in ​​the bottom coating is 3%, wherein the mass ratio of Pt to Pd is 1:9, the mass fraction of the cerium-aluminum composite oxide is 95%, and the mass fraction of the binder is 2%; and the upper coating is an active component protective layer, and, by mass fraction, the components of the upper coating include 99% Al2O3 and 1% pseudo-boehmite.

[0023] The total coating amount is 120 g / L, of which the coating amount of the bottom coating is 90 g / L and the coating amount of the upper coating is 30 g / L.

[0024] The preparation method of the methane combustion catalyst comprises the following steps:

[0025] (1) Preparation of Pt-Pd / CeO2-Al2O3: Commercial cerium-aluminum composite oxide (CeO2 mass fraction 8%) was calcined at 1100°C for 4 h. Using the equal volume impregnation method, a mixed solution of platinum nitrate and palladium nitrate was impregnated onto the calcined cerium-aluminum composite oxide at a mass ratio of precious metal to cerium-aluminum composite oxide of 3:95. The mixture was then allowed to stand for 10 h, dried at 120°C for 8 h, and finally calcined at 550°C for 2 h.

[0026] (2) Preparation of bottom coating: Pt-Pd / CeO2-Al2O3 and binder aluminum sol were added to deionized water with a solid content of 30%, stirred evenly to form a slurry, and the slurry was treated by ball milling to control the particle size D 90 Finally, the catalyst was coated on the support and dried rapidly at 120°C for 10 minutes to obtain a semi-finished catalyst.

[0027] (3) Preparation of the upper coating: γ-Al2O3 and pseudo-boehmite were added to deionized water with a solidified material content of 30%, stirred evenly to form a slurry, and the slurry was treated by ball milling to control the particle size D 90 The catalyst was then coated on the semi-finished catalyst, dried rapidly at 120°C for 10 min, and calcined at 550°C for 2 h to obtain the finished catalyst.

[0028] Example 2

[0029] A methane combustion catalyst with improved sulfur resistance comprises a substrate and a coating coated on the substrate, wherein the substrate is a 400-mesh cordierite ceramic carrier with a carrier volume of 1.65 L; the coating comprises a bottom coating and an upper coating, wherein the bottom coating is a methane oxidation active layer, and the components of the bottom coating include precious metals Pt and Pd, a cerium-aluminum composite oxide, and a binder aluminum sol, wherein the mass fraction of the precious metals Pt and Pd in ​​the bottom coating is 3%, wherein the mass ratio of Pt to Pd is 1:5, the mass fraction of the cerium-aluminum composite oxide is 95%, and the mass fraction of the binder is 2%; and the upper coating is an active component protective layer, and the components of the upper coating include, by mass fraction, 99% Al2O3 and 1% pseudo-boehmite.

[0030] The total coating amount is 170 g / L, of which the coating amount of the bottom coating is 120 g / L and the coating amount of the top coating is 50 g / L.

[0031] The preparation method of the methane combustion catalyst with improved sulfur resistance in this embodiment is the same as that in Example 1.

[0032] Example 3

[0033] A methane combustion catalyst with improved sulfur resistance comprises a substrate and a coating coated on the substrate, wherein the substrate is a 400-mesh cordierite ceramic carrier with a carrier volume of 1.65 L; the coating comprises a bottom coating and an upper coating, wherein the bottom coating is a methane oxidation active layer, and the components of the bottom coating include precious metals Pt and Pd, a cerium-aluminum composite oxide, and a binder aluminum sol, wherein the mass fraction of the precious metals Pt and Pd in ​​the bottom coating is 3%, wherein the mass ratio of Pt to Pd is 1:9, the mass fraction of the cerium-aluminum composite oxide is 95%, and the mass fraction of the binder is 2%; the upper coating is an active component protective layer, and the components of the upper coating include 98% ZrO2 and 2% pseudo-boehmite by mass.

[0034] The total coating amount is 120 g / L, of which the coating amount of the bottom coating is 90 g / L and the coating amount of the upper coating is 30 g / L.

[0035] The preparation method of the methane combustion catalyst comprises the following steps:

[0036] Steps (1) and (2) are the same as in Example 1;

[0037] (3) Add ZrO2 and pseudo-boehmite to deionized water with a solid content of 30%, stir evenly to form a slurry, and process the slurry by ball milling to control the particle size D 90 Then coated on the semi-finished catalyst prepared in step (2), quickly dried at 120°C for 10 minutes, and calcined at 550°C for 2 hours.

[0038] Comparative Example

[0039] A methane combustion catalyst comprises a substrate and a coating applied to the substrate. The substrate is a 400-mesh cordierite ceramic support with a support volume of 1.65 L. The coating has a coating weight of 120 g / L, comprises 3% by mass of the precious metals Pt and Pd, wherein the mass ratio of Pt to Pd is 1:5, comprises 95% by mass of a cerium-aluminum composite oxide, and comprises 2% by mass of a binder. Compared to Example 2, the upper coating layer containing an active component is not provided.

[0040] Preparation of Pt-Pd / CeO2-Al2O3: Commercial cerium aluminum composite oxide (CeO2 mass fraction 8%) was calcined at 1100℃ for 4h. Using the equal volume impregnation method, a mixed solution of platinum nitrate and palladium nitrate was impregnated onto the cerium aluminum composite oxide after high temperature calcination according to the mass ratio of precious metal to cerium aluminum composite oxide of 3:95. The mixture was then allowed to stand for 10h, dried at 120℃ for 8h, and finally calcined at 550℃ for 2h.

[0041] Pt-Pd / CeO2-Al2O3 and aluminum sol were added to deionized water with a solid content of 30%, stirred evenly to form a slurry, and the slurry was treated by ball milling to control the particle size D 90 At 12μm, it was finally coated on the carrier, quickly dried at 120℃ for 10min, and calcined at 550℃ for 2h.

[0042] Methane oxidation ignition evaluation

[0043] Methane oxidative combustion evaluations were conducted at 250-550°C, starting at 250°C and ramping to 550°C at a rate of 5°C / min. The evaluation atmosphere contained 100 ppm NO, 800 ppm CH4, 1000 ppm CO, 8% O2, 10% H2O, and 7.5% CO2, with N2 as the balance gas. The volumetric space velocity was 60,000 h-1. -1 The outlet product concentration was detected using a Fourier transform infrared spectroscopy (FTIR) analyzer.

[0044] Table 1 Methane oxidation activity evaluation results

[0045]

[0046] From the results in Table 1, it can be seen that compared with the comparative example, the ignition temperature T of the catalyst coated with the active protective layer in Examples 1-3 when catalyzing methane combustion is 50 and 90% conversion temperature T 90 This indicates that the catalysts prepared in Examples 1-3 have better catalytic methane combustion performance.

[0047] Sulfur resistance test

[0048] The catalyst was subjected to a 25h continuous sulfur resistance test at 450°C with 3ppm SO2 added to the methane oxidation ignition evaluation atmosphere. The sulfur resistance test results of the catalysts prepared in Examples 1-3 and the comparative example are shown in Figure 1 As shown, it can be seen that during the 25h continuous sulfur resistance test, the methane oxidation activity of Examples 1-3 decreased significantly less quickly than that of the comparative example, indicating that the active protective layer can significantly improve the sulfur resistance of the catalyst.

[0049] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A methane combustion catalyst with improved sulfur resistance, characterized in that: The invention is applied to a lean-burn natural gas engine exhaust purification system, comprising a substrate and a coating coated on the substrate, wherein the coating comprises a bottom coating and an upper coating, wherein the bottom coating is a methane oxidation active layer, and the components of the bottom coating include precious metals Pt and Pd, a cerium-aluminum composite oxide, and a binder; and the upper coating is an active component protective layer, and the components of the upper coating include Al2O3 or ZrO2, and pseudo-boehmite. The mass ratio of Pt to Pd is 1:5-1:9, and the cerium-aluminum composite oxide is calcined at 1000-1200° C. for 3-6 h.

2. The methane combustion catalyst with improved sulfur resistance according to claim 1, characterized in that: The coating amount of the bottom coating is 80-120 g / L, and the coating amount of the upper coating is 30-50 g / L.

3. The methane combustion catalyst with improved sulfur resistance according to claim 1, characterized in that: The mass fraction of precious metals Pt and Pd in ​​the base coating is 2%-5%, the mass fraction of cerium-aluminum composite oxide is 92%-96%, and the mass fraction of binder is 2%-3% based on the mass of oxides.

4. The methane combustion catalyst with improved sulfur resistance according to claim 1 or 3, characterized in that: The mass fraction of CeO2 in the cerium-aluminum composite oxide is 5%-10%.

5. The methane combustion catalyst with improved sulfur tolerance according to claim 1, characterized in that: The D90 particle size of the bottom coating is in the range of 10-15 μm; the D90 particle size of the upper coating is in the range of 2-5 μm.

6. The methane combustion catalyst with improved sulfur resistance according to claim 1, characterized in that: The binder is aluminum sol.

7. The methane combustion catalyst with improved sulfur resistance according to claim 1, characterized in that: The mass fraction of Al2O3 or ZrO2 in the upper coating is 98%-99%, and the mass fraction of pseudo-boehmite is 1%-2% calculated on the basis of the mass of the oxides.

8. The methane combustion catalyst with improved sulfur resistance according to claim 1, characterized in that: The reaction temperature of the methane combustion catalyst when catalyzing methane combustion is 250-550°C.

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