Palladium-based catalyst as well as preparation method and application thereof

Abstract

The invention provides a palladium-based catalyst and a preparation method and application thereof, and belongs to the technical field of methane catalytic combustion. The preparation method comprises the following steps: firstly, dispersing palladium salt and a silicon-containing compound in a solvent to prepare a precursor solution; the precursor solution is sprayed into flames through jet flow atomization for a combustion reaction, then calcination treatment is carried out, and the palladium-based catalyst is obtained. The palladium-based catalyst is prepared by adopting a flame spray pyrolysis method, the high-dispersion and anti-sintering palladium-based catalyst is obtained by optimizing the composition of a precursor solution and flame spray pyrolysis process parameters, and the catalyst shows excellent activity and stability in catalytic combustion of low-concentration methane, and has a good application prospect. The catalyst is suitable for catalytic combustion reaction of low-concentration methane in coal mine ventilation air methane.

Description

Technical Field

[0001] This invention relates to the field of methane catalytic combustion technology, and in particular to a palladium-based catalyst, its preparation method, and its application. Background Technology

[0002] Methane has a greenhouse effect more than 28 times that of carbon dioxide. Methane emissions from coal mine exhaust gas account for about 70% of total methane emissions during coal mining, and more than 9% of global methane emissions. Methane emissions from coal mine exhaust gas are characterized by low concentration (usually below 1%), large total amount, strong persistence, and wide distribution, making it difficult to directly recover methane using traditional gas utilization technologies, and thus posing a high challenge for control.

[0003] Methane catalytic combustion is a reaction process that achieves efficient methane oxidation at relatively low temperatures (300–600°C) using a catalyst. Its characteristics include: low ignition temperature (saving energy compared to direct combustion), high reaction selectivity (products are mainly CO2 and H2O, reducing byproduct formation), and applicability to low-concentration methane (suitable for treating low-concentration gas sources such as exhaust gas). The high CH bond energy of methane leads to its structural stability, and the catalytic oxidation of methane generally requires high activation temperatures. Patent CN103191733A discloses a low-concentration methane catalytic combustion catalyst and its preparation method, which can achieve efficient methane removal. Noble metal materials have been extensively studied due to their excellent low-temperature catalytic performance. Palladium-based catalysts are currently recognized as having the best activity for methane catalytic combustion; however, existing palladium-based catalysts suffer from high-temperature sintering. Therefore, synthesizing catalysts that combine good low-temperature catalytic activity and stability is one of the core directions for low-concentration gas treatment. Summary of the Invention

[0004] The purpose of this invention is to provide a palladium-based catalyst, its preparation method, and its application, so as to solve the problem of deactivation of palladium-based catalysts in the catalytic combustion of low-concentration methane in the prior art.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a palladium-based catalyst, comprising the following steps:

[0007] (1) Palladium salt and silicon-containing compound are dispersed in a solvent to prepare a precursor solution;

[0008] (2) The precursor solution is sprayed into a flame through jet atomization for combustion reaction, and then calcined to obtain a palladium-based catalyst.

[0009] Preferably, in step (1), the palladium salt comprises palladium acetylacetonate or palladium acetate; and the silicon-containing compound comprises one or more of tetraethyl silicate, hexamethyldisiloxane, and triethoxyzinc silane.

[0010] Preferably, the solvent comprises one or more of toluene, ethanol, xylene, and acetylacetone.

[0011] Preferably, the mass ratio of the palladium salt to the silicon-containing compound is 0.01–0.05:2–8.

[0012] Preferably, the total concentration of the precursor solution is 0.1–0.6 mol / L.

[0013] Preferably, in step (2), the gas flow rate of the jet atomization is 3 to 10 L / min.

[0014] Preferably, in step (2), the temperature of the flame is 1000-2000℃; the temperature of the calcination treatment is 400-600℃; and the calcination treatment time is 1-3h.

[0015] This invention provides a palladium-based catalyst prepared by the method described above.

[0016] This invention provides an application of the palladium-based catalyst described above in the catalytic combustion reaction of methane.

[0017] Preferably, the concentration of methane is 0.1–0.5 vol.%; and the temperature of the catalytic combustion reaction is 200–600 °C.

[0018] The beneficial effects of this invention are:

[0019] This invention enables the one-step production of palladium-based catalysts via flame spray pyrolysis, eliminating the need for cumbersome post-processing. This is primarily due to the high-temperature preparation atmosphere, where the high-temperature flame ensures complete combustion and decomposition of the precursor solution, and the intense combustion environment promotes uniform mixing of metal ions.

[0020] This invention uses flame spray pyrolysis to prepare palladium-based catalysts. By optimizing the composition of the precursor solution and the flame spray pyrolysis process parameters, a highly dispersed palladium-based catalyst with anti-sintering properties is obtained. This catalyst exhibits excellent low-temperature catalytic activity and stability in the catalytic combustion of low-concentration methane and is suitable for the catalytic combustion reaction of low-concentration methane in coal mine exhaust gas. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the flame spray pyrolysis apparatus used in this invention;

[0022] Figure 2This is a high-angle annular dark-field scanning transmission electron microscope image of the palladium-based catalyst in Example 1;

[0023] Figure 3 The graph shows the stability test results of the palladium-based catalyst for methane catalytic combustion in Example 3.

[0024] Figure 4 The graph shows the stability test results of the Pd / CeO2 catalyst for methane catalytic combustion in Comparative Example 1. Detailed Implementation

[0025] This invention provides a method for preparing a palladium-based catalyst, comprising the following steps:

[0026] (1) Palladium salt and silicon-containing compound are dispersed in a solvent to prepare a precursor solution;

[0027] (2) The precursor solution is sprayed into a flame through jet atomization for combustion reaction, and then calcined to obtain a palladium-based catalyst.

[0028] In this invention, in step (1), the palladium salt comprises palladium acetylacetonate or palladium acetate, preferably palladium acetylacetonate; the silicon-containing compound comprises one or more of tetraethyl silicate, hexamethyldisiloxane and triethoxyzinc silane, preferably tetraethyl silicate or hexamethyldisiloxane.

[0029] In this invention, the solvent comprises one or more of toluene, ethanol, xylene and acetylacetone, preferably toluene, ethanol or xylene.

[0030] In this invention, the mass ratio of the palladium salt to the silicon-containing compound is 0.01-0.05:2-8, preferably 0.02-0.04:2.4357-7, and more preferably 0.0258-0.03:2.4357-6.2499.

[0031] In this invention, the total concentration of the precursor solution is 0.1 to 0.6 mol / L, preferably 0.2 to 0.5 mol / L, and more preferably 0.3 to 0.4 mol / L.

[0032] In this invention, the precursor solution is preferably injected into the capillary via an injection pump, wherein the flow rate of the injection pump is 1 to 8 mL / min, preferably 2 to 6 mL / min, and more preferably 3 to 5 mL / min.

[0033] In this invention, in step (2), the gas flow rate of the jet atomization is 3 to 10 L / min, preferably 4 to 8 L / min, and even more preferably 5 to 7 L / min, wherein oxygen is used as the dispersion gas in the jet atomization.

[0034] In this invention, in step (2), the temperature of the flame is 1000-2000℃, preferably 1200-1800℃, and more preferably 1500℃; the temperature of the calcination treatment is 400-600℃, preferably 450-550℃, and more preferably 500℃; and the calcination treatment time is 1-3h, preferably 1.5-2.5h, and more preferably 2h.

[0035] This invention provides a palladium-based catalyst prepared by the method described above.

[0036] This invention provides an application of the palladium-based catalyst described above in the catalytic combustion reaction of methane.

[0037] In this invention, the concentration of methane is 0.1–0.5 vol.%, preferably 0.2–0.4 vol.%; the temperature of the catalytic combustion reaction is 200–600°C, preferably 300–500°C, and more preferably 370–400°C.

[0038] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1

[0040] 0.0258 g of palladium acetylacetone and 6.2499 g of tetraethyl silicate were added to a 100 mL volumetric flask, and the volume was adjusted to 100 mL with xylene. The mixture was sonicated for 30 min to obtain a precursor solution with a total concentration of 0.3 mol / L.

[0041] A premixed gas consisting of CH4 and O2 was ignited, with a CH4 flow rate of 0.7 L / min and an O2 flow rate of 1.4 L / min, forming a stable supported flame at a temperature of 1500 °C. The prepared precursor solution was injected into the capillary tube from the center of the burner at a flow rate of 3 mL / min using a syringe pump. The precursor was dispersed and broken into fine droplets by a dispersing gas of O2 at a flow rate of 5.0 L / min. These droplets were ignited by the supported flame to form a high-temperature turbulent flame, during which metal ions reacted. The resulting catalyst was collected by filtration through glass fiber cloth under the action of a water circulation pump. After preparation, the collected catalyst was calcined in a muffle furnace at 500 °C for 2 h to obtain a palladium-based catalyst, designated Pd / SiO2-1 catalyst, with a palladium loading of 0.5 wt.%.

[0042] The Pd / SiO2-1 catalyst was used for methane catalytic combustion tests under the following conditions: 0.4 vol.% CH4, 4 vol.% O2, and the remainder N2, with a space velocity of 60,000 h⁻¹. -1 Methane catalytic combustion T90 =400℃.

[0043] from Figure 2 It can be seen that in the flame-sprayed Pd / SiO2-1 catalyst, Pd is supported on the SiO2 support in the form of single atoms, exhibiting good catalytic activity.

[0044] Example 2

[0045] Add 0.0258 g of palladium acetylacetone and 6.2499 g of tetraethyl silicate to a 100 mL volumetric flask, bring the volume to 100 mL with anhydrous ethanol, and sonicate for 30 min to obtain a precursor solution with a total concentration of 0.3 mol / L.

[0046] A premixed gas consisting of CH4 and O2 was ignited, with a CH4 flow rate of 0.7 L / min and an O2 flow rate of 1.4 L / min, forming a stable supported flame at a temperature of 1000 °C. The prepared precursor solution was injected into the capillary tube from the center of the burner at a flow rate of 3 mL / min using a syringe pump. The precursor was dispersed and broken into fine droplets by a dispersing gas of O2 at a flow rate of 5.0 L / min. These droplets were ignited by the supported flame to form a high-temperature turbulent flame, during which metal ions reacted. The resulting catalyst was collected by filtration through glass fiber cloth under the action of a water circulation pump. After preparation, the collected catalyst was calcined in a muffle furnace at 500 °C for 2 h to obtain a palladium-based catalyst, designated as Pd / SiO2-2 catalyst, with a palladium loading of 0.5 wt.%.

[0047] The Pd / SiO2-2 catalyst was used for methane catalytic combustion tests under the following conditions: 0.4 vol.% CH4, 4 vol.% O2, and the remainder N2, with a space velocity of 60,000 h⁻¹. -1 Methane catalytic combustion T 90 =400℃.

[0048] Example 3

[0049] 0.0258 g of palladium acetylacetone and 2.4357 g of hexamethyldisiloxane were added to a 100 mL volumetric flask, and the volume was adjusted to 100 mL with xylene. The mixture was sonicated for 30 min to obtain a precursor solution with a total concentration of 0.3 mol / L.

[0050] A premixed gas consisting of CH4 and O2 was ignited, with a CH4 flow rate of 0.7 L / min and an O2 flow rate of 1.4 L / min, forming a stable supported flame at a temperature of 2000 °C. The prepared precursor solution was injected into the capillary tube from the center of the burner at a flow rate of 3 mL / min using a syringe pump. The precursor was dispersed and broken into fine droplets by a dispersing gas of O2 at a flow rate of 5.0 L / min. These droplets were ignited by the supported flame to form a high-temperature turbulent flame, during which metal ions reacted. The resulting catalyst was collected by filtration through a glass fiber cloth under the action of a water circulation pump. After preparation, the collected catalyst was calcined in a muffle furnace at 500 °C for 2 h to obtain a palladium-based catalyst, designated as Pd / SiO2-3 catalyst, with a palladium loading of 0.5 wt.%.

[0051] The Pd / SiO2-3 catalyst was used for methane catalytic combustion tests under the following conditions: 0.4 vol.% CH4, 4 vol.% O2, and the remainder N2, with a space velocity of 60,000 h⁻¹. -1 Methane catalytic combustion T 90 =390℃.

[0052] from Figure 3 It can be seen that after continuous operation at 370℃ for 300 hours, the activity of the Pd / SiO2-3 catalyst decreases by less than 1%.

[0053] Example 4

[0054] 0.0258 g of palladium acetylacetone and 2.4357 g of hexamethyldisiloxane were added to a 100 mL volumetric flask, and the volume was adjusted to 100 mL with anhydrous ethanol. The mixture was sonicated for 30 min to obtain a precursor solution with a total concentration of 0.3 mol / L.

[0055] A premixed gas consisting of CH4 and O2 was ignited, with a CH4 flow rate of 0.7 L / min and an O2 flow rate of 1.4 L / min, forming a stable supported flame at a temperature of 1800 °C. The prepared precursor solution was injected into the capillary tube from the center of the burner at a flow rate of 3 mL / min using a syringe pump. The precursor was dispersed and broken into fine droplets by a dispersing gas of O2 at a flow rate of 5.0 L / min. These droplets were ignited by the supported flame to form a high-temperature turbulent flame, during which metal ions reacted. The resulting catalyst was collected by filtration through glass fiber cloth under the action of a water circulation pump. After preparation, the collected catalyst was calcined in a muffle furnace at 500 °C for 2 h to obtain a palladium-based catalyst, designated Pd / SiO2-4 catalyst, with a palladium loading of 0.5 wt.%.

[0056] The Pd / SiO2-4 catalyst was used for methane catalytic combustion tests under the following conditions: 0.4 vol.% CH4, 4 vol.% O2, and the remainder N2, with a space velocity of 60,000 h⁻¹. -1 Methane catalytic combustion T 90 =370℃.

[0057] Comparative Example 1

[0058] 0.0746 g of palladium acetylacetone and 34.8814 g of cerium 2-ethylhexanoate were added to a 100 mL volumetric flask, and the volume was adjusted to 100 mL with anhydrous ethanol. The mixture was sonicated for 30 min to obtain a precursor solution with a total concentration of 0.3 mol / L.

[0059] A premixed gas consisting of CH4 and O2 was ignited, with a CH4 flow rate of 0.7 L / min and an O2 flow rate of 1.4 L / min, forming a stable supported flame at a temperature of 1800 °C. The prepared precursor solution was injected into the capillary tube from the center of the burner at a flow rate of 3 mL / min using a syringe pump. The precursor was dispersed and broken into fine droplets by a dispersing gas of O2 at a flow rate of 5.0 L / min. These droplets were ignited by the supported flame to form a high-temperature turbulent flame, during which metal ions reacted. The resulting catalyst was collected by filtration through a glass fiber cloth under the action of a water circulation pump. After preparation, the collected catalyst was calcined in a muffle furnace at 500 °C for 2 h to obtain a palladium-based catalyst, designated as the Pd / CeO2 catalyst, with a palladium loading of 0.5 wt.%.

[0060] The Pd / CeO2 catalyst was used for methane catalytic combustion tests under the following conditions: 0.4 vol.% CH4, 4 vol.% O2, and the remainder N2, with a space velocity of 60,000 h⁻¹. -1 Methane catalytic combustion T 90 =450℃.

[0061] from Figure 4 It can be seen that after continuous operation at 370℃ for 55 hours, the activity of the Pd / CeO2 catalyst decreases by more than 20%.

[0062] Comparative Example 2

[0063] 0.0574 g of palladium acetylacetone and 14.6296 g of zirconium acetylacetone were added to a 100 mL volumetric flask, and the volume was adjusted to 100 mL with xylene. The mixture was sonicated for 30 min to obtain a precursor solution with a total concentration of 0.3 mol / L.

[0064] A premixed gas consisting of CH4 and O2 was ignited, with a CH4 flow rate of 0.7 L / min and an O2 flow rate of 1.4 L / min, forming a stable supported flame at a temperature of 1800 °C. The prepared precursor solution was injected into the capillary tube from the center of the burner at a flow rate of 3 mL / min using a syringe pump. The precursor was dispersed and broken into fine droplets by a dispersing gas of O2 at a flow rate of 5.0 L / min. These droplets were ignited by the supported flame to form a high-temperature turbulent flame, during which metal ions reacted. The resulting catalyst was collected by filtration through a glass fiber cloth under the action of a water circulation pump. After preparation, the collected catalyst was calcined in a muffle furnace at 500 °C for 2 h to obtain a palladium-based catalyst, designated as the Pd / ZrO2 catalyst, with a palladium loading of 0.5 wt.%.

[0065] The Pd / ZrO2 catalyst was used for methane catalytic combustion tests under the following conditions: 0.4 vol.% CH4, 4 vol.% O2, and the remainder N2, with a space velocity of 60,000 h⁻¹. -1 Methane catalytic combustion T 90 =500℃.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a palladium-based catalyst, characterized in that, Includes the following steps: (1) Palladium salt and silicon-containing compound are dispersed in a solvent to prepare a precursor solution; (2) The precursor solution is sprayed into a flame through jet atomization for combustion reaction, and then calcined to obtain a palladium-based catalyst.

2. The method for preparing the palladium-based catalyst according to claim 1, characterized in that, In step (1), the palladium salt comprises palladium acetylacetonate or palladium acetate; the silicon-containing compound comprises one or more of tetraethyl silicate, hexamethyldisiloxane and triethoxyzinc silane.

3. The method for preparing the palladium-based catalyst according to claim 1 or 2, characterized in that, The solvent comprises one or more of toluene, ethanol, xylene, and acetylacetone.

4. The method for preparing the palladium-based catalyst according to claim 3, characterized in that, The mass ratio of the palladium salt to the silicon-containing compound is 0.01–0.05:2–8.

5. The method for preparing the palladium-based catalyst according to claim 2 or 4, characterized in that, The total concentration of the precursor solution is 0.1–0.6 mol / L.

6. The method for preparing the palladium-based catalyst according to claim 5, characterized in that, In step (2), the gas flow rate of the jet atomization is 3 to 10 L / min.

7. The method for preparing the palladium-based catalyst according to claim 2, 4, or 6, characterized in that, In step (2), the temperature of the flame is 1000-2000℃; the temperature of the calcination treatment is 400-600℃, and the calcination treatment time is 1-3h.

8. A palladium-based catalyst prepared by the method of any one of claims 1 to 7.

9. The application of the palladium-based catalyst according to claim 8 in the catalytic combustion reaction of methane.

10. The application of the palladium-based catalyst according to claim 9 in the catalytic combustion reaction of methane, characterized in that, The concentration of methane is 0.1–0.5 vol.%; the temperature of the catalytic combustion reaction is 200–600 °C.

Images