Sulfur-tolerant methane-poor oxidation noble metal catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalytic oxidation, and particularly relates to a sulfur-tolerant methane-poor oxidation noble metal catalyst as well as a preparation method and application thereof. The sulfur-tolerant methane-poor oxidized noble metal catalyst provided by the invention takes an Ir (at) Pt core-shell structure as an active component and TiO2 as a carrier, and Al2O3 is added as a sulfur-tolerant sacrificial agent in a physical mixing manner, so that the stability of the catalyst is improved. The preparation method of the catalyst comprises the following steps: preparing Ir (at) Pt nano-particles with Ir as a core and Pt as a shell by adopting an epitaxial growth method, uniformly loading the Ir (at) Pt nano-particles on a TiO2 carrier, and then physically grinding and mixing the obtained Ir (at) Pt / TiO2 catalyst and a sacrificial agent Al2O3. The catalyst disclosed by the invention has the advantages of high activity and high stability, has high sulfur-tolerant activity and high sulfur-tolerant stability, can be continuously used for 50 hours without obvious inactivation when being applied to complete oxidation of lean methane, and achieves a good technical effect.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic oxidation, and specifically relates to a sulfur-resistant, methane-poor oxidation noble metal catalyst, a preparation method and an application thereof. Background Art

[0002] As the main component of natural gas and shale gas, methane is a clean energy source with the advantages of high reserves, high calorific value and low carbon emissions. At present, methane is increasingly replacing coal and oil for natural gas vehicles, fuel cells and direct combustion. However, in the process of methane utilization, some trace amounts of methane that are not fully utilized will escape into the atmosphere, causing a serious greenhouse effect. Studies have shown that through catalytic oxidation technology, methane can be converted into CO2, which has a warming potential 23 times weaker, greatly reducing the greenhouse effect caused by it.

[0003] At present, precious metal catalysts have attracted extensive attention due to their excellent methane oxidation activity at low temperatures. However, trace amounts of sulfur-containing gases (H2S and SO2) are inevitably mixed into the natural gas extraction process and the use of natural gas vehicles, which in turn causes the precious metal catalysts to deactivate. Therefore, it is crucial to find a catalyst with high sulfur resistance and stability for lean methane oxidation. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the present invention proposes a sulfur-resistant and poor methane oxidation noble metal catalyst. The catalyst uses an Ir@Pt core-shell structure as an active component, TiO2 as a carrier, and Al2O3 as a sulfur-resistant sacrificial agent is added in a physical mixing manner. The catalyst is used in the reaction of complete oxidation of methane and has high activity and high sulfur resistance stability.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The first aspect of the present invention provides a sulfur-resistant and poor-methane oxidation catalyst, which includes a carrier, an active component loaded on the carrier, and a sacrificial agent added in a physical mixing manner; the active component is metal Ir@Pt core-shell structured nanoparticles, the carrier is TiO2, and the sacrificial agent is Al2O3.

[0007] Preferably, the mass ratio of the metal Ir@Pt core-shell structure nanoparticles to the carrier TiO2 is 0.01-0.04:1.

[0008] Preferably, the mass ratio of the carrier TiO2 to the sacrificial agent Al2O3 is 1:0.3-0.7.

[0009] The second aspect of the present invention provides a method for preparing the sulfur-resistant and low-methane oxidation catalyst according to the first aspect, comprising the following steps:

[0010] S1. Adding a core metal precursor H2IrCl6 and a precipitant to a solution containing a template agent CTAB, and obtaining core metal nanoparticles after standing and centrifuging;

[0011] S2, dissolving the core metal nanoparticles obtained in step S1 in water, adding the shell metal precursor H2PtCl6 and the reducing agent, and mixing to obtain a suspension of Ir@Pt core-shell structure nanoparticles;

[0012] S3, adding carrier TiO2 to the Ir@Pt core-shell structure nanoparticle suspension of S2, evaporating the water and calcining to obtain Ir@Pt / TiO2 catalyst;

[0013] S4. The Ir@Pt / TiO2 catalyst of S3 is mixed with the sacrificial agent Al2O3, ground and then calcined to obtain a sulfur-resistant and poor-methane oxidation catalyst.

[0014] The present invention synthesizes Ir@Pt core-shell structure nanoparticles on a TiO2 carrier by epitaxial growth method, achieving high activity of lean methane oxidation. In addition, the Al2O3 mixed by physical grinding does not change the catalytic performance of the active component, but can be used as a sacrificial agent for adsorbing SO2 to protect the active component, thereby greatly improving the sulfur resistance stability of the catalyst.

[0015] Preferably, the mass ratio of active metal Ir to Pt is 0.3 to 3:1.

[0016] Preferably, the precipitant is NaBH4 and the reducing agent is ascorbic acid (AA).

[0017] Preferably, the solution containing the template agent CTAB is an ethylene glycol solution containing the template agent CTAB, and the concentration is 4-6 mmol / 20 mL.

[0018] Preferably, the calcination in S3 and S4 is carried out in air at 400-700° C. for 1-3 hours.

[0019] Preferably, S1 is prepared into 7-15 mmol·L before adding the core metal precursor H2IrCl6. -1 The volume ratio of the H2IrCl6 solution to the solution containing the template CTAB is 1:3-5.

[0020] The third aspect of the present invention provides use of the sulfur-resistant lean methane oxidation catalyst described in the first aspect in a lean methane oxidation reaction.

[0021] Preferably, the lean methane oxidation reaction is specifically as follows: placing the sulfur-resistant lean methane oxidation catalyst described in the first aspect in a quartz tube, introducing a 10% H2 / Ar mixed gas, and heating at 10°C min -1The temperature was raised to 500℃ for pretreatment for 1h. After cooling to room temperature, the reaction gas was introduced to heat the catalyst from room temperature at a rate of 10℃min -1 The heating rate is raised to the reaction temperature; the reaction gas inlet volume ratio is: CH4 = 0.25% ~ 1%, O2 = (5% ~ 20%), N2 is the reaction balance gas, the catalyst dosage is 0.02 ~ 0.2g, and the total space velocity reaches 30000 ~ 600000mL g -1 ·h -1 , the reaction temperature is 200-600°C, and the reaction pressure is 0.1MPa.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention discloses a sulfur-resistant noble metal catalyst for poor methane oxidation, which uses an Ir@Pt core-shell structure as an active component, TiO2 as a carrier, and adds Al2O3 as a sulfur-resistant sacrificial agent in a physically mixed manner, thereby effectively improving the sulfur-resistant stability of the catalyst. The preparation method of the catalyst is to first prepare Ir@Pt nanoparticles with Ir as a core and Pt as a shell by an epitaxial growth method, and uniformly load the Ir@Pt nanoparticles on a TiO2 carrier, and then physically grind and mix the obtained Ir@Pt / TiO2 catalyst with the sacrificial agent Al2O3. The catalyst of the present invention has the advantages of high activity and high stability, and has high sulfur-resistant activity and high sulfur-resistant stability. It is applied to the complete oxidation of poor methane and can be used continuously for 50 hours without obvious deactivation, achieving good technical effects. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0026] Embodiment 1:

[0027] This embodiment provides a sulfur-resistant and poor-methane oxidation catalyst, which includes an active component, a carrier and a sacrificial agent, wherein the active component is Ir@Pt core-shell structure nanoparticles, the carrier is TiO2, and the sacrificial agent Al2O3 is mixed by physical grinding.

[0028] The preparation method of the sulfur-resistant and poor-methane oxidation catalyst comprises the following steps:

[0029] (1) Add 5 mmol of hexadecyltrimethylammonium bromide into 20 mL of ethylene glycol solution and heat to 60°C to completely dissolve the particles;

[0030] (2) Add 5 mL of 10 mmol·L -1 0.0567 g of chloroiridic acid solution and 0.0567 g of sodium borohydride were allowed to stand for 6 h to obtain a suspension. -1 After centrifugation for 15 min, the obtained particles are Ir nanoparticles;

[0031] (3) Ir nanoparticles (2-10 nm) were dispersed in 200 mL of deionized water, stirred vigorously, and 10 mmol·L -1 chloroplatinic acid aqueous solution, so that the mass ratio of Ir and Pt elements is 3:1;

[0032] (4) adding 5 mL of ascorbic acid aqueous solution dropwise to make the molar ratio of Pt to ascorbic acid be 1:20, and stirring to obtain an Ir@Pt core-shell structure nanoparticle suspension;

[0033] (5) adding a TiO2 carrier to the Ir@Pt core-shell structure nanoparticle suspension so that the mass ratio of the active components (Ir and Pt) to the carrier TiO2 is 0.02:1, drying at 80°C to evaporate the water, and calcining at 500°C in air for 2 h to obtain an Ir@Pt / TiO2 catalyst;

[0034] (6) The Ir@Pt / TiO2 catalyst and the sacrificial agent Al2O3 were ground to make the mass ratio of the carrier TiO2 and the sacrificial agent Al2O3 be 1:1, and then the obtained solid particles were calcined at 500°C in air for 2h to obtain a sulfur-resistant and poor methane oxidation catalyst.

[0035] Embodiment 2:

[0036] This embodiment provides a sulfur-resistant and poor-methane oxidation catalyst, which includes an active component, a carrier and a sacrificial agent, wherein the active component is Ir@Pt core-shell structure nanoparticles, the carrier is TiO2, and the sacrificial agent Al2O3 is mixed by physical grinding.

[0037] The method for preparing the sulfur-resistant and poor-methane oxidation catalyst comprises the following steps:

[0038] (1) Add 5 mmol of hexadecyltrimethylammonium bromide into 20 mL of ethylene glycol solution and heat to 60°C to completely dissolve the particles;

[0039] (2) Add 5 mL of 10 mmol·L -10.0567 g of chloroiridic acid solution and 0.0567 g of sodium borohydride were allowed to stand for 6 h to obtain a suspension. -1 After centrifugation for 15 min, the obtained particles are Ir nanoparticles;

[0040] (3) Ir nanoparticles were dispersed in 200 mL of deionized water, stirred vigorously, and 10 mmol·L -1 chloroplatinic acid aqueous solution, so that the mass ratio of Ir to Pt is 1:1;

[0041] (4) adding 5 mL of ascorbic acid aqueous solution dropwise to make the molar ratio of Pt to ascorbic acid be 1:20, and stirring to obtain an Ir@Pt core-shell structure nanoparticle suspension;

[0042] (5) adding a TiO2 carrier to the Ir@Pt core-shell structure nanoparticle suspension so that the mass ratio of the active component to the carrier TiO2 is 0.02:1, drying at 80°C to evaporate the water, and calcining at 500°C in air for 2 h to obtain an Ir@Pt / TiO2 catalyst;

[0043] (6) The Ir@Pt / TiO2 catalyst and the sacrificial agent Al2O3 were ground to make the mass ratio of the carrier TiO2 and the sacrificial agent Al2O3 be 1:1, and then the obtained solid particles were calcined at 500°C in air for 2h to obtain a sulfur-resistant and poor methane oxidation catalyst.

[0044] Embodiment 3:

[0045] This embodiment provides a sulfur-resistant and poor-methane oxidation catalyst, which includes an active component, a carrier and a sacrificial agent, wherein the active component is Ir@Pt core-shell structure nanoparticles, the carrier is TiO2, and the sacrificial agent Al2O3 is mixed by physical grinding.

[0046] The preparation method of the sulfur-resistant and poor-methane oxidation catalyst comprises the following steps:

[0047] (1) Add 5 mmol of hexadecyltrimethylammonium bromide into 20 mL of ethylene glycol solution and heat to 60°C to completely dissolve the particles;

[0048] (2) Add 5 mL of 10 mmol·L -1 0.0567 g of chloroiridic acid solution and 0.0567 g of sodium borohydride were allowed to stand for 6 h to obtain a suspension. -1 After centrifugation for 15 min, the obtained particles are Ir nanoparticles;

[0049] (3) Ir nanoparticles were dispersed in 200 mL of deionized water, stirred vigorously, and 10 mmol·L -1chloroplatinic acid aqueous solution, so that the mass ratio of Ir to Pt is 1:3;

[0050] (4) adding 5 mL of ascorbic acid aqueous solution dropwise to make the molar ratio of Pt to ascorbic acid be 1:20, and stirring to obtain an Ir@Pt core-shell structure nanoparticle suspension;

[0051] (5) adding a TiO2 carrier to the Ir@Pt core-shell structure nanoparticle suspension so that the mass ratio of the active component to the carrier TiO2 is 0.02:1, drying at 80°C to evaporate the water, and calcining at 500°C in air for 2 h to obtain an Ir@Pt / TiO2 catalyst;

[0052] (6) The Ir@Pt / TiO2 catalyst and the sacrificial agent Al2O3 were ground to make the mass ratio of the carrier TiO2 and the sacrificial agent Al2O3 be 1:1, and then the obtained solid particles were calcined at 500°C in air for 2h to obtain a sulfur-resistant and poor methane oxidation catalyst.

[0053] Comparative Example 1:

[0054] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, step (6) of adding sacrificial agent Al2O3 is omitted, and the remaining steps are the same as those in Example 1 to obtain Ir@Pt / TiO2 catalyst.

[0055] Comparative Example 2:

[0056] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, step (6) of adding sacrificial agent Al2O3 is omitted, and the TiO2 carrier in step (5) is replaced with an Al2O3 carrier, and the rest is the same as Example 1, to obtain an Ir@Pt / Al2O3 catalyst.

[0057] Experimental example: Lean methane oxidation performance test

[0058] First, 10% H2 / Ar was introduced to make the catalyst rise from room temperature at 10℃·min -1 The temperature was raised to 500°C at a rate of 10°C / min and maintained for 1 h. After cooling to room temperature, the reaction gas was introduced and the catalyst was heated from room temperature to room temperature at a rate of 10°C / min. -1 The heating rate is increased to the reaction temperature. The reaction gas inlet volume ratio is: CH4 = 0.25% ~ 1%, O2 = (5% ~ 20%), N2 is the reaction balance gas, some experiments contain 50ppm SO2 or 10ppm SO2, and the total space velocity reaches 30000mL·g -1 ·h -1 or 600000mL·g -1 ·h -1 The catalyst dosage is 0.2 g (corresponding to 30000 mL g -1 ·h -1) or 0.02 g (corresponding to 600000 mL g -1 ·h -1 ), the reaction temperature is 200-600°C, and the reaction pressure is 0.1 MPa. The catalysts obtained in Example 1-3 and Comparative Example 1-2 were heated to 30000 mL·g -1 ·h -1 The lean methane catalytic oxidation reaction was carried out at a space velocity of 1:20:79 (reaction gas was CH4:O2:N2=1:20:79, with or without 50 ppm SO2), and the results are shown in Table 1. The catalysts obtained in Example 1 and Comparative Examples 1-2 were heated to 600000 mL·g -1 ·h -1 The lean methane catalytic oxidation reaction was carried out at a space velocity of (reaction gas was CH4:O2:N2=0.25:5:94.75, with or without 10 ppm SO2), and the results are shown in Table 2.

[0059] As shown in Table 1 and Table 2, the catalyst prepared by the present invention has both high activity and high sulfur resistance stability. When CH4:O2:N2=1:20:79 and the total space velocity reaches 30000 mL·g -1 ·h -1 At 325°C, the conversion rate of methane can reach 90%, and the conversion rate of methane at 350°C is close to 100%. At the same time, the catalyst prepared by the present invention is heated to 500°C with CH4:O2:N2=1:20:79, 50ppm SO2, 30000mL·g -1 ·h -1 When the space velocity of 100000 mL / g was continuously reacted for 50 h, the catalyst activity did not decrease significantly. -1 ·h -1 When the reaction is continued for 12 hours under extreme conditions, the catalyst activity can still be maintained above 80%.

[0060] Table 1 Catalyst at space velocity of 30000 mL g -1 ·h -1 Activity and sulfur resistance performance table

[0061]

[0062] Table 2 Catalyst at space velocity of 600000 mL g -1 ·h -1 Activity and sulfur resistance performance table

[0063]

[0064]

[0065] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A sulfur-tolerant, poor-methane oxidation catalyst, characterized in that: The catalyst comprises a carrier, an active component loaded on the carrier and a sacrificial agent added in a physical mixing manner; the active component is metal Ir@Pt core-shell structure nanoparticles, the carrier is TiO2, and the sacrificial agent is Al2O3.

2. The sulfur-tolerant, poor-methane oxidation catalyst according to claim 1, characterized in that: The mass ratio of the metal Ir@Pt core-shell structure nanoparticles to the carrier TiO2 is 0.01-0.04:

1.

3. The sulfur-tolerant and poor-methane oxidation catalyst according to claim 1, characterized in that: The mass ratio of carrier TiO2 to sacrificial agent Al2O3 is 1:0.3-0.

7.

4. The method for preparing the sulfur-resistant and poor-methane oxidation catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Adding a core metal precursor H2IrCl6 and a precipitant to a solution containing a template agent CTAB, and obtaining core metal nanoparticles after standing and centrifuging; S2, dissolving the core metal nanoparticles obtained in step S1 in water, adding the shell metal precursor H2PtCl6 and the reducing agent, and mixing to obtain a suspension of Ir@Pt core-shell structure nanoparticles; S3, adding carrier TiO2 to the Ir@Pt core-shell structure nanoparticle suspension of S2, evaporating the water and calcining to obtain Ir@Pt / TiO2 catalyst; S4. The Ir@Pt / TiO2 catalyst of S3 is mixed with the sacrificial agent Al2O3, ground and then calcined to obtain a sulfur-resistant and poor-methane oxidation catalyst.

5. The method for preparing the sulfur-resistant and poor-methane oxidation catalyst according to claim 4, characterized in that: The mass ratio of active metal Ir to Pt is 0.3 to 3:

1.

6. The method for preparing the sulfur-resistant and poor-methane oxidation catalyst according to claim 4, characterized in that: The precipitant is NaBH4 and the reducing agent is ascorbic acid.

7. The method for preparing the sulfur-resistant and poor-methane oxidation catalyst according to claim 4, characterized in that: The solution containing the template agent CTAB is an ethylene glycol solution containing the template agent CTAB, and the concentration is 4-6 mmol / 20 mL.

8. The method for preparing the sulfur-resistant and poor-methane oxidation catalyst according to claim 4, characterized in that: The calcinations described in S3 and S4 are both carried out in air at 400-700° C. for 1-3 hours.

9. The method for preparing the sulfur-resistant and poor-methane oxidation catalyst according to claim 4, characterized in that: Before adding the core metal precursor H2IrCl6, S1 was first prepared into 7-15mmol·L -1 The volume ratio of the H2IrCl6 solution to the solution containing the template CTAB is 1:3-5.

10. Use of the sulfur-tolerant lean methane oxidation catalyst according to any one of claims 1 to 3 in lean methane oxidation reactions.

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