High-activity selective oxidation catalyst for carbon monoxide and method for producing the same

Abstract

To provide a high-performance selective oxidation (PROX) catalyst for CO reduction and a method for producing the same.SOLUTION: A method for producing a selective oxidation catalyst, which is a method for producing a selective oxidation (PROX) catalyst for CO removal, comprises a step in which a RuCl3 precursor solution is sprayed onto an α-alumina support to support Ru metal, followed by calcination, and residual chlorides are removed by ion exchange.SELECTED DRAWING: Figure 3a

Description

Technical Field

[0001] The present invention relates to a selective oxidation (PROX) catalyst for high-performance CO reduction and a method for manufacturing the same. More specifically, the present invention relates to a method for manufacturing a PROX catalyst that maintains high dispersibility and active sites of a noble metal Ru having activity in a CO removal reaction and achieves economy and mass productivity, and a PROX catalyst showing high conversion rate and selectivity.

Background Art

[0002] For the purpose of producing electricity by utilizing hydrogen as a transport / power generation fuel cell, a proton-exchange membrane fuel cell (PEMFC) has attracted attention. Therefore, in order to utilize the conventional LNG infrastructure, hydrogen is produced from methane, which is the main component of LNG, through a methane reforming reaction. However, a large amount of CO is generated in this process. The CO generated in the methane reforming reaction acts as CO poisoning on the electrode catalyst (such as Pt / C) in the PEMFC, rapidly reducing the electrode catalyst activity. For this reason, most of the CO is removed through a water-gas shift catalyst reaction after the methane reforming catalyst in the reformer. However, additional CO removal is required to a level of less than several ppm. Therefore, in order to control the final CO content in the feed gas before injection into the fuel cell stack, a selective (Preferential) CO oxidation (Oxidation) (PROX: CO+(1 / 2)O 2 →CO 2 ) catalyst is applied to the final stage of the LNG fuel reformer.

[0003] Patent Document 1 discloses a selective oxidation catalyst for carbon monoxide in a hydrogen-containing gas, which contains 1 wt% or less of an active metal Ru and / or Pt / α-Al 2 O 3A catalyst is disclosed. On the other hand, Patent Document 2 discloses a catalyst for selectively oxidizing carbon monoxide in reformed gas, in which ruthenium and / or platinum is supported on an α-alumina carrier with an alumina purity of 99.95% or more, for a selective oxidation catalyst for CO reduction.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the conventional technology requires a high content of Ru at the 1 wt% level, not only needs a high-purity alumina carrier of 99.95% or more, but also has problems such as improvement in economy due to the price of expensive ruthenium precursors. Therefore, there is still a need for a method for manufacturing an economical PROX catalyst that can achieve high conversion and selectivity even with a low content of Ru by using a low-cost precursor through high dispersion of the active metal.

Means for Solving the Problems

[0006] As a result of research to solve the above problems, the inventors of the present invention have found that when a specific ruthenium precursor is supported on a specific alumina carrier in a specific shape, a selective oxidation catalyst for CO reduction with improved activity and selectivity can be produced even when a low content of Ru at the 0.2 to 1.0 wt% level is supported.

[0007] The method for manufacturing a PROX catalyst according to the present invention is a) a step of producing an α-alumina carrier by heat-treating spherical gamma alumina in the range of 1100 to 1300 °C, and b) RuCl3 Injecting a ruthenium solution in which a precursor is dissolved in an ethanol solvent onto an α-alumina support to support ruthenium in an egg-shell form; c) Firing the supported carrier with ruthenium at 200-400°C; d) Manufacturing a pre-catalyst by completely removing chlorine impurities by stirring the fired ruthenium-supported carrier in an aqueous ammonia solution; e) Manufacturing a final catalyst by reducing the pre-catalyst with hydrogen gas.

[0008] In addition, the PROX catalyst according to the manufacturing method of the present invention is spherical at a diameter level of 2-3 mm, and on an α-alumina support with a specific surface area of less than 10 m 2 / g, ruthenium is supported in the form of an egg-shell with a thickness of 50-300 μm and a uniform form, and chlorine impurities are present at less than 10 ppm.

Advantages of the Invention

[0009] The present invention provides a manufacturing method of an economical PROX catalyst that can achieve high conversion rates and selectivities even with a low content of Ru through the high dispersion of ruthenium. 1. By using a low-cost RuCl 3 precursor and effectively removing the generated Cl ions, the conversion rate can be improved by 5%-15% compared with the conventional manufacturing method using an expensive Ru precursor. 2. While using α-alumina as the support and an ethanol solvent as the active metal coating solution to control the Ru coating shape in the form of an egg-shell and a uniform form, the conversion rate is improved in the PROX reaction at a high space velocity. 3. Even though Ru is supported at a low content, it has similar CO removal performance compared with a catalyst using a high content, but rather, by suppressing side reactions, the selectivity can be improved by 10-70% compared with a high-content catalyst.

Brief Description of the Drawings

[0010]

Figure 1a

Figure 1b

Figure 2

Figure 3a

Figure 3b

Mode for Carrying Out the Invention

[0011] (Definition) In this specification, “%” represents weight percentage unless otherwise specified. In the present invention, the “pre-catalyst” is a catalyst in a state where a carrier supporting a ruthenium active metal is calcined and impurities such as chlorine are removed, and is contrasted with the final catalyst reduced by hydrogen. In this description, “coating” means that a ruthenium precursor is supported on a carrier. For the supported active metal, in the case of the egg-shell form, the concentration of the active metal in the egg-shell region is not constant and gradually decreases from the surface, that is, it can show a concentration gradient. In the case of the uniform form, it can be uniform throughout the carrier or show a concentration gradient that gradually decreases from the surface. The egg-shell form is defined as a form in which more than 90% of the ruthenium distribution exists until it reaches a certain thickness from the surface of the carrier. In this specification, the term “chloride” is used interchangeably with chlorine impurity or chlorine.

[0012] The present inventors designed a catalyst for the selective CO oxidation reaction according to the following criteria. First, Ru was applied as the active metal. This shows high activity compared to Rh, Pt, and Ir in the PROX reaction temperature range of 80 to 120 °C. Also, α-alumina was selected as the carrier because it is advantageous for removing acid sites, maintaining the metallic state of Ru, and dispersing Ru.

[0013] On the other hand, while using RuCl as the ruthenium precursor for cost reduction, the problem of impurities caused by this could be solved by applying an ammonia exchange washing process to complete the present invention. 3 This enabled the completion of the present invention by applying an ammonia exchange washing process to address the impurity issues resulting from this.

[0014] Hereinafter, the method for manufacturing the selective oxidation catalyst for carbon monoxide of the present invention will be described in detail. a) Carrier preparation step Spherical γ-alumina with a specific surface area of 100 m 2 / g or more is heat-treated in the range of 1100 to 1300 °C to prepare an α-alumina carrier with a specific surface area of less than 10 m 2 / g.

[0015] For the PROX reaction with a high space velocity (SV), a carrier with large pores is preferred. However, γ-Al 2 O 3 has many pores and can exhibit a high dispersion effect for Ru metal. However, when the feed gas is supplied to the reactor at a high SV, the air permeability inside the carrier decreases, and the amount of CO removed per unit time may decrease due to a decrease in the CO oxidation reaction activity. On the other hand, the α-alumina carrier is advantageous for coating in the form of a Ru nano layer and for suppressing the methanation reaction mainly occurring in the form of Ru clusters coating. Therefore, through the carrier preparation step, the spherical γ-Al 2 O 3 carrier is heat-treated to induce a phase transformation and pore deformation to α-Al 2 O 3 .

[0016] b) Preparation / coating step of the Ru coating solution To achieve economy and mass productivity, inexpensive RuCl 3 The precursor is dissolved in an ethanol solvent to produce a coating solution, and the coating solution is supported on the α-alumina support produced in a) by a spray injection method at room temperature. A supported layer with an egg-shell structure is formed by the coating solution using ethanol. However, in the case of manufacturing a catalyst with a uniform structure, deionized water (DIW) is used as the solvent instead of ethanol.

[0017] Low-cost RuCl 3 The precursor is used, but an ammonia exchange washing process is introduced to remove chloride, which is an element that reduces the activity of Ru nanoparticles, and low-cost RuCl 3 When using the precursor, the chloride content that may cause problems such as toxicity is reduced to the level of several ppm. On the other hand, in order to realize the egg-shell Ru supported form, an ethanol solvent is applied in the active metal (Ru) coating solution. By selecting ethanol as the solvent, due to its low acid point, it is possible to coat the α-Al 2 O 3 support with an egg-shell form that is advantageous for a high SV, and not only can the supported amount of the active metal (Ru) be reduced, but the low-content Ru catalyst can minimize side reactions such as methanation and RWGS (reverse water gas shift) reactions.

[0018] c) Drying / firing and impurity removal step After ruthenium is supported, it is dried at 100 - 120 °C, fired at 200 - 400 °C, and stirred in an aqueous ammonia solution (4 - 9%) to wash impurities such as chloride, thereby producing a pre-catalyst. The immobilization of ruthenium metal in the support is improved by washing with an aqueous ammonia solution.

[0019] d) Reduction step After washing, the ruthenium / α-alumina oxidation catalyst is reduced using hydrogen gas at 200 to 250 °C to produce the final catalyst.

[0020] The catalyst produced according to the present invention is characterized by high dispersibility, high activity, and low Ru loading. With respect to the total catalyst weight, the Ru loading of the final catalyst is 0.2 to 1.0 wt%, the chlorine impurity content is 0 to 10 ppm, and Ru is supported in an egg-shell or uniform form. In the egg-shell form, Ru is distributed with a thickness of 50 μm to 300 μm from the surface of the support. Also, it shows high CO conversion and selectivity in the PROX reaction under the condition of a space velocity of the feed gas of 3,000 to 10,000 / h.

[0021] Hereinafter, the present invention will be described in more detail with reference to the examples and comparative examples of the present invention, but the present invention is not limited to these examples. Example 1 Support preparation step The spherical γ-alumina support was heat-treated at 1150 °C to prepare an α-alumina support with a bulk density of 0.86 and a specific surface area of 8 m 2 / g level. The phase change of the alumina support was confirmed by XRD analysis (Figure 1a), and the specific surface area was confirmed by BET analysis (Figure 1b).

[0022] Preparation / coating step of Ru coating solution To produce an egg-shell shaped catalyst, ruthenium chloride (RuCl 3 ·xH 2 O) was used as the ruthenium precursor. The ruthenium precursor was dissolved in ethanol, and Ru was supported on the spherical α-alumina support at 0.5 wt% using the pressure injection method.

[0023] Drying / firing step The α-alumina (Ru / α-Al 2 O 3 ) coated with Ru was dried at 120 °C for 12 hours to completely remove the moisture in the catalyst, and then heat-treated at 250 °C for 3 hours in an air atmosphere to fix Ru.

[0024] Ammonia water washing / drying step Heat-treated Ru / α-Al 2 O 3 In order to remove the chlorine component remaining in 2

[0025] Reduction step After heating the preliminary catalyst to 200 °C in a nitrogen atmosphere, rapid reduction was carried out in a hydrogen atmosphere to complete the preliminary catalyst as the final catalyst.

[0026] Example 2 It was carried out in the same manner as in Example 1, except that Ru was supported with a content of 1.0 wt%.

[0027] Example 3 It was carried out in the same manner as in Example 1, except that the ruthenium precursor was dissolved in deionized water (DIW) and coated on the support by a pressure injection method to produce a Uniform-shaped catalyst.

[0028] Comparative Example 1 It was carried out in the same manner as in Example 1, except that a spherical γ-alumina support was used without heat treatment.

[0029] Comparative Example 2 Fired Ru / α-Al 2 O 3 It was carried out in the same manner as in Example 1, except that 2

[0030] Comparative Example 3 A spherical γ-alumina support was used without heat treatment, and 2 2 O 3 It was carried out in the same manner as in Example 1, except that 2

[0031] The catalysts produced in Examples 1 to 2 were confirmed to have less than 1.0 wt% ruthenium and less than 10 ppm chloride ions, and ruthenium was distributed in an egg-shell form inside the carrier. Also, in the catalyst produced in Example 3, ruthenium was distributed in a uniform form. The distributions of Ru and Cl inside the catalysts according to each example and comparative example are shown in Figure 2.

[0032] (Comparison of Shapes) When ruthenium chloride (RuCl 3 ·xH 2 O) is used as the ruthenium precursor and deionized water is applied as the solvent, the distribution of Ru forms a uniform distribution even inside, and when an ethanol solvent is applied, more than 90% of the Ru distribution exists at a depth of 300 μm from the surface, and only 10% or less of the remaining Ru level is distributed inside. When ruthenium chloride (RuCl 3 ·xH 2 O) is used as the ruthenium precursor, if it is not washed with aqueous ammonia after the firing step, chlorides exist throughout the carrier.

[0033] Evaluation method of PROX catalyst For the catalysts produced in the examples and comparative examples, the performance was evaluated as follows. To measure the catalytic activity, the PROX reaction was carried out using a process simulation gas. The reactor was evaluated using a fixed-bed reaction system. The catalyst was filled with 23 ml in a tubular reactor, and the catalyst was reduced for 1 hour while flowing hydrogen gas at a constant rate of 10 cc / min to remove oxygen on the catalyst surface before the reaction. Then, after maintaining the temperature of the reactor at 100 °C constantly, the feed gas, which is the raw material used in the reaction, was continuously supplied to the reactor at a constant rate of 8,800 / hr. The reaction pressure was evaluated under atmospheric pressure conditions. The substances produced after the reaction were quantitatively analyzed by FT-IR (Fourier Transform Infrared Spectroscopy) through an injection line.

[0034] Composition of the feed gas: H 2 O: 10%, CO: 0.6%, CO 2: 18%, O 2 : 0.9%, H 2 : 65%, N 2 : balance (O 2 / CO ratio: 1.5), GHSV: 8,800 / hr The activities of these catalysts were compared by calculating the conversion rate and selectivity of CO gas with respect to the reactants according to the following criteria. CO conversion rate (%) = [moles of CO input before reaction - moles of CO remaining after reaction] / [moles of CO input before reaction] × 100 CO selectivity (%) = [moles of CO input before reaction - moles of CO remaining after reaction - CH 4 moles of generation] / [moles of CO input before reaction] × 100 Figure 3a shows the CO conversion rate & selectivity, and Figure 3b shows the amount of CO remaining after the reaction.

[0035] (Comparison of efficiency) The PROX catalyst produced by the production method according to the present invention shows sufficient conversion rate even with a low content of Ru supported at 1.0 wt% or less. Rather, as the Ru content increases, Ru clusters that promote side reactions (methanation reaction) are generated, resulting in a higher selectivity for Ru-supported catalysts with a lower content compared to this (comparison between Example 1 (0.5 wt%) and Example 2 (1.0 wt%)). When RuCl 3 is used as the ruthenium precursor, the catalyst that has not been washed with aqueous ammonia after the calcination step has a large residual amount of impurities (Cl), which reduces the activity of Ru and promotes side reactions, causing a decrease in selectivity (comparison between Example 1 and Comparative Example 2). Also, when deionized water is applied instead of ethanol as the solvent for the ruthenium precursor, the Ru distribution in the catalyst is uniformly generated, which can cause a decrease in conversion rate and selectivity under high SV conditions compared to an egg-shell coating catalyst in which most of the Ru is distributed on the surface of the catalyst. However, it still shows good activity under low SV conditions in the range of GHSV 3,000 to 10,000 (comparison between Example 1 and Example 3).

Claims

1. 1. A method for producing a selective oxidation (PROX) catalyst for reducing CO, comprising: RuCl ３ The precursor solution is sprayed onto an α-alumina support to support Ru metal, followed by calcination, and then removing residual chloride by ion exchange. A method for producing a selective oxidation catalyst comprising the steps of:

2. RuCl ３ The precursor solution was RuCl ３ The precursor is dissolved in ethanol. A method for producing the selective oxidation catalyst according to claim 1.

3. Ru metal is supported on the α-alumina support in an eggshell or uniform form. A method for producing the selective oxidation catalyst according to claim 1.

4. Residual chloride is removed by ion exchange in aqueous ammonia. A method for producing the selective oxidation catalyst according to claim 1.

5. As a selective oxidation (PROX) catalyst for reducing CO, Ru metal is supported on the surface of an α-alumina support in an egg-shell or uniform form with a coating thickness of 50 to 300 μm. A selective oxidation catalyst comprising:

6. The amount of Ru metal supported is 0.2 to 1.0 wt % based on the total catalyst weight. The selective oxidation catalyst according to claim 5.

7. Chloride is present at less than 10 ppm The selective oxidation catalyst according to claim 5.

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