Preparation method of catalyst comprising a ruthenium-containing catalyst layer formed on the body surface

Abstract

The present invention relates to a method for preparing a catalyst comprising a ruthenium-containing catalyst layer highly dispersed with a uniform thickness on a surface of a substrate having a structure, which comprises first aging a mixed solution of a ruthenium precursor-containing solution and a precipitating agent to form a ruthenium-containing precipitate seeds, secondarily aging the first aged mixed solution to grow the seeds thereby forming ruthenium-containing precipitate particles, and then contacting the particles with a substrate to deposit the particles on the surface of the substrate. Since the catalyst has a structure in which the round shaped ruthenium-containing precipitate particles are piled to form the ruthenium-containing catalyst layer, it has a large specific surface area. Thus, the catalyst may exhibit excellent catalytic performance in various reactions for producing hydrogen using a ruthenium catalyst.

Claims

1. A method of preparing a catalyst comprising a ruthenium-containing catalyst layer formed on a surface of a substrate having a structure, which comprises: adding a precipitating agent to a ruthenium (Ru) precursor-containing solution to obtain a mixed solution (step 1); first aging the mixed solution of the step 1 at 10 C. to 40 C. to form ruthenium-containing precipitate seeds (step 2); secondarily aging the first aged mixed solution at 80 C. to 100 C. to grow the ruthenium-containing precipitate seeds, thereby forming ruthenium-containing precipitate particles (step 3); contacting the secondarily aged mixed solution with the substrate to coat the surface of the substrate with the ruthenium-containing precipitate particles, thereby inducing the formation of a ruthenium-containing layer (step 4); and conducting a heat treatment of the ruthenium-containing layer (step 5).

2. The method of claim 1, wherein the step 2 and the step 3 are performed in order.

3. The method of claim 1, wherein the ruthenium (Ru) precursor-containing solution further comprises a precursor of platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Tr), osmium (Os) or a mixed metal thereof.

4. The method of claim 1, wherein the precipitating agent is ammonia, KOH, NaOH, urea, Na.sub.2CO.sub.3, K.sub.2CO.sub.3 or a mixture thereof.

5. The method of claim 1, wherein the mixed solution in the step 1 has a pH of 6 to 11.

6. The method of claim 1, wherein the first aging is performed with stirring.

7. The method of claim 1, wherein the first aging is performed for 3 h to 48 h.

8. The method of claim 1, wherein the secondary aging is performed for 36 h to 100 h.

9. The method of claim 1, wherein the substrate consists of a FeCr alloy, SiC, Al, an Al alloy, Ti, a Ti alloy or stainless steel.

10. The method of claim 1, wherein the substrate has a structure of monolith, foam, felt, mat, mesh, foil or pin.

11. A method of preparing a catalyst comprising a ruthenium-containing catalyst layer formed on a surface of a substrate having a structure, which comprises: Adding a precipitating agent to a ruthenium (Ru) precursor-containing solution to obtain a mixed solution (step 1); first aging the mixed solution of the step 1 at 10 C. to 40 C. to form ruthenium-containing precipitate seeds (step 2); introducing a substrate to the first aged mixed solution (step 3); secondarily aging the first aged mixed solution at 80 C. to 100 C. to grow the ruthenium-containing precipitate seeds, thereby forming ruthenium-containing precipitate particles (step 4), whereby the ruthenium-containing precipitate particles are formed and simultaneously coated on the surface of the substrate; conducting a heat treatment of the ruthenium-containing layer (step 5).

12. A method of forming a ruthenium-containing layer on a surface of a substrate having a structure, which comprises: adding a precipitating agent to a ruthenium (Ru) precursor-containing solution to obtain a mixed solution (step 1); first aging the mixed solution of the step 1 at 10 C. to 40 C. to form ruthenium-containing precipitate seeds (step 2); secondarily aging the first aged mixed solution at 80 C. to 100 C. to grow the ruthenium-containing precipitate seeds, thereby forming ruthenium-containing precipitate particles (step 3); and contacting the secondarily aged mixed solution with the substrate to coat the surface of the substrate with the ruthenium-containing precipitate particles, thereby inducing the formation of a ruthenium-containing layer (step 4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram illustrating the process of forming the ruthenium-containing layer on the surface of the substrate according to the present invention.

(2) FIG. 2 shows the results of analyzing the surface and cross section (SEM, ion-milling analysis) of FeCr alloys prepared by varying pH of the precursor solution.

(3) FIG. 3 shows SEM images of FeCr alloy surfaces coated with Ru, which are prepared by an impregnation method or a precipitation method under various conditions. Sample 5 is one Ru-supported by the impregnation method and Samples 6 to 8 are those prepared from Ru precursor solutions having various concentrations.

(4) FIG. 4 shows SEM images of FeCr alloy cross sections coated with Ru, which are prepared under various aging conditions.

(5) FIG. 5 shows the performance evaluation results of Ru/Al.sub.2O.sub.3 pellet catalyst vs. Ru/Al.sub.2O.sub.3 coated FeCr alloy monolith catalyst.

(6) FIG. 6 shows the performance evaluation results of Ru/Al.sub.2O.sub.3 pellet catalyst vs. Ru/Al.sub.2O.sub.3 coated SiC monolith catalyst.

(7) FIG. 7 shows the performance evaluation results of Ru/Al.sub.2O.sub.3 pellet catalyst vs. Ru/Al.sub.2O.sub.3 coated FeCr alloy monolith catalyst.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(8) Hereinafter, the present invention will be explained in detail through the following examples. However, these examples are intended to illustrate the present invention, but not to limit the scope thereof.

Example 1: Analysis of Ruthenium Coating Layer Depending on pH of Precipitation Reaction Solution of Ruthenium Precursor

(9) First, in the same manner as Korean Patent No. 1019234, a surface of an FeCr alloy foil, a metal substrate of a ferrochrome alloy material, was electrochemically treated at 5 V for 30 min and then heat-treated at 900 C. for 6 h to prepare the metal substrate for ruthenium coating wherein an alumina layer is uniformly formed as a carrier on the surface thereof.

(10) Ruthenium nitrosyl nitrate as a ruthenium precursor was mixed with distilled water to give a solution in the concentration of 230 mM. Different amounts of ammonia solution as a precipitating agent were added to the above solution to prepare Samples 1 to 4 having a pH of 6, 7, 8 and 11, respectively. After each of the solutions thus obtained was first aged by stirring at room temperature (25 C.) for 24 h, the FeCr alloy foil, a substrate as prepared above, was immersed in the above aged solution and secondarily aged at 100 C. for 48 h.

(11) Surfaces of the FeCr alloy foils prepared by a different pH and by a different amount of precipitating agent added to the ruthenium precursor solution were analyzed by a scanning electron microscope (SEM). The results are shown in FIG. 2. From FIG. 2, it can be confirmed that the deposition morphology of particles on the surface of the FeCr alloy foil was varied depending on the pH change of the reaction solution. In particular, the round shaped particles, i.e., the spherical particles, were formed much more in Sample 2.

(12) Furthermore, from the cross section ion milling analysis, the thickness of the catalyst layer coated on the metal foil surface was measured. Sample 2 showed the thickest coating layer, whereas the other samples showed a relatively thin coating layer of about 1 m. In the case of the reaction solutions having a pH of lower than 7 (Sample 1 of pH 6) or a pH of higher than 8.5 (Sample 4 of pH 11), coating on the surface of the substrate was not performed well due to the slow formation of Ru particles. However, if the time of forming the Ru particles and coating, i.e., the time of secondary aging, was kept long, the Ru coating was made on the FeCr alloy foil surface. In other words, in the case of Samples 1 and 4, the surface of the substrate was not coated well with Ru during the initial period of the secondary aging, but coated with the lapse of aging time.

(13) Thus, it was found that particle size and shape may be controlled by pH adjustment of the precipitation reaction solution, and accordingly the thickness of the coated Ru layer may be controlled.

(14) Also, composition of the FeCr alloy surface coated with Ru was analyzed by EDS (energy-dispersive X-ray spectroscopy). The results are summarized in Table 1 below.

(15) TABLE-US-00001 TABLE 1 Sample 1 2 3 4 pH of Reaction 6 7 8 11 Solution Al (At. %) 37.8 6.5 32.3 40.0 Cr (At. %) 0.2 0.3 0.3 Fe (At. %) 0.6 0.8 0.6 0.7 Ru (At. %) 1.1 16.7 5.9 0.8 O (At. %) 60.3 76.0 60.9 58.2

(16) From the above Table 1, it can be seen that the Ru content is highest in Sample 2.

(17) Thus, it can be confirmed that the content of Ru coated can be controlled by pH adjustment of the precipitation reaction solution.

(18) According to the results of FIG. 2 and Table 1, it can also be confirmed that a pH of 7 to 8 of the solution obtained by adding the precipitating agent to the ruthenium precursor solution is desirable in aspects of the size and shape of Ru particles thus formed as well as the thickness of the Ru coating layer and the Ru content.

Comparative Example 1: Analysis of Ruthenium Coating Layer Depending on Impregnation Method and Single Step Aging Method

(19) The same substrate as Example 1 was used.

(20) Ruthenium nitrosyl nitrate as the ruthenium precursor was mixed with distilled water to prepare a ruthenium precursor solution of the desired concentration.

(21) Ru was supported according to the impregnation method in Sample 5. Specifically, Sample 5 was prepared by immersing the substrate as above into 300 mM of the ruthenium precursor solution and then drying at 90 C.

(22) Samples 6 to 8 were prepared with different concentrations of Ru precursor solutions according to the process of adding an ammonia solution as a precipitating agent to each of the Ru precursor solutions to adjust the pH to 11, immersing the substrate into this solution, and aging it at 90 C. for 64 h to make the Ru coating.

(23) The composition of the sample surface prepared above was analyzed by EDS. The results are summarized in Table 2 below.

(24) TABLE-US-00002 TABLE 2 Sample 5 6 7 8 Concentration of 300 mM 300 mM 500 mM 1000 mM precursor solution Al (At. %) 33.01 37.32 31.97 29.20 Cr (At. %) 0.68 0.22 0.43 0.83 Fe (At. %) 1.47 0.55 0.77 1.74 Ru (At. %) 1.78 0.26 0.35 0.53 O (At. %) 63.05 61.65 66.47 67.70

(25) Comparing Tables 1 and 2, it can be seen that Samples 2 and 3 prepared according to the present invention have a greater content of Ru coating than Sample 5 prepared by the impregnation method. In Samples 6 to 8, which are obtained by directly immersing the FeCr alloy foil substrate without the first aging, and by coating with forming the Ru precipitate in one aging step, the amount of Ru coated increases as the concentration of the precursor solution increases. However, Sample 8, prepared by using 1000 mM of the Ru precursor solution (4-fold higher concentration of the precursor solution), showed a Ru coating amount of only 66% under the same condition of pH 11, in comparison to Sample 4, prepared by the two aging steps according to the present invention using 230 mM of the Ru precursor solution. Thus, the method of performing the first aging prior to the immersion of FeCr alloy foil substrate and then the secondary aging with the immersion of the substrate as in the present invention has been confirmed to make the highly dispersed immersion of Ru metal on the surface of the substrate easier than the method of a single aging step.

(26) Furthermore, the FeCr alloy foil surfaces of Samples 5 to 8 coated with Ru were analyzed by SEM. The results are shown in FIG. 3.

(27) As shown in FIG. 3, Sample 5 prepared by the impregnation method has many cracks on the surface thereof despite that it was merely dried at 90 C. This indicates that the active metal Ru is not stably coated (deposited) or supported. In this case, the Ru layer may be easily peeled off during the calcination or reaction so as not to exhibit stable catalytic activity. It was also confirmed that the alumina layer on the FeCr alloy surface is filled as the concentration of ruthenium precursor solution increases in Samples 6 to 8.

Example 2: Analysis of Ruthenium Coating Layer Depending on the Aging Condition

(28) Among the aging conditions, the time of the first aging and the temperature of the secondary aging were changed, and then the amount of Ru coated and the thickness of coating layer were measured, respectively.

(29) In Samples 9 and 10, the precursor-containing precipitation reaction solutions of pH 7 were first aged at room temperature (25 C.) with stirring for 6 h and 12 h, respectively, whereas the secondary aging time was fixed to 48 h at 100 C.

(30) In Samples 11 and 12, the precursor-containing precipitation reaction solutions of pH 7 were first aged at room temperature (25 C.) with stirring for a fixed time of 24 h, whereas the secondary aging was performed at 80 C. and 90 C., respectively, for 48 h.

(31) The FeCr alloy foils coated with Ru, prepared by changing the stirring time and temperature, were ion-milled and cross sections thereof were analyzed, and SEM images are shown in FIG. 4.

(32) From FIG. 4, it was confirmed that the thickness of the Ru coating layer increases as the stirring time and temperature increase. Furthermore, the Ru particle size thus formed further increases.

Experiment: Performance Evaluation of Structured Catalyst

(33) The surface of the substrate of various materials (FeCr alloy, SiC) was coated with Ru highly dispersed according to the two step aging method of the present invention, and the performance of the structured catalyst thus obtained was then evaluated. The structured catalyst was applied to the steam reforming reaction of natural gas as a typical hydrogen producing reaction (Experiments 1 and 2) and to the preferential oxidation of CO for removing CO from synthetic gas (Experiment 3).

Experiment 1: Performance Evaluation of Ru/Al2O3 Pellet Catalyst Vs. Ru/Al2O3 Coated FeCr Alloy Monolith Catalyst

(34) A Ru coating layer was formed on the surface of FeCr alloy monolith on which an alumina carrier was formed in advance according to the same procedure as Sample 2 of Example 1, except that the substrate had a monolith form, not a foil form.

(35) Catalyst performance evaluation on the steam reforming reaction of natural gas was carried out against the above-obtained FeCr alloy monolith catalyst on which the Ru coating layer was formed (Ru/Al.sub.2O.sub.3 coated FeCr alloy monolith catalyst) under the following experimental conditions. Prior to the catalyst performance evaluation, the catalyst was reduced under a hydrogen atmosphere at 700 C. for 3 h.

(36) For comparison, the Ru/Al.sub.2O.sub.3 pellet catalyst was also reduced under the same conditions and subjected to the catalyst performance evaluation under the following experimental conditions. Here, the Ru/Al.sub.2O.sub.3 pellet catalyst was obtained from Clariant Co. (Switzerland).

(37) The Ru metal loading in the pellet catalyst and the monolith catalyst was 0.14 g and 0.038 g, respectively.

(38) Experimental condition: Steam/Carbon (S/C)=3.0, Temperature=700 C., Normal Pressure

(39) The results are shown in FIG. 5 below. From FIG. 5, it was confirmed that the FeCr alloy monolith catalyst shows very excellent catalytic activity, i.e., high CH.sub.4 conversion, in the steam reforming reaction of natural gas even though a smaller amount of Ru metal is loaded therein than in the pellet catalyst.

(40) This result suggests that when the structured catalyst of the present invention having a small amount of Ru metal coated in a highly dispersed manner is used instead of the conventional pellet catalyst in the hydrogen producing reactor and system, reduced reactor size and cost savings can be achieved.

Experiment 2: Performance Evaluation of Ru/Al2O3 Pellet Catalyst Vs. Ru/Al2O3 Coated SiC Monolith Catalyst

(41) A Ru coating layer was formed on the surface of SiC monolith on which an alumina carrier was formed in advance according to the same procedure as Sample 2 of Example 1, except that a monolith of non-oxide SiC ceramics was used as a substrate.

(42) Catalyst performance evaluation on the steam reforming reaction of natural gas was carried out against the above-obtained SiC monolith catalyst on which the Ru coating layer was formed (Ru/Al.sub.2O.sub.3 coated SiC monolith catalyst) under the following experimental conditions. Prior to the catalyst performance evaluation, the catalyst was reduced under a hydrogen atmosphere at 700 C. for 3 h.

(43) For comparison, the Ru/Al.sub.2O.sub.3 pellet catalyst was also reduced under the same conditions and subjected to the catalyst performance evaluation under the following experimental conditions. Here, the Ru/Al.sub.2O.sub.3 pellet catalyst was obtained from Clariant Co. (Switzerland).

(44) The Ru metal loading in the pellet catalyst and the monolith catalyst was 0.14 g and 0.083 g, respectively.

(45) Experimental condition: Steam/Carbon (S/C)=3.0, F/W=314-530 L/g.sub.Ru.Math.h, Temperature=550 C. to 700 C., Normal Pressure (GHSV was converted to F/W by applying the catalyst weight)

(46) The results are shown in FIG. 6 below. From FIG. 6, it was confirmed that the SiC monolith catalyst shows very excellent catalytic activity, i.e., high CH.sub.4 conversion, in the steam reforming reaction of natural gas even though a smaller amount of Ru metal is loaded therein than in the pellet catalyst.

(47) In addition, the result of FIG. 6 suggests that a small amount of Ru (active metal) can be supported on the surface of the substrate in a highly dispersed manner regardless of the kind of monolith, and the catalyst of the present invention shows better catalytic activity than the conventional pellet catalyst.

Experiment 3: Performance Evaluation of Ru/Al2O3 Pellet Catalyst Vs. Ru/Al2O3 Coated FeCr Alloy Monolith Catalyst

(48) A small amount of Ru was coated on FeCr alloy monolith, and performance thereof was evaluated in the preferential oxidation of CO.

(49) A Ru coating layer was formed on the surface of FeCr alloy monolith on which an alumina carrier was formed in advance according to the same procedure as Sample 2 of Example 1, except that 57 mM of the Ru precursor solution was used.

(50) Catalyst performance evaluation on the preferential oxidation of CO was carried out against the above-obtained FeCr alloy monolith catalyst on which the Ru coating layer was formed (Ru/Al.sub.2O.sub.3 coated FeCr alloy monolith catalyst) under the following experimental conditions. Prior to the catalyst performance evaluation, the catalyst was reduced under a hydrogen atmosphere at 200 C. for 2 h.

(51) For comparison, the Ru/Al.sub.2O.sub.3 pellet catalyst was also reduced under the same conditions and subjected to the catalyst performance evaluation under the following experimental conditions. Here, the Ru/Al.sub.2O.sub.3 pellet catalyst was obtained from Tanaka Precious Metals International Inc. (Japan).

(52) The Ru metal loading in the pellet catalyst and the monolith catalyst was the same, 0.014 g.

(53) Experimental condition: 59% H.sub.2, 0.61% CO, 0.61% O.sub.2, 16% CO.sub.2, 19% H.sub.2O, N.sub.2 bal., =2, F/W=2,755 L/g.sub.Ru.Math.h, Normal Pressure

(54) The results are shown in FIG. 7 below. From FIG. 7, it was confirmed that the monolith catalyst of the present invention shows remarkably high CO conversion and selectivity for CO.sub.2 compared to the pellet catalyst at a low temperature of 140 C. or lower.