Water gas shift catalyst composition and preparation method thereof

Abstract

To provide a low-temperature water gas shift catalyst composition; a preparation method thereof; and a method for converting carbon monoxide and water into hydrogen and carbon dioxide at low temperatures by using the catalyst.SOLUTION: A water gas shift reaction catalyst according to the present invention is a Cu / Zn / Al catalyst, which does not have a hydrotalcite-like or Aurichalcite crystal structure. The water gas shift reaction catalyst furthest reduces the formation of a specific crystal structure which is unfavorable for the dispersion of active metals, and has high catalyst activity and durability in the low-temperature field at 200°C to 300°C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a low-temperature aqueous gas conversion catalyst composition, a method for producing the same, and a method for converting carbon monoxide and water into hydrogen and carbon dioxide by reaction at low temperature using the catalyst.

Background Art

[0002] When an LNG fuel reforming system is applied as a technology for providing hydrogen, which is a fuel for a fuel cell, if carbon monoxide (CO) in the composition of the mixed gas produced in the fuel reforming system flows in at a concentration equal to or higher than the reference concentration of the fuel cell, the fuel cell electrode catalyst is poisoned and its activity decreases. In the worst case, it leads to a permanent performance degradation. Therefore, the performance and stability of an aqueous gas conversion catalyst for the purpose of CO removal in a fuel reforming system are important. Water-gas shift reaction: CO + H 2 O → CO 2 + H 2 (ΔH = -41 kJ / h) As a catalyst applied to a low-temperature aqueous gas conversion reaction at 200 to 300°C, which is carried out to remove a small amount of carbon monoxide, a Cu / Zn / Al-based catalyst is known.

[0003] Patent Document 1: International Patent Application Publication Gazette WO2020 / 080775 discloses a method for manufacturing a medium-temperature aqueous gas shift reaction catalyst for producing hydrogen gas from carbon monoxide. Specifically, a copper-zinc coprecipitation step of mixing a metal precursor solution containing a copper (Cu) precursor and a zinc (Zn) precursor with a precipitant solution to form a copper-zinc coprecipitate, and an aluminum (Al) precursor solution is injected into the solution containing the copper-zinc coprecipitate to precipitate aluminum on the surface of the copper-zinc coprecipitate to produce a CuZnAl catalyst precursor having an aluminum-rich layer on the surface. An Al precipitation step, and a firing step of firing the CuZnAl catalyst precursor to produce a CuZnAl catalyst are included, and a method for manufacturing an aqueous gas shift reaction catalyst is disclosed. Further, Patent Document 2: International Patent Application Publication Gazette WO2022 / 069854 discloses a copper-containing catalyst method for aqueous gas shift reaction and methanol synthesis. Specifically, it is a method by two-step coprecipitation, including (a) a step of combining a first basic precipitant solution and an acidic copper-containing solution in a first precipitation step for forming a first precipitate, and (b) a second precipitation step for forming a second precipitate. A step of combining a second basic precipitant solution with an acidic aluminum-containing solution containing one or more metal compounds selected from a copper compound, a zinc compound, and an accelerator compound, and (c) a step of contacting the first precipitate and the second precipitate in a mixing step for forming a catalyst precursor, and (d) a step of washing, drying, and firing the catalyst precursor are included, and a copper-containing catalyst method in which a silica precursor is included in the first precipitation step, the second precipitation step, or the mixing step is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional Cu / Zn / Al ternary catalyst, there was a problem that the Al content was proportional to the catalyst durability but inversely proportional to the catalyst performance. In the experiments for improving the CuZnAl catalyst performance, while searching for the cause of the decrease in catalyst performance accompanying the increase in the Al content during the CuZnAl catalyst production process, the inventors confirmed that if the Al content was reduced and the formation of a CuZnAl catalyst precursor with a specific crystal structure was suppressed, it was possible to produce a catalyst with excellent catalyst performance while ensuring the durability of the catalyst.

[0006] Specifically, it was confirmed that the problem of the decrease in catalyst performance caused by the increase in the Al content added for improving the durability of the CuZnAl catalyst was due to the formation of a precursor with a hydrotalcite-like structure. The inventor established a method for producing a CuZnAl catalyst in which the formation of the hydrotalcite-like precursor was not formed or minimized, and completed the present invention.

Means for Solving the Problems

[0007] The present invention relates to a Cu / Zn / Al-based catalyst for the water gas shift reaction, which is a Cu / Zn / Al-based catalyst having no hydrotalcite-like or Aurichalcite crystal structure.

[0008] The present invention relates to a Cu / Zn / Al-based catalyst for the water gas shift reaction, which is a Cu / Zn / Al-based catalyst having a Rosasite and Malachite crystal structure.

[0009] The present invention relates to a method for producing a water gas shift catalyst for minimizing the formation of a precursor with a hydrotalcite-like or Aurichalcite crystal structure and maximizing the formation of a precursor with a Rosasite and Malachite crystal structure, and particularly for maximizing the production of Rosasite.

[0010] Finally, the present invention provides a method for producing hydrogen at a low temperature by reacting the catalyst of the present invention or the catalyst produced by the method of the present invention with a mixed gas for the water gas shift reaction.

Advantages of the Invention

[0011] The water gas shift reaction catalyst according to the present invention has high catalytic activity and durability in the low temperature range of 200 to 300 °C by minimizing the formation of a specific crystal structure that is disadvantageous to the dispersion of the active metal.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. (Definitions)

[0014] The term "coprecipitation" used in the present invention is also described as "precipitation", and the "precursor" means a precipitated substance in the stage before the formation of the completed catalyst in the form of metal oxide. In the present invention, the term "catalyst" has the same meaning as "catalyst composition". In this specification, the metal ratio is the ratio of each metal oxide constituting the catalyst, that is, CuO:ZnO:Al 2 O 3means the weight ratio, and can be simply expressed as Cu:Zn:Al.

[0015] In the process of manufacturing the CuZnAl catalyst, depending on the composition of the starting metals / precipitation and aging temperature / pH of the coprecipitation solution, etc., the crystal structures of the precursors that can form Cu / Zn / Al are different, as exemplified in Table 1.

[0016]

Table 1

[0017] The inventors of the present invention have found that a hydrotalcite-like or Aurichalcite structure, which is a specific crystal structure of the precursor formed in the process of manufacturing a low-temperature aqueous gas shift catalyst, is a structure that hinders catalytic activity. In particular, the hydrotalcite-like structure is the most avoidable precursor in the process of manufacturing the CuZnAl catalyst, and the Rosasite or Malachite structure is favorable for catalytic activity. In particular, it has been confirmed that the Rosasite structure (Figure 1) is the most favorable structure for catalytic activity.

[0018] The present invention presents a method for manufacturing a CuZnAl catalyst in which precursors of a hydrotalcite-like or Aurichalcite structure are minimally generated and precursors of a Rosasite structure are generated at a high ratio. The catalyst manufactured according to the present invention exhibits high stability and activity in the low-temperature aqueous gas shift reaction.

[0019] The method for manufacturing the Cu / Zn / Al catalyst according to the present invention is achieved by a specific (specfic) precipitation (coprecipitation) process of injecting Cu, Zn, and Al solutions and a precipitant and a subsequent specific aging process so that precursors of the Rosasite crystal structure are maximally formed.

[0020] Specifically, Cu, Zn, and Al solutions as starting materials form an amorphous precursor through a precipitation process, and the precursor crystallizes into a specific structure through an ageing process. The crystalline precursor is completed into a catalyst in the form of metal oxide through a calcination process, and the catalyst is activated through a reduction process. The inventor has developed a method for producing a CuZnAl catalyst that minimizes the formation of precursors of hydrotalcite-like or Aurichalcite, which are crystal structures that hinder catalytic activity, while maximizing the formation of precursors of Rosasite, which is a crystal structure advantageous for catalytic activity, through a specific precipitation process and a specific ageing process in which Cu, Zn, and Al solutions and a precipitating agent are injected.

[0021] Figure 2 shows the XRD patterns of a catalyst (improved catalyst) produced by a manufacturing method that suppresses the formation of a hydrotalcite-like precursor and a catalyst (conventional catalyst) produced by a conventional coprecipitation method. As a result of performance evaluation, it can be seen that the CO conversion rate of the improved catalyst is 94.84%, which is significantly higher than the CO conversion rate of 89.72% of the conventional catalyst.

[0022] The CuZnAl catalyst produced according to the present invention uses Cu, Zn, and Al solutions as starting precursors. The inventors coprecipitate the starting precursors in one step to form an amorphous precursor and convert it into a crystalline precursor through an ageing process. By controlling the coprecipitation and ageing processes, the formation of precursors of hydrotalcite-like or Aurichalcite, which are crystal structures that hinder catalytic activity, is minimized, and the formation of precursors of Rosasite, which is a crystal structure advantageous for catalytic activity, is maximized.

[0023] The method for manufacturing the aqueous gas shift catalyst of the present invention includes a coprecipitation step of mixing a metal precursor solution containing a Cu precursor, a Zn precursor, and an Al precursor with a precipitant solution to coprecipitate copper, zinc, and aluminum to form a CuZnAl catalyst precursor, a step of aging the CuZnAl catalyst precursor to minimize the formation of precursors of hydrotalcite-like or aurichalcite and maximize the formation of precursors of roezite, and a firing step of firing the CuZnAl catalyst precursor to produce a CuZnAl catalyst.

[0024] 1) One-step coprecipitation step of Cu, Zn, and Al

[0025] The Cu, Zn, Al coprecipitation step is to inject the Cu precursor, Zn precursor, and Al precursor into the precipitant solution to produce a precipitate in one step. By preparing a Cu precursor solution, a Zn precursor solution, and an Al precursor solution and injecting the solutions containing these metal precursors into the solution containing the precipitant, Cu, Zn, and Al are precipitated. The coprecipitation process is maintained at around pH 7.5 at 50 - 70°C for 2 to 5 hours.

[0026] The Cu precursor, Zn precursor, or Al precursor can be respective nitrates, acetates, or other water-soluble compounds or salts, but metal precursors of nitrates without catalyst toxicity are preferred.

[0027] The optimal concentration of the solution containing the metal precursor is 1.2M, but it can be adjusted considering factors such as the solution maintenance state. Each of the Cu / Zn / Al precursors can be introduced so that the weight ratio of CuO:ZnO:Al of the catalyst is the optimal 62:31:7, that is, the optimal molar ratio of the Cu:Zn:Al precursors is 60:30:10, but it can be adjusted considering the activity and stability of the finished catalyst. 2 O 3 The weight ratio of the catalyst is the optimal 62:31:7, that is, the optimal molar ratio of the Cu:Zn:Al precursors is 60:30:10, but it can be adjusted considering the activity and stability of the finished catalyst.

[0028] It is preferably basic as a precipitant, for example, it contains carbonates or bicarbonates of alkali metals or ammonium. The concentration of the precipitant is preferably about 1.0 M in order to achieve a pH of 7.5 after injecting the metal precursor.

[0029] 2) Aging step

[0030] A solution containing a copper-zinc-aluminum co-precipitate is synthesized and maintained at the same temperature as in the co-precipitation step for 2 to 5 hours, minimizing the formation of precursors of hydrotalcite-like or aurichalcite, which are crystal structures that hinder catalytic activity, and maximizing the formation of precursors of rosasite, which is a crystal structure advantageous for catalytic activity. The formation of precursors of these specific structures is confirmed by XRD.

[0031] Optionally, after completion of aging, the reaction system is cooled to room temperature, and a filtration and washing step is performed to remove unnecessary ions except for the CuZnAl catalyst precursor obtained through the aging process. The CuZnAl catalyst precursor is put into distilled water, stirred to dilute the unnecessary ions remaining in the precipitate, and the precipitate is recovered through a filtration device. Such a process is repeated several times. Then, in order to remove the moisture of the CuZnAl catalyst precursor, it can be dried in an oven at 120°C or higher and 180°C or lower.

[0032] 3) Calcination step

[0033] This is a step for transforming the catalyst into an oxide form before activation, and it is calcined at 300 to 400°C, but the calcination temperature can be adjusted considering catalytic activity and stability.

[0034] Hereinafter, the present invention will be described more specifically by specific examples. The following examples are merely illustrative for helping to understand the present invention, and the scope of the present invention is not limited thereto.

[0035] Example 1 Solution manufacturing step

[0036] Dissolve the Cu / Zn / Al nitrate precursor in water to prepare a 1.25 M Cu / Zn / Al precursor solution. For each of the Cu / Zn / Al precursors, the CuO:ZnO:Al of the prepared catalyst 2 O 3 was charged so that the weight ratio was 62:31:7. For the precipitation of metal ions, Na, a basic precipitating agent 2 CO 3 was used to prepare an aqueous solution of about 1.0 M.

[0037] Precipitation step

[0038] First, put a certain amount of distilled water into the coprecipitation reactor and heat it to 60 °C. After heating, simultaneously inject the Cu / Zn / Al precursor solution and the Na 2 CO 3 precipitating agent solution into the coprecipitation reactor. Adjust the input flow rate of the Cu / Zn / Al precursor solution so that the total input time is 4 hours, and adjust the flow rate of the precipitating agent so that the pH in the reactor is maintained at 7.5 and then input. At this time, the temperature was maintained at 60 °C.

[0039] Aging step After the input of the Cu / Zn / Al solution is completed, aging is carried out. The aging was carried out for 4 hours while maintaining the same temperature as the initial coprecipitation reactor, which was 60 °C.

[0040] Washing and filtration step After aging, filtration and washing are carried out to remove other ions except the Cu / Zn / Al precipitate.

[0041] Drying step This is the step of removing the moisture of the filtered precipitate, which is carried out at 120 - 180 °C. The Cu / Zn / Al-based precursor analysis was carried out on the dried product at 120 °C.

[0042] Firing step

[0043] The firing step is a step of transforming a hydroxycarbonate-based precursor into the form of a metal oxide, and it was carried out at 350 °C in an oxygen atmosphere.

[0044] Example 2 It was carried out in the same manner as in Example 1, except that the aging time was set to 2 hours. Example 3 It was carried out in the same manner as in Example 2, except that the charging time in the precipitation step was set to 2 hours. Example 4 It was carried out in the same manner as in Example 1, except that the precipitation-maintaining pH in the precipitation step was set to 8.5. Example 5 It was carried out in the same manner as in Example 4, except that the aging time was set to 2 hours. Example 6 CuO:ZnO:Al 2 O 3 It was carried out in the same manner as in Example 1, except that CuO:ZnO:Al Example 7 CuO:ZnO:Al 2 O 3 It was carried out in the same manner as in Example 1, except that CuO:ZnO:Al

[0045] Comparative Example 1 CuO:ZnO:Al 2 O 3 It was carried out in the same manner as in Example 1, except that CuO:ZnO:Al Comparative Example 2 CuO:ZnO:Al 2 O 3 It was carried out in the same manner as in Example 1, except that CuO:ZnO:Al Comparative Example 3 CuO:ZnO:Al 2 O 3 It was carried out in the same manner as in Example 2, except that CuO:ZnO:Al Comparative Example 4 CuO:ZnO:Al 2 O 3 It was carried out in the same manner as in Example 4, except that CuO:ZnO:Al Comparative Example 5 CuO:ZnO:Al 2 O 3 Except for 43.5:43.5:13, it was carried out in the same manner as in Example 1.

[0046] The crystal structures and CO conversion rates of the catalysts synthesized in the examples and comparative examples are summarized in Table 2 and shown in Figure 3. Based on the CO conversion rate of the precursor composition of Example 1, Examples 2 to 7 and Comparative Examples 1 to 5 were compared. In the case of the CO conversion rate, H 2 0.4751, CO 0.1272, CO 2 0.0174, H 2 O 0.3804 with a GHSV of 4500 h -1 , and the reaction was carried out under the conditions of a reaction temperature of 200 °C. The ratio of the crystal structure was quantified using the Rietveld refinement method. In this specification, the ratio of the precursor indicates the ratio of each precursor to the total amount of four types of precursors, namely, the majority of the crystal structures formed in the catalyst manufacturing process, malachite, rosasite, aurichalcite, and hydrotalcite-like precursors. Example 1 is the optimal condition according to the present invention. Hereinafter, the process for designing the optimal condition will be described.

[0047] In Examples 1 to 3, the catalysts were manufactured by adjusting the charging time and aging time with the same composition. However, the shorter the total coprecipitation time, that is, the charging time and the aging time, the higher the ratio of the hydrotalcite-like precursor and malachite, and the lower the ratio of rosasite. After the metal ions are precipitated by the precipitating agent and receive appropriate energy, they can be structurally changed or converted into other forms of metal precursors. According to Examples 1 to 3, as aging progresses, the hydrotalcite-like precursor and malachite are decomposed / rearranged, and a structural change to rosasite is confirmed.

[0048] In Examples 1, 2, 4, and 5, catalysts were produced by adjusting the pH during precipitation to 8.5 with the same composition. In Example 4, the formation of aurichalcite, which is an OH-rich species, could be confirmed due to the influence of a higher pH compared to Example 1. Comparing Example 4 and Example 5, it could be confirmed that malachite was changed to rosasite during aging and was partially changed to aurichalcite after 2 hours of aging. Also, comparing Example 2 and Example 5, it could be confirmed that at a higher pH, the change to rosasite is relatively less smooth.

[0049] In Examples 1, 6, and 7, catalysts were produced by adjusting the composition ratio of Cu:Zn:Al. In Example 6, the production amounts of hydrotalcite-like precursor and malachite increased compared to Example 1. In Example 7, the ratio of the hydrotalcite-like precursor decreased, but the ratio of aurichalcite increased.

[0050] In Comparative Examples 1 and 3, the ratio of alumina was adjusted while maintaining the ratio of Cu:Zn at the same level as 2:1 compared to Example 1. When the ratio of alumina was low, the formation of the hydrotalcite-like precursor was suppressed and the production ratio of rosasite was high, so it showed high initial activity. However, since the alumina content was low and ultimately the catalyst durability decreased, high catalyst deactivation was shown during the reaction. Conversely, when the ratio of alumina was high, the formation of the hydrotalcite-like precursor was promoted and the formation of rosasite, which is advantageous for the dispersion of copper particles, was suppressed, showing low activity.

[0051] In Examples 7 and Comparative Examples 2 and 5, while maintaining the Cu:Zn ratio at 1:1, the ratio of alumina was adjusted. In the case of Comparative Example 2 with a lower alumina ratio than the normal alumina ratio, the formation of the hydrotalcite-like precursor was suppressed at a low alumina content, resulting in an increased production ratio of Rosasite and Aurichalcite and showing high initial activity, but ultimately showing high deactivation at a low alumina content. In Comparative Example 5, as the alumina content increased, the production ratio of the hydrotalcite-like precursor increased, thereby showing low activity.

[0052] Comparative Example 4 is a catalyst produced under the conditions of a composition with a Cu:Zn ratio of 1:1 and a pH of 8.5. Due to the high pH conditions favorable for the formation of Aurichalcite, it showed a very high Aurichalcite production ratio and a very low Rosasite production ratio. It showed high initial activity according to the excessive Aurichalcite content, but ultimately a low conversion rate could be confirmed due to catalyst deactivation.

[0053] Comparative Example 5 is a catalyst produced under the conditions of a composition with a Cu:Zn ratio of 1:1 and a high alumina ratio. It was possible to confirm the formation of the hydrotalcite-like precursor due to the high alumina ratio, and thereby it was possible to confirm that no Aurichalcite was formed. It showed a low CO conversion rate with a relatively high ratio of the hydrotalcite-like precursor and a low ratio of Rosasite.

[0054] When examining the catalytic activities according to the examples and comparative examples of the present invention, the catalyst derived from Rosasite exhibits high activity. The catalyst derived from Aurichalcite shows high activity at the initial stage of the reaction, but the activity decreases as the reaction progresses, and as a result, the catalyst shows relatively low activity. On the other hand, since the catalyst derived from Malachite shows medium activity and deactivation, it was confirmed that Cu ions that do not form Rosasite are most advantageous for forming Malachite. The hydrotalcite-like precursor generally consists only of Zn and Al, and the catalyst derived from the precursor forms the precursor without affecting the dispersion degree of Cu, but it is judged that it becomes difficult to form Rosasite, which is advantageous for activity, because Zn ions are consumed.

[0055] Therefore, the inventors, similar to Example 1, set the ratio of Cu:Zn to 2:1, the alumina to 7% by weight ratio, the pH for maintaining the coprecipitation reaction to 7.5, and the aging time to 4 hours, minimizing the formation of the hydrotalcite-like precursor and Aurichalcite, and maximizing the formation of Rosasite, and were able to produce a catalyst showing a high CO conversion rate and low initial catalyst deactivation.

[0056]

Table 2

Claims

1. A Cu / Zn / Al catalyst for the water gas shift reaction that does not have a hydrotalcite-like or aurichalcite crystal structure A Cu / Zn / Al catalyst characterized in that

2. Cu / Zn / Al catalyst for water gas shift reaction, having only Rosasite and Malachite crystal structures A Cu / Zn / Al catalyst characterized in that

3. A Cu / Zn / Al catalyst for the water gas shift reaction, having 65% or more of Rosasite crystal structure A Cu / Zn / Al catalyst characterized in that

4. The ratio of Cu:Zn:Al is 1:0.5 to 1:0.08 to 0.

11. The Cu / Zn / Al catalyst according to any one of claims 1 to 3.

5. A method for preparing a water gas shift catalyst for minimizing the formation of precursors with hydrotalcite-like or aurichalcite crystal structures and maximizing the formation of precursors with rosasite and malachite crystal structures, the method comprising the steps of: mixing a metal precursor solution containing a Cu precursor, a Zn precursor, and an Al precursor with a precipitant solution to co-precipitate copper, zinc, and aluminum to produce a CuZnAl catalyst precursor; aging the precipitated CuZnAl catalyst precursor; and forming the aged CuZnAl catalyst precursor. A method for producing a water gas shift catalyst comprising the steps of:

6. The co-precipitation step is carried out for 2-5 hours at a temperature of 50-70° C. and maintained at a pH of around 7.

5. A method for producing the water gas shift catalyst according to claim 5.

7. The aging step is maintained at a temperature of 50-70° C. for 2-5 hours. A method for producing the water gas shift catalyst according to claim 5 or 6.

8. providing a catalyst according to any one of claims 1 to 3 or a catalyst produced by the method according to claim 5 to carry out a water gas shift reaction. A method for producing hydrogen.

9. The water gas shift reaction is carried out at a reaction temperature of 200 to 300° C. The method for producing hydrogen according to claim 8.

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