Patent Application
20250222437
The present application claims priority to Korean Patent Application No. 10-2024-0001904, filed on Jan. 5, 2024, the entire contents of which are incorporated herein for all purposes by this reference.
The present disclosure discloses a catalyst with a perovskite structure, a method for manufacturing the same, and a dry reforming method using the same.
Dry reforming of methane is a promising route to convert carbon dioxide and methane into valuable synthesis gas (syn gas), which can be further converted into other useful chemicals or fuels. The commercialization success of this dry reforming process largely depends on the development of effective catalysts that can promote the desired reactions while suppressing undesirable reactions.
Dry reforming catalysts offer several attractive advantages for industrial applications. First, the dry reforming process can effectively convert carbon dioxide and methane into syn gas, which can be used as a feedstock for chemical and fuel production. Second, it is more environmentally friendly than the conventional steam reforming process because it can help reduce greenhouse gas emissions by utilizing carbon dioxide as a feedstock. Third, unlike the conventional steam reforming process, the dry reforming process does not use water, so it is energy efficient because the process of heating water and supplying it as steam can be eliminated. In particular, when applied to fuel cell power generation, the dry reforming process is an environmentally friendly reforming method that can produce hydrogen without using water even in water-scarce countries such as the Middle East and produce/supply water as a byproduct.
As such, dry reforming catalysts have many potential advantages, but they also have some disadvantages to consider. First, the biggest problem with dry reforming catalysts is that they are prone to deactivation due to carbon deposition, sintering, and other factors, which can reduce catalyst activity and selectivity, and require frequent catalyst regeneration or replacement, which reduces industrial productivity. Second, the performance of dry reforming catalysts is easily affected by impurities in the feedstock, such as sulfur, halides, and other contaminants, which contaminate the catalyst and cause a decrease in activity, selectivity, and stability of the catalysts. Third, some precious metal-based dry reforming catalysts have high material costs, which may limit their practicality for large-scale industrial applications. Therefore, it is necessary to minimize the use of precious metal materials and improve the catalyst life to reduce the catalyst cost required for the dry reforming process.
Conventionally known dry reforming catalysts can be largely classified into conventional metal-based catalysts and non-metal-based catalysts. In particular, metal-based catalysts such as nickel and cobalt have been extensively studied and used in the past, but they have several disadvantages such as carbon deposition, deactivation, and low selectivity. Recently, non-metal-based catalysts such as ceria-based material have emerged as promising alternative catalyst materials due to their high oxygen storage capacity and redox properties. However, the biggest problems of dry reforming catalysts, such as carbon deposition and decreased thermal stability, are fundamental causes that make demonstration operations for hundreds of hours or more impossible. Accordingly, despite various modifications to the strategy, such as transition metal doping and morphology control, basic data for more than 1,000 hours for commercialization have not yet been secured.
Dry reforming catalysts have made significant progress in recent years and offer several strengths and advantages for industrial applications. The development of effective and sustainable catalysts can enable the utilization of waste carbon dioxide streams and diversify feedstock options for chemical and fuel production. Therefore, dry reforming, which is a representative Carbon Capture Utilization & Storage (CCUS) technology that utilizes carbon dioxide, requires additional research and development to overcome the above-described problems in order to optimize catalyst performance and improve process stability and efficiency.
In one aspect, an object of the present disclosure is to provide a catalyst with a perovskite structure that has excellent catalytic activity and effects of suppressing carbon deposition and enhancing thermal stability.
In another aspect, an object of the present disclosure is to provide a method for manufacturing the catalyst with the perovskite structure.
In another aspect, an object of the present disclosure is to provide a dry reforming method using the catalyst with the perovskite structure.
In one aspect, the present disclosure provides a catalyst with a perovskite structure, which is represented by Chemical Formula 1, and includes Ru nanoparticle exsoluted onto a surface of the catalyst.
A1-yA′yTi1-xRuxO3 [Chemical Formula 1]
In the Chemical Formula 1, A is Sr, Ca, or a combination thereof, A′ is La, Y, or a combination thereof, x is greater than 0 and less than or equal to 0.5, and y is greater than 0 and less than 1.0.
In an exemplary embodiment, the catalyst may be a single phase homogeneous catalyst represented by the Chemical Formula 1.
In an exemplary embodiment, the exsoluted Ru nanoparticle may be formed by heat-treating a single phase homogeneous catalyst represented by the Chemical Formula 1 at 600 to 1,200° C. under a reducing atmosphere.
In an exemplary embodiment, the catalyst may contain 0.1 to 50% by weight of Ru based on the total weight of the catalyst.
In an exemplary embodiment, in the Chemical Formula 1, A may be Sr and A′ may be La, or A may be Ca and A′ may be Y.
In an exemplary embodiment, in the Chemical Formula 1, x may be greater than 0 and less than or equal to 0.3, and y may be greater than 0 and less than or equal to 0.5.
In an exemplary embodiment, the catalyst may be for dry reforming of methane and/or carbon dioxide.
In another aspect, the present disclosure provides a method for manufacturing the catalyst with the perovskite structure, comprising preparing a mixture of a metal precursor solution; drying and calcining the mixture; and heat-treating the mixture under a reducing atmosphere at 600 to 1,200° C. after the calcination.
In an exemplary embodiment, the drying may be performed at 70 to 90° C. for 60 to 180 minutes.
In an exemplary embodiment, the calcination may be performed at 600 to 800° C. for 60 to 180 minutes.
In an exemplary embodiment, the heat treatment for exsolution of nanoparticles after the calcination may be performed under a reducing atmosphere of 600 to 1,200° C. for 60 to 600 minutes.
In still another aspect, the present disclosure provides a dry reforming method using the catalyst with the perovskite structure, the method comprising supplying a reaction raw material gas containing methane and/or carbon dioxide to a reactor including the catalyst with the perovskite structure to perform a dry reforming reaction.
In an exemplary embodiment, the reaction raw material gas may be a mixture of methane and carbon dioxide in a molar ratio of 1:1 or more.
In one aspect, the technology disclosed in the present disclosure has the effect of providing a catalyst with a perovskite structure with excellent catalytic activity and effects of suppressing carbon deposition and enhancing thermal stability. The catalyst formed (exsolution) with Ru nanoparticles on the surface of the perovskite has the characteristics of high activity, suppressing carbon deposition, and maintaining high reaction activity for a long time due to high thermal stability compared to conventional catalysts. These characteristics enable it to overcome the weak carbon deposition suppression ability and thermal stability, which are the biggest problems of dry reforming, and thus it can become a key catalyst material essential for the synthesis gas production and carbon dioxide reduction process.
In another aspect, the technology disclosed in the present disclosure has the effect of providing a method for manufacturing the catalyst with the perovskite structure.
In another aspect, the technology disclosed in the present disclosure has the effect of providing a method for manufacturing a catalyst having the characteristic of maximally exsoluting Ru nanoparticles by forming Ca/Sr at the A site and La/Y at the A′ site in the perovskite A1-yA′yTi1-xRuxO3 structure.
In another aspect, the technology disclosed in the present disclosure has the effect of providing a dry reforming method using the catalyst with the perovskite structure.
Hereinafter, the present disclosure will be described in detail.
In one aspect, the present disclosure provides a catalyst with a perovskite structure, wherein the catalyst is represented by Chemical Formula 1, and includes Ru nanoparticle exsoluted on the surface of the catalyst.
A1-yA′yTi1-xRuxO3 [Chemical Formula 1]
In the above formula, A is Sr, Ca, or a combination thereof, A′ is La, Y, or a combination thereof, x is greater than 0 and less than or equal to 0.5, and y is greater than 0 and less than 1.0.
In an exemplary embodiment, the catalyst may be a single phase homogeneous catalyst represented by Chemical Formula 1.
In an exemplary embodiment, the exsoluted Ru nanoparticle may be formed by heat-treating a single phase homogeneous catalyst represented by Chemical Formula 1 at 600 to 1,200° C. under a reducing atmosphere. The catalyst includes a plurality of Ru nanoparticles exsoluted on the surface, and thus has the effect of significantly improving catalytic activity and thermal stability and enhancing resistance to carbon deposition.
The homogeneous catalyst refers to a structure in which an active material that is substituted within a material lattice is included to maintain a single phase. While conventional general catalysts are so-called heterogeneous catalysts that are composed of two or more phases by loading an active material on a support and performing heat treatment, the catalyst according to the present disclosure is a catalyst having a structure in which a homogeneous catalyst of a single phase is manufactured and then the catalytic active material is exsoluted in the form of nanoparticles on the surface. That is, in the perovskite A1-yA′yTi1-xRuxO3 structure, since some of the A sites are doped (substituted) with A′ and some of the Ti sites are doped (substituted) with Ru, the basic perovskite structure can be maintained and a single phase can be achieved.
In particular, in order to maintain the single phase of the perovskite, it is preferable to have a tolerance factor (t) value between 0.75 and 1, as in the equation below, and since the ionic radius difference (Ti4+0.64 Å, Ru4+0.62 Å) with the active material Ru to be doped in the Ti site is about 3.1%, which is very small compared to the size difference of 15 to 20% for general solid solution formation, the single phase of A1-yA′yTi1-xRuxO3 can be maintained, which can be confirmed by XRD analysis.
In the A1-yA′yTi1-xRuxO3 catalyst having the single phase perovskite structure, which has been manufactured in this way, the Ru nanoparticles can be uniformly exsoluted onto the catalyst surface by additionally heat-treating the catalyst under specific conditions, that is, under a high-temperature reducing atmosphere in the range of 600 to 1,200° C. In this case, the single phase homogeneous form changes into a multi-phase heterogeneous catalyst in the form of ruthenium metal nanoparticles+oxide catalyst, but has a catalyst structure that is distinguished from the conventional multi-phase heterogeneous catalyst. That is, the conventional catalyst is in the form of metal particles dispersed on an oxide or other metal support, but the catalyst according to the present disclosure is a catalyst of a perovskite structure in the form of ruthenium nanoparticles uniformly exsoluted on the catalyst surface. In particular, the ruthenium nanoparticles exsoluted onto the surface are anchored inside the crystal lattice in a form that is exsoluted from the perovskite crystal lattice, so not only is their resistance to sintering far superior to that of general dispersed catalysts, but since the exsoluted phenomenon occurs in the form of atoms or ions inside the crystal lattice, it has the effect of maximizing catalytic activity by ensuring nano-form and uniformity.
The present disclosure provides a catalyst with a perovskite structure represented by A1-yA′yTi1-xRuxO3, which is a homogeneous catalyst having a perovskite single phase in which the A site is composed of Sr, Ca, or a combination thereof, the A′ site is doped with La, Y, or a combination thereof, and some of the Ti sites are doped with Ru, and which is heat-treated at 600 to 1,200° C. under a reducing atmosphere to exsolute uniform Ru nanoparticles on the surface of the catalyst. In this case, the Ti exsoluted together exists in the form of TiO2 oxide on the surface of the catalyst to suppress the sintering phenomenon of Ru nanoparticles existing in a metallic state in a reforming reaction, thereby maximizing thermal stability and enabling a reforming reaction at a higher temperature due to high thermal stability even at high temperatures.
In Chemical Formula 1 above, the reason why the maintenance of the single phase of the perovskite is important is because it affects the process of exsoluting ruthenium nanoparticles onto the catalyst surface by performing a second heat treatment under a high-temperature reducing atmosphere after manufacturing the catalyst of Chemical Formula 1 above. That is, if the single phase of the perovskite as in Chemical Formula 1 above is not maintained, it is difficult to uniformly exsolute ruthenium nanoparticles onto the catalyst surface during the second heat treatment under a high-temperature reducing atmosphere, and thus the catalytic activity decreases.
The catalyst structurally maximizes thermal stability and reforming reaction sites, and can be used as a steam reforming (S/C<2) and dry reforming catalyst which are superior in suppressing carbon deposition. While the conventional catalysts show a decline in catalytic activity in dry reforming over several to several tens of hours due to a decrease in catalytic activity caused by carbon deposition, the catalyst according to the present disclosure has the effect of providing stable activity for more than 1,000 hours and a deterioration rate of less than 1%/1,000 hours in a dry reforming experiment.
In an exemplary embodiment, the catalyst may be prepared by a pechini method or a solid state mixing method.
In an exemplary embodiment, the catalyst may include 0.1 to 50% by weight of Ru based on the total weight of the catalyst. For example, when x in the above formula is 0.2, the Ru content is about 10% by weight. In another exemplary embodiment, the catalyst can contain Ru in an amount of 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, 2% by weight or more, 3% by weight or more, 4% by weight or more, 5% by weight or more, 6% by weight or more, 7% by weight or more, 8% by weight or more, 9% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more, and 50% by weight or less, 45% by weight or less, 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, 9% by weight or less, 8% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight or less, or 1% by weight or less, based on the total weight of the catalyst. The above catalyst can provide excellent catalytic activity even with a low content of Ru. In addition, when the catalyst contains Ru exceeding 20% by weight, there may be little difference in catalytic activity depending on the addition of Ru doping amount. Therefore, in terms of efficiency, it may be preferable that the catalyst contains 0.1 to 15% by weight or 0.1 to 10% by weight of Ru based on the total weight of the catalyst.
In an exemplary embodiment, in the above formula, A may be Sr and A′ may be La, or A may be Ca and A′ may be Y.
In an exemplary embodiment, in the above formula, A may have an ionic radius difference of 20% or less with respect to the A′ doping material.
In an exemplary embodiment, in the above formula, x may be greater than 0 and less than or equal to 0.3 or less than or equal to 0.2, since a minimum doping amount may be preferable.
In an exemplary embodiment, in the above formula, y may be greater than 0 and less than or equal to 0.5.
Preferably, the x may be greater than 0 and less than or equal to 0.3, and y may be greater than 0 and less than or equal to 0.5. Even in the range where both the x and y are greater than 0 and less than or equal to 0.5, single phase can be maintained, but in particular, in terms of carbon deposition mitigation and reforming performance, it may provide excellent effects when the y value does not exceed 0.5 and the x value does not exceed 0.3. This is also preferable in order to reduce the catalyst cost burden.
In an exemplary embodiment, the catalyst may be for steam reforming. For example, the catalyst may be suitable for steam reforming with a small steam supply ratio.
In an exemplary embodiment, the steam/carbon (S/C) ratio in the steam reforming may be less than or equal to 2.
In an exemplary embodiment, the catalyst may be for dry reforming.
In an exemplary embodiment, the catalyst may be for dry reforming of biogas.
Biogas is a gaseous fuel that can be produced by anaerobic digestion, gasification, or pyrolysis of biomass such as sewage sludge and food waste. Such biogas may contain methane (about 55 to 70%) and carbon dioxide (about 30 to 45%) as main components, and may contain impurities such as sulfur(S). In an exemplary embodiment, the biogas may contain methane and/or carbon dioxide.
In an exemplary embodiment, the catalyst may be for dry reforming of methane and/or carbon dioxide. For example, the catalyst has the effect of suppressing carbon deposition and having excellent long-term thermal stability in a dry reforming reaction that produces synthesis gas (CO and H2) using methane and carbon dioxide.
In the present disclosure, dry reforming may mean a reaction that produces carbon monoxide and hydrogen from carbon dioxide and methane.
In this regard, among reforming processes for converting methane, which is used as fuel for high-temperature fuel cells, into hydrogen, the dry reforming is useful in terms of recycling carbon dioxide and using less energy compared to the steam reforming, and has endothermic properties that help cool the fuel cell power generation system. For reference, Reaction Formula 1 below is a reaction formula for the dry reforming reaction of carbon dioxide.
CH4+CO2→2CO+2H2,ΔH0298=247KJ/mol [Reaction Formula 1]
This dry reforming reaction thermodynamically shows a higher conversion rate and a larger yield of hydrogen or carbon monoxide at higher temperatures, but conventional nickel-based catalysts, for example, show problems of deactivation due to sintering and aggregation and carbon deposition under operating conditions, especially 700° C. or less. On the other hand, the perovskite-based catalyst according to the present disclosure hardly shows problems of deactivation due to sintering of the catalyst or carbon deposition even at high temperatures, and has a technical advantage of no carbon deposition at 700° C. or less.
Therefore, the catalyst of the present disclosure can be usefully used as a reforming catalyst for a fuel cell, especially a high-temperature fuel cell, that performs direct and indirect reforming reactions of carbon dioxide. In addition, a high-temperature fuel cell using the catalyst of the present disclosure can be stably operated for a long time under dry reforming conditions.
In another aspect, the present disclosure provides a method for preparing the catalyst with the perovskite structure, and the method is a method for manufacturing a metal nanoparticle exsolution catalyst with the perovskite structure, comprising preparing a mixture of a metal precursor solution; drying and calcining the mixture; and heat-treating the mixture under a reducing atmosphere at 600 to 1,200° C. after the calcination.
In an exemplary embodiment, the drying may be performed at 70 to 90° C.
In an exemplary embodiment, the drying may be performed for 60 to 180 minutes.
In an exemplary embodiment, the calcination may be performed at 600 to 800° C.
In an exemplary embodiment, the calcination may be performed for 60 to 180 minutes.
In an exemplary embodiment, the heat treatment for nanoparticle exsolution after the calcination may be performed under a reducing atmosphere at 600 to 1,200° C. for 60 to 600 minutes.
In still another aspect, the present disclosure provides a dry reforming method using the catalyst with the perovskite structure, which includes supplying a reaction raw material gas containing methane and/or carbon dioxide to a reactor containing the catalyst with the perovskite structure to perform a dry reforming reaction.
Unlike the steam reforming, the dry reforming uses carbon dioxide as a gas, so energy consumption is less than the steam reforming that injects water, and thus has small difference in efficiency according to the amount of carbon dioxide injected. In an exemplary embodiment, the reaction raw material gas may be a mixture of methane and carbon dioxide at a molar ratio of 1:1 or more, 1:1 to 10, 1:1 to 5, or 1:1 to 3. In order to control the flow rate of the reaction gas, an inert gas such as nitrogen (N2) or argon (Ar) may be used in a diluted manner. The present disclosure has an effect of providing an excellent conversion rate of methane even when the amount of carbon dioxide supplied increases.
In an exemplary embodiment, the dry reforming reaction may be performed at a weight hourly space velocity (WHSV) of 100 to 300 L/(h·gcat).
In an exemplary embodiment, the dry reforming reaction may be performed at 600 to 900° C.
In an exemplary embodiment, the dry reforming reaction may be performed for 1 hour or more, 100 hours or more, 500 hours or more, 1,000 hours or more, 1,500 hours or more, 2,000 hours or more, 1 to 2,000 hours, 1 to 1,500 hours, or 1 to 1,000 hours.
The dry reforming method according to the present disclosure has the effect of providing stable dry reforming performance without carbon deposition during operation at 600 to 900° C. for 1,000 hours or more. For example, it can show a conversion rate of methane about 98% or more and a conversion rate of carbon dioxide of about 99% or more at operation at 900° C., and it can show a conversion rate of methane of 93% and a conversion rate of carbon dioxide of 91%, which are close to the thermodynamic equilibrium value, even at operation at 700° C.
Hereinafter, the present disclosure will be described in more detail through Examples. It will be apparent to those skilled in the art that these Examples are intended only to illustrate the present disclosure, and the scope of the present disclosure is not to be construed as being limited by these Examples.
In this Example, perovskite single-phase powder of Sr0.92La0.08Ti0.95Ru0.05O3, in which in the A1-yA′yTi1-xRuxO3 structure, the A site is composed of Sr, the A′ site is doped with La, and some of the Ti sites are doped with Ru, was prepared using a citric acid method as follows.
To prepare 5 g of the SLT-Ru catalyst, 0.91 g of lanthanum nitrate hydrate [La(NO3)3·xH2O], 5.12 g of strontium nitrate hydrate [Sr(NO3)3·xH2O], and 5 g of citric acid were simultaneously dissolved in 50 mL of deionized water (DI water). 7.10 g of titanium isopropoxide {Ti[OCH(CH3)2]4} and 0.34 g of ruthenium chloride hydrate (RuCl3·xH2O) were dissolved in 5 mL of ethylene glycol [C2H5O2] for stabilization. Each solution was mixed together for 24 hours, dried at 80° C., and calcined in air at 650° C. After the formation of a perovskite single phase was confirmed through XRD analysis, it was heat-treated at 900° C. for 2 hours under a reducing atmosphere (10% H2+90% N2) to finally obtain the dry deforming catalyst of Sr0.92La0.08Ti0.95Ru0.05O3 (hereinafter referred to as SLT-Ru). The Ru usage of this catalyst was 2.66% by weight.
In this Example, a perovskite single phase powder of Ca0.92Y0.08Ti0.95Ru0.05O3, in which in the A1-yA′yTi1-xRuxO3 structure, the A site is composed of Ca, the A′ site is doped with Y, and some of the Ti sites are doped with Ru, was prepared using a citric acid method as follows.
To prepare 5 g of the CYT-Ru catalyst, 1.07 g of yttrium nitrate hydrate [Y(NO3)3·xH2O], 7.62 g of calcium nitrate hydrate [Ca(NO3)3·xH2O], and 5 g of citric acid were simultaneously dissolved in 50 mL of deionized water (DI water). 9.47 g of titanium isopropoxide {Ti[OCH(CH3)2]4} and 0.36 g of ruthenium chloride hydrate (RuCl3·xH2O) were dissolved in 5 mL of ethylene glycol [C2H5O2] for stabilization. Each solution was mixed together for 24 hours, dried at 80° C., and calcined in air at 650° C. After the formation of a perovskite single phase was confirmed through XRD analysis, it was heat-treated at 900° C. for 2 hours under a reducing atmosphere (10% H2+90% N2) to finally obtain a dry reforming catalyst of Ca0.92Y0.08Ti0.95Ru0.05O3 (hereinafter referred to as CYT-Ru). The Ru usage of this catalyst was 3.55% by weight.
Unlike the catalyst of Example 1 above, a catalyst with x=0, y=0.08 that was not doped with ruthenium (i.e., Sr0.92La0.08TiO3; hereinafter referred to as SLT) was prepared by a citric acid method as follows.
To prepare 5 g of an SLT catalyst, 0.92 g of lanthanum nitrate hydrate [La(NO3)3·xH2O], 5.19 g of strontium nitrate hydrate [Sr(NO3)3·xH2O], and 7.57 g of titanium isopropoxide {Ti[OCH(CH3)2]4} were mixed in 50 mL of deionized water, and 5 mL of ethylene glycol [C2H5O2] and 5 g of citric acid were added to prepare a nitrate aqueous solution, which was dried at 80° C. and calcined at 650° C. in air. Finally, the catalyst was prepared by heat-treating at 900° C. for 2 hours under a reducing atmosphere (10% H2+90% N2).
Unlike the catalyst of the above Example 1, a catalyst in which 3% by weight of ruthenium was loaded on Sr0.92La0.08TiO3 prepared in Comparative Example 1 without doping ruthenium (i.e., 3% by weight of Ru/Sr0.92La0.08TiO3; hereinafter referred to as Ru/SLT) was prepared by an impregnation method as follows.
A mixture of 5 g of Sr0.92La0.08TiO3 support, 0.28 g of ruthenium chloride hydrate (RuCl3·xH2O), and 50 mL of deionized water (DI water) was stirred at room temperature for 6 hours and dried at 80° C. using a rotary evaporator. The dried powder was calcined at 650° C. in air and heat-treated at 900° C. for 2 hours under a reducing atmosphere (10% H2+90% N2). When the total weight of Sr0.92La0.08TiO3 and ruthenium was 100%, a catalyst was obtained in which ruthenium was impregnated on the catalyst surface at 3.0% by weight.
In this Comparative Example, a perovskite single-phase powder of Sr0.92Ca0.08Ti0.95Ru0.05O3, in which in the A1-yA′yTi1-xRuxO3 structure, the A site is composed of Sr, the A′ site is doped with Ca, and some of the Ti sites are doped with Ru, was prepared using a citric acid method as follows.
To prepare 5 g of the SCT-Ru catalyst, 0.52 g of calcium nitrate hydrate [Ca(NO3)3·xH2O], 5.34 g of strontium nitrate hydrate [Sr(NO3)3·xH2O], and 5 g of citric acid were simultaneously dissolved in 50 mL of deionized water (DI water). 7.40 g of titanium isopropoxide {Ti[OCH(CH3)2]4} and 0.28 g of ruthenium chloride hydrate (RuCl3·xH2O) were dissolved in 5 mL of ethylene glycol [C2H5O2] for stabilization. Each solution was mixed together for 24 hours, dried at 80° C., and calcined in air at 650° C. After the formation of a perovskite single phase was confirmed through XRD analysis, it was heat-treated at 900° C. for 2 hours under a reducing atmosphere (10% H2+90% N2), to finally obtain a dry reforming catalyst of Sr0.92Ca0.08Ti0.95Ru0.05O3 (hereinafter referred to as SCT-Ru). The Ru usage of this catalyst was 2.77% by weight.
In this Comparative Example, a perovskite single-phase powder of Sr0.92Ba0.08Ti0.95Ru0.05O3, in which the A1-yA′yTi1-xRuxO3 structure, the A site is composed of Sr, the A′ site is doped with Ba, and some of the Ti sites are doped with Ru, was prepared using a citric acid method as follows.
To prepare 5 g of the SBT-Ru catalyst, 0.55 g of barium nitrate hydrate [Ba(NO3)3·xH2O], 5.12 g of strontium nitrate hydrate [Sr(NO3)3·xH2O], and 5 g of citric acid were simultaneously dissolved in 50 mL of deionized water (DI water). 7.10 g of titanium isopropoxide {Ti[OCH(CH3)2]4} and 0.27 g of ruthenium chloride hydrate (RuCl3·xH2O) were dissolved in 5 mL of ethylene glycol [C2H5O2] for stabilization. Each solution was mixed together for 24 hours, dried at 80° C., and calcined in air at 650° C. After the formation of a perovskite single phase was confirmed through XRD analysis, it was heat-treated at 900° C. for 2 hours under a reducing atmosphere (10% H2+90% N2) to finally obtain a dry forming catalyst of Sr0.92Ba0.08Ti0.95Ru0.05O3 (hereinafter referred to as SBT-Ru). The Ru usage of this catalyst was 2.66% by weight.
In this Comparative Example, a perovskite single-phase powder of Sr0.92Y0.08Ti0.95Ru0.05O3, in which in the A1-yA′yTi1-xRuxO3 structure, the A site is composed of Sr, the A′ site is doped with Y, and some of the Ti sites are doped with Ru, was prepared using a citric acid method as follows.
To prepare 5 g of SYT-Ru catalyst, 0.82 g of yttrium nitrate hydrate [Y(NO3)3·xH2O], 5.23 g of strontium nitrate hydrate [Sr(NO3)3·xH2O], and 5 g of citric acid were simultaneously dissolved in 50 mL of deionized water (DI water). 7.25 g of titanium isopropoxide {Ti[OCH(CH3)2]4} and 0.28 g of ruthenium chloride hydrate (RuCl3·xH2O) were dissolved in 5 mL of ethylene glycol [C2H5O2] for stabilization. Each solution was mixed together for 24 hours, dried at 80° C., and calcined in air at 650° C. After the formation of a perovskite single phase was confirmed through XRD analysis, it was heat-treated at 900° C. for 2 hours under a reducing atmosphere (10% H2+90% N2) to finally obtain a dry reforming catalyst of Sr0.92Y0.08Ti0.95Ru0.05O3 (hereinafter referred to as SYT-Ru). The Ru usage of this catalyst was 2.71% by weight.
XRD diffraction analysis was performed using a diffractometer from Rigaku (RINT-5200 model, Rigaku). The samples were measured at 2θ=20° to 80°.
As described above, in the XRD analysis results of
The catalysts obtained by high-temperature reduction treatment in Examples 1 and 2 and Comparative Examples 1 to 4 were observed using a transmission electron microscope (TEM, Tecnai F20, FEI) and are shown in
The catalyst of Comparative Example 1 (SLT) was found to not form nanoparticles exsoluted on the surface.
As shown in
The catalyst of Comparative Example 2 (Ru/SLT) is a catalyst in which Ru particles are dispersed on the surface of Comparative Example 1 (SLT) by an impregnation method. Since large Ru particles of several hundred nanometers in size were formed on the surface from the beginning of catalyst production, it was difficult to observe the formation of additional nanoparticles after the exsolution process. Therefore, the TEM image of the catalyst surface of Comparative Example 2 confirmed in
In particular, in the catalysts of Examples 1 and 2, Ru could not be observed in the XRD analysis after the exsolution process under a high-temperature reducing atmosphere due to the small doping amount of Ru (approximately 2.66% by weight). However, it was confirmed through the TEM image of
From these results, it was confirmed in the catalysts of Examples 1 and 2 that a perovskite single phase was maintained after calcination at 650° C., and after heat treatment at 900° C. for 2 hours under a reducing atmosphere, a large number of ruthenium nanoparticles were uniformly exsoluted on the catalyst surface as shown in
To measure the high-temperature activity, methane dry reforming was performed using the catalysts of Examples 1 and 2 and Comparative Examples 1 to 4 in a fixed-bed continuous flow system under atmospheric pressure.
A quartz tube (inner diameter of 2 mm) was used as an out-of-cell reactor. Each catalyst (20 mg) was placed on quartz wool in the middle of the reactor. Before measurement, each catalyst was further reduced in situ under a diluted hydrogen gas (10% H2/Ar) flow at 900° C. for 2 hours, and then reforming experiments were performed.
The temperature of the reforming experiment was 600 to 900° C., and the reforming reaction at each measurement temperature was maintained for 90 minutes, and the conversion rate of methane was measured. The composition of the raw material gas used for reforming was CH4/CO2/N2 (flow molar ratio was 20 sccm/20 sccm/40 sccm). A weight hourly space velocity (WHSV) (which is the mass flow of reactants divided by the mass of catalyst) was 120 L/(h·gcat).
The reactants were analyzed using a gas chromatograph (GC, Agilent 6900 model) equipped with a TCD detector. The conversion rates of methane and carbon dioxide were calculated by the following equation.
As confirmed in
The conversion rate of the carbon dioxide in
In
According to the methane dry reforming reaction method described in Experimental Example 3 above, a long-term reaction was performed at 700° C. for 1,000 hours. The catalysts used were the catalyst of Example 1 (SLT-Ru), the catalyst of Comparative Example 2 (Ru/SLT), the catalyst of Comparative Example 5 (SYT-Ru), and a commercial catalyst (Ni/Al2O3). The commercial catalyst was obtained from Clariant AG® and used.
While the specific parts of the present disclosure have been described in detail, it will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the present disclosure. Accordingly, the substantial scope of the present disclosure is defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2024-0001904 | Jan 2024 | KR | national |
The research was conducted at the Korea Institute of Science and Technology under the management of the Korea Institute of Science and Technology under the Ministry of Science and ICT. The research project name is the research operation expense support (main project expense) of the Korea Institute of Science and Technology, and the research project name is development of green hydrogen production-liquid storage integration technology (Project Unique Number: 1711196511, Project Number: 2E32460). In addition, the research was conducted at the Korea Institute of Science and Technology under the management of the Korea Institute of Energy Technology Evaluation and Planning under the Ministry of Trade, Industry and Energy. The research project name is development of new and renewable energy core technology (electricity), and the research project name is development of a 1 kW-class molten carbonate type high-temperature electrolysis cell (MCEC) prototype (Project Unique Number: 1415186453, Project Number: 20213030040080).
