KR102644506B1 - Perovskite metal oxide catalyst for high-nickel-containing hydrocarbon reforming reaction and method for producing the same - Google Patents

Abstract

The present invention relates to a perovskite metal oxide catalyst for methane dry reforming reaction and a method for producing the same to suppress carbon deposition due to increase in nickel content, and more specifically, to the perovskite metal oxide catalyst (SrTiO ₃ ). It relates to a catalyst capable of suppressing carbon deposition and improving the stability of the catalyst by substituting Ti with Ni and Sr with Y, and a method for producing the same.

Description

Perovskite metal oxide catalyst for high-nickel-containing hydrocarbon reforming reaction and method for producing the same

The present invention relates to a perovskite metal oxide catalyst and a method for producing the same. More specifically, it relates to a catalyst for hydrocarbon reforming in which some of the titanium and strontium in the SrTiO ₃ -based perovskite metal oxide are replaced with nickel and yttrium, respectively, and a method for producing the same. Hydrocarbons of the present invention refer to compounds having four or less carbons, and include methane, ethane, ethene, propane, propylene, butane, butadiene, isobutane, etc.

Hydrocarbon reforming reactions, especially methane reforming reactions that use methane (CH ₄ ) to produce synthetic gas mixed with hydrogen (H ₂ ) and carbon monoxide (CO), can be classified according to the oxidizing agent used.

The first methane reforming reaction is steam methane reforming (SMR), which uses steam (H ₂ O, steam) as an oxidizing agent, and is the most widely used. The reaction equation is shown in Scheme 1 below, and since it is a very large endothermic reaction, heat must be continuously supplied to maintain the reaction, which limits the design of the reactor.

[Scheme 1]

CH ₄ + H ₂ O → 3H ₂ + CO ΔH ₁₁₇₃ = 225.7 kJ/mol

In the steam methane reforming reaction, a catalyst in which metallic nickel, which is an active site, is supported on an alumina support to which magnesium (Mg), calcium (Ca), strontium (Sr), etc. are added alone or in combination, is used. In order for the catalyst to remain active for a long time, coke deposition must be suppressed, so unlike Scheme 1 above, commercial operation is performed by supplying an excess amount of water vapor compared to CH ₄ (H ₂ O/CH ₄ = 3). . Many commercialized processes are already widely used across industries. However, because excessive water vapor must be supplied, the SMR process poses problems in energy efficiency. If the high temperature steam generated through the SMR process is not used effectively, the energy efficiency (high heating value (HHV)) for hydrogen production may be lowered to less than 70%, and in this case, the method of using CH ₄ by directly burning it is recommended. Compared to this, there is no benefit in terms of energy efficiency. Therefore, to date, the SMR process has been installed inside an oil refinery/petrochemical complex where high-temperature steam can be used from the surrounding area. In order to widely distribute independent hydrogen charging stations based on the SMR process in the future, efforts must be made to reduce excessive water vapor supply through groundbreaking improvements in existing commercial catalysts or to improve thermal efficiency of the SMR process overall.

The second methane reforming reaction is partial oxidation of methane (POM), which uses oxygen (O ₂ ) as an oxidizing agent. The reaction equation is shown in Scheme 2 below.

[Scheme 2]

CH ₄ + 0.5O ₂ → 2H ₂ + COΔH ₁₁₇₃ = -23.1 kJ/mol

Partial oxidation of metahne (POM) is a mildly exothermic reaction because it uses oxygen as an oxidizing agent. Therefore, heat supply to maintain the reaction is less restricted compared to the SMR reaction. Looking at the product, synthesis gas with a ratio of H ₂ /CO = 2 is produced, so it is suitable for the Fischer-Tropsch Synthesis reaction, which is a hydrocarbon production reaction. However, if the catalyst's selectivity for synthesis gas decreases due to long-term operation, a complete combustion reaction (CH ₄ + 2O ₂ → 2H ₂ O + CO ₂ ) occurs, which may lead to explosion, which poses a safety problem. For this reason, for commercialization, it is necessary to confirm the selectivity and long-term stability of the catalyst. Therefore, commercialization of autothermal reforming (ATR), which causes a partial oxidation reaction at high temperature without a catalyst, is being considered. In order for the partial oxidation reforming reaction using a catalyst to be commercialized, the development of a stable and highly selective catalyst is urgently needed.

The third methane reforming reaction is dry reforming of methane (DRM), which uses carbon dioxide (CO ₂ ) as an oxidizing agent, and the reaction equation is shown in Scheme 3 below.

[Scheme 3]

CH ₄ + CO ₂ → 2H ₂ + 2COΔH ₁₁₇₃ = 258.8 kJ/mol

Dry reforming of hydrocarbons is a very strong endothermic reaction that uses carbon dioxide (CO ₂ ) as an oxidizing agent. The stability of the process is very high because very stable CO ₂ is supplied as an oxidizing agent, but since it is an endothermic reaction like the SMR reaction, there are limitations in reactor design because heat must be effectively supplied from the outside. Since the SMR reactor is commercialized, it is expected that there will be no major difficulties in commercializing the DRM reactor. However, the reason that the DRM reaction has not yet been commercialized is because the catalyst for the DRM reaction has not yet been developed. In other words, the biggest problem with the DRM reaction is carbon deposition due to the catalyst's low selectivity for synthesis gas. When the DRM reaction is carried out, carbon deposition occurs very heavily on the catalyst surface, so the lifespan of the catalyst is very short.

According to the patent applied by the same inventor of the present invention (Application No. 10-2017-0119442), if less than 5% of Ni ²⁺ is substituted for Ti ⁴⁺ in the perovskite-structured metal oxide SrTiO ₃ It was confirmed that Ni ²⁺ was substituted inside the SrTiO ₃ lattice structure, and that when used as a catalyst for DRM reaction, the reaction was maintained stably without carbon deposition. Ni ²⁺ substituted in the lattice structure of perovskite SrTiO ₃ is the active site of the DRM reaction.

However, when more than 5% of Ni ²⁺ was substituted for Ti ⁴⁺ , a portion of Ni ²⁺ formed nickel oxide (NiO) outside the SrTiO ₃ lattice structure. It was confirmed that the formation of NiO formed metallic Ni under DRM reaction conditions, and through this, carbon was deposited, albeit in a small amount. Considering only the activity of the catalyst, increasing the Ni ²⁺ content is advantageous because it forms metallic Ni with Ni ²⁺ contained in the lattice structure, but considering the gradual decline in catalytic activity due to carbon deposition, the appropriate Ni ²⁺ content is It is preferable that it is less than 5%. If the Ni ²⁺ substitution amount is lowered to less than 5%, the DRM reaction remains stable for a long time without carbon deposition, but there is a limit to increasing the number of Ni ²⁺ , which is the active site of the catalyst.

Catalysts with less nickel substitution have a smaller number of active sites, so they can show high conversion rates at low space velocities, but the conversion rate is lowered at high space velocities, so there is a limit to the products that the catalyst can produce per unit time. If the conversion rate is low and a lot of reactants are mixed with the products, additional operating costs are required to separate the reactants and products, so if possible, high conversion rates should be maintained at high space velocities to increase the economic feasibility of the process using these catalysts. To achieve this, a method to increase the number of catalytic active sites is needed.

In summary, in order to commercialize the DRM reactor, a catalyst with suppressed carbon deposition must be developed. To increase the productivity of the catalyst, increase the number of nickel substitutions used as active sites of the catalyst while suppressing carbon deposition of nickel oxide formed outside the lattice. A method is required.

The object of the present invention is to provide a perovskite metal oxide catalyst for hydrocarbon reforming reaction with reduced carbon deposition and a method for producing the same. The present inventors have proposed a method for producing strontium (Sr) in a SrTiO ₃ -based perovskite metal oxide (SrTiO ₃ ) catalyst. ) was partially replaced with yttrium (Y), and it was discovered that a catalyst could be obtained that could stably maintain hydrocarbon reforming reactions, including DRM reactions, for a long time without carbon deposition while increasing the number of Ni ²⁺ , which is the active site of the reaction. This invention has been completed.

Therefore, the purpose of the present invention is to provide a catalyst that can replace part of strontium (Sr) with yttrium (Y) to increase the number of nickel substitutions used as active sites in the catalyst or to suppress carbon deposition of nickel oxide formed outside the lattice. and to provide a method for manufacturing the same.

In one embodiment of the present invention, it is a multi-component metal oxide catalyst having a SrTiO ₃ -based perovskite lattice structure, in which some of the strontium and titanium in the perovskite lattice structure are replaced with yttrium and nickel, and the following formula 1 A catalyst for hydrocarbon reforming having a composition represented by is provided.

[Formula 1]

Sr _1-y Y _y Ti _1-x Ni _x O _3-δ

In the above equation,

y is 0.04 < y ≤ 0.15, x is 0.05 ≤ x ≤ 0.25,

δ is a value determined by x - 0.5y.

In another embodiment of the present invention, it is a multi-component metal oxide catalyst having a SrTiO ₃ -based perovskite lattice structure, represented by the following formula (2) in which some of the strontium and titanium in the perovskite lattice structure are replaced with yttrium and nickel. Provided is a catalyst for hydrocarbon reforming of the composition.

[Formula 2]

Sr _1-y Y _y Ti _1-x Ni _x O _3-δ

In the above formula, 0.05 ≤ x ≤ 0.25,

y satisfies 0 < y ≤ 0.15 and (x-0.03)/y < 1.5,

δ is a value determined by x - 0.5y.

In another embodiment of the present invention, a multi-component metal oxide catalyst having a SrTiO ₃ -based perovskite lattice structure has the following formula 3 in which some of the strontium and titanium in the perovskite lattice structure are replaced with yttrium and nickel. A catalyst for hydrocarbon reforming having the indicated composition and having a standard carbon deposition of 0.3% by weight or less based on the weight of the catalyst before reaction is provided.

[Formula 3]

Sr _1-y Y _y Ti _1-x Ni _x O _3-δ

In the above equation,

y is 0 < y ≤ 0.15, x is 0.05 ≤ x ≤ 0.25,

δ is a value determined by x - 0.5y.

On the other hand, the present invention is a method for producing the metal oxide catalyst of Chemical Formula 1 described above,

i) Dissolve strontium precursor, yttrium precursor, nickel precursor, citric acid and ethylene glycol in distilled water at 50 to 90°C and adjust the molar ratio. Preparing a first solution of 1.00 ~ 0.85 : 0 ~ 0.15 : 0.05 ~ 0.25 : 3.6 ~ 4.4 : 8 ~ 10;

ii) Prepare a second solution by dissolving the titanium precursor in an alcohol solution at a molar ratio of 0.75 to 0.95 at 50 to 90°C, then adjust the (strontium + yttrium + nickel) concentration of the first solution and the (titanium) concentration of the second solution. After making the same mixture, reacting by mixing at a volume ratio of 1:1;

iii) first calcining the reaction mixture in an oxygen atmosphere at 300 to 400°C; and

iv) secondary calcination of the first calcination product under an oxygen atmosphere at 800 to 1200° C.

According to the present invention, it is possible to provide a long-life SrTiO ₃ -based perovskite catalyst that does not require concern about performance degradation due to carbon deposition in reforming reactions of hydrocarbons including methane, especially dry reforming reactions.

Figure ¹ shows the results observed according to the ^size of the diffraction angle of _the (A: SrTiO ₃ , B: SrTi _0.97 Ni _0.03 O _3-δ , C: SrTi _0.93 Ni _0.07 O _3-δ , D: SrTi _0.85 Ni _0.15 O _3-δ )
Figure 2 shows the X-ray diffraction patterns of catalysts according to the present invention observed according to the size of the diffraction angle. (D: SrTi _0.85 Ni _0.15 O _3-δ , E: Sr _0.96 Y _0.04 Ti _0.85 Ni _0.15 O _3-δ , F: Sr _0.92 Y _0.08 Ti _0.85 Ni _0.15 O _3-δ )
Figure 3 shows the results of observing changes in CH ₄ and CO ₂ conversion rates over time when a DRM reaction was performed using catalysts according to the present invention. (D: SrTi _0.85 Ni _0.15 O _3-δ , E: Sr _0.96 Y _0.04 Ti _0.85 Ni _0.15 O _3-δ , F: Sr _0.92 Y _0.08 Ti _0.85 Ni _0.15 O _3-δ )
Figure 4 shows the correlation between Ni substitution amount and space velocity measured using Example and Comparative Example catalysts according to the present invention. (B: SrTi _0.97 Ni _0.03 O _3-δ , F: Sr _0.92 Y _0.08 Ti _0.85 Ni _0.15 O _3-δ )
Figure 5 shows changes in CH ₄ conversion rate and H ₂ /CO ratio measured when POM reaction was performed using the catalysts prepared in the present invention.

Hereinafter, the present invention will be described in more detail.

One aspect of the present invention provides a multi-component metal oxide catalyst having a SrTiO ₃ -based perovskite lattice structure, and a catalyst for hydrocarbon reforming in which a portion of strontium and titanium in the lattice structure is replaced with yttrium and nickel.

In the prior art (Patent No. 10-1457098), as in the present invention, a catalyst was used in which Y ³⁺ was partially substituted at the Sr ²⁺ position, which is the A site site of the perovskite structure. However, in this prior art, the catalyst was used as the active site of the catalyst. A catalyst of the composition Sr _1-y Y _y Ti _1-x Ru _x O _3-δ with some Ru substituted at the B site was used. Ru, a noble metal, is a material with excellent catalytic activity that does not naturally cause carbon deposition. In the prior art, ruthenium (Ru), an expensive precious metal with excellent catalytic activity, was used as a catalytic activity point to produce a metal oxide catalyst for carbon dioxide reforming reaction, but in the present invention, nickel (Ni), which is prone to carbon deposition but is economical, was used. Thus, a catalyst can be manufactured.

Additionally, the main effect of the present invention is to increase the amount of Ni ²⁺ substitution, which was limited to less than 5% by Y ⁺ substitution. In the prior art, the effect of increasing the substitution amount of uniformly doped Ru by Y ³⁺ doping was not confirmed. In ^other words, compared to a catalyst ^of _{SrTi 1-} ^x _Ru There is no specific data showing that the number of (Ru) has increased. However, in the present invention, the data clearly shows that the substitution amount of the catalytically active site Ni ²⁺ substituted for Ti ⁴⁺ can be increased by increasing the amount of Y ³⁺ substitution.

In the catalyst of the present invention having a composition of _{Sr 1-} y Y _{y Ti 1-} x Ni am. In the structure of the catalyst of the present invention, δ is determined as x - 0.5y depending on the degree of substitution of nickel and yttrium.

In one embodiment of the present invention, the catalyst for hydrocarbon reforming is represented by the following formula (1) and can be used in hydrocarbon reforming reactions such as methane dry reforming reaction. This catalyst has the following composition in which some of the titanium (Ti) is replaced with nickel (Ni) and some of the strontium (Sr) is replaced with yttrium (Y) in the SrTiO ₃ -based perovskite lattice structure.

[Formula 1]

Sr _1-y Y _y Ti _1-x Ni _x O _3-δ

In the above equation,

y is 0.04 < y ≤ 0.15, x is 0.05 ≤ x ≤ 0.25,

δ is a value determined by x - 0.5y.

In the case of reforming reactions of hydrocarbons including methane, especially dry reforming reactions, catalyst deactivation due to carbon deposition is very severe, and preventing carbon deposition is essential to use the reforming reaction catalyst for a long time.

Meanwhile, in order to increase the reaction conversion rate of the catalyst, the content of Ni(II) must be increased during synthesis in order to increase Ni(II), which is an active site in the catalyst. Ti(IV) of SrTiO ₃ , a metal oxide with a perovskite structure, ), when more than 5% of Ni(II) is added, nickel oxide or nickel oxide (NiO) is formed by separating from SrTiO ₃ of perovskite structure, which is converted into metallic nickel (Ni(0)) under methane reforming reaction conditions. ), and through this, carbon deposition occurs, impairing the long-term stability of the catalyst. Therefore, if the number of Ni(II) that can be substituted in the lattice of the perovskite structure is less than 5% of the number of Ti(IV) in the lattice, the operational safety of the catalyst can be guaranteed.

However, this method has the limitation that the activity of the catalytic reaction remains low due to the low content of Ni(II), which is the active point of the catalyst. Catalysts with less nickel substitution have fewer active sites, so increasing the space velocity lowers the conversion rate, so there is a limit to the amount of product the catalyst can produce per unit time. In addition, when the conversion rate is low, a mixture containing a lot of reactants and products is created, so additional operating costs are required to separate the reactants and products. Therefore, in order to improve the economic feasibility of the process, it is necessary to develop a catalyst that maintains a high conversion rate of reactants even when the space velocity is increased, so a method of increasing the number of catalytic active sites per unit mass or unit volume is needed. Additionally, even if the number of catalytic active sites is increased, side reactions such as carbon deposition must be suppressed.

According to the present invention, even if the proportion of Ni ²⁺ that can be substituted for the Ti ⁴⁺ position, which is the B site in the perovskite SrTiO ₃ structure, increases, _the A site ( site), carbon deposition can be suppressed by partially substituting Y ³⁺ instead of Sr ²⁺ . On the other hand, when Sr at the A site of the perovskite structure is not substituted with Y, carbon deposition can be completely suppressed unless substitution of Ni is less than 3%. If there is no substitution of Sr with Y and Ni substitution is more than 5%, a small amount of carbon deposition may occur. Therefore, in the catalyst of the prior art, it is preferable that Ni substitution is less than 5%, and less than 3% is preferred for the catalyst. It was more desirable for its stability and lifespan.

The SrTiO ₃ -based perovskite catalyst of the present invention is a high nickel content catalyst in which more than 5% of Ti sites are replaced with Ni. In the SrTiO ₃ -based perovskite catalyst of the present invention, it is appropriate that the Ni substitution at the Ti site is 5% or more and 25% or less to achieve high hydrocarbon reforming reaction catalytic activity while maintaining the perovskite structure.

In the above-described embodiment of the SrTiO ₃ -based perovskite catalyst of the present invention, carbon deposition is achieved by substituting 4% to 15% of strontium sites in the perovskite lattice structure with yttrium in response to this high nickel content. can be suppressed.

In one specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.05 ≤ x ≤ 0.15.

In another specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.07 ≤ x ≤ 0.25, and the yttrium formula coefficient y is 0.08 ≤ y ≤ 0.15. In a more specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.15 ≤ x ≤ 0.25, and the yttrium formula coefficient y is 0.08 ≤ y ≤ 0.15.

In another specific embodiment of the present invention, δ is 0.03 ≤ δ ≤ 0.23.

In another embodiment of the present invention, it is a multi-component metal oxide catalyst having a SrTiO ₃ -based perovskite lattice structure, in which part of strontium and titanium in the perovskite lattice structure is replaced with yttrium and nickel, and is represented by the following formula 2: A high nickel content catalyst for hydrocarbon reforming of the indicated composition is provided.

[Formula 2]

Sr _1-y Y _y Ti _1-x Ni _x O _3-δ

In the above formula, x is 0.05 ≤ x ≤ 0.25,

y satisfies 0 < y ≤ 0.15 and (x-0.03)/y ≤1.5,

δ is a value determined by x - 0.5y.

In the above-described embodiment of the SrTiO _3- based perovskite high-nickel content catalyst of the present invention, carbon deposition can be suppressed by replacing strontium sites in the perovskite lattice structure with yttrium in conjunction with the nickel content in response to the high nickel content. You can. Specifically, when the chemical formula coefficient of nickel is x, the chemical formula coefficient y of yttrium is set to satisfy 0 < y ≤ 0.15 and (x-0.03)/y ≤ 1.5. If the chemical formula coefficient ratio of nickel to yttrium (x-0.03)/y is 1.5 or less, yttrium suppresses carbon deposition by nickel oxide formed outside the perovskite lattice structure. In one specific embodiment, the (x-0.03)/y ratio is less than or equal to 1.1. Furthermore, in a more specific embodiment, the (x-0.03)/y ratio is 1.0 or less.

Regarding the action of the catalyst of the present invention, it is not intended to fit or be bound by any theoretical framework, but to provide an explanation solely for the purpose of helping understanding of the present invention, in light of the prior patents of the present inventor mentioned above. , if there is only nickel substitution in the SrTiO ₃ -based perovskite structure without any other changes, an amount corresponding to 3% (x = 0.03) of the titanium sites among the added nickel is nickel at the titanium site in the perovskite lattice structure. It is thought that the remaining nickel is included and settled as ions and forms nickel oxide outside the lattice structure or on the surface. In STiO ₃ , a multi-component metal oxide having the perovskite structure, a portion of the +4-valent titanium ion (Ti ⁴⁺ ) located at the B site of the lattice structure is replaced with a +2-valent nickel ion (Ni ²⁺ ). In this case, in order to maintain charge neutrality, some of the anionic oxygen ions (O ^2- ) must leave the lattice. Therefore, in the catalyst according to the present invention, Ni ²⁺ is not a cation located at the typical B site that binds to 6 oxygen ions, but is maintained in a state with a bond number lower than 6 coordination, and Ni ²⁺ located in the lattice is saturated. It is believed to exhibit catalytic activity because it maintains a coordination number lower than 6 coordination. As described previously, the nickel ions contained within the lattice structure do not cause carbon deposition but cause a reforming reaction of hydrocarbons, including methane, contributing to the smooth production of synthesis gas, a mixture of CO and H ₂ , but the perovskite lattice structure Nickel oxide (NiO) formed externally causes carbon deposition. The present inventors found that by adding more than 67% of yttrium (Y) to the perovskite lattice for each molar ratio (x-0.03) of nickel atoms corresponding to NiO formed with excess nickel substitution exceeding 3%, carbon deposition occurred. was found to suppress. In other words, carbon deposition could be suppressed when the ratio of (number of moles of nickel (NiO) existing as nickel oxide) divided by (number of moles of yttrium (Y) added) outside the grid was 1.5 or less.

In one specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.05 ≤ x ≤ 0.15.

In another specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.07 ≤ x ≤ 0.25, and the yttrium formula coefficient y is 0.08 ≤ y ≤ 0.15. In a more specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.15 ≤ x ≤ 0.25, and the yttrium formula coefficient y is 0.08 ≤ y ≤ 0.15.

In another specific embodiment of the present invention, δ is 0.05 ≤ δ ≤ 0.25.

In another embodiment of the present invention, a multi-component metal oxide catalyst having a SrTiO ₃ -based perovskite lattice structure has the following formula 3 in which some of the strontium and titanium in the perovskite lattice structure are replaced with yttrium and nickel. A catalyst for hydrocarbon reforming having the indicated composition and having a standard carbon deposition of 0.3% by weight or less based on the weight of the catalyst before reaction is provided.

[Formula 3]

Sr _1-y Y _y Ti _1-x Ni _x O _3-δ

In the above equation,

y is 0 < y ≤ 0.15, x is 0.05 ≤ x ≤ 0.25,

δ is a value determined by x - 0.5y.

In the present invention, the standard carbon deposition degree of a catalyst is a relative value expressed by the weight change value according to the degree of carbon deposition on the catalyst after catalyzing the dry reforming reaction of methane using carbon dioxide, based on the weight of the catalyst before the reaction. Specifically, the reference carbon deposition degree was applied to Y/Ni-substituted SrTiO ₃ -based perovskite catalyst pellets with a pellet average diameter in the range of 100 to 200 νm at a molar ratio CH ₄ : CO ₂ : N ₂ = 1.0 : 1.1 : 1.0. Thermogravimetric analysis of the weight change of the catalyst after supplying a reaction mixture gas at a rate of 6,000 mL·g ^-1 ·h ^-1 per unit weight of catalyst and reacting at 800°C for 50 hours. ) and expressed as a percentage of the weight of the catalyst before reaction. Thermogravimetric analysis of a catalyst can be accomplished by methods known in the art, such as methods for quantifying carbon deposited on the catalyst.

When measuring the standard carbon deposition, Mettler Toledo's 'TGA 2' was used. If possible, collect the sample within 1 day after the catalytic reaction is completed and then measure the standard carbon deposition degree. In principle, the amount of sample used is 50 mg for accurate comparison, but since it is very difficult to accurately weigh and transport the sample, it is permissible to use more than 45 mg and less than 55 mg. When the sample is mounted on the equipment, the standard carbon deposition degree is measured by flowing air at a rate of 60 mL/min, raising the temperature by 10 degrees per minute, and recording the change in sample weight. If the amount of sample in which the catalytic reaction has been completed is sufficient, the standard carbon deposition experiment is repeated three times for the same sample for more accurate measurement, and the values obtained are averaged.

If the standard carbon deposition degree is less than 0.3% by weight, it is the lower limit measured by thermogravimetric analysis, meaning that carbon deposition did not actually occur. A carbon deposition degree of 0.3% by weight or more means that carbon deposition on the catalyst was definitely found. Since the operation time of the hydrocarbon reforming reaction is at least 2 years, once carbon deposition occurs, the reaction conditions of the catalyst deteriorate due to carbon accumulation, and this phenomenon results in exponential accumulation of carbon. Therefore, catalytic activity can be maintained for a long time only if even a trace amount of carbon is not generated.

In one specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.05 ≤ x ≤ 0.15.

In another specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.07 ≤ x ≤ 0.25, and the yttrium formula coefficient y is 0.08 ≤ y ≤ 0.15. In a more specific embodiment of the present invention, the nickel formula coefficient x of the above-described catalyst is 0.15 ≤ x ≤ 0.25, and the yttrium formula coefficient y is 0.08 ≤ y ≤ 0.15.

In another specific embodiment of the present invention, δ is 0.05 ≤ δ ≤ 0.25.

In one most specific embodiment, the catalyst according to the present invention may be represented by the following formula (4).

[Formula 4]

Sr _0.96 Y _0.04 Ti _0.93 Ni _0.07 O _3-δ

In another most specific embodiment, the catalyst according to the present invention may be represented by the following formula (5).

[Formula 5]

Sr _0.92 Y _0.08 Ti _0.85 Ni _0.15 O _3-δ

In Formulas 4 and 5, δ is 0.05 and 0.11, respectively.

In another aspect, the present invention relates to a method for producing the above-described multi-component metal oxide catalyst for methane dry reforming reaction,

(i) Dissolve aqueous solutions of strontium precursor, yttrium precursor, nickel precursor, citric acid, and ethylene glycol in distilled water at 50 to 90°C at a molar ratio of 1.00 to 0.85: 0.00 to 0.15: 0.05 to 0.25: 3.6 to 4.4: 8 to 10. Preparing a first solution by mixing;

(ii) After preparing the second solution, which is a low-cost alcohol solution with a titanium precursor concentration of 0.75 to 0.95 mol%, the (strontium + yttrium + nickel) concentration of the first solution and the (titanium) concentration of the second solution are made the same. Mixing at a volume ratio of 1:1 and reacting at 50 to 90°C;

iii) first calcining the reaction mixture in an oxygen atmosphere at 300 to 400°C; and

iv) secondary calcination of the first calcination product under an oxygen atmosphere at 800 to 1200° C.

In one specific embodiment of the manufacturing method of the present invention, the step of heat treatment under a reducing atmosphere at 700 to 900° C. after secondary firing may be further included. For example, this reducing atmosphere may be selected from hydrogen, carbon monoxide, and mixtures thereof. On the other hand, a mixed gas of the above-described reducing gas and inert gas may be used in the heat treatment step. Examples of inert gases include, but are not limited to, nitrogen, helium, argon, and mixtures thereof.

In one embodiment of the present invention, the strontium precursor is strontium nitrate, the yttrium precursor is yttrium(Ⅲ) nitrate hexahydrate, and the titanium precursor is titanium isopropoxide (Titanium ( Ⅳ) isopropoxide), and the nickel precursor is nickel(II) nitrate hexahydrate.

In one embodiment of the present invention, the first firing is performed under firing conditions of a temperature increase time of 1 hour and 10 minutes and a maximum temperature holding time of 5 hours, and the secondary firing is performed under the firing conditions of a temperature increase time of 4 hours and a maximum temperature holding time of 5 hours. It is performed under the firing conditions of temperature holding time.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, and it is obvious to those skilled in the art that the scope of the present invention is not limited to these examples.

In Example 1 below, a perovskite structure in which Y ³⁺ was substituted at the Sr ²⁺ site, the A site, of strontium titanium oxide (SrTiO ₃ , STO), and Ni ²⁺ was partially substituted at the Ti ⁴⁺ site, the B site. Metal oxide Sr _1-y Y _y Ti _1-x Ni _x O _3-δ was prepared.

Example 1: Synthesis of Sr _0.92 Y _0.08 Ti _0.85 Ni _0.15 O _3-δ catalyst of perovskite (ABO ₃ ) structure (sample F)

1) While stirring at 70°C, add 0.092 mol of Strontium nitrate (Sigma aldrich, 99.0%), 0.008 mol of Yttrium(Ⅲ) nitrate hexahydrate (Sigma aldrich, 99.8%), and 0.015 mol of Nickel(Ⅱ) nitrate hexahydrate (97%) in 200 mL of distilled water. When mol was added and completely dissolved, 0.4 mol of Citric acid (Sigma aldrich, 99%) and 0.9 mol of Ethylene glycol (99%) were added and completely dissolved.

2) While stirring at 70°C, 0.085 mol of Titanium(IV) isopropoxide (Sigma aldrich, 97%) was added to 200 mL of ethyl alcohol anhydrous (Daejung, 99.9%) and completely dissolved.

3) The solution in 1) was slowly poured into the solution in 2) and stirred at 70°C for 24 h.

4) Afterwards, it was maintained at 100°C for 24 h.

5) First firing was performed under an oxygen atmosphere at 350°C (temperature rise for 1 h 10 min, maintenance for 5 h).

6) The Sr _0.92 Y _0.08 Ti _0.85 Ni _0.15 O _3-δ catalyst was synthesized by secondary calcination under an oxygen atmosphere at 900°C (temperature rise for 4 h, maintenance for 5 h).

Comparative Example 1: Synthesis of SrTiO ₃ catalyst (Sample A)

Example 1 above, except that 0.1 mol of Strontium nitrate was used in step 1), Yttrium (III) nitrate hexahydrate, and Nickel (II) nitrate hexahydrate were not used, and 0.1 mol of Titanium (IV) isopropoxide was used in step 2). SrTiO ₃ catalyst was prepared in the same manner.

Comparative Example 2: Synthesis of SrTi _0.97 Ni _0.03 O _3-δ catalyst with perovskite (ABO ₃ ) structure (Sample B)

The above procedure was performed except that 0.1 mol of Strontium nitrate and 0.003 mol of Nickel(Ⅱ) nitrate hexahydrate were used in step 1), Yttrium(Ⅲ) nitrate hexahydrate was not used, and 0.097 mol of titanium(IV) isopropoxide was used in step 2). A SrTi _0.97 Ni _0.03 O _3-δ catalyst was prepared in the same manner as Example 1.

Comparative Example 3: Synthesis of SrTi _0.93 Ni _0.07 O _3-δ catalyst of perovskite (ABO ₃ ) structure (Sample C)

The above procedure was performed except that 0.1 mol of Strontium nitrate and Yttrium(Ⅲ) nitrate hexahydrate were not used in step 1), but 0.007 mol of nickel(Ⅱ) nitrate hexahydrate was used, and 0.093 mol of titanium(Ⅳ) isopropoxide was used in step 2). A SrTi _0.93 Ni _0.07 O _3-δ catalyst was prepared in the same manner as Example 1.

Comparative Example 4: Synthesis of SrTi _0.85 Ni _0.15 O _3-δ catalyst of perovskite (ABO ₃ ) structure (Sample D)

The above procedure was performed except that 0.1 mol of Strontium nitrate and 0.015 mol of Nickel(Ⅱ) nitrate hexahydrate were used in step 1), Yttrium(Ⅲ) nitrate hexahydrate was not used, and 0.085 mol of titanium(Ⅳ) isopropoxide was used in step 2). A SrTi _0.85 Ni _0.15 O _3-δ catalyst was prepared in the same manner as Example 1.

Comparative Example 5: Synthesis of Sr _0.96 Y _0.04 Ti _0.85 Ni _0.15 O _3-δ catalyst of perovskite (ABO ₃ ) structure (Sample E)

The above procedure was performed except that 0.096 mol of Strontium nitrate, 0.004 mol of Yttrium(Ⅲ) nitrate hexahydrate, and 0.015 mol of Nickel(Ⅱ) nitrate hexahydrate (97%) were used in step 1), and 0.085 mol of titanium(Ⅳ) isopropoxide was used in step 2). A Sr _0.96 Y _0.04 Ti _0.85 Ni _0.15 O _3-δ catalyst was prepared in the same manner as Example 1.

The catalyst samples prepared in Example 1 and Comparative Examples 1 to 5 were classified into sample names A to F, respectively, and the following experimental examples were performed. Each classified sample is shown in Table 1 below.

Experimental Example 1: Structural analysis through XRD

The structures of the catalyst samples prepared through Example 1 (Sample F) and Comparative Examples 1 to 5 (Samples A to E) were determined through X-ray diffraction analysis.

Figure 1 shows X-ray diffractograms of prepared catalyst samples. It was confirmed through Figure 1-a that the prepared catalyst samples were SrTiO ₃ with a perovskite structure. Figures 1-b, 1-c, and 1-d show enlarged peak positions corresponding to NiO. For samples A (SrTiO ₃ ) and B (SrTi _1-x Ni _x O _3-δ , x = 0.03), no peak corresponding to nickel oxide (NiO) was found, but for sample C (SrTi _1-x Ni _x O _{3 -δ} , x = 0.07) and sample D ( _{SrTi 1 -} x Ni

These experimental results are related to the content of Ni ²⁺ added during synthesis. When synthesizing a sample, in order to increase the number of Ni ²⁺ that can be substituted for Ti ⁴⁺ at the B site, if the number of Ni ²⁺ is increased by more than 5% compared to the total number of Ti ⁴⁺ , a NiO peak is observed. It has been done. This means that the proportion of Ni ²⁺ that can be substituted for the Ti ⁴⁺ site, which is the B site, in the perovskite SrTiO ₃ structure is less than 5%.

In the X-ray diffraction diagram of FIG. 2-a, in the case of sample D (SrTi _1-x Ni _x O _3-δ , x = 0.15), Ni ²⁺ was added in excess to form NiO. However, for sample E (Sr _1-y Y _y Ti _1-x Ni _x O ₃ , y = 0.04, x = 0.15) and sample F (Sr _1-y Y _y Ti _1-x Ni _x O ₃ , y = 0.08 , x = 0.15), the size of the NiO peak decreased in samples with 4% and 8% Y ³⁺ substitution compared to the number of Sr ²⁺ at the A site.

Figure 2-b shows an enlarged view of only the peak between 37.0 and 37.5° corresponding to NiO. It was confirmed that the intensity of the NiO peak decreased as the Y ³⁺ substitution addition ratio increased from 0% to 4% and 8%. This means that Y ³⁺ suppresses the formation of NiO due to the addition of excessive Ni ²⁺ by substitution and addition of Y ³⁺ .

Experimental Example 2: Methane reforming reaction experiment - Dry Reforming of Methane reaction

Catalyst sample F synthesized in Example 1 was heated at 800°C (temperature raised for 2 hours and 40 minutes, maintained at 2) under the conditions of 10 vol.% H ₂ /N ₂ (space velocity, SV = 30,000 mL·g ^-1 ·h ^-1 ). Time) After the reduction process, the DRM reaction was performed (reaction temperature 800°C, CH ₄ : CO ₂ : N ₂ = 1.0 : 1.1 : 1.0, SV = 6,000 mL·g ^-1 ·h ^-1 , pellet size = 100 ~200 μm).

Based on the X-ray diffraction analysis shown in Figure 1, DRM reaction was performed on samples D, E, and F as shown in Figure 3. CH ₄ conversion rate and CO ₂ conversion rate over reaction time were shown for each sample. In all three samples, the substitution ratio of Ni ²⁺ to Ti ⁴⁺ was 15%. Although the active point of the DRM reaction is nickel, each sample showed significant differences in reactivity. In the case of SrTiO ₃ , the maximum rate for substitution of Ni ²⁺ at the B site of the perovskite lattice structure is less than 5%, so in the case of samples D, E, and F, NiO, which is expected to cause carbon deposition in the DRM reaction, will not be formed. There is no choice but to do so.

When Sample _D (SrTi _{1-x Ni} Therefore, the CH ₄ conversion rate and CO ₂ conversion rate decreased rapidly within 1 hour after the reaction started. In other words, Sample D was not suitable for DRM reaction. However, Sample E (Sr _1-y Y _y Ti _1-x ^Ni _x O ₃ , y = 0.04, x = 0.15) and Sample F (Sr _1- In the case of _y Y _y Ti _{1- x Ni}

In order to determine the extent to which carbon is deposited on the catalyst, DRM reaction was performed on each of samples D, E, and F for 50 hours, then recovered, and the content of carbon deposited in the sample was measured by thermogravimetric analysis (10 Measure the weight change from 50℃ to 900℃ at a rate of ℃/min). In the case of sample D, a large amount of carbon (carbon content of 30 wt.% or more) was deposited after 50 hours of DRM reaction. However, in the case of sample E, when the Y ³⁺ substitution ratio increased to 4% compared to 0 % in sample D, the carbon deposition amount was very low to less than 3 wt.%, and when the Y ³⁺ substitution ratio increased to 8 % as in sample F, As shown in Figure 2, NiO was formed, but carbon deposition was not measured.

Through these experimental results, it was confirmed that if an appropriate amount of Y ³⁺ is substituted for Sr ²⁺ , the catalysts according to the present invention can suppress carbon deposition even under conditions where carbon deposition occurs very severely on the catalyst during the DRM reaction.

To further specify this, the Ni ²⁺ substitution ratio at the B site of the perovskite structured Sr _1-y Y _y Ti _1-x Ni _x O ₃ catalyst (x = 0, 0.03, 0.05, 0.07, 0.11, 0.15 ) and the degree of coke formation according to the Y ³⁺ substitution ratio at the A site by DRM reaction for samples of the corresponding composition (reaction temperature 800°C, CH ₄ : CO ₂ : N ₂ = 1.0 : 1.1 : 1.0, SV = 6,000 mL·g ^-1 ·h ^-1 , pellet size = 100~200 μm, reaction time 50 hours), and the degree of carbon deposition was measured after the reaction.

Table 2 below shows the DRM reaction applied to the perovskite structure (Sr _1-y Y 0.04, 0.06, 0.08, x = 0, 0.03, 0.05, 0.07, 0.11, 0.15) and the degree of carbon deposition.

Table 2 shows the results of recovering the catalyst after 50 hours of reaction under the conditions presented above and measuring the content of carbon deposited inside the catalyst using a thermogravimetric analysis (TGA). In the case of “No coke,” it means a degree of carbon deposition within 0.3 wt% per weight of catalyst. In the case of “small coke,” it means a degree of carbon deposition exceeding 0.3 wt% and within 3 wt% per weight of catalyst. “Coke” means a degree of carbon deposition per weight of catalyst. It means carbon deposition of more than 3 wt% and less than 35 wt% per weight. When the Ni ²⁺ substitution ratio was 0%, there were no catalytic active sites for the DRM reaction, so the results were the same as the non-catalytic reaction (blank test). Therefore, there was no activity for DRM response. Catalysts to which nickel was added all showed excellent catalytic activity with a CH ₄ conversion rate of over 95% and a CO ₂ conversion rate of over 90%. Since the catalytic activity was very excellent, the amount of carbon deposition was measured to confirm the long-term stability of the catalysts. When the Ni ²⁺ substitution ratio was 3%, carbon deposition did not occur regardless of the Y ³⁺ addition ratio and the DRM reaction was maintained stably for more than 50 hours. When the Ni ²⁺ substitution ratio was 5% and the Y ³⁺ addition ratio was 0 % (without Y ³⁺ addition), some carbon deposition occurred due to the formed NiO (small coke, carbon deposition 2 wt%). However, when the Y ³⁺ addition ratio increased to 2, 4, 6, and 8 %, carbon deposition did not occur (no coke, carbon deposition within 0.3 wt%). When the Ni ²⁺ substitution ratio was 7% and the Y ³⁺ addition ratio was 0% (without Y ³⁺ addition), carbon deposition occurred (Coke, carbon deposition 15 wt%). However, when the Y ³⁺ addition ratio was 2%, some carbon deposition occurred (Small coke, carbon deposition 3 wt%), and when the Y ³⁺ addition ratio was 4, 6, and 8 %, no carbon deposition occurred (No coke, carbon deposition within 0.3 wt%). When the Ni ²⁺ substitution ratio was 11% and the Y ³⁺ addition ratio was 0 and 2%, carbon deposition occurred (Coke and carbon deposition 27 and 8 wt%, respectively). However, when the Y ³⁺ addition ratio was 4%, some carbon deposition occurred (small coke, carbon deposition 3 wt%), and when the Y ³⁺ addition ratio was 6 or 8 %, no carbon deposition occurred (no coke, carbon). deposition within 0.3 wt%). When the Ni ²⁺ substitution ratio was 15% and the Y ³⁺ addition ratio was 0, 2, and 4%, carbon deposition occurred (Coke, carbon deposition 35, 25, and 10 wt%, respectively). However, when the Y ³⁺ addition ratio was 6%, some carbon deposition occurred (small coke, carbon deposition 3 wt%), and when the Y ³⁺ addition ratio was 8 %, no carbon deposition occurred (no coke, carbon deposition 0.3 wt%). within wt%). It was confirmed that even if the amount of Ni ²⁺ substitution increases, carbon deposition is suppressed when the amount of Y ³⁺ substitution is also increased.

As a more specific example, when the Ni ²⁺ substitution ratio increased to 7%, 11%, and 15%, carbon deposition was suppressed only when the Y ³⁺ addition ratio was increased. When the Ni ²⁺ substitution ratio was 15% and the Y ³⁺ addition ratio was 8%, carbon deposition was suppressed (Example 1).

If organized based on the amount of Y ³⁺ substitution, it is as follows. When the Y ³⁺ substitution amount is 2%, the Ni ²⁺ substitution amount at which carbon deposition does not occur is 5% or less (no coke, carbon deposition amount is 0.3 wt% or less), and when the Ni ²⁺ substitution amount is 7%, carbon deposition occurs slightly. (small coke, carbon deposition amount 3 wt%), and when the Ni ²⁺ substitution amount was 11 and 15 %, a large amount of carbon deposition occurred (Coke, carbon deposition amount 8 and 25 wt%, respectively). When the Y ³⁺ substitution amount is 4%, the Ni ²⁺ substitution amount at which carbon deposition does not occur is 7% or less (no coke, carbon deposition amount is 0.3 wt% or less), and when the Ni ²⁺ substitution amount is 11%, carbon deposition occurs slightly. (small coke, carbon deposition amount 3 wt%), and when the Ni ²⁺ substitution amount was 15%, a large amount of carbon deposition occurred (Coke, carbon deposition amount 10 wt% each). When the Y ³⁺ substitution amount is 6%, the Ni ²⁺ substitution amount at which carbon deposition does not occur is 11 % or less (no coke, carbon deposition amount is 0.3 wt% or less), and when the Ni ²⁺ substitution amount is 15 %, some carbon deposition occurs. (small coke, carbon deposition 3 wt%). When the Y ³⁺ substitution amount was 8%, carbon deposition did not occur in the Ni ²⁺ substitution amount range (3 to 15%) implemented in the present invention (no coke, carbon deposition amount less than 0.3 wt%). Through this, it was confirmed that Y ³⁺ substitution for Sr ²⁺ in perovskite-structured Sr _1-y Y _y Ti _1-x Ni _x O ₃ samples suppresses carbon deposition in the DRM reaction.

Experimental Example 3: Methane reforming reaction experiment - correlation between nickel substitution amount and space velocity

Catalyst sample F synthesized in Example 1 and catalyst sample B synthesized in Comparative Example 2 were reacted under the conditions of 10 vol.% H ₂ /N ₂ (space velocity, SV = 30,000 mL·g ^-1 ·h ^-1 ). After a reduction process at 800°C (temperature rise for 2 hours and 40 minutes, maintenance for 2 hours), the DRM reaction was performed. (Reaction temperature 800℃, CH ₄ : CO ₂ : N ₂ = 1.0 : 1.1 : 1.0, SV = 6,000 ~ 30,000 mL·g ^-1 ·h ^-1 , pellet size = 100~200 μm)

Sr _0.92 Y ^0.08 _Ti ^0.85 Ni ^0.15 _O 3 ^- _δ sample ( _Example 1, Sample F) is superior to the SrTi _0.97 Ni _0.03 O _3-δ sample (Comparative Example 2, Sample B) in which the amount of Ni ²⁺ substitution is limited to 3% due to the absence of Y ³⁺ substitution at the Sr ²⁺ position, which is the A site. It is shown as 4. When the space velocity was low (SV = 6,000 mL·g ^-1 ·h ^-1 ), there was no difference in the conversion rates of CH ₄ and CO ₂ between Sample B and Sample F. However, in the case of sample B, which lacks substituted nickel, which is a catalytically active site, the conversion rates decreased rapidly as the space velocity increased. However, in the case of sample F, which had about 5 times more catalytic active sites, the conversion rates were almost the same or slightly decreased even as the space velocity increased. If the conversion rate is maintained even as the space velocity increases, the amount of product that can be produced with the same reactor volume per unit time in the DRM process increases, thereby increasing productivity. However, if the number of catalytic active sites is insufficient, there is a limit to increasing productivity. Therefore, it was found that manufacturing a catalyst with increased Ni ²⁺ substitution through the addition of Y ³⁺ could increase the productivity of the process without carbon deposition.

Experimental Example 4: Methane reforming reaction experiment - Partial Oxidation of Methane reaction

The synthesized samples were reduced at 800°C (temperature raised for 2 hours and 40 minutes, maintained for 2 ^hours ) under the conditions of 10 vol.% H ₂ ^/ 90 vol.% N ₂ (space velocity, SV = 30,000 mL·g -1 ·h 1 ). After going through this process, the POM reaction was performed. (Reaction temperature: 850 ℃, CH ₄ : O ₂ = 1 : 0.5, space velocity = 20,000 mL·g ^-1 ·h ^-1 , pellet size = 100~200 μm)

As shown in Figure 5, it was confirmed that the catalytic activity was stably maintained while the POM reaction was carried out for more than 50 hours under the conditions presented above. Analysis of the composition of the product showed that the H ₂ /CO ratio was close to 2.0, which is believed to be because the complete combustion reaction was excluded and the POM reaction was dominant.

As the specific parts of the present invention have been described in detail above, it is clear to those skilled in the art that these specific techniques are merely preferred embodiments and do not limit the scope of the present invention. do. Anyone skilled in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

The perovskite metal oxide catalyst according to the present invention can be used as a catalyst for methane dry reforming reaction and can be used for a long time without worrying about performance degradation due to carbon deposition.

Claims (17)

delete In the multi-component metal oxide catalyst having a SrTiO ₃ -based perovskite lattice structure,
The catalyst has a composition represented by the following formula (2) in which some of the strontium and titanium in the perovskite lattice structure are replaced with yttrium and nickel,
Catalyst for hydrocarbon reforming in which a nickel oxide peak is observed in the 2θ value range of 37.0˚~37.5˚ during X-ray diffraction analysis:
[Formula 2]
Sr _1-y Y _y Ti _1-x Ni _x O _3-δ
In the above equation, x is 0.07 ≤ x ≤ 0.25,
y satisfies 0.04 < y ≤ 0.15 and (x-0.03)/y < 1.5,
δ is a value determined by x - 0.5y. delete delete The catalyst for hydrocarbon reforming according to claim 2, wherein y is 0.08 ≤ y ≤ 0.15. The catalyst for hydrocarbon reforming according to claim 5, wherein x is 0.15 ≤ x ≤ 0.25. The catalyst for hydrocarbon reforming according to claim 2, wherein (x-0.03)/y ≤ 1.1. delete The catalyst for hydrocarbon reforming according to claim 2, wherein δ is 0.05 ≤ δ ≤ 0.25. The catalyst for hydrocarbon reforming according to claim 2, wherein (x-0.03)/y < 1.0. A catalyst having a composition represented by the following formula (4),
During X-ray diffraction analysis, a nickel oxide peak is observed in the 2θ value range of 37.0˚~37.5˚,
Catalyst for hydrocarbon reforming with a standard carbon deposition degree of 0.3% by weight or less based on the weight of the catalyst before reaction:
[Formula 4]
Sr _0.96 Y _0.04 Ti _0.93 Ni _0.07 O _3-δ
In the above equation, δ is 0.05. A catalyst for hydrocarbon reforming that has the composition represented by the following formula (5) and in which a nickel oxide peak is observed in the 2θ value range of 37.0˚ to 37.5˚ during X-ray diffraction analysis:
[Formula 5]
Sr _0.92 Y _0.08 Ti _0.85 Ni _0.15 O _3-δ
In the above equation, δ is 0.11. delete delete delete delete delete

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