WO2023163573A1 - Catalyst for hydrocarbon compound synthesis through direct reaction between carbon dioxide and hydrogen, preparation method therefor, and hydrocarbon compound synthesis method using same - Google Patents

Abstract

A catalyst for accelerating hydrogenation of carbon dioxide is disclosed. The catalyst may comprise a core including a metal cobalt phase, and a shell positioned on the surface of the core and including a Co3O4 phase and a Co2C phase.

Description

Catalyst for hydrocarbon compound synthesis reaction through direct reaction of carbon dioxide and hydrogen, method for preparing the same, and method for synthesizing hydrocarbon compound using the same

The present invention relates to a catalyst that can be applied to synthesize a hydrocarbon compound through a direct reaction of carbon dioxide and hydrogen, a method for preparing the same, and a method for synthesizing a hydrocarbon compound using the same.

The development of technologies that effectively use carbon dioxide (CO ₂ ) to form fuels and chemicals is a very promising strategy for establishing CO ₂ -neutral and sustainable societies. The thermal catalytic conversion of carbon dioxide, mainly based on the Reverse Water-Gas Shift (RWGS) reaction and the subsequent Fischer-Tropsch synthesis (FTS) reaction, is a gas fuel containing 1 to 4 carbon atoms (C ₁ -C ₄ ), carbon atoms 5 or more (C ₅₊ ) is considered a promising approach to create value-added platform compounds such as liquid fuels, olefins, acids, alcohols, aromatics, etc.

[Scheme 1]

CO ₂ (g) + H ₂ (g) → CO (g) + H ₂ O (g)

Iron (Fe)-based catalysts and cobalt (Co)-based catalysts were mainly used as FTS reaction catalysts that produce alkanes, alkenes, and oxygenates using syngas, which is a mixture of hydrogen (H ₂ ) and carbon monoxide (CO). , A number of studies have been conducted on using these catalysts as catalysts for hydrogenation of carbon dioxide.

Fe-based catalysts showed similar catalytic performance regardless of whether CO or CO ₂ was used as the feed. In the case of Fe-based catalysts, the RWGS reaction of CO ₂ on the Fe ₃ O ₄ site is promoted through a redox cycle, followed by a continuous FTS reaction on the Fe ₅ C ₂ site to generate C ₅₊ hydrocarbons at high yields. can create (About 20% or more at gas hourly space velocity (GHSV)≥4000 mL g ^-1 h ^-1 )

Co-based catalysts are characterized by high chain growth probability (>0.94), high cycle rate, high selectivity to linear paraffins, low WGS reaction activity, high inactivation resistance to water molecules formed during FTS, and high long-term stability. It is very effective for FTS reactions at relatively low temperatures (<240 °C). When producing long-chain hydrocarbons under typical FTS reaction conditions, metallic Co centers have been considered as the major active sites for the hydrogenation of carbon monoxide, and recently it has been suggested that hydrogenation activity of carbon monoxide on Co ₂ C is possible when producing lower olefins. It became.

However, in the case of direct carbon dioxide hydrogenation on a Co-based catalyst, the main product is methane (CH ₄ ), and the yield of C ₅₊ hydrocarbons (<5% at GHSV≥4000 mL g ^-1 h ^-1 ) is very low. There is a problem. The high carbon dioxide methanation activity of the Co-based catalyst is due to the absence of active sites that can promote RWGS and the low C/H ratio on the active surface leading to hydrogenation of CO ₂ adsorbed species rather than chain extension reactions.

In order to solve the problem of these Co-based catalysts, a method for directly converting carbon dioxide into light olefins and ethanol using two-component metal CoFe and CoNi catalysts, respectively, has been proposed. Because of the lack of comprehensive understanding, designing Co-based catalysts still remains a difficult technical problem.

One object of the present invention is a core formed of metal cobalt when exposed to a hydrogen / carbon dioxide mixed gas containing Mn; and a shell formed of a mixture including a Co ₃ O ₄ phase and a Co ₂ C phase on the surface of the core, and when the carbon dioxide hydrogenation reaction proceeds, a high CO ₂ of about 60% or more. It is to provide a catalyst for hydrogenation of carbon dioxide capable of achieving a conversion rate and a remarkably high C ₅₊ hydrocarbon selectivity of about 30% or more.

Another object of the present invention is to provide a method for preparing the catalyst.

Another object of the present invention is to provide a method for synthesizing a hydrocarbon compound having 5 or more carbon atoms using the catalyst.

A catalyst for a hydrogenation reaction of carbon dioxide according to an embodiment of the present invention may be used as a catalyst for promoting a hydrogenation reaction of carbon dioxide, and may include a core including a metal cobalt phase; and a shell located on the surface of the core and including a Co ₃ O ₄ phase and a Co ₂ C phase.

In one embodiment, the ratio of the number of moles of manganese to the total number of moles of cobalt and manganese in the catalyst [Mn/(Co+Mn)] may be about 3 or more and about 20% or less.

In one embodiment, the fraction of the metal cobalt phase in the cobalt-containing phase of the entire catalyst may be about 90% or more and less than 100%.

In one embodiment, the core may include a metal cobalt phase having a crystal phase of a hexagonal close-packed lattice structure, and pores exposing the core to the outside may be formed in the shell.

In one embodiment, the shell may further include CoO in addition to the Co ₃ O ₄ as a cobalt oxide phase, and in this case, the [CoO+Co ₃ O ₄ ]/Co ^O ratio may be about 1.5 to 1.9. .

In one embodiment, the area ratio of the Co ₂ C phase in the shell may be about 10 to 30%.

In one embodiment, the shell may further include a manganese-containing phase, and in this case, the manganese-containing phase may include a MnCO ₃ phase, Mn ₂ O ₃ and Mn ₃ O ₄ . For example, the fraction of the MnCO ₃ phase in the manganese-containing phase may be about 90 to 99%.

In one embodiment, the catalyst may further include a carbon layer located on the surface of the shell.

A method for preparing a catalyst for hydrogenation of carbon dioxide according to an embodiment of the present invention is a method of forming a suspension solution by mixing a reaction solution in which a cobalt precursor compound and a manganese precursor compound are dissolved and a precipitant solution in which a basic precipitant is dissolved. Level 1; A second step of aging the suspension solution; A third step of separating powder from the aged suspension solution; and a fourth step of drying and heat-treating the separated powder to form first catalyst powder.

In one embodiment, the method may further include a fifth step of forming second catalyst powder by reducing the first catalyst powder in a hydrogen atmosphere.

In one embodiment, the method may further include a sixth step of forming a third catalyst powder by exposing the second catalyst powder to a flow of a mixed gas of carbon dioxide (CO ₂ ) and hydrogen (H ₂ ). there is.

In one embodiment, in the first step, the cobalt precursor and the manganese precursor have a ratio of moles of manganese ions to total moles of cobalt ions and manganese ions in the reaction solution of about 3 to 20%. It may be added to the reaction solution as much as possible.

In one embodiment, the total concentration of the cobalt precursor and the manganese precursor in the reaction solution may be about 1.5 to 3 mol/L.

In one embodiment, the basic precipitant may include sodium carbonate (Na ₂ CO ₃ ).

In one embodiment, the separated powders in the fourth step may be dried at a temperature of about 90 to 110 ° C and then heat-treated for about 2 to 5 hours under air flow conditions of about 300 to 360 ° C.

In one embodiment, the first catalyst powder may include a cobalt oxide phase, a manganese oxide phase, and a phase each of which is doped with sodium.

In one embodiment, the fifth step is performed by supplying hydrogen gas into the tubular reactor at a temperature of 320 to 400 ° C. for 4 to 8 hours after fixing the first catalyst powder in the tubular reactor, and the fifth During the step, the first catalyst powder may be converted into the second catalyst powder comprising a metallic cobalt phase, a cobalt oxide phase and a manganese oxide phase.

In one embodiment, the sixth step is performed by supplying a mixed gas of hydrogen and carbon dioxide after adjusting the temperature inside the tubular reactor in which the second catalyst powder is fixed to 250 to 300 ° C. During step 6, the second catalyst powder includes a core formed of metallic cobalt; and the third catalyst powder including a shell formed of a mixture including a Co ₃ O ₄ phase and a Co ₂ C phase on the surface of the core.

In one embodiment, the pressure inside the tubular reactor may be adjusted to about 3.5 to 5.0 MPa during the sixth step.

In one embodiment, a mixed gas in which hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) are mixed at a ratio of about 2.5:1 to 3.5:1 may be supplied into the tubular reactor during the sixth step.

In the method for synthesizing a hydrocarbon compound according to an embodiment of the present invention, a hydrocarbon compound having 5 or more carbon atoms can be produced by inducing a hydrogenation reaction of carbon dioxide by supplying a mixed gas of hydrogen and carbon dioxide into a tubular reactor in which a catalyst is fixed, The catalyst comprises a core comprising a metallic cobalt phase; and a shell located on the surface of the core and including a Co ₃ O ₄ phase and a Co ₂ C phase.

* In one embodiment, the temperature inside the tubular reactor may be adjusted to about 250 to 300 ° C. during the hydrogenation of carbon dioxide.

In one embodiment, the pressure inside the tubular reactor may be adjusted to about 3.5 to 5.0 MPa during the hydrogenation of carbon dioxide.

In one embodiment, during the hydrogenation reaction of carbon dioxide, a mixed gas in which hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) are mixed at a ratio of about 2.5:1 to 3.5:1 may be supplied into the tubular reactor.

In one embodiment, the proportion of linear paraffin in the hydrocarbon compound having 5 or more carbon atoms may be about 90% or more and less than 100%.

The catalyst according to the present invention includes a core formed of metal cobalt when exposed to a hydrogen/carbon dioxide mixture gas containing Mn together with Co; and a shell formed of a mixture including a Co ₃ O ₄ phase and a Co ₂ C phase on the surface of the core. As a result, when hydrogenation of carbon dioxide is performed using the shell, about 60 % or more and remarkably high C _{5+ hydrocarbon} selectivity of about 30% or more can be achieved, as well as carbon monoxide production can be highly suppressed with a selectivity of less than about 0.5%. In addition, the ratio of linear paraffin among the C ₅₊ hydrocarbons produced using the catalyst may be about 90% or more.

1 is a flow chart for explaining a method for preparing a cobalt-manganese composite catalyst according to an embodiment of the present invention.

FIG. 2 is a view for explaining a catalyst synthesized according to the method shown in FIG. 1 .

3 are graphs showing the results of catalytic performance evaluation of CMO-y catalysts according to changes in Mn content.

Figure 4a is a CO ₂ conversion rate and products according to the reaction time on the CMO-0 catalyst and the CMO-10 catalyst under pressure conditions of 1.0 MPa (A, B), 2.0 MPa (C, D), and 3.0 MPa (E, F) Graphs showing the results of measuring selectivity, and FIG. 4b is CO ₂ as a function of reaction time on CMO-0, CMO-10, CMO-25, CMO-50, CMO-75, and CMO-100 catalysts at 4.0 MPa. These are graphs showing the results of measuring conversion rate and product selectivity.

Figure 5a is a graph showing the results of measuring the CO ₂ conversion rate and product selectivity according to the reaction pressure of the CMO-0 catalyst (A) and the CMO-10 catalyst (B), and Figure 5b is a graph showing the reaction time of the CMO-10 catalyst It is a graph showing the results of measuring the CO ₂ conversion rate and product selectivity.

6 is graphs showing the results of measuring the CO ₂ conversion rate and product selectivity according to the reaction temperature (A) of the CMO-10 catalyst, the H ₂ /CO ₂ ratio of syngas (B), and GHSV (C).

7a shows XRD patterns measured in fresh, reduced, and spent states of CMO-0 and CMO-10 catalysts, respectively, and FIGS. 7b and 7c show CMO-0, CMO- 10, CMO-25, CMO-50, CMO-70 and CMO-100 catalysts in fresh state (A, B, C) and reduced state (D, E, F) respectively The measured XRD patterns are shown, and FIG. 7d shows the XRD patterns measured in the spent state of each of the CMO-0, CMO-10, CMO-25, CMO-50, CMO-70 and CMO-100 catalysts, Figure 7e shows XRD patterns measured for CMO-10 catalysts converted at 230 °C, 250 °C, 270 °C, 290 °C, and 310 °C, respectively.

Figure 8a shows Co K-edge XANES spectra for CMO-y catalysts after reduction (A) and converted CMO-y catalysts (B), and Figure 8b shows Co K-edge XANES profiles evaluated from linear combination fitting. 8c is a graph showing the relationship between metallic Co content and C ₅₊ hydrocarbon yield, and FIG. 8c is a relationship between surface carbide content and C ₅₊ hydrocarbon yield evaluated from C 1s XPS spectrum (D) and [CoO +CO3O4]/CoO and the graph showing the relationship (E) between the C ₅₊ hydrocarbon yield, and FIG. 8d shows the relationship between the crystal size measured by XRD and the C ₅₊ hydrocarbon yield (F) and Co It is a graph showing the relationship (G) between the metallic Co content evaluated from the linear combination fitting of the K-edge XANES profiles and the crystallite size measured by XRD.

FIG. 9a shows normalized Co K-edge XANES spectra measured for a converted CMO-0 catalyst (A) and a converted CMO-10 catalyst (B) at various reaction pressures (1 MPa, 2 MPa, 3 MPa, 4 MPa), respectively. FIG. 9 b is at various reaction temperatures (230 ℃, 250 ℃, 270 ℃, 290 ℃, 310 ℃) (C) and various H ₂ /CO ₂ mixing ratio (H ₂ /CO ₂ =1, 2, 3, 4) (D) Co K-edge XANES spectra measured for the converted CMO-10 catalyst, respectively, and FIG. 9c shows various GHSV (4000 mL g ^-1 h ^-1 , 8000 mL g ^-1 h ^-1 , 12000 mL g ^-1 h ^{- 1} ) and after various reaction times (120 hr, 1440 hr) Co K-edge XANES spectra measured for the converted CMO-10 catalyst, respectively.

10 is a k ³ -weighted Fourier transform (k ³ -weighted Fourier transforms, FTs) (A) and CMO-10 catalyst converted at 270°C fitted with only metallic Co (B), CMO-10 catalyst converted at 290°C fitted only with metallic Co (C) and metallic Co and Filtered K ³ -weighted χ(k) spectra of CMO-10 catalyst (D) converted at 310 °C fitted with CoO are ^shown .

Figure 11 shows the normalized Mn K-edge XANES spectra of the CMO-y catalyst (A) and the converted CMO-y catalyst (B) after reduction.

12 shows CMO-10 catalyst before reduction, CMO-10 catalyst after reduction and conversion (125 hr, 1425 hr) CMO in C 1s (A), Co 2p (B), O 1s (C) and Mn 2p (D) regions. High-resolution XPS profiles of -10 catalysts are shown.

13 shows high-resolution XPS profiles of CMO-0 catalysts before reduction, CMO-0 catalysts after reduction, and converted (125 hr) CMO-10 catalysts in C 1s (A), Co 2p (B), and O 1s (C) regions. indicate

14a is a diagram showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of the CMO-0 catalyst before reduction, and FIG. HAADF-STEM image of 0 catalyst (F) and its corresponding Co (G); O (H); C (I); Na(J); Co and O (K); It is a diagram showing EDX images of Co, C and O (L).

15a is a view showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of the CMO-10 catalyst before reduction, and FIG. HAADF-STEM image of 10 catalyst (F) and its corresponding Co (G); O (H); C (I); Mn (J); Na(K); Co and O (L); It is a diagram showing EDX images of Co, C and O (M).

16a is a diagram showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of the CMO-0 catalyst after reduction, and FIG. HAADF-STEM image of 0 catalyst (F) and its corresponding Co (G); O (H); C (I); Na(J); Co and O (K); It is a diagram showing EDX images of Co, C and O (L).

Figure 17a is a diagram showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of CMO-10 catalyst after reduction, and Figure 17b is a diagram showing CMO-10 catalyst after reduction HAADF-STEM image of 10 catalyst (F) and its corresponding Co (G); O (H); C (I); Mn (J); Na(K); Co and O (L); It is a diagram showing EDX images of Co, C and O (M).

18a shows HR-TEM images (A-C, E) and FFT images (D) of the converted CMO-0 catalyst, and FIG. 18B shows HAADF-STEM images (F) of the converted CMO-0 catalyst and the corresponding Co ( G); O (H); C (I); Co and O (J); Co, O and C (K); and EDX images of Na (L), FIG. 18C shows Co (M); Co and O (N); Shows the enlarged outermost shell layer of Co, O and C(O).

19a shows HR-TEM images (A-C, E) and FFT images (D) of the converted CMO-10 catalyst, and FIG. 19B shows HAADF-STEM images (F) of the converted CMO-10 catalyst and the corresponding Co ( G); O (H); C (I); Mn (J); Co, Mn and O (K); and EDX images of Co, Mn, C, and O (L), FIG. 19C shows Co (M); Co and O (N); Shows the enlarged outermost shell layer of Co, O and C(O).

20 shows N ₂ adsorption-desorption contours of the pre-reduction CMO-y catalyst (A), the post-reduction CMO-y catalyst (B), and the converted CMO-y catalyst (C).

21 shows HR-TEM images of the converted CMO-0 catalyst converted under the reaction pressure condition of 1.0 MPa.

22 shows HR-TEM images of the converted CMO-10 catalyst converted under the reaction pressure condition of 1.0 MPa.

Figure 23a shows SEM, HR-TEM and FFT images of the converted CMO-10 catalyst converted under reaction temperature conditions of 230 °C (A), 250 °C (B), 290 °C (C) and 310 °C (D), Figure 23b is HR-TEM of the converted CMO-10 catalyst converted under reaction temperature conditions of 230 °C (A), 250 °C (B), 270 °C (C), 290 °C (D) and 310 °C (E, F) represent images.

24 shows SEM, HR-TEM and FFT images of converted CMO-10 catalysts converted under conditions of H ₂ /CO ₂ ratios of 1:1, 2:1 and 4:1.

25 shows SEM and HR-TEM images of the CMO-10 catalyst after 1425 hours of reaction.

Figure 26a shows the H ₂ -TPR profile for the CMO-y catalyst before reduction heat treatment at 330 ° C, and FIGS. 26b to 26d show the CO ₂ -TPD profile, CO-TPD profile and H ₂ of the CMO-y catalyst after reduction. -Indicates each TPD profile.

27A-D show in situ DFIFT CO ₂ adsorption profiles on CMO-10 catalyst.

28A-28C show in situ DFIFT CO ₂ adsorption profiles on CMO-0 catalysts.

29A-29C show in situ DFIFT CO adsorption profiles on CMO-0 catalysts.

30A-30C show in situ DFIFT CO adsorption profiles on CMO-10 catalyst.

31A and 31B show QMS profiles of products released from the DRIFT cell during H ₂ flow over CMO-O catalyst (A), CMO-10 catalyst (B) after CO pressurization to 3.0 MPa and temperature rise to 270 °C. indicate

32A to 32C show reaction profiles of in situ DFIFT CO ₂ and H ₂ over CMO-0 catalyst after reduction.

33A to 33C show reaction profiles of in situ DFIFT CO ₂ and H ₂ over CMO-10 catalyst after reduction.

34A and 34B show in situ DFIFT CO ₂ and H ₂ reaction profiles (A) for 60 _{minutes on CMO-10 catalyst after reduction under varying reaction pressure conditions and CO 2 -adsorbed} species, adsorbed Evolution of CO, gaseous CO and CH ₄ is shown (B).

35A and 35B _show in situ DFIFT CO ₂ and H ₂ reaction profiles (A) for 60 minutes on CMO-0 catalyst after reduction under varying reaction temperature conditions and CO ₂ -adsorbed species, adsorbed Evolution of CO, gaseous CO and CH ₄ is shown (B).

36 shows the hydrogenation pathway of CO2 (A), the surface structure of Co-containing phases (B), and the free energies of CO ₂ hydrogenation (C, D) for CH and CO under the conditions of a temperature of 270 °C and a pressure of 4.0 MPa. indicate

37 shows the free energy profiles (A, B) calculated by DFT of the RWGS reaction with HCOO and HOCO intermediates and the free energy profile of CO hydrogenation to CH formation (C).

Hereinafter, a catalyst for synthesizing a hydrocarbon compound through a direct reaction of carbon dioxide and hydrogen according to an embodiment of the present invention, a method for preparing the same, and a method for synthesizing a hydrocarbon compound using the same will be described in detail with reference to the accompanying drawings. Since the present invention can have various changes and various forms, specific embodiments will be illustrated in the drawings and described in detail in the text. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals have been used for like elements throughout the description of each figure. In the accompanying drawings, the dimensions of the structures are shown enlarged than actual for clarity of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as "comprise" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

1 is a flowchart for explaining a method for preparing a cobalt-manganese composite catalyst according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining a catalyst synthesized according to the method shown in FIG. 1.

1 and 2, the method for preparing a cobalt-manganese composite catalyst according to an embodiment of the present invention is a suspension by mixing a reaction solution in which a cobalt precursor compound and a manganese precursor compound are dissolved and a precipitant solution in which a basic precipitant is dissolved. (S110) a first step of forming a suspension solution; A second step (S120) of aging the suspension solution; A third step (S130) of separating powder from the aged suspension solution; and a fourth step (S140) of drying and heat-treating the separated powder to form first catalyst powder.

In one embodiment, the manufacturing method of the cobalt-manganese composite catalyst may further include a fifth step ( S150 ) of forming a second catalyst powder by reducing the first catalyst powder in a hydrogen atmosphere.

In one embodiment, the manufacturing method of the cobalt-manganese composite catalyst includes exposing the second catalyst powder to a flow of a mixed gas of carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) to form a sixth catalyst powder. A step S160 may be further included.

The cobalt-manganese composite catalyst prepared according to the present invention directly reacts carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) to produce a hydrocarbon compound, for example, a liquid hydrocarbon compound having 5 or more carbon atoms (C ₅₊ ). can be used as a catalyst for

In the first step S110, the cobalt precursor is not particularly limited as long as it is a material capable of providing cobalt (Co) ions to the reaction solution, and may include, for example, cobalt nitride. The manganese precursor compound is not particularly limited as long as it is a material capable of providing manganese ions to the reaction solution, and may include, for example, manganese (Mn) nitride.

In one embodiment, the cobalt precursor and the manganese precursor are added to the reaction solution so that the ratio of the number of moles of manganese ion to the total number of moles of cobalt ion and manganese ion in the reaction solution is about 3 or more and less than or equal to 20%. may be added. The solvent of the reaction solution is not particularly limited as long as it can dissolve the cobalt precursor and the manganese precursor, and for example, water such as deionized water may be used as the solvent. For example, in the cobalt precursor and the manganese precursor, the ratio of the number of moles of manganese ion to the total number of moles of cobalt ion and manganese ion in the reaction solution is about 4 or more and 18% or less, about 5 or more and 15% or less, about 6 or more and about 14% or less, about 7 or more and 13% or less, about 8 or more and 12% or less, or about 9 or more and 11% or less.

In addition, the total concentration of the cobalt precursor and the manganese precursor in the reaction solution may be about 1 to 5 mol/L. For example, concentrations of the cobalt precursor and the manganese precursor in the reaction solution may be about 1.5 to 3 mol/L.

Meanwhile, the basic precipitant may precipitate a reaction product of cobalt ions dissociated from the cobalt precursor and manganese ions dissociated from the manganese precursor by adjusting the suspension solution to be basic. As the basic precipitating agent, a basic compound may be used without limitation. In one embodiment, the basic precipitant may include sodium carbonate, for example, sodium carbonate (Na ₂ CO ₃ ). The solvent of the basic precipitant solution may be the same as the solvent of the reaction solution, and the concentration of the sodium carbonate in the basic precipitant solution may be about 1 to 5 mol/L. For example, in the basic precipitant solution, the concentration of the sodium carbonate may be about 1.5 to 3 mol/L.

In one embodiment, in order to form the suspension solution, the reaction solution and the precipitant solution are mixed in the same solvent as the solvent of the reaction solution and the precipitant solution, respectively, at a temperature of about 20 to 40 ° C. and stirring conditions. By adding dropwise, the cobalt ions dissociated from the cobalt precursor and the manganese ions dissociated from the manganese precursor may react. At this time, the pH of the suspension solution may be maintained at about 7.5 to 8.5. In one embodiment, a bright purple precipitate may be formed by dropwise addition of the reaction solution and the precipitant solution.

In the second step (S120), the suspension solution may be aged for about 4 to 10 hours without stirring at about 20 to 40 ° C. after stirring for about 4 to 10 hours in a sealed container.

In the third step (S130), it is possible to separate the powders produced by the reaction of the cobalt ions and the manganese ions from the aged suspension through centrifugation, and the separated powders are washed using deionized water. can Centrifugation conditions for separating the powders are not particularly limited.

In the fourth step (S140), the separated powders may be dried at a temperature of about 90 to 110 ° C. and then heat-treated for about 2 to 5 hours under air flow conditions of about 300 to 360 ° C. A first catalyst powder containing cobalt oxide and manganese oxide may be formed by heat treatment.

In one embodiment, the first catalyst powder may include a cobalt oxide phase, a manganese oxide phase, and a phase each of which is doped with sodium.

In the fifth step (S150), the second catalyst powder may be produced by exposing the first catalyst powder to a flow of hydrogen gas to reduce a part of the cobalt oxide phase of the first catalyst powder to a metallic cobalt phase. there is. In one embodiment, the second catalyst powder is a metallic cobalt phase; cobalt oxide phases such as CoO, Co ₃ O ₄ ; Manganese oxide phases such as MnO, MnO ₂ , Mn ₂ O ₃ , and Mn ₃ O ₄ may be included. Meanwhile, manganese contained in the first catalyst powder may reduce the reduction reaction of the cobalt oxide phase and inhibit crystal growth of the metallic cobalt phase, and as a result, reduce the entire cobalt oxide phase to the metallic cobalt phase. In addition, a metal cobalt phase with a relatively small crystal size can be formed. For example, the metallic cobalt phase may include a hexagonal close-packed lattice structure crystal phase, and may further include a relatively small amount of a face centered cubic lattice structure crystal phase. .

In one embodiment, the first catalyst powder is exposed to the hydrogen gas flow for about 4 to 8 hours while being heated to about 320 to 400 ° C. at a heating rate of about 1 to 5 ° C after being fixed in a tubular reactor. It may be converted into a second catalyst powder, and at this time, the pressure inside the tubular reactor may be adjusted to about 3.5 to 5.0 MPa. Meanwhile, the first catalyst powder may be mixed with silica powder as a thermal diluent and then fixed inside the tubular reactor by a porous support such as quartz wool.

In the sixth step (S160), a part of the cobalt oxide phase of the second catalyst powder may be additionally reduced to a metal cobalt phase by hydrogen, and a part of manganese oxide by carbon species generated by decomposition of carbon dioxide. Silver may be converted into manganese carbonate, a cobalt carbide (Co ₂ C) phase may be formed on the surface of the metallic cobalt phase, and agglomeration may occur between the second catalyst powders in the process of forming the third catalyst powder. .

As a result, as shown in FIG. 2, during the sixth step (S160), the second catalyst powder includes a core on metal cobalt; and a shell having a porous structure formed on the surface of the core, including a cobalt oxide phase, a cobalt carbide phase, and the like, and having pores exposing a portion of the surface of the core to the outside. It can be. The structure and composition of the third catalyst powder will be described later.

In one embodiment, the sixth step (S160) is to adjust the temperature inside the tubular reactor to about 250 to 300 ° C. in a state in which the second catalyst powder is fixed in the tubular reactor, and then hydrogen (H ₂ ) and carbon dioxide ( It can be performed by flowing a mixed gas (H ₂ /CO ₂ ) of CO ₂ for a certain period of time. When the temperature inside the tubular reactor is less than 250 ° C, the decomposition reaction of carbon dioxide is weak, and the problem of insufficient production of cobalt metal phase or cobalt carbide phase may occur, and when it exceeds 300 ° C, structural collapse of the third catalyst powder may occur as well as a problem that the methanation reaction of carbon dioxide occurs more predominantly than the RWGS reaction due to the re-oxidation of the metal Co phase caused by the aggregation of the nanoparticles. For example, in the sixth step (S160), the temperature inside the tubular reactor may be adjusted to about 270 to 290 °C.

In one embodiment, in the sixth step (S160), hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) by flowing a mixed gas (H ₂ /CO ₂ ) for a certain period of time. When the pressure inside the reactor is less than 3.5 MPa, the production of Co ₂ C and Co ₃ O ₄ is reduced, which may negatively affect the yield of C5+ hydrocarbons. For example, the pressure inside the tubular reactor in the sixth step (S160) may be adjusted to about 3.5 to 5.0 MPa, the same as or similar to the pressure inside the tubular reactor in the fifth step (S150).

In one embodiment, in the sixth step (S160), a flow of a mixed gas in which hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) are mixed at a ratio of about 2.5: 1 to 3.5: 1 is formed inside the tubular reactor. It can be. When the H ₂ /CO ₂ ratio is less than 2.5, the amount of metal cobalt formed by reduction of cobalt oxide is small, which may cause a problem of lowering the FTS reaction, and when it exceeds 3.5, the metal Co phase due to aggregation of particles Re-oxidation may cause a problem of lowering the FTS reaction. Meanwhile, the mixed gas may be supplied to the tubular reactor at a gas hourly space velocity (GHSV) of about 4000 to 10000 mL g ⁻¹ h ⁻¹ .

As shown in Figure 2, the catalyst prepared by the above method, the core formed on the metal cobalt; and a shell formed of a mixture including a Co ₃ O ₄ phase and a Co ₂ C phase on the surface of the core.

In one embodiment, in the catalyst, the ratio of the number of moles of manganese elements to the total number of moles of cobalt and manganese elements [Mn/(Co+Mn)] may be about 3 or more and about 20% or less. When the ratio of the number of moles of manganese to the total number of moles of cobalt and manganese is less than 3%, it is difficult to expect improvement in the chain-growth reaction by the manganese-containing phase. Problems such as a decrease in the degree of carbon dioxide conversion and a decrease in the conversion rate of carbon dioxide may occur due to a decrease in the proportion of the cobalt oxide phase that promotes the direct decomposition reaction of carbon dioxide. And, when the ratio of the number of moles of the manganese element to the total number of moles of the cobalt and manganese elements exceeds 20%, the production of the metallic cobalt phase may be insufficient, and the conversion rate of carbon dioxide may decrease. For example, in the cobalt-manganese composite catalyst, the ratio of the number of moles of the manganese element to the total number of moles of the cobalt and manganese elements is about 4 or more and 18% or less, about 5 or more and 15% or less, about 6 or more about 14% or less, about 7 or more and 13% or less, about 8 or more and 12% or less, or about 9 or more and 11% or less.

In one embodiment, the core may include a metallic cobalt phase having a crystal phase of a hexagonal close-packed lattice structure, and the shell may include a Co ₃ O ₄ phase containing oxygen vacancies and cobalt carbide. (Co ₂ C) phase. Pores exposing the core to the outside may be formed in the shell.

In one embodiment, the fraction of the metallic cobalt phase in the cobalt-containing phase in the catalyst may be about 90% or more and less than 100%, about 91% or more and 99% or less, or about 92% or more and 98% or less.

In one embodiment, the shell of the catalyst may further include CoO in addition to Co ₃ O ₄ as a cobalt oxide phase, and in this case, the [CoO+Co ₃ O ₄ ]/Co ^O ratio may be about 1.5 to 1.9. .

In one embodiment, the area ratio of the Co ₂ C phase in the shell of the catalyst may be about 10 to 30%, about 11 to 20%, or about 12 to 17%.

Meanwhile, the shell may further include a manganese-containing phase. The manganese-containing phase may include a manganese carbonate phase and a manganese oxide phase. In one embodiment, the manganese carbonate phase may include a MnCO ₃ phase, and the manganese oxide phase may include Mn ₂ O ₃ and Mn ₃ O ₄ . In one embodiment, the fraction of the MnCO ₃ phase in the manganese-containing phase may be about 90 to 99%, about 91 to 97, or about 92 to 95%.

In one embodiment, the cobalt oxide containing oxygen vacancies in the shell can improve the activity of a decomposition reaction of carbon dioxide, for example, a reverse water gas shift (RWGS) reaction, and the cobalt carbide phase and the metal cobalt phase are Hydrogenation of intermediate products such as CHO radicals (CHO*) and CO radicals (CO*) generated by the decomposition reaction of carbon dioxide, for example, Fischer-Tropsch Synthesis (FTS), and The activity of the chain growth reaction can be enhanced. For example, a decomposition reaction of carbon dioxide may occur at an oxygen vacancy site on cobalt oxide in the shell to produce intermediates of CHO* and CO*, and these intermediates may form adjacent cobalt carbide phases (Co ₂ C) and the core. may migrate onto the metal cobalt (Co) phase of hydrogenation and chain growth reactions.

Meanwhile, a graphitic carbon layer may be additionally formed on the outermost surface of the third catalyst powder, and this carbon layer may contribute to further increasing the activity of the hydrocarbon chain growth reaction.

The catalyst may be used as a catalyst for a reaction in which hydrocarbons having 5 or more carbon atoms are formed through hydrogenation of carbon dioxide.

In one embodiment, a hydrocarbon having 5 or more carbon atoms may be produced by inducing a hydrogenation reaction of carbon dioxide by supplying a mixed gas of hydrogen and carbon dioxide into a tubular reactor in which the catalyst is fixed.

In one embodiment, after adjusting the temperature inside the tubular reactor in which the catalyst is fixed to about 250 to 300 ° C., a mixture of hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) (H ₂ /CO ₂ ) is introduced into the tubular reactor. It can be supplied at a constant rate into the reactor. When the temperature inside the tubular reactor is less than 250 ° C, the methanation reaction of carbon dioxide predominantly occurs, which may cause a decrease in the yield of hydrocarbons having 5 or more carbon atoms, and when the temperature inside the tubular reactor exceeds 300 ° C In this case, not only structural collapse of the catalyst may occur, but also a problem in that the methanation reaction of carbon dioxide occurs more predominantly due to reoxidation of the metal Co phase caused by the aggregation of nanoparticles. For example, the temperature inside the tubular reactor in which the catalyst is fixed may be adjusted to about 270 to 290°C.

In one embodiment, for the hydrogenation reaction of carbon dioxide, the pressure inside the tubular reactor is adjusted to about 3.5 MPs or more, and then the mixed gas (H ₂ /CO ₂ ) can be supplied into the tubular reactor at a constant rate. . When the pressure inside the reactor is less than 3.5 MPa, re-adsorption of C ₂ to C ₄ hydrocarbons may be reduced, resulting in a decrease in the yield of C ₅₊ hydrocarbons. For example, the pressure inside the tubular reactor may be adjusted to about 3.5 to 5.0 MPa.

In one embodiment, for the hydrogenation reaction of carbon dioxide, a mixed gas in which hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) is mixed at a ratio of about 2.5: 1 to 3.5: 1 may be supplied into the tubular reactor. . When the H ₂ /CO ₂ ratio is less than 2.5, there may be a problem that the FTS reaction is deteriorated due to insufficient hydrogen, and when it exceeds 3.5, the FTS reaction is caused by re-oxidation of the metal Co phase of the catalyst due to aggregation of particles Deterioration problems may occur. Meanwhile, the mixed gas may be supplied to the tubular reactor at a gas hourly space velocity (GHSV) of about 4000 to 10000 mL g ⁻¹ h ⁻¹ .

When hydrogenation of carbon dioxide is performed using the catalyst, a high CO ₂ conversion rate of about 60% or more and a remarkably high C ₅₊ hydrocarbon selectivity of about 30% or more can be achieved, with a selectivity of less than about 0.5%. The production of carbon monoxide can be highly suppressed.

In addition, the proportion of linear paraffin among the C5+ hydrocarbons produced using the catalyst may be about 90% or more. For example, in C5+ hydrocarbons produced using the catalyst, the ratio of olefins/paraffins may be less than about 0.5%, and the ratio of oxygenated species may also be extremely low, such as less than about 1%.

Hereinafter, specific embodiments of the present invention will be described in detail. However, the following examples are merely some embodiments of the present invention, and the scope of the present invention is not limited to the following examples.

[Example]

A Mn-promoted core-shell Co@CoO _x /Co ₂ C catalyst (CMO-y, where y represents mol% of Mn) was synthesized using a co-precipitation method, and hydrogenation of carbon dioxide was performed using the same.

Catalysts	Concentration (mol L -1 )
	Co(NO 3 ) 2 6H 2 O	Mn(NO 3 ) 2 4H 2 O	Na 2 CO 3
CMO-0	2.0	-	2.0
CMO-10	1.8	0.2	2.0
CMO-25	1.5	0.5	2.0
CMO-50	1.0	1.0	2.0
CMO-75	0.5	1.5	2.0
CMO-100	-	2.0	2.0

First, cobalt nitride [Co(NO ₃ ) ₂ 6H ₂ O] and manganese nitride [Mn(NO ₃ ) ₂ 4H ₂ O] were dissolved in distilled and deionized water at the ratios shown in Table 1 to obtain 2 A reaction solution having a concentration of mol/L was prepared, and a precipitant solution was prepared by dissolving sodium carbonate [Na ₂ CO ₃ ] in deionized water at a concentration of 2 mol/L. Subsequently, 40 mL of the reaction solution and 40 mL of the precipitant solution were added dropwise to 50 mL of deionized water under vigorous stirring conditions at 25 ° C. At this time, the pH of the mixed solution was maintained at 8.0 ± 0.1. A light purple precipitate was formed by dropwise addition of the reaction solution and the precipitant solution.

Subsequently, after stirring for 6 hours in a sealed container, the mixed solution was aged at 25° C. for 6 hours without stirring.

Subsequently, the aged mixed solution suspension was centrifuged 4 times with deionized water at 4000 rpm to collect powder, washed with deionized water, and dried at 100° C. for 12 hours.

Subsequently, the dried powder was heat-treated at 330° C. under an air flow condition of 100 mL/h for 3 hours to prepare ‘catalyst powder before reduction (hereinafter referred to as ‘CMO-y before reduction’)’.

Subsequently, 1 g of the pre-reduction catalyst powder was mixed with 3 g of silica powder used as a thermal diluent in a stainless steel tubular reactor having an inner diameter of 10 mm, and then it was fixed to the center of the tubular reactor using quartz wool. made it

Subsequently, a hydrogen (H ₂ ) flow condition of 50 mL/min, a temperature condition of 350 °C with a temperature increase rate of 2.5 °C/min, and a pressure condition of 4.0 MPa were formed in the tubular reactor to form the catalyst powder before reduction. was reduced in advance for 6 hours to prepare 'catalyst powder after reduction (hereinafter referred to as 'reduced CMO-y')'.

Subsequently, while maintaining the pressure at 4.0 MPa, the internal temperature of the tubular reactor is lowered to a predetermined range of 230 to 310 °C, and the flow of hydrogen (H ₂ ) is converted into a flow of a mixed gas of CO ₂ /H ₂ at a predetermined mixing ratio. 'Converted catalyst powder (hereinafter referred to as 'converted CMO-y')' was prepared by exposing the catalyst powder after reduction to a mixed gas for 125 hours, and hydrogenation of carbon dioxide was continuously performed under the same conditions for 1425 hours. .

[Experimental Example 1]: Hydrogenation performance

3 is graphs showing the catalytic performance evaluation results of CMO-y catalysts according to changes in Mn content, and Table 2 below shows experimental data of C ₅₊ hydrocarbon production through carbon dioxide hydrogenation of the catalyst of the present invention.

catalyst	T(℃)	P(Mpa)	H 2 /CO 2 ratio	Flow rate (mL/gh)	CO 2 conversion (%)	CO selectivity (%)	Oxygenate selectivity (%)	hydrocarbon distribution (%)				C 5+ yield (%)
								CH4	C 2 -C 4	C 5+	Aromatics in C 5+
CMO-0	270	4.0	3	4000	34.3	1.1	0.5	50.3	24.5	25.3	0	8.7
CMO-10	270	4.0	3	4000	64.3	0.2	0.7	44.2	22.9	32.9	0	21.1

Referring to FIG. 3 and Table 2, the CMO-10 catalyst with a Na content of 0.12 wt% resulted in a high CO ₂ conversion of 64.3%, a significantly high C ₅₊ selectivity of 32.9% and a significantly low CO of 0.2%. was found to have a selectivity of And the C ₅₊ hydrocarbon yield of the CMO-10 catalyst was found to be 21.1%, which is significantly higher than that of the conventional Co-based catalyst (0 to 1.4%), as previously reported at GHSV≥4000 mL g ^-1 h ^-1 It was comparable to the reported Fe-based catalyst (11.7~26.4%).

From this, it is judged that the carbon dioxide conversion behavior of the CMO-10 catalyst is different from previously reported Co-based catalysts. Previously reported Co-based catalysts produced a small proportion of _C2 - _C4 hydrocarbons and a negligible proportion of C5+ hydrocarbons, with a 70-100% volume fraction of methane (C1).

The chain growth probability of C ₅₊ hydrocarbons on the CMO-10 catalyst was 0.74, which was significantly higher than other Co-based catalysts (<0.25). And, the distribution of hydrocarbons formed on the CMO-10 catalyst was measured as 32.9% of C ₅₊ hydrocarbons, 44.2% of methane (CH ₄ ) and 22.9% of C ₂ ~C ₄ hydrocarbons, from which the CMO-10 catalyst It was confirmed that gas and liquid fuels can be produced at a high yield through the applied one-pass carbon dioxide stream (CO ₂ stream).

On the other hand, considering strict regulations on the content of aromatic compounds in transportation fuels, it is required to produce C ₅₊ hydrocarbons with a low proportion of aromatic compounds. As shown in Table 2, in the case of C ₅₊ hydrocarbon products produced using the “metal oxide/zeolite” composite catalyst proposed to increase the yield of C ₅₊ hydrocarbons, the proportion of aromatic compounds is 60 to 90 was %. On the other hand, as shown in B of FIG. 3, most of the C ₅₊ hydrocarbons produced on the CMO-10 catalyst were linear paraffins (n-parafin), and a small fraction of branched hydrocarbons (isoparaffion) (2.5%) and olefins ( 4.5%) were included. That is, in the case of C ₅₊ hydrocarbons produced on the CMO-10 catalyst, the ratio of olefins/paraffins was generally very low (0.07%), and the formation of oxygenates was negligible (<0.6%). .

On the other hand, the one-pass CO ₂ conversion rate on the Fe-based catalyst was 40% or less at GHSV≥4000 mL g ^-1 h ^-1 , and showed a high residual CO selectivity of 15% or more. Therefore, in order to construct a carbon dioxide conversion device using an Fe-based catalyst on a practical commercial scale, a wastewater recycling device or an FTS reaction system equipped with a two-stage RWGS and water removal device is required. In contrast, the CMO-10 catalyst exhibits high CO ₂ conversion (64.3%), high C ₅₊ hydrocarbon yield (21.1%), negligible CO selectivity (0.7%), and relatively low temperature (270%). ℃), it is evaluated to have a clear advantage over Fe-based catalysts.

As shown in Fig. 3A, negligible CO ₂ conversion (<0.3%) was observed on the CMO-100 catalyst without Co, and 34.3% of CMO-0 catalyst without Mn. It exhibited high CO ₂ conversion and high C ₅₊ hydrocarbon selectivity of 25.3%, and highly suppressed selectivity towards CO (1.1%). From this, it can be seen that manganese oxide is not an active site for CO ₂ conversion.

As shown in B to D of FIG. 3, the chain growth probability on CMO-10 was slightly higher than that on CMO-0 catalyst, and the chain growth probability increased with increasing Mn content in CMO-y catalyst. From this, it can be seen that in the CMO-y catalyst, Mn can perform a function of suppressing the chain termination reaction, so that longer chain hydrocarbons can be formed as the Mn content increases. Specifically, it was confirmed that C ₁₀₊ carbon hydrogen was the main species in the hydrocarbons produced on the CMO-75 catalyst.

Figure 4a is a CO ₂ conversion rate and products according to the reaction time on the CMO-0 catalyst and the CMO-10 catalyst under pressure conditions of 1.0 MPa (A, B), 2.0 MPa (C, D), and 3.0 MPa (E, F) Graphs showing the results of measuring selectivity, and FIG. 4b is CO ₂ as a function of reaction time on CMO-0, CMO-10, CMO-25, CMO-50, CMO-75, and CMO-100 catalysts at 4.0 MPa. These are graphs showing the results of measuring conversion rate and product selectivity. And Figure 5a is graphs showing the results of measuring the CO ₂ conversion rate and product selectivity according to the reaction pressure of the CMO-0 catalyst (A) and the CMO-10 catalyst (B), and Figure 5b is the reaction time of the CMO-10 catalyst It is a graph showing the results of measuring the CO ₂ conversion rate and product selectivity according to The results of FIGS. 4a, 4b, 5a, and 5b show that H ₂ /CO ₂ syngas (GHSV = 4000 mL g ^-1 h ^-1 ; CO ₂ = 1000 ^{; _} _{_} ^{_ _} _{_} It was reduced for 6 hours under temperature conditions of °C (heating rate of 2.5 °C/min). In addition, FIG. 6 is a graph showing the results of measuring the CO ₂ conversion rate and product selectivity according to the reaction temperature (A) of the CMO-10 catalyst, the H ₂ /CO ₂ ratio of syngas (B), and GHSV (C). admit. In FIG. 6, A is 4.0 MPa reaction pressure, H ₂ /CO ₂ = 3: 1 syngas and GHSV = 4000 mL g ^-1 h ^-1 (CO ₂ = 1000 mL g ^-1 h ^-1 ; H2 = 3000 mL g ^-1 h ^-1 ), B is a reaction temperature of 270 °C, a reaction pressure of 4.0 MPa and GHSV = 4000 mL g ^-1 h ^-1 (CO ₂ = 1000 mL g ^-1 h ^{- 1} ; H2 = 3000 mL g ^-1 h ^-1 ), and C was measured under the reaction temperature of 270 °C, the reaction pressure of 4.0 MPa, and the syngas condition of H ₂ /CO ₂ = 3:1.

Referring to Figures 4a, 4b, 5a, 5b and 6, it was confirmed that the C ₅₊ hydrocarbon selectivity increased as the reaction pressure increased on the CMO-0 catalyst, which was confirmed by the increase in pressure in the H / C range It is believed that this is due to a decrease in coverage and an increase in re-adsorption of C ₂ to C ₄ hydrocarbons.

The effect of reaction pressure on CO ₂ conversion was found to be greater on the CMO-10 catalyst than on the CMO-0 catalyst, which is believed to be due to the higher reaction pressure and the Mn promoter facilitating the chain propagation reaction more.

The methanation activity on the CMO-10 catalyst was increased under high temperature (310 °C), high H ₂ /CO ₂ ratio (4:1) and high GHSV (12000 mL g ^-1 h ^-1 ) conditions. . A similar behavior was observed in the FTS reaction of typical H ₂ /CO syngas, and also an increase in methanation activity at high temperature (310 °C) and high H ₂ /CO ₂ ratio (4:1) was previously reported. similar to the CO ₂ conversion on a Co-based catalyst.

As shown in FIG. 6, on the CMO-10 catalyst, under the conditions of a reaction temperature of about 290 ° C., an H ₂ /CO ₂ ratio of about 2.5 to 3.5, and a GHSV of about 3000 to 5000 mL g ^-1 h ^-1 , It showed a significantly higher C ₅₊ hydrocarbon selectivity, indicating that the FTS reaction was predominantly generated compared to the methanation reaction on the CMO-10 catalyst under the above reaction conditions.

As shown in FIG. 5B, it was confirmed that the CMO-10 catalyst has stability capable of stably converting CO ₂ and generating long-chain hydrocarbons for 1425 hours in the hydrogenation of CO ₂ . In view of this excellent stability for more than 1425 hours, it is judged that the performance of the CMO-10 catalyst is maintained despite sintering of the active site and deposition of polymeric carbon or coke.

For the C ₅₊ hydrocarbon products produced over the CMO-10 catalyst, as the reaction time increased from 125 to 1425 hours, the C ₅ to C ₂₀ hydrocarbon selectivity decreased from 24.5% to 12.6%, but the C ₂₁₊ hydrocarbons The selectivity increased from 6.5% to 14.9%. Therefore, as the reaction time increases, it is believed that partial poisoning of the FTS active site of the catalyst by continuous accumulation of high resistivity graphitic carbon can contribute to promoting the chain growth reaction.

[Experimental Example 2]: Characterization of CMO-y catalysts

7a shows XRD patterns measured in fresh, reduced, and spent states of CMO-0 and CMO-10 catalysts, respectively, and FIGS. 7b and 7c show CMO-0, CMO- 10, CMO-25, CMO-50, CMO-70 and CMO-100 catalysts in fresh state (A, B, C) and reduced state (D, E, F) respectively The measured XRD patterns are shown, and FIG. 7d shows the XRD patterns measured in the spent state of each of the CMO-0, CMO-10, CMO-25, CMO-50, CMO-70 and CMO-100 catalysts, Figure 7e shows XRD patterns measured for CMO-10 catalysts converted at 230 °C, 250 °C, 270 °C, 290 °C, and 310 °C, respectively. 7a to 7d, the catalyst after each reduction was reduced for 6 hours at a pressure of 4.0 MPa, a H ₂ flow of 50 mL/min, and a temperature condition of 350° C. (heating rate of 2.5° C./min) before reduction. was prepared, and each spent catalyst was mixed with H ₂ /CO ₂ syngas (GHSV = 4000 mL g) at a temperature of 270 ° C., a pressure of 4.0 MPa and a ratio of 3: 1 for each spent catalyst. ^-1 h ^-1 ; CO ₂ = 1000 mL g ^-1 h ^-1 ; H ₂ = 3000 mL g ^-1 h ^-1 ) for 125 hours.

7a to 7e, in the CMO-10 catalyst after reduction, a crystal structure in which CoO, hcp-structured Co phase, and a small fraction of the fcc Co phase were mixed was induced, and in the converted CMO-10 catalyst, the CoO phase converted to the hcp Co phase. reduced, and fcc Co and MnCO ₃ were present in small fractions. From this, it can be seen that the Mn promoter inhibited the complete reduction of Co ₃ O ₄ to metallic Co during the H ₂ reduction process.

For the reduced CMO-y catalyst, as the Mn content increased from 25% to 75%, as shown in Figs. were each rapidly downshifted towards MnO, indicating the formation of spinel structure Co _x Mn _3-x O ₄ (0<x<3). And as shown in Fig. 7d, the spinel Co _x Mn _3-x O ₄ and bulk Co ₂ C phases were not observed in the converted CMO-y catalysts.

On the other hand, as shown in Figure 7e, in the case of the converted CMO-10 catalyst at 270 to 290 ° C, it was confirmed that the metal Co and MnCO ₃ phases were the main species, but in the case of the converted CMO-10 catalyst at 310 ° C, It was found that the intensity of the peaks associated with the metallic Co and MnCO ₃ phases were significantly reduced. This means that when the CMO-10 catalyst is exposed to H ₂ /CO ₂ syngas at a high temperature of 310° C. or higher, structural collapse of the CMO-10 catalyst occurs.

XAS was used to investigate the oxidation state and local chemical structure of the CMO-y catalysts after reduction and after use.

Figure 8a shows Co K-edge XANES spectra for CMO-y catalysts after reduction (A) and converted CMO-y catalysts (B), and Figure 8b shows Co K-edge XANES profiles evaluated from linear combination fitting. 8c is a graph showing the relationship between metallic Co content and C ₅₊ hydrocarbon yield, and FIG. 8c is a relationship between surface carbide content and C ₅₊ hydrocarbon yield evaluated from C 1s XPS spectrum (D) and [CoO +CO3O4]/CoO and the graph showing the relationship (E) between the C ₅₊ hydrocarbon yield, and FIG. 8d shows the relationship between the crystal size measured by XRD and the C 5+ hydrocarbon yield (F) and Co K- It is a graph showing the relationship (G) between the metallic Co content evaluated from the linear combination fitting of the edge XANES profiles and the crystallite size measured by XRD. And Table 3 below shows the results of linear combination fitting of Co K-edge XANES profiles for reduced and spent CMO-y catalysts.

	Crystallite size (nm)
	Co 3 O 4	CoO	hcp Co	fcc Co
Fresh CMO-0	9.7
Reduced CMO-0		-	21.2	22.5
Spent CMO-0			27.0	34.5
Fresh CMO-10	5.9
Reduced CMO-10		9.9	20.9	19.9
Spent CMO- 10c			23.4	21.4
Mn/[Co+Mn]
Spent CMO-0			27.0	34.5
Spent CMO-10			23.4	21.4
Spent CMO-25			21.4	18.2
Spent CMO-50			24.7	16.6
Spent CMO-75			29.9	20.1
Pressure (MPa)
Spent CMO-0 at 1 MPa			29.8	23.0
Spent CMO-0 at 2 MPa			24.7	26.7
Spent CMO-0 at 3 MPa			25.1	27.2
Spent CMO-0 at 4 MPa			27.0	34.5
Spent CMO-10 at 1 MPa			20.5	21.4
Spent CMO-10 at 2 MPa			20.9	18.0
Spent CMO-10 at 3 MPa			22.2	18.5
Spent CMO-10 at 4 MPa			23.4	21.4
Temperature (℃)
Spent CMO-10 at 230 °C			11.5	13.6
Spent CMO-10 at 250 °C			19.4	15.0
Spent CMO-10 at 270 °C			23.4	21.4
Spent CMO-10 at 290 °C			13.6	16.4
Spent CMO-10 at 310 °C			13.8	10.9
H 2 /CO 2 ratio
Spent CMO-10 at H 2 /CO 2 of 1			22.4	22.1
Spent CMO-10 at H 2 /CO 2 of 2			20.3	16.5
Spent CMO-10 at H 2 /CO 2 of 3			23.4	21.4
Spent CMO-10 at H 2 /CO 2 of 4			21.3	23.6
GHSV (mL g -1 h -1 )
Spent CMO-10 at GSHV of 4000			23.4	21.4
Spent CMO-10 at GSHV of 8000			22.7	22.0
Spent CMO-10 at GSHV of 12000			30.5	28.9
Stability (h)
Spent CMO-10 collected after 1425 h reaction			24.0	20.4

8a to 8d and Table 3, the Co ₃ O ₄ crystal size (5.9 nm) in the CMO-10 catalyst before reduction is smaller than the Co ₃ O ₄ crystal size (9.7 nm) in the CMO-0 catalyst before reduction. significantly smaller, from which it can be seen that the Mn promoter inhibits the growth of Co ₃ O ₄ crystals during heat treatment to reduce their size. In the case of the reduced CMO-0 catalyst and the reduced CMO-10 catalyst, it was found to contain hcp Co and fcc Co phases with similar crystal sizes (20-23 nm).

Compared to the reduced CMO-0 catalyst, the crystallite sizes of hcp Co and fcc Co were significantly increased to 27.0 nm and 34.5 nm, respectively, in the converted CMO-0 catalyst. In contrast, in the case of the converted CMO-10 catalyst, the crystallite size of hcp Co and fcc Co slightly increased to 23.4 nm and 21.4 nm, respectively, compared to the CMO-10 catalyst after reduction. From this, it can be seen that the Mn promoter included in the CMO-10 catalyst inhibits the crystal growth of metal Co during the hydrogenation of CO ₂ .

The Co K-edge XANES spectrum of the reduced CMO-0 catalyst was similar to the standard metallic Co, indicating almost complete reduction from Co ₃ O ₄ to the metallic Co phase, from which the Mn promoter contained in the catalyst was reduced to Co ₃ O It can be further confirmed that the complete reduction of ₄ to metal Co is inhibited.

Local and long-range order characteristics of CMO-y catalysts (CMO-25, CMO-50, and CMO-75) after reduction with Mn content of 25% or more are local and long-range order characteristics of standard CoO. approached. For the CMO-10 catalyst after reduction, both metallic Co and CoO _x properties coexisted.

The Mn-promoters in CMO-y catalysts can suppress the reduction of Co. The low reducibility of the Mn-rich CMO-y catalyst is due to the increased formation of spinel structure Co _x Mn _3-x O ₄ as the Mn-content increases.

Conversion of CoO to metallic Co was observed in the XANES spectrum of the converted CMO-y catalyst, as shown in Fig. 8B. In the converted CMO-y catalyst with y≤25%, the proportion of metal Co was 93~99%, which was the dominant species.

*As the content of Mn increased from 25% to 75%, the beginning of the absorption edge was upshifted in the XANES spectrum, and the height of the peak of the white line increased, indicating that as the Mn content increased in the converted CMO-y catalyst, CoO and Co ₃ O ₄ phase increases.

As shown in FIG. 8B, there is a positive correlation between the metal Co content in the CMO-y catalyst and the yield of C ₅₊ hydrocarbons, and under conditions leading to high yields of C ₅₊ hydrocarbons, converted CMO-y The metal Co content of the catalyst was found to increase. Under the prevailing FTS reaction conditions, the metallic Co content was above 98%, and under the prevailing methanation reaction conditions, the metallic Co contents were 60-90%. Therefore, the metal Co content included in the catalyst can be evaluated as a precondition for establishing the FTS reaction in CO ₂ hydrogenation, and the active site for the synthesis of long-chain hydrocarbons from syngas is judged to be the metal Co phase.

XPS profiles of the converted CMO-0 catalyst and CMO-10 catalyst were measured to investigate the correlation between the surface species of the catalyst and the C ₅₊ hydrocarbon yield under varying reaction conditions, and the results are shown in FIG. 8C. is shown

As shown in FIG. 8c, the C ₅₊ hydrocarbon yield was maximized at a carbide area ratio of 14.7% and a [CoO+Co ₃ O ₄ ]/Co ^O ratio of 1.7. Thus, it can be seen that some fractions of Co ₂ C and CoO _x are required to be present on the catalyst surface in order for the FTS reaction to be established in CO ₂ hydrogenation.

To determine the correlation between metallic Co phase and C ₅₊ hydrocarbon yield, XAS was used to investigate changes in the local chemical structure of the converted CMO-y catalyst as the reaction conditions were varied.

FIG. 9a shows normalized Co K-edge XANES spectra measured for a converted CMO-0 catalyst (A) and a converted CMO-10 catalyst (B) at various reaction pressures (1 MPa, 2 MPa, 3 MPa, 4 MPa), respectively. FIG. 9 b is at various reaction temperatures (230 ℃, 250 ℃, 270 ℃, 290 ℃, 310 ℃) (C) and various H ₂ /CO ₂ mixing ratio (H ₂ /CO ₂ =1, 2, 3, 4) (D) Co K-edge XANES spectra measured for the converted CMO-10 catalyst, respectively, and FIG. 9c shows various GHSV (4000 mL g ^-1 h ^-1 , 8000 mL g ^-1 h ^-1 , 12000 mL g ^-1 h ^{- 1} ) and after various reaction times (120 hr, 1440 hr) Co K-edge XANES spectra measured for the converted CMO-10 catalyst, respectively. And FIG. 10 shows the k ³ - weighted Fourier transform (k ³ - weighted Fourier transforms, FTs) (A) and CMO-10 catalyst converted at 270 °C fitted only with metallic Co (B), CMO-10 converted at 290 °C catalyst fitted only with metallic Co (C) and metallic Co Filtered K ³ -weighted χ(k) ^spectra of the CMO-10 catalyst (D) converted at 310 °C fitted with CoO and Normalized Mn K-edge XANES spectra of CMO-y catalyst (A) and converted CMO-y catalyst (B) are shown. In addition, Table 4 below shows the results of linear combination fitting of Mn K-edge XANES profiles for the CMO-y catalyst after reduction and the converted CMO-y catalyst, and Table 5 shows the results of the linear combination fitting of the CMO-y catalyst after reduction and the converted CMO-y catalyst. Co-Co and Co-O coordinate shell fitting parameters of EXAFS profiles for

	Oxidation state
	MnO 2	Mn2O3	Mn 3 O 4	MnO	MnCO 3
Reduced CMO-0	0.309		0.329	0.362
Reduced CMO-10	0.255	0.007	0.277	0.462
Reduced CMO-25	0.191		0.287	0.522
Reduced CMO-50			0.518	0.482
Reduced CMO-75		0.009	0.241	0.750
Mn/[Co+Mn]
Spent CMO-10		0.036		0.027	0.937
Spent CMO-25		0.083	0.130		0.787
Spent CMO-50		0.062	0.163		0.775
Spent CMO-75			0.197		0.803
Pressure (MPa)
Spent CMO-10 at 1MPa		0.007		0.031	0.962
Spent CMO-10 at 2MPa				0.008	0.992
Spent CMO-10 at 3 MPa
Spent CMO-10 at 4 MPa		0.036		0.027	0.937
Temperature (℃)
Spent CMO-10 at 230℃		0.001		0.001	0.996
Spent CMO-10 at 250℃			0.039		0.961
Spent CMO-10 at 270℃		0.036		0.027	0.937
Spent CMO-10 at 290℃		0.001		0.009	0.990
Spent CMO-10 at 310℃			0.091		0.909
H 2 /CO 2 ratio
Spent CMO-10 at H 2 /CO 2 of 1:1		0.090	0.187	0.655	0.092
Spent CMO-10 at H 2 /CO 2 of 2:1			0.003	0.021	0.976
Spent CMO-10 at H 2 /CO 2 of 3:1		0.036		0.027	0.937
Spent CMO-10 at H 2 /CO 2 of 4:1				0.003	0.997
GHSV (mL g -1 h -1 )
Spent CMO-10 at GHSV of 4000		0.036		0.027	0.937
Spent CMO-10 at GHSV of 8000			0.001	0.001	0.998
Spent CMO-10 at GHSV of 12000			0.001		0.999
Stability (h)
Spent CMO-10 collected after 1425 h		0.017			0.983

Sample	Shell	N	R (Å)	ΔE 0 (eV)		Δσ 2 *10 3 (Å 2 )		R-factor
Reduced catalysts
CMO-0	Co-Co (hcp Co)	5.69	2.50		3.75		5.95		0.06
CMO-10	Co-O (CoO)	1.87	2.14		3.47		9.43		0.4
	Co-Co (hcp Co)	2.54	2.50		1.57		6.63
	Co-Co (CoO)	4.07	3.03		3.47		8.06
CMO-25	Co-O (CoO)	4.64	2.09		0.61		11.80		0.4
	Co-Co (CoO)	10.58	3.02		0.61		11.02
CMO-50	Co-O (CoO)	5.38	2.11		0.61		13.93		0.3
	Co-Co (CoO)	10.79	3.04		0.61		11.43
CMO-75	Co-O (CoO)	5.64	2.14		0.53		11.78		0.6
	Co-Co (CoO)	11.96	3.07		0.53		10.77
Spent catalysts
CMO-0	Co-Co (hcp Co)	6.48	2.50		7.91		5.63		0.2
CMO-10	Co-Co (hcp Co)	5.98	2.50		3.25		5.98		0.2
CMO-25	Co-Co (hcp Co)	4.50	2.49		5.19		5.42		0.4
CMO-50	Co-Co (hcp Co)	4.58	2.50		1.00		5.09		0.4
CMO-75	Co-Co (hcp Co)	7.93	2.50		0.68		6.71		0.3
Spent CMO-10 catalyst at varying temperatures (℃)
230	Co-Co (hcp Co)	7.96	2.50		0.03		5.76		0.2
250	Co-O (CoO)	0.55	2.05		2.45		8.83		0.02
	Co-Co (hcp Co)	5.68	2.49		-0.84		5.46
	Co-Co (CoO)	0.17	2.97		2.45		9.52
270	Co-Co (hcp Co)	5.98	2.50		3.25		5.98		0.2
290	Co-Co (hcp Co)	6.77	2.49		-0.21		5.74		0.05
310	Co-O (CoO)	0.97	2.09		4.15		6.36		0.09
	Co-Co (hcp Co)	4.39	2.49		-0.75		5.36
	Co-Co (CoO)	0.38	3.10		4.15		6.85

Referring to FIGS. 9a to 9c, FIGS. 10 and 11, and Tables 4 and 5, in the CoO phase in the CMO-10 catalyst converted at 310 ° C, the coordination number of Co-O bonds in CoO is It was 2-3 times higher than that of Co-Co, suggesting that CoO produced in the methanation reaction exhibited an oxygen-rich nanocluster structure. In the case of the chemical structure of the Mn-promoter, various oxidation states of Mn such as MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , and MnO coexisted in reduced CMO-y catalysts. In the converted CMO-y catalyst, the dominant Mn species was MnCO ₃ , and small fractions of Mn ₂ O ₃ and Mn ₃ O ₄ were present. The MnCO ₃ content increased from 93.7% to 98.3% as the reaction time increased from 125 hours to 1425 hours.

As shown in A of FIG. 9A, in the k ³ -weighted Fourier transform magnitude of the Co K-edge extended EXAFS spectrum of the CMO-0 catalyst after reduction, the peak at 2.50 Å corresponds to the Co—Co bond of hcp Co. . Two additional peaks at 2.14 and 3.30 Å were observed for the CMO-10 catalyst after reduction, and these peaks correspond to Co-O and Co-Co bonds in CoO, respectively.

As shown in Fig. 9B, the Co K-edge EXAFS spectrum of the converted CMO-10 catalyst showed one prominent peak centered at 2.50 Å, which is related to the Co-Co bond of hcp Co.

12 shows CMO-10 catalyst before reduction, CMO-10 catalyst after reduction, and conversion (125 hr, 1425 hr) CMO in C 1s (A), Co 2p (B), O 1s (C) and Mn 2p (D) regions. 13 shows high-resolution XPS profiles of -10 catalysts, and FIG. 13 shows CMO-0 catalyst before reduction, CMO-0 catalyst after reduction and conversion (125 hr) in the C 1s (A), Co 2p (B) and O 1s (C) regions. ) high-resolution XPS profiles of the CMO-10 catalyst.

12 and 13, the converted CMO-10 catalyst after the reaction proceeded for 125 hours showed a new peak at 283.2 eV corresponding to Co ₂ C. From this, it can be seen that in the initial state of the reaction, Co ₂ C was formed on the Co surface by surface carbon species decomposed from adsorbed CO ₂ species. As the reaction time increased from 125 hours to 1425 hours, the area ratio of Co ₂ C in the converted CMO-10 catalyst increased from 14.7% to 29.1%.

In the Co 2p spectrum of the CMO-10 catalyst after reduction, a peak at 778.4 eV corresponding to metal Co appeared, and the area ratio of metal Co was small at about 8.7% because of the incomplete reduction of the catalyst by the Mn promoter. As the reaction time increased from 125 hours to 1425 hours, in the converted CMO-10 catalysts, the area ratios of peaks corresponding to metal Co and Co ₂ C respectively increased to 28.7% and 27.6%, respectively.

In the O 1s spectrum, two main peaks at 529.6 and 531.2 eV may correspond to lattice oxygen and oxygen vacancies of the metal oxide, respectively. The area ratio of peaks related to oxygen vacancies in the converted CMO-10 catalyst increased from 26.8% (CMO-10 catalyst after reduction) to 53.4% (converted CMO-10 catalyst after 1425 hours reaction). In the converted CMO-10 catalyst after 125 hours of reaction, the main Mn species was Mn ²⁺ .

Changes in the chemical environment at the surface of the CMO-0 catalyst during reduction and CO ₂ hydrogenation were shown to be similar to those of the CMO-10 catalyst. Even in the absence of the Mn promoter, complete reduction of Co oxide to metallic Co did not occur at the surface of the reduced CMO-0 catalyst, and the reduction temperature of 350 °C was not high enough for this complete conversion.

14a is a diagram showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of the CMO-0 catalyst before reduction, and FIG. HAADF-STEM image of 0 catalyst (F) and its corresponding Co (G); O (H); C (I); Na(J); Co and O (K); It is a diagram showing EDX images of Co, C and O (L). 15a is a view showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of the CMO-10 catalyst before reduction, and FIG. HAADF-STEM image of 10 catalyst (F) and its corresponding Co (G); O (H); C (I); Mn (J); Na(K); Co and O (L); It is a diagram showing EDX images of Co, C and O (M). 16a is a diagram showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of the CMO-0 catalyst after reduction, and FIG. HAADF-STEM image of 0 catalyst (F) and its corresponding Co (G); O (H); C (I); Na(J); Co and O (K); It is a diagram showing EDX images of Co, C and O (L). Figure 17a is a diagram showing FE-SEM images (A, B), HR-TEM images (C, D), and particle size distribution (E) of CMO-10 catalyst after reduction, and Figure 17b is a diagram showing CMO-10 catalyst after reduction HAADF-STEM image of 10 catalyst (F) and its corresponding Co (G); O (H); C (I); Mn (J); Na(K); Co and O (L); It is a diagram showing EDX images of Co, C and O (M). 18a shows HR-TEM images (AC, E) and FFT images (D) of the converted CMO-0 catalyst, and FIG. 18B shows HAADF-STEM images (F) of the converted CMO-0 catalyst and the corresponding Co ( G); O (H); C (I); Co and O (J); Co, O and C (K); and EDX images of Na (L), FIG. 18C shows Co (M); Co and O (N); An enlarged outermost shell layer of Co, O and C(O) is shown. 19a shows HR-TEM images (AC, E) and FFT images (D) of the converted CMO-10 catalyst, and FIG. 19B shows HAADF-STEM images (F) of the converted CMO-10 catalyst and the corresponding Co ( G); O (H); C (I); Mn (J); Co, Mn and O (K); and EDX images of Co, Mn, C, and O (L), FIG. 19C shows Co (M); Co and O (N); An enlarged outermost shell layer of Co, O and C(O) is shown. 20 shows N ₂ adsorption-desorption contours of the pre-reduction CMO-y catalyst (A), the post-reduction CMO-y catalyst (B), and the converted CMO-y catalyst (C).

Referring to FIGS. 14A to 20 , the CMO-0 catalyst before reduction showed spherical Co ₃ O ₄ nanoparticles with an average diameter of 9.0 nm. HAADF-STEM (high-angle annular dark-field STEM) and EDX images showed that Na was uniformly distributed over the entire catalyst.

In the CMO-10 catalyst before reduction, the average diameter of the Co ₃ O ₄ nanoparticles was 5.1 nm, which was reduced compared to that of the CMO-0 catalyst before reduction. The particle size of the CMO-10 catalysts before reduction, evaluated using HR-TEM, was similar to their crystal size, indicating a single crystal structure. From these results, it can be seen that the Mn promoter included in the CMO-10 catalyst suppressed the crystal growth of Co ₃ O ₄ during heat treatment.

The BET surface area of the CMO-10 catalyst before reduction (185.3 m ² /g) was found to be significantly larger than that of the CMO-0 catalyst before reduction (103.5 m ² /g). And the BET surface areas of the CMO-25 catalyst before reduction and the CMO-50 catalyst before reduction increased to 214.1 and 210.5 m ² /g, respectively. Therefore, it can be seen that Mn included in the CMO-y catalyst inhibited the aggregation of internal particles during heat treatment.

In the case of the CMO-0 catalyst, aggregation between adjacent nanoparticles occurred during reduction, resulting in an increase in particle size after reduction compared to before reduction. The average particle diameter of the reduced CMO-0 catalyst increased significantly to 224 nm. In contrast, in the case of the CMO-10 catalyst, the particle growth was inhibited by the Mn promoter during reduction, and as a result, the average particle diameter (18.4 nm) of the CMO-10 catalyst after reduction was about 10 times larger than that of the CMO-0 catalyst after reduction. It was small. Mn and Na species were uniformly distributed on the CMO-10 catalyst after reduction.

For the CMO-0 catalyst after reduction and the CMO-10 catalyst after reduction, the Na content was measured to be 0.11 and 0.12 wt%, respectively.

It was found that the overall morphology and particle size of the converted CMO-0 catalyst did not change significantly compared to that of the CMO-0 catalyst after reduction. A 10-15 nm thick layer covered the outermost surface of the catalyst particles. FFT and high-magnification images revealed the presence of diffraction patterns associated with CoO (111), Co ₃ O ₄ (311), Co ₂ C (020) and hcp Co (012) and (101) planes in the converted CMO-0 catalyst. shown, which indicates the formation of CoO _x and Co ₂ C phases during CO ₂ hydrogenation. For the CoO _x /Co ₂ C layer, the interlayer spacing was in the range of 2.44–2.56 Å, which is due to the presence of oxygen vacancies in the lattice-extended (311) plane of Co ₃ O ₄ (2.44 Å) and CoO (2.46 Å). is consistent with the (111) plane of HAADF-STEM images and corresponding EDX images showed that oxygen and carbon species covered the surface of the metallic Co particles. Closer examination of the EDX images of Co revealed that a dense metallic Co phase in the core and a highly porous Co phase in the shell layer coexist in the catalyst. The porous Co phase was found to overlap O and C elements, indicating that an oxygen- and carbon-rich shell with a thickness of 10 to 15 nm was formed on the surface of the metallic Co core. In the outermost surface region, a carbon layer with a thickness of about 5 nm was observed, which was formed by the FTS reaction. That is, the carbon layer was deposited on the outermost surface of the converted CMO-0 catalyst, and the CoO _x and Co ₂ C phases were present almost on the surface area. As a result, the converted CMO-0 catalyst was Co@Co ₂ C/CoO _x It was confirmed to have a core-shell structure. However, in some parts of the converted CMO-0 catalyst, the Co ₂ C/CoO _x shell layer was not uniform, and carbon-rich phases desorbed from the catalyst surface were observed.

Compared to the particle size of the CMO-10 catalyst after reduction (18.4 nm), the particle size of the converted CMO-10 catalyst was found to be increased to almost 100 nm, indicating that interparticle agglomeration occurred during CO ₂ hydrogenation. However, the particle size of the converted CMO-10 catalyst was much smaller compared to the converted CMO-0 catalyst, indicating that the Mn promoter inhibited particle aggregation during CO ₂ hydrogenation.

Similar to the case of the CMO-0 catalyst, the converted CMO-10 catalyst was found to have an hcp Co core and a CoO _x /Co ₂ C shell structure. Considering that in the converted CMO-10 catalyst, the amount of Co oxide detected through the bulk analysis technique (XRD and XAS) was extremely small, while the amount of Co oxide detected through the surface detection technique (XPS) was quite large, It can be seen that the Co oxide species observed in the EDX images are mostly present on the outermost surface of the metal Co core. The Mn promoter inhibited the formation of a carbon-rich layer on the outermost surface of the CMO-10 catalyst, and isolated carbon-rich sheets separated from the catalyst surface. This is due to the formation of a uniform CoO _x /Co ₂ C shell layer on the surface of the metal Co core nanoparticles.

21 shows HR-TEM images of the converted CMO-0 catalyst converted under the reaction pressure condition of 1.0 MPa, and FIG. 22 shows HR-TEM images of the converted CMO-10 catalyst converted under the reaction pressure condition of 1.0 MPa.

Referring to FIGS. 21 and 22 together with FIGS. 18A and 19A, the thickness of the shell layer present in the converted CMO-0 catalyst converted at a reaction pressure of 1.0 MPa was about 5 nm, which is the thickness of the CMO-0 converted at a reaction pressure of 4.0 MPa. It was considerably thinner than the thickness of the shell layer of the catalyst (10-15 nm). In addition, the surface layer of the converted CMO-0 catalyst converted at 1.0 MPa has a higher [CoO+Co ₃ O ₄ ]/Co ⁰ ratio (3.1%) and smaller carbide area than that of the converted CMO-0 catalyst converted at 4.0 MPa. The ratio (3.0%) is shown. The metal Co content of the converted CMO-0 catalyst converted at 1.0 MPa (89.1%) was significantly lower than that of the converted CMO-0 catalyst converted at 4.0 MPa (98.6%).

In the case of the converted CMO-10 catalyst at 1.0 MPa (C ₁ ~C ₄ selectivity = 93.8%, C 5+ selectivity = 6.2%), the cuboid-shaped Co ₂ C particles with a size of about 5 nm are the size of the metal Co particles. formed on the surface. This indicates that the Mn promoter promotes the formation of Co ₂ C. However, the formation of cuboid-shaped Co ₂ C particles did not increase the C ₅₊ hydrocarbon yield. Similar to the case of the CMO-0 catalyst, the converted CMO-10 catalyst converted at 1.0 MPa has a higher [CoO+Co ₃ O ₄ ]/Co ⁰ ratio ( 2.1), higher carbide area ratio (20.6%) and lower metal Co content (83.5%). From this, it can be seen that the abundant Co oxide and Co ₂ C phases in the catalyst formed at low pressure negatively affect the C5+ hydrocarbon yield.

The cuboid-shaped Co ₂ C particles were formed at a low reaction temperature of 230 °C. As the reaction temperature increased to 250 °C, the Co ₂ C cuboid morphology disappeared, and instead a shell layer of about 4 nm thickness formed of a mixture of Co ₂ C and CoO _x was formed to cover the metallic Co core. At a reaction temperature of 270 °C, the thickness of the shell layer (10-15 nm) increased. In the case of the CMO-10 catalyst converted at a reaction temperature of 310 °C, a rapid morphology change was observed. At a reaction temperature of 310 °C, severe intergranular aggregation between adjacent Co nanoparticles could lead to separation of the carbon-rich layer. Through close-up examination, it was confirmed that carbon-rich sheets containing small Co ₂ C phases were desorbed from the surface of the metallic Co particles. Thus, some portions of the catalyst surface exposed to water were formed as by-products, which re-oxidized the catalyst surface to form Co ₃ O ₄ phases within the bulk Co core. The Co ₃ O ₄ and CoO content (37.8%) in the CMO-10 catalyst converted at a reaction temperature of 310 °C was significantly higher than that of the CMO-10 catalyst converted at 270 °C. Thus, it can be seen that the high methane (CH ₄ ) selectivity at low reaction temperature results from incomplete development of the mixed CoO _x and Co ₂ C shell layer. And, at high reaction temperatures, reoxidation of the metallic Co phase caused by aggregation of Co@CoO _x /Co ₂ C nanoparticles is believed to be responsible for the high methane (CH ₄ ) selectivity.

Figure 23a shows SEM, HR-TEM and FFT images of the converted CMO-10 catalyst converted under reaction temperature conditions of 230 °C (A), 250 °C (B), 290 °C (C) and 310 °C (D), Figure 23b is HR-TEM of the converted CMO-10 catalyst converted under reaction temperature conditions of 230 °C (A), 250 °C (B), 270 °C (C), 290 °C (D) and 310 °C (E, F) 24 shows SEM, HR-TEM and FFT images of the converted CMO-10 catalyst converted under conditions of H ₂ /CO ₂ ratios of 1:1, 2:1 and 4:1, and FIG. SEM and HR-TEM images of the CMO-10 catalyst after 1425 hours of reaction are shown.

Referring to FIGS. 23a, 23b, 24, and 25, in the case of the CMO-10 catalyst in which the ratio of H ₂ /CO ₂ was converted from 1:1, the selectivity for C1 hydrocarbons was 82.4% and the selectivity for C5+ hydrocarbons was 1.6%. In the case of the CMO-10 catalyst in which the H ₂ /CO ₂ ratio was converted at 2:1, the C1 hydrocarbon selectivity of 84.3% and the C ₅₊ hydrocarbon selectivity of 2.3% were shown. And in the case of the CMO-10 catalyst converted at H ₂ /CO ₂ ratios of 1:1 and 2:1, mixed phases of Co ₂ C and CoO were formed with a thickness of about 5 nm, and Co ₃ O ₄ and CoO were 12.9% and 8.8%, respectively, higher than 0.9% of the CMO-10 catalyst converted at a H ₂ /CO ₂ ratio of 3:1. In the case of the CMO-10 catalyst converted at a H ₂ /CO ₂ ratio of 4:1, the C1 hydrocarbon selectivity of 87.8% and the C ₅₊ hydrocarbon selectivity of 3.2% were exhibited, the particles were highly agglomerated, and the Co ₃ The content of O ₄ and CoO was increased to 10.1%, and the content of surface carbides was decreased to 1.2%.

Incomplete conversion of cobalt oxide to metallic Co under hydrogen deficient conditions and reoxidation on metallic Co by agglomeration of particles under hydrogen sufficient conditions can degrade the FTS response. The morphology of the converted CMO-10 catalyst was maintained even after 1425 hours of reaction.

Figure 26a shows the H ₂ -TPR profile for the CMO-y catalyst before reduction heat treatment at 330 ° C, and FIGS. 26b to 26d show the CO ₂ -TPD profile, CO-TPD profile and H ₂ of the CMO-y catalyst after reduction. -Indicates each TPD profile. And Table 6 shows the phase and composition of the peak of the H ₂ -TPR profile for the CMO-y catalyst before reduction, and Tables 7 to 9 show the CO ₂ -TPD data, CO-TPD data, and H ₂ -TPD data. The amounts of CO ₂ , CO and H ₂ desorbed from the CMO-y catalyst calculated using each are shown respectively.

Catalyst	peak (℃)	Area (%)	Assignment	composition (%)
CMO-0	254	22.7	Co 3 O 4 → CoO	Co 3 O 4 (22.7)
	308	9.4	Co 3 O 4 → CoO, CoO → Co	Co 3 O 4 (2.3), CoO (7.1)
	367	57.7	CoO → Co	CoO (57.7)
	416	10.2	CoO → Co	CoO (10.2)
CMO-10	209	9.5	MnO 2 → Mn 2 O 3 , Co 3 O 4 → CoO	MnO 2 (3.9), Co 3 O 4 (5.6)
	257	15.6	Co 3 O 4 → CoO	Co 3 O 4 (15.6)
	359	23.8	Mn 2 O 3 → Mn 3 O 4 , Co 3 O 4 → CoO, CoO → Co	Mn 2 O 3 (1.2), Co 3 O 4 (1.9), CoO (20.7)
	444	51.1	Mn 3 O 4 → MnO, CoO → Co	Mn 3 O 4 (2.6), CoO (48.5)
CMO-25	214	14.0	MnO 2 → Mn 2 O 3 , Co 3 O 4 → CoO	MnO 2 (10), Co 3 O 4 (4.0)
	275	18.9	Mn 2 O 3 → Mn 3 O 4 , Co 3 O 4 → CoO	Mn 2 O 3 (3.3), Co 3 O 4 (15.6)
	428	67.1	Mn 3 O 4 → MnO, CoO → Co	Mn 3 O 4 (6.7), CoO (60.4)
CMO-50	118	3.5	MnO 2 → Mn 2 O 3	MnO 2 (3.5)
	213	21.8	MnO 2 → Mn 2 O 3 , Co 3 O 4 → CoO	MnO 2 (18), Co 3 O 4 (3.8)
	300	17.8	Mn 2 O 3 → Mn 3 O 4 , Co 3 O 4 → CoO, CoO → Co	Mn 2 O 3 (7.1), Co 3 O 4 (10.5), CoO (9.2)
	336	9.0	Mn 2 O 3 → Mn 3 O 4 , Co 3 O 4 → CoO, CoO → Co
	453	47.9	Mn 3 O 4 → MnO, CoO → Co	Mn 3 O 4 (14.3), CoO (33.6)
CMO-75	154	7.5	MnO 2 → Mn 2 O 3	MnO 2 (7.5)
	233	32.9	MnO 2 → Mn 2 O 3 , Co 3 O 4 → CoO	MnO 2 (27.1), Co 3 O 4 (5.8)
	346	21.3	Mn 2 O 3 → Mn 3 O 4 , Co 3 O 4 → CoO, CoO → Co	Mn 2 O 3 (11.5), Co 3 O 4 (1.9), CoO (7.9)
	376	10.6	Mn 3 O 4 → MnO, CoO → Co	Mn 3 O 4 (23.2), CoO (15.1)
	470	27.7	Mn 3 O 4 → MnO, CoO → Co
CMO-100	190	10.87	MnO 2 → Mn 2 O 3	MnO 2 (10.87)
	251	29.58	MnO 2 → Mn 2 O 3	MnO 2 (29.58)
	268	14.58	MnO 2 → Mn 2 O 3 , Mn 2 O 3 → Mn 3 O 4	MnO 2 (9.54)Mn 2 O 3 (5.04)
	367	31.41	Mn 2 O 3 → Mn 3 O 4 , Mn 3 O 4 → MnO	Mn 2 O 3 (11.66) Mn 3 O 4 (19.75)
	399	13.56	Mn 3 O 4 → MnO	Mn 3 O 4 (13.56)

Amount of desorbed CO 2 (mmol g -1 )
Catalyst	Weak < 250 ℃	Medium 250-600℃	Strong >600 ℃	Total
CMO-0	-	-	0.003	0.003
CMO-10	0.001	0.015	0.001	0.017
CMO-25	0.027	0.003	-	0.030
CMO-50	0.007	0.001	-	0.008
CMO-75	0.006	0.002	0.001	0.009

Amount of desorbed CO (mmol g -1 )
Catalyst	Weak < 250 ℃	Medium 250-600℃	Strong >600 ℃	Total
CMO-0	0.009	0.006	0.004	0.019
CMO-10	0.074	0.053	0.028	0.155
CMO-25	0.106	0.123	0.017	0.246
CMO-50	0.191	0.208	0.069	0.468
CMO-75	0.018	0.042	0.144	0.204

Amount of desorbed H 2 (mmol g -1 )
Catalyst	Weak < 250 ℃	Medium 250-600℃	Strong >600 ℃	Total
CMO-0	0.023	0.031	0.001	0.055
CMO-10	0.013	0.014	0.001	0.028
CMO-25	0.009	0.007	-	0.016
CMO-50	0.004	0.017	-	0.021
CMO-75	0.003	0.013	-	0.016

Referring to FIGS. 26A to 26D and Tables 6 to 9, the high-temperature peaks at 427-470° C. for the CMO-y catalysts (10≤y≤75) show that the spinel structure of Co _x Mn _3-x O ₄ is Indicates that the reducing properties of the catalyst are hindered. In addition, as the Mn content increased, the reduction temperature of Co ₃ O ₄ to CoO increased from 258 °C (CMO-0) to 345 °C (CMO-75), indicating that the presence of Mn inhibits the reduction of cobalt oxide. The presence of Mn increased the adsorption of CO ₂ and CO, but decreased the adsorption of H ₂ . Thus, strong adsorption for CO and CO ₂ and weak adsorption for H ₂ on CMO-y catalysts containing Mn can increase the C/H surface coverage ratio and thus increase the FTS rate across methanation. can help to improve CO ₂ conversion and C ₅₊ hydrocarbon selectivity.

[Experimental Example 3]: In-situ operando DRIFT analysis

To understand the reaction mechanism underlying the formation of C ₅₊ hydrocarbons, a series of in situ DRIFT experiments were performed to investigate the evolution of reaction intermediates on CMO-0 and CMO-10 catalysts.

DRIFT spectra were collected during pressurization of the DRIFT cell from 0.1 _MPa to 3.0 MPa with CO 2 to identify species of intermediate products derived from CO ₂ adsorbed on the surface of the catalyst, at which time the DRIFT cell was operated at 350 °C. contained a previously H ₂ -reduced CMO-0 catalyst.

27A to 27D show in situ DFIFT CO ₂ adsorption profiles on CMO-10 catalyst, FIGS. 28A to 28C show in situ DFIFT CO ₂ adsorption profiles on CMO-0 catalyst, and FIGS. 29A to 29C show In situ DFIFT CO adsorption profiles on CMO-0 catalyst are shown, FIGS. 30A-30C show in situ DFIFT CO adsorption profiles on CMO-10 catalyst, and FIGS. 31A and 31B show CO pressurization to 3.0 MPa and 270° C. QMS profiles of the products released from the DRIFT cell during H ₂ flow over the CMO-O catalyst (A) and CMO-10 catalyst (B) after the temperature rise to . and FIGS. 32A to 32C show reaction profiles of in situ DFIFT CO ₂ and H ₂ on CMO-0 catalyst after reduction, and FIGS. 33A to 33C show reaction profiles of in situ DFIFT CO ₂ and H on CMO-10 catalyst after reduction. ₂ , FIGS. 34A and 34B show in situ DFIFT CO ₂ and H ₂ reaction profiles (A) for 60 minutes over CMO-10 catalyst after reduction under varying reaction pressure conditions and CO ₂ during hydrogenation of CO ₂ - Evolution of adsorbed species, adsorbed CO, gaseous CO and CH ₄ (B), FIGS. 35A and 35B show in situ DFIFT CO over 60 min over CMO-0 catalyst after reduction under varying reaction temperature conditions. ₂ and H ₂ reaction profiles (A) and evolution of CO ₂ -adsorbed species, adsorbed CO, gaseous CO and CH ₄ during CO 2 hydrogenation ( _B ).

27A to 27D , A is the result measured while increasing the temperature to 270° C. after pressurizing the cell to 3.0 MPa with CO ₂ , and B is caused by switching the gas flow from CO ₂ to H ₂ is the result measured during hydrogenation of the CO ₂ -adsorbed species, C represents the evolution of the selected CO ₂ -adsorbed species, CO and CH ₄ during hydrogenation, and D is the QMS profile of the product released from the DRIFT cell under H ₂ flow conditions. am. 28A to 28C, A is the result measured while the temperature is increased to 270° C. after pressurizing the cell to 3.0 MPa with CO ₂ , and B is caused by switching the gas flow from CO ₂ to H ₂ is the result measured during hydrogenation of the CO ₂ -adsorbed species, and C represents the evolution of the selected CO ₂ -adsorbed species, CO and CH ₄ during hydrogenation. In Figures 29a to 29c, A is the result measured while increasing the temperature to 270 ℃ after pressurization to 3.0MPa using 5% CO / He, B is the gas flow by switching from CO to H ₂ Results measured during the hydrogenation of the resulting CO-adsorbing species, C represents the evolution of selected CO-adsorbing species, CO and CH ₄ during hydrogenation. 30A to 30C, A is the result measured while increasing the temperature to 270° C. after pressurization to 3.0 MPa using 5% CO/He, and B is the result obtained by converting the gas flow from CO to H ₂ Results measured during hydrogenation of the resulting CO-adsorbing species, and C represents the evolution of selected CO ₂ -adsorbing species, CO and CH ₄ during hydrogenation. 32A to 32C and 33A to 33C, A is the measured result during CO ₂ and H ₂ injection at a pressure of 3.0 MPa and a temperature of 270° C., and B is the gas flow from CO ₂ /H ₂ to H ₂ Results measured during the H ₂ flow induced by conversion, C represents the evolution of selected CO 2 -adsorbing species, CO and CH ₄ during hydrogenation.

Referring to FIGS. 27 to 35a and 35b, the intensities of the infrared bands of gaseous CH ₄ at 3015 and 1305 cm ^-1 and bending of the =CH group at 949 cm ^-1 are obtained when the CO ₂ flow time is from 1 minute to 90 increased with increasing minutes. CH ₄ formation on the reduced CMO-0 catalyst indicates that the CO ₂ methanation reaction has occurred due to pre-adsorbed H ₂ remaining after reduction. When the CO ₂ flow time was further increased to 170 min, the IR bands associated with CH ₄ and ═CH decreased because the H ₂ previously adsorbed on the catalyst surface was gradually consumed.

Small peaks appeared at 2200-2000 cm ^-1 during the 3 min CO ₂ flow. The peaks at 2130, 2094, 2078 and 2059 cm-1 are linearly adsorbed CO on the Co ²⁺ site ([Co ²⁺ -(CO)]), partially reduced Co ^δ+ site ([Co ^{δ+ +} -(CO)]), and a metal Co site ([Co ⁰ -(CO)]), respectively. The peaks at 1933 and 1914 cm-1 represent CO bridged on the metal Co site ([Co _two-fold -(CO)]).

Thus, in the reduced CMO-0 catalyst, fully reduced metallic Co ⁰ , partially oxidized Co ^δ+ (1<δ<2) and Co ⁽²⁺⁾ O centers coexisted. The intensity of the [Co ^δ+ -(CO)] peak is high, indicating that CO adsorbed on the oxygen vacancy-Co oxide site is dominant. In the 1200-900 cm ^-1 region, the bands at 1082 and 1051 cm ^-1 represent methoxy groups. The small peak at 1637 cm ⁻¹ corresponds to adsorbed water. The evolution of adsorbed CO, H ₂ O and gaseous CH ₄ indicate the activity and methanation reaction of RWGS on the CMO-0 catalyst.

After 170 minutes of CO ₂ flow, the pressure in the DRIFT cell was increased to 3.0 MPa. Then, while maintaining the pressure of the cell at 3.0 MPa, the temperature of the cell was increased to 270°C. The intensity of the IR spectrum under the conditions of 270°C and 3.0 MPa was very similar to that under the conditions of 50°C and 3.0 MPa.

Under conditions of 270° C. and 3.0 MPa, IR spectra were collected after the gas flow in the DRIFT cell was switched from CO ₂ to H ₂ . After 40 min of H2 flow, the intensity of the IR bands associated with =CH, methoxy and adsorbed CO species decreased, while those associated with CH ₄ increased. When the H ₂ flow time was increased to 60 minutes, evolution of gaseous CO (CO _gas ) was observed at 2110 and 2170 cm ⁻¹ . In addition, unique peaks related to reaction intermediates were observed in the region of 1800-1200 cm ⁻¹ ; (1) Peaks at 1508 and 1340 cm ^-1 represent asymmetric and symmetric vibrations [ν _as (OCO) and ν _s (OCO)] of monodentate carbonate (m-CO ₃ ^2- ), respectively, (2 ) peaks at 1617, 1269 and 976 cm ^-1 represent ν(C=O), ν _as (OCO) and ν _s (OCO) of bidentate carbonate (b-CO32-), respectively. In addition, (3) peaks at 1652, 1436, 1222 and 1038 cm ^-1 are ν(C=O), ν _as (OCO), δ(OH), and ν _s (OCO) of bicarbonate (HCO3-) , and (4) the peaks at 1577, 1374 and 1362 cm ^-1 can be assigned to ν _as (OCO), δ(CH), and ν _s (OCO) of formate (HCOO ^- ) .

The formation of CO ₂ -adsorption spectra (m-CO ₃ ^2- , b-CO ₃ ^2- , HCO ₃ ^- and HCOO ^- ) was aggressively activated by increasing the partial pressure of H ₂ . The time-evolution intensities of the IR bands of m-CO ₃ ^2- , HCOO ^- , [Co ^δ+ -(CO)], CO _gas and CH ₄ under continuous H ₂ flow conditions are shown in FIGS. 28a to 28c. . At an initial H ₂ flow of about 30 minutes, m-CO ₃ because the hydrogen partial pressure was not high enough to drive the hydrogenation reaction while the continuous gas flow maintained desorption of surface adsorbed species and dilution of gaseous products. The intensity of the IR bands of ^2- , HCOO ^- , [Co ^δ+ -(CO)], CO _gas and CH ₄ decreased. Through close examination of the induction period, m-CO ₃ ^2- and ^HCOO- peaks had minimum intensity in the initial 30 min H ₂ flow, and peaks of CO _gas and CH ₄ were observed in the 40 min H ₂ flow. In addition, the changes in IR band intensities of m-CO ₃ ^2- , HCOO ^- , CO and CH ₄ were different from each other; [Co ^δ+ -(CO)] and CO _gas reached maximum intensity at 90 min of H ₂ flow and decreased to near zero as the H ₂ flow time was further increased. On the other hand, the m-CO ₃ ^2- and ^HCOO- species reached their maximum intensity at 170 min and maintained their intensity constant with further increase in H2 flow time. The different evolutionary trends of CO and m-CO ₃ ^2- /HCOO ^- suggest that the formation of m-CO ₃ ^2- /HCOO ^- and CO follow different reaction pathways. The intensity of CH ₄ increased during the time interval of 90–170 min, and the intensity of the IR band of CO decreased, suggesting that CO is an intermediate product of CH ₄ formation.

The CO ₂ adsorption behavior on the CMO-10 catalyst showed a similar trend to that of the CMO-0 catalyst. Unlike previous Mn-promoted Co-based FTS catalysts, Mn in the Co catalyst redshifts [Co ²⁺ -(CO)], [Co ^δ+ -(CO)] and [Co ⁰ -(CO)] peaks. and did not change the intensity of the [Co _two-fold -(CO)] peak. Therefore, in the CMO-10 catalyst, Mn played little role as an electromagnetic promoter to change the absorption geometry of CO. During CO ₂ adsorption, the intensities of the IR bands of gaseous CH ₄ at 3015 and 1305 cm ⁻¹ and bending of ═CH groups at 949 cm ⁻¹ reached a maximum at 170 min, which was observed for the CMO-0 catalyst (90 minutes) slower than above. This indicates that the Mn promoter inhibits the methanation reaction under H ₂ -starvation conditions. Again, the decoupling in the evolution of m-CO ₃ ^2- /HCOO ^- and CO _gas at H ₂ flow times of 30-60 min indicates different reaction pathways in the formation of formic acid and CO. Quadrupole mass spectrometry (QMS) profiles of products released from the DRIFT cell during H ₂ flow show the formation of CO and H ₂ O by RWGS reaction and CH ₄ , C ₂ H ₆ and C ₃ by FTS on CMO-10 catalyst. Indicates the formation of H ₅ .

DRIFTS spectra as the pressure in the DRIFT cell was increased from 0.1 MPa to 3.0 MPa were collected by flowing CO to characterize the intermediate species derived from the adsorption of CO on the surface of the catalyst, wherein the DRIFT cell was preheated at 350 °C. It contained H ₂ -reduced CMO-0 catalyst. Unlike CO ₂ adsorption, no formation of CH ₄ was observed during CO adsorption, indicating that direct hydrogenation of CO to CH ₄ does not occur under H ₂ deficient conditions. Thus, CH ₄ formation during pressurization of CO ₂ over the previously H 2 -reduced CMO-0 catalyst indicates that direct hydrogenation of CO ₂ to CH ₄ occurred without passing CO, and under H ₂ -starved conditions It indicates that surface adsorbed CO species are not precipitated in the methanation reaction. The CO ₂ peaks at 2333 and 2364 cm ⁻¹ were prominent during the initial 15 min of CO adsorption, indicating the high WGS activity of the CMO-0 catalyst. When the temperature increased from 50 °C to 270 °C, the peaks associated with CO ₂ increased due to the increase in WGS reaction activity with increasing temperature. After CO adsorption at 3.0 MPa, the gas flow through the DRIFT cell was switched from CO to H ₂ under conditions of 270° C. and 3.0 MPa, and IR spectra were collected. Due to the presence of CO ₂ produced in situ by the WGS reaction, the spectrum collected during hydrogenation of pre-adsorbed CO was similar to that during hydrogenation of pre-adsorbed CO ₂ .

The CO adsorption and hydrogenation behavior of the adsorbed CO on the CMO-10 catalyst was similar to that on the CMO-0 catalyst. The main difference is the WGS activity in the initial 5 minutes of CO flow, the intensity of gaseous CO ₂ reaches a maximum on the CMO-10 catalyst, which is significantly faster than on the CMO-0 catalyst. Both gaseous CO ₂ and CO were present at the end of the temperature ramp from 3.0 MPa to 270 °C. At the initial state of the H ₂ flow to the DRIFT cell containing both CO ₂ and CO gases, the formation of H ₂ O by RWGS over the CMO-10 catalyst was more pronounced than over the CMO-0 catalyst. Thus, as the H ₂ partial pressure was increased compared to that over the CMO-0 catalyst, the more abundant CO produced by RWGS over the CMO-10 catalyst promoted the formation of C ₂ H ₆ followed by the formation of CH ₄ .

To investigate the instantaneous response of reaction intermediates during CO2 hydrogenation on a pre-H ₂ -reduced CMO-0 catalyst, in situ operational number DRIFT profiles were analyzed under conditions of 270°C and 3.0 MPa and 3:1 H ₂ / Collected under the flow of CO ₂ gas mixture. The collected DRIFT spectra and the intensities of IR bands of selected surface adsorbed species (m-CO ₃ ^2- , HCOO-, HCO ^- , [Co ^δ+ -(CO)]) and gas phase (CH ₄ , CO ₂ , CO) Changes over time are shown in FIGS. 32A to 32C. After the introduction period of 13 min, the methanation reaction was highly active, and peaks related to m-CO ₃ ^2- , HCOO-, HCO ^- , [Co ^δ+ -(CO)] and CO _gas gradually increased. After 40 min of H ₂ /CO ₂ flow, the intensity of the peaks related to CO _gas , m-CO ₃ ^2- , HCOO ^- , and HCO ^- were maintained, but the intensity of the CH ₄ peak decreased. Thus, after consuming the previously adsorbed H ₂ to produce CH ₄ , the ability of the CMO-0 catalyst for the fissile adsorption of H ₂ and subsequent hydrogenation of CO ₂ to CH ₄ was suppressed.

After 120 minutes of H ₂ /CO ₂ flow, the flow gas was converted from H ₂ /CO ₂ to H ₂ and a DRIFT spectrum was collected. The peak of CO _gas reached maximum intensity at 10 minutes of H ₂ flow, but the CH ₄ and CO ₂ -adsorption peaks reached maximum intensity at 70 minutes of H ₂ flow, indicating that the methanation reaction under H ₂ -sufficient conditions. indicates that it is activated. Methanation was highly active during the initial H ₂ /CO ₂ flow on the CMO-10 catalyst, which may be due to the smaller size of the metallic Co nanoparticles compared to that on the CMO-0 catalyst. Also, during CO ₂ /H ₂ and subsequent H ₂ flow, the intensity of the peaks associated with m-CO ₃ ^2- and HCOO ^- on the CMO-10 catalyst was higher than that on the CMO-0 catalyst, indicating that the CMO-10 catalyst Indicates enhanced CO ₂ adsorption on the phase. As the pressure and temperature increased, more formation of CO ₂ -adsorbed species was observed in FIGS. 34A and 34B and FIGS. 35A and 35B , respectively.

[Experimental Example 4]: Simulation of Density Functional Theory

CMO-y catalysts are mixtures of metallic Co, Co-carbide and Co-oxide phases, which can modify reaction intermediates, so that it is necessary to characterize their respective role in the CO ₂ conversion by decoupling of each phase. do. To this end, the atomic level mechanism of CO ₂ hydrogenation on Co (001), Co ₂ C (101) and Co ₃ O ₄ (110) surfaces was investigated using DFT calculations.

Although the CoO structure was observed in the HR-TEM images of the converted CMO-10 catalyst, DFT calculations found that the CoO flakes were destabilized by adsorbates. Therefore, Co ₃ O ₄ was selected as a representative structure of Co-oxide, and the mechanism was comparatively analyzed. Also, the effect of surface oxygen vacancies (vac-Co ₃ O ₄ (110)) on Co ₃ O ₄ on the catalytic energetics was investigated.

36 shows the CO ₂ hydrogenation pathway (A), the surface structure of Co-containing phases (B), and the free energies of CO ₂ hydrogenation (C, D) for CH and CO under conditions of a temperature of 270 °C and a pressure of 4.0 MPa. 37 shows the free energy profiles (A, B) calculated by DFT of the RWGS reaction through HCOO intermediates and HOCO intermediates and the free energy profile of CO hydrogenation to CH formation (C). (* indicates surface-bound species)

Referring to FIGS. 36 and 37 , initial CO ₂ activation proceeded by the formation of three different intermediates, HCOO*, COOH*, and CO*. For the HCOO* pathway, continuous oxygen removal resulted in the formation of CH*, which served as a precursor for FTS and methanation.

Formation of HCOO* on Co ₃ O ₄ and oxygen-deficient Co ₃ O ₄ (vac-Co ₃ O ₄ ) surfaces (CO ₂ * -> H-COO -> HCOO*) is advantageous because it has small mechanical barriers of 0.73 and 0.97 eV. The subsequent oxygen removal of HCOO* to produce HCO* and CH* occurs on vac-Co ₃ O ₄ , where the kinetic barrier is significantly smaller than that of Co ₃ O ₄ . Thus, the HCOO*-species shown in the DRIFT spectrum are present on the outermost CO oxide surface, and they can be readily converted to CHO* and CH* at adjacent oxygen vacancies. As shown in Fig. 36D, in addition to CH* formation via the HCOO* pathway, Co oxide phases are active sites for the RWGS reaction to proceed through direct cleavage of OC-O bonds. Activation of OC-O bond cleavage on vac-Co ₃ O ₄ required only 0.15 eV. On the other hand, the RWGS route through the HOCO* intermediate was not favorable because of the high activation barrier that occurred regardless of the Co phase.

As shown in FIG. 37 , unlike the initial activation of CO ₂ , CO adsorption and subsequent hydrogenation are favored on the Co ₂ C and metallic Co surfaces. Deoxygenation from CHO* to CH* on the Co ₂ C surface shows an activation energy of 0.86 eV, which is 0.4 eV lower than on vac-Co ₃ O ₄ .

Based on the reaction energies obtained using DFT simulations and DRIFT spectra, two possible reaction pathways from CO ₂ to C ₅₊ hydrocarbons on CMO-y catalysts are presented, first the oxygen vacancies of cobalt oxide in the shell. CO ₂ activation occurs at , which produces intermediates CHO* and CO*. These intermediates migrate to the Co ₂ C and metallic Co of the adjacent core, where additional hydrogenation or chain growth reactions occur.

The high yield of C5+ hydrocarbons on the CMO-0 and CMO-10 catalysts is due to the activated FTS reaction on the hcp Co site. In addition, the thermodynamic limitations of RWGS (e.g., CO ₂ conversion of about 18% at 270 °C and H ₂ /CO ₂ ratio of 3) promote continuous CO consumption by the C-C coupling reaction on the metallic Co center. can be overcome by Little CO was observed in the product stream during CO ₂ hydrogenation, except under low pressure conditions where methanation reactions were predominantly observed. The evolution of CO and CO ₂ during CO ₂ adsorption and CO ₂ hydrogenation and in the DRIFT profiles during CO hydrogenation indicate that the CMO-0 and CMO-10 catalysts are highly active for both RWGS and WGS reactions. Thus, the negligible amount of CO in the product is due to the rapid conversion of CO on the hcp Co metal center.

Conversion of CO 2 to CO through RWGS, considering the compositional geometry, electromagnetic state and DRIFT simulations of _the converted CMO-0 and CMO-10 catalysts (Co@CoO _x /Co ₂ C core-shell) occurs on the porous CoO _x shell layer. Oxygen vacancies in the Co ₃ O ₄ phase that are retained due to the incomplete conversion of Co ₃ O ₄ to metallic Co during reduction or regenerated due to the production of water during the reaction help to adsorb CO ₂ and enhance the RWGS reaction. In addition, sufficient production of CO by RWGS of CO ₂ can help maintain the Co ₂ C shell layer through CO carbonization (2CoO + 4CO -> Co ₂ C + 3CO ₂ ). The produced CO then migrated to the metallic Co centers in the Co ₂ C phase and nearby cores, where the active chain propagation reaction takes place. The presence of metallic Co in the core and the CoO _x /Co ₂ C layer in the shell can influence the direct contact of the CO ₂ with the metallic Co phase, which thermodynamically leads to the RWGS reaction (CO ₂ + H ₂ → CO + H ₂ O, Direct methanation of CO ² ( _{CO 2 +} 4H ₂ → ^CH ₄ + 2H ₂ O, ΔH ⁰ (298K) = -165 kJ mol ^-1 ) can be suppressed. Production of alcohols or other oxygenated species proceeding by intercalation of CO adsorbed on cobalt oxide (CoO _x ) or cobalt carbide (Co ₂ C) was rarely observed in the liquid product, which is consistent with the CMO-0 and CMO-10 catalysts. indicates that little CO intercalation occurred in the phase.

In the CMO-10 catalyst, Mn sufficiently enhanced CO ₂ conversion and C ₅₊ hydrocarbon selectivity. In addition, the Mn promoter effectively inhibited particle aggregation during CO ₂ hydrogenation, which further enhanced CO ₂ adsorption and RWGS response. However, as demonstrated in the CO and CO ₂ DRIFT analysis, the IR band of the linearly adsorbed CO was not red-shifted on the CMO-10 catalyst (which was previously observed for Mn-promoted Co/TiO ₂ and Co-Mn) and was not empty. The significantly larger metal Co size in the delayed CMO-10 catalyst can minimize the electron donor effect from MnCO ₃ to metal Co in the CO adsorption state. Mn facilitated the formation of the CoO _x /Co ₂ C shell layer, which further activated the RWGS reaction.

At a high temperature reaction of 310 °C, the separation of the CoO _x /Co ₂ C shell from the metallic Co center caused re-oxidation of hcp Co and a decrease in FTS activity. Another property of the CMO-10 catalyst in FTS-dominated reactions is its ability to maintain high metallic Co centers. Since the metallic Co center is the active site for the chain propagation reaction, it is necessary to suppress the re-oxidation of metallic Co caused by direct contact of CO ₂ or by H ₂ O generated in the RWGS reaction. In the FTS reaction, nano-sized Co particles (<4-6 nm) are known to be highly re-oxidizable due to their low FTS activity. Therefore, the high yield of C5+ hydrocarbons on the CMO-10 catalyst means that the moderate reaction temperature (270 °C) and high reaction pressure (4.0 MPa) of the metal Co core of the Co@CoO _x /Co ₂ C catalyst Indicates that it helps to maintain metallic properties.

The catalyst's long-term stability, high selectivity towards gas/liquid fuels and lube base oil, and low temperature synthesis conditions make Mn-promoted core-shell Co@CoO _x /Co ₂ C catalysts suitable for use in CO ₂ under industrially relevant conditions. can make it promising.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. You will understand that you can.

Catalysts according to embodiments of the present invention may be used for hydrogenation of carbon dioxide.

Claims (20)

1. In the catalyst for promoting the hydrogenation reaction of carbon dioxide,

   a core comprising a metallic cobalt phase; and

   A catalyst for hydrogenation of carbon dioxide, comprising a shell located on the surface of the core and including a Co ₃ O ₄ phase and a Co ₂ C phase.
2. According to claim 1,

   A catalyst for hydrogenation of carbon dioxide, characterized in that the ratio of the number of moles of the manganese element to the total number of moles of the cobalt and manganese elements in the catalyst [Mn / (Co + Mn)] is 3 or more and 20% or less.
3. According to claim 1,

   A catalyst for hydrogenation of carbon dioxide, characterized in that the fraction of the metallic cobalt phase in the cobalt-containing phase of the entire catalyst is 90% or more and less than 100%.
4. According to claim 1,

   The core includes a metallic cobalt phase having a crystal phase of a hexagonal close-packed lattice structure,

   Catalyst for the hydrogenation reaction of carbon dioxide, characterized in that pores are formed in the shell to expose the core to the outside.
5. According to claim 4,

   The shell further includes CoO in addition to the Co ₃ O ₄ as a cobalt oxide phase,

   Characterized in that the [CoO+Co ₃ O ₄ ]/Co ^O ratio is 1.5 to 1.9,

   Catalyst for hydrogenation of carbon dioxide, characterized in that the area ratio of the Co ₂ C phase in the shell is 10 to 30%.
6. According to claim 1,

   the shell further comprises a manganese containing phase;

   Characterized in that the manganese-containing phase includes MnCO ₃ phase, Mn ₂ O ₃ and Mn ₃ O ₄ , and the fraction of the MnCO ₃ phase in the manganese-containing phase is 90 to 99%, for hydrogenation of carbon dioxide. catalyst.
7. According to claim 1,

   Catalyst for the hydrogenation reaction of carbon dioxide, characterized in that it further comprises a carbon layer located on the surface of the shell.
8. A first step of mixing a reaction solution in which a cobalt precursor compound and a manganese precursor compound are dissolved and a precipitant solution in which a basic precipitant is dissolved to form a suspension solution;

   A second step of aging the suspension solution;

   A third step of separating powder from the aged suspension solution; and

   A method for producing a catalyst for hydrogenation of carbon dioxide, comprising: a fourth step of drying and heat-treating the separated powder to form a first catalyst powder.
9. According to claim 8,

   Method for producing a catalyst for hydrogenation of carbon dioxide, characterized in that it further comprises a fifth step of reducing the first catalyst powder in a hydrogen atmosphere to form a second catalyst powder.
10. According to claim 9,

    A sixth step of exposing the second catalyst powder to a flow of a mixed gas of carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) to form a third catalyst powder, characterized in that it further comprises, for hydrogenation of carbon dioxide Method for preparing a catalyst.
11. According to claim 10,

    In the first step, the cobalt precursor and the manganese precursor are added to the reaction solution so that the ratio of the number of moles of manganese ions to the total number of moles of cobalt ions and manganese ions in the reaction solution is 3 or more and 20% or less. Characterized in that, the total concentration of the cobalt precursor and the manganese precursor in the reaction solution is characterized in that 1.5 to 3 mol / L, a method for producing a catalyst for hydrogenation of carbon dioxide.
12. According to claim 8,

    The basic precipitant is a method for producing a catalyst for hydrogenation of carbon dioxide, characterized in that it comprises sodium carbonate (Na ₂ CO ₃ ).
13. According to claim 10,

    In the fourth step, the separated powders are dried at a temperature of 90 to 110 ° C. and then heat-treated for 2 to 5 hours at a temperature of 300 to 360 ° C. and under air flow conditions. manufacturing method.
14. According to claim 13,

    The first catalyst powder is a method for producing a catalyst for a hydrogenation reaction of carbon dioxide, characterized in that it comprises a cobalt oxide phase, a manganese oxide phase and each of them doped with sodium.
15. According to claim 10,

    The fifth step is performed by supplying hydrogen gas into the tubular reactor at a temperature of 320 to 400 ° C. for 4 to 8 hours after fixing the first catalyst powder in the tubular reactor,

    During the fifth step, the first catalyst powder is converted into the second catalyst powder including a metal cobalt phase, a cobalt oxide phase and a manganese oxide phase.
16. According to claim 15,

    The sixth step is performed by supplying a mixed gas of hydrogen and carbon dioxide after adjusting the temperature inside the tubular reactor in which the second catalyst powder is fixed to 250 to 300 ° C,

    During the sixth step, the second catalyst powder may include a core formed of metal cobalt; and a shell formed of a mixture including a Co ₃ O ₄ phase and a Co ₂ C phase on the surface of the core and converted into the third catalyst powder comprising a shell.
17. According to claim 16,

    During the sixth step, the pressure inside the tubular reactor is adjusted to 3.5 to 5.0 MPa,

    During the sixth step, a mixed gas in which hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) are mixed at a ratio of 2.5: 1 to 3.5: 1 is supplied into the tubular reactor, a catalyst for hydrogenation of carbon dioxide. Manufacturing method of.
18. A method for generating a hydrocarbon compound having 5 or more carbon atoms by inducing a hydrogenation reaction of carbon dioxide by supplying a mixed gas of hydrogen and carbon dioxide into a tubular reactor in which a catalyst is fixed,

    The catalyst comprises a core comprising a metallic cobalt phase; and a shell located on the surface of the core and comprising a Co ₃ O ₄ phase and a Co ₂ C phase.
19. According to claim 18,

    During the hydrogenation reaction of carbon dioxide, the temperature inside the tubular reactor is adjusted to 250 to 300 ° C,

    The method for synthesizing hydrocarbon compounds, characterized in that the pressure inside the tubular reactor is adjusted to 3.5 to 5.0 MPa during the hydrogenation reaction of carbon dioxide.
20. According to claim 18,

    Characterized in that a mixed gas in which hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) are mixed at a ratio of 2.5: 1 to 3.5: 1 is supplied into the tubular reactor during the hydrogenation reaction of carbon dioxide,

    A method for synthesizing hydrocarbon compounds, characterized in that the ratio of linear paraffins in the produced hydrocarbon compounds having 5 or more carbon atoms is 90% or more and less than 100%.

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