Method for producing two-dimensional nickel silicate molecular sieve catalyst for dry reforming reaction of methane and two-dimensional nickel silicate molecular sieve catalyst for dry reforming reaction of methane produced thereby

Abstract

The present invention relates to a method for producing a nickel silicate molecular sieve catalyst for dry reforming of methane, and more particularly, to a method for producing a two-dimensional nickel silicate molecular sieve catalyst for dry reforming of methane, the catalyst having structural stability and activity and containing a two-dimensional large external surface area and nickel bound to the surface area, in a one-step reaction through hydrothermal treatment.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a nickel silicate molecular sieve catalyst for the dry reforming reaction of methane, and to a method for manufacturing a two-dimensional nickel silicate molecular sieve catalyst for the dry reforming reaction of methane, which produces a catalyst having a two-dimensional wide external surface area and structural stability and activity including nickel bonded to the surface area through a one-step reaction by hydrothermal treatment.

Background Art

[0002] The dry reforming of methane (DRM) is a reaction that converts CH4 and CO2, which are greenhouse gases, into syngas (a mixed gas of H2 and CO) (Reaction Formula 1). The dry reforming reaction of methane recycles CO2 into valuable chemicals such as synthetic fuels, methanol, and dimethyl ether, and is one of the core technologies for building a circular carbon economy that mitigates environmental emissions, so it has attracted the attention of the environmental and industrial fields.

[0003] <Reaction Formula 1> CH4 + CO2 → 2CO + 2H2 △H° 298 = 247 kJ / mol -1

[0004] However, regardless of its high impact on the environment and industry, due to the complexity and endothermic nature of the reaction, the successful commercialization of the dry reforming reaction of methane is difficult. In fact, the dry reforming reaction of methane produces carbon deposits through reactions such as the Boudouard reaction (2CO ⇔ C + CO2, △H° 298 = -190 kJ / mol -1 ) and methane cracking (CH4 → C + 2H2, △H° 298 = 75 kJ / mol -1 ) and the reverse water-gas shift reaction (RWGS, CO2 + H2 ⇔ CO + H2O, △H° 298 = 41 kJ / mol -1) It involves side reactions that reduce the H2 / CO ratio of the syngas.

[0005] Therefore, in order to successfully commercialize the dry reforming reaction of methane, the development of highly active, active and stable catalysts is necessary.

[0006] For such dry reforming reactions of methane, many studies have been mainly conducted on the potential utilization of catalysts of various types of transition metals. Among them, in particular, the development of catalysts containing metals platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), nickel (Ni) and cobalt (Co) of Group VIII has been carried out. However, among these, in the case of Pt, Ru, Rh and Pd, they are noble metals, which are good from the viewpoints of catalyst activity, selectivity and stability, but are expensive and have low economic efficiency for industrial use.

[0007] Therefore, research has been underway on the applicability of transition metals such as tungsten (W), titanium (Ti), vanadium (V), nickel (Ni), iron (Fe), copper (Cu), molybdenum (Mo), cobalt (Co), etc., which are cheaper than noble metals, as catalysts for the dry reforming reaction of methane.

[0008] Among these, in the case of nickel, although it is relatively inexpensive compared to other transition metals, it has relatively high selectivity and conversion rate for the CO2 reforming of methane and is widely used as a catalyst for the dry reforming reaction of methane.

[0009] However, in the case of such Ni catalysts, during the dry reforming reaction of methane, deactivation due to coke deposition and active metal sintering progresses, and it is difficult to maintain long catalyst activity for a relatively long time.

[0010] Therefore, in order to compensate for such disadvantages of the active nickel metal, research on catalyst carriers has been actively carried out. In the case of catalysts, not only the type and size of the active metal, but also the type, surface area of the carrier on which the metal is supported, and their interactions can significantly change the catalytic activity and stability. Therefore, alumina is mainly used as the carrier.

[0011] Korean Registered Patent No. 10-1959379 (Publication date: March 18, 2019) relates to a nickel-based catalyst for the combined reforming reaction of methane, and discloses that the active components nickel (Ni) and antimony (Sb), molybdenum (Mo) are supported on a gamma-alumina carrier. However, in the gamma-alumina, it is not easy to disperse the active metal, and the external surface area in contact with the reactants is not sufficiently large, so it is difficult to improve the catalytic activity.

[0012] In addition, Korean Registered Patent No. 10-1487387 (Publication date: January 28, 2015) relates to a method for manufacturing a metal carbide-based methane reforming catalyst, and discloses that a porous carbonaceous material carrier and nickel and molybdenum precursor active components can be included to increase the specific surface area and improve the catalytic activity. However, when following the manufacturing method of the prior literature, aggregation and clusters of nickel may occur, which may lead to a decrease in catalytic activity.

[0013] Therefore, in order to solve the problem of the decrease in catalytic activity due to coke generation and nickel reduction associated with sintering during the dry reforming reaction of methane, which contains nickel as the active metal, by changing the carrier, the bond between the carrier and nickel, the catalyst skeleton, etc., a new form of manufacturing method and catalyst development for a catalyst for the dry reforming reaction of methane that can improve structural stability, catalytic activity, and activity maintenance are required.

Summary of the Invention

Problems to be Solved by the Invention

[0014] In order to solve the above problems, the present invention simplifies the catalyst manufacturing process through a one-step reaction in a hydrothermal treatment process, while including a two-dimensional wide external surface area and nickel bonded to the surface area through the process, and provides a method for manufacturing a two-dimensional nickel silicate molecular sieve catalyst for the dry reforming reaction of methane, which improves structural stability and catalytic activity.

[0015] Further, the present invention provides a two-dimensional nickel silicate molecular sieve catalyst for the dry reforming reaction of methane manufactured by the above method.

Means for Solving the Problems

[0016] To achieve the above object, the present invention includes (a) synthesizing a layered borosilicate MWW Zeolite framework Before the type precursor [B-MWW(P)]; and (b) adding a nickel precursor to the B-MWW(P) and performing hydrothermal treatment. The present invention provides a method for manufacturing a two-dimensional nickel silicate molecular sieve catalyst for the dry reforming reaction of methane.

[0017] In one embodiment, in step (a), B-MWW(P) with an Si / B molar ratio of 5.0 to 20.0 can be synthesized.

[0018] In one embodiment, in step (b), the concentration of the nickel precursor may be 0.1 to 5.0 M.

[0019] In one embodiment, the hydrothermal treatment temperature in step (b) may be 100 to 200 °C.

[0020] Further, the present invention provides a two-dimensional nickel silicate molecular sieve catalyst for the dry reforming reaction of methane manufactured by the above manufacturing method.

[0021] In one embodiment, the Si / Ni molar ratio of the catalyst may be 1.5 to 30.

[0022] In one embodiment, the catalyst may have a catalyst deactivation rate of less than 5% with respect to methane and carbon dioxide in the dry reforming reaction of methane at 700 °C.

Advantages of the Invention

[0023] The present invention can produce a two-dimensional nickel silicate molecular sieve catalyst by hydrothermally treating B-MWW(P) and a nickel precursor, substituting boron with nickel in a one-step reaction, and exfoliating three-dimensional MWW, thereby improving process efficiency.

[0024] In addition, in the case of the present invention, boron in B-MWW(P) is substituted with nickel during the hydrothermal treatment process, and the active nickel can be bonded to specific positions of the MWW framework-type zeolite. The three-dimensional MWW exfoliates to form a two-dimensional framework in which the nickel bond is exposed to the outside, and the catalytic activity is significantly increased by the increase in the large external surface areas having active nickel.

[0025] The present invention also relates to a nickel silicate molecular sieve for the dry reforming reaction of methane and a method for producing the same. Using nickel as an active metal can reduce the cost of the catalyst, transform 3D zeolite into 2D molecular sieve to increase the surface area, and bond a large amount of active metal to the carrier to improve the stability and activity of the catalyst.

Brief Description of the Drawings

[0026] [Figure 1] FIG. 1 is a schematic diagram of a method for producing a nickel silicate molecular sieve catalyst and a dry reforming reaction of methane according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing (a) nickel content through ICP elemental analysis, (b) N2 adsorption isotherm, and (c) BET surface area according to an embodiment of the present invention. [Figure 3]Figure 3 shows the (a) CH4 conversion rate, (b) CO2 conversion rate, and (c) H2 / CO ratio of Examples 1 to 4, Comparative Example 1, and Comparative Example 2 during the DRM reaction at 700 °C, and the (d) CH4 conversion rate, (e) CO2 conversion rate, and (f) H2 / CO ratio of Examples 1 to 4, Comparative Example 1, and Comparative Example 2 during the DRM reaction at 750 °C. Figures (g) CH4 conversion rate, CO2 conversion rate, and H2 / CO ratio and (h) Raman spectrum for 10 days, 12 hours, and unused (fresh) of Example 3 in the DRM reaction at 750 °C are shown. [Figure 4] Figure 4 shows the (a) CH4 conversion rate, (b) CO2 conversion rate, and (c) H2 / CO ratio according to the hydrothermal treatment time of Examples 4 to 7 during the DRM reaction at 750 °C, the (d) CH4 conversion rate for 10 days, 12 hours, and unused (fresh) of Example 3 in the DRM reaction at 750 °C, and the (d) CH4 conversion rate, (e) CO2 conversion rate, and (f) H2 / CO ratio according to the concentration of the nickel precursor of Examples 4, 8, and 9 (Ni-DML-160-4-Z) during the DRM reaction at 750 °C.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by a person skilled in the art to which this invention belongs. In general, the nomenclature used in this specification is well known and commonly used in the technical field.

[0028] Throughout this specification, when any part states that a certain component "comprises", this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0029] Hereinafter, the present invention will be described in detail. In one aspect, the present invention provides (a) a layered borosilicate MWW Zeolite skeleton Before the typeA method for manufacturing a two-dimensional nickel silicate molecular sieve catalyst for dry reforming of methane is provided, including: (a) synthesizing a precursor [B-MWW(P)]; and (b) adding a nickel precursor to the B-MWW(P) and performing hydrothermal treatment.

[0030] FIG. 1 is a diagram showing a method for manufacturing a two-dimensional nickel silicate molecular sieve catalyst for dry reforming of methane according to the present invention, and the present invention will be described in detail with reference to this.

[0031] In the present invention, step (a) is a step of synthesizing a precursor [B-MWW(P)] of a layered borosilicate MWW Zeolite framework Before the type skeleton.

[0032] The MWW is one of zeolite framework topologies existing in a lamellar form. The MWW framework structure is a three-dimensional zeolite including two independent pore systems, which consists of a pore system of a two-dimensional sinusoidal 10-membered ring (10-MR) channel having an elliptical ring cross-section of 4.1 Å × 5.1 Å and a pore system including a large 12-MR supercage connected to a 10-MR window.

[0033] In the step (a), boron is included in the framework of the three-dimensional MWW framework type zeolite having such structural specificity to synthesize a layered borosilicate MWW Zeolite framework Before the type precursor [B-MWW(P)]. The boron is bonded in the form of Si-O-B in the MWW framework, and the molar ratio of Si / B may be 5.0 to 20.0, preferably 10 to 15. When the molar ratio of Si / B is less than 5, B is excessively contained in B-MWW(P) and the Si content is relatively insufficient, making it difficult to form a three-dimensional MWW framework type zeolite. When it is greater than 20, the relative content of B to Si in B-MWW(P) decreases, and the sites that can be substituted with nickel metal during hydrothermal treatment decrease, thus inducing a decrease in catalytic activity.

[0034] In one embodiment, the step (a) can be synthesized using an organic structure derivative (SDA), and during the synthesis process, the organic structure derivative can be removed by calcination and a three-dimensional MWW can be formed by condensation. However, the step (a) is not limited thereto and can be synthesized by generally known methods, and detailed descriptions thereof are omitted herein.

[0035] In the present invention, the step (b) is a step of adding an acidic nickel precursor aqueous solution with a pH of 4.0 or less to the B-MWW(P) and performing hydrothermal treatment. Specifically, in the step (b), a nickel precursor aqueous solution is added to the synthesized B-MWW(P), and hydrothermal treatment is performed at 100 to 200 °C to exfoliate the B-MWW(P) by a one-step reaction, and at the same time, boron is replaced with nickel metal to produce a two-dimensional multilayer nickel silicate molecular sieve.

[0036] At this time, the amount of the nickel precursor aqueous solution added can be adjusted according to the hydrothermal treatment temperature, and the concentration of the nickel precursor aqueous solution is 0.1 to 5.0 M. When the concentration of the nickel precursor aqueous solution is less than 0.1 M, the pH of the pretreatment aqueous solution increases, the detachment of boron and the exfoliation of the MWW skeleton decrease, and the substitution of nickel metal becomes difficult. When it exceeds 5.0 M, the structure of the MWW skeleton may collapse due to an excessively low pH.

[0037] In addition, the nickel precursor aqueous solution contains an acid component, preferably nitric acid, and has a pH of 4.0 or less. This is because boron can be removed from the B-MWW(P) by the acidic nickel precursor solution during the hydrothermal treatment in the step (b) and replaced with nickel, which is an active metal. In this process, the interlayer bond of the MWW is broken and exfoliated, so that the three-dimensional B-MWW can be transformed into a two-dimensional nickel silicate molecular sieve.

[0038] Also, the temperature during the hydrothermal treatment is set to 100 - 200°C. This is because when the temperature is less than 100°C, three-dimensional B-MWW(P) does not exfoliate sufficiently, the degree of nickel substitution at the deboronation sites decreases, and difficulties may arise in forming two-dimensional nickel silicate molecular sieves. Also, while the number of defect sites in the carrier increases, the nickel content bound to the framework decreases, and the catalytically active sites can decrease. When the temperature exceeds 200°C, the formation of nickel clusters due to the aggregation of nickel precursors increases rather than the nickel bound to the MWW exfoliated by the high temperature, making it difficult to obtain a uniform composition. Therefore, the hydrothermal treatment is carried out at 100 - 200°C, preferably at 140 - 160°C.

[0039] Also, the hydrothermal treatment time can be adjusted according to the process rate and reaction environment and is not limited. As an example, it may be 1 - 4.

[0040] After the step (b), it may further include steps of filtration, drying, and calcining this. Such a process can be carried out by generally known methods and will not be described in detail here. Through the calcining step, the blocked organic structure derivatives present in the framework can be removed from the two-dimensional nickel silicate molecular sieve.

[0041] According to such a production method of the present invention, nickel is basically substituted at the sites where boron is located within the MWW framework, forming Si - O - Ni bonds within the MWW framework, which can improve the control of nickel binding positions and the interaction with zeolites. In particular, the three-dimensional MWW exfoliates the layers to form a two-dimensional framework in which the nickel bonds are exposed to the outside, increasing the catalytic activity due to the increase in the external surface area with active nickel.

[0042] Therefore, the two-dimensional nickel silicate molecular sieve catalyst for the dry reforming reaction of methane produced by the above method shows improved dry reforming reactivity of methane, i.e., improved CH4 and CO2 conversion rates, depending on the characteristics of the two-dimensional nickel silicate molecular sieve framework and the nickel content.

[0043] Specifically, the Si / B molar ratio of the two-dimensional nickel silicate molecular sieve catalyst is 11 to 130, and the Si / Ni molar ratio is 1.5 to 30. The two-dimensional nickel silicate molecular sieve catalyst may contain B in addition to Si and Ni in the framework. However, when the boron is contained at less than 11 in the Si / B ratio, there is a problem that the catalytic activity becomes insufficient because the active Ni does not sufficiently replace the boron in the two-dimensional nickel silicate molecular sieve framework.

[0044] On the other hand, when the nickel in the two-dimensional nickel silicate molecular sieve catalyst framework is contained at less than 1.5 in the Si / Ni ratio, an excessive amount of Ni is contained in the molecular sieve catalyst. In addition to the Si-O-Ni bond in the molecular sieve, Ni exists in the form of aggregation in the molecular sieve or on the surface, which can instead inhibit the catalytic activity. When it exceeds 30, the content of Ni having activity in the molecular sieve is insufficient and the catalytic activity decreases.

[0045] Therefore, the two-dimensional nickel silicate molecular sieve catalyst has Si and Ni in the framework, the Si / Ni molar ratio is 1.5 to 30, preferably 4 to 25, and the Si / B molar ratio is 11 or more.

[0046] The two-dimensional nickel silicate molecular sieve catalyst having such a configuration and framework characteristics may have a catalyst deactivation rate of less than 5% for methane and carbon dioxide in the dry reforming reaction of methane at 700 °C.

Example

[0047] Hereinafter, for a more specific description of the present invention, it will be described based on examples. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples.

[0048] <Example> 1. Materials Hexamethyleneimine (99%) and sodium hydroxide (99%) used for the synthesis of the B-MWW precursor were purchased from Sigma-Aldrich (USA), boric acid (99.5%) was purchased from Junsei Chemical (Japan), and fumed silica was purchased from Evonik (Japan). Nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O) (98%) was purchased from Samchun (Korea) as the nickel precursor.

[0049] 2. Production of nickel silicate catalyst for dry reforming reaction of methane (1) Production of Examples 1 to 9 : Ni-DML (Delaminated MWW layers)-X-Y-Z catalyst a) Production of B-MWW precursor [B-MWW(P)] Hexamethyleneimine and sodium hydroxide were dissolved in deionized water, and then boric acid was added at 50°C. After the boric acid was completely decomposed, fumed silica was gradually added and the solution was homogenized.

[0050] The homogenized final solution was transferred to a Teflon (registered trademark) -lined stainless steel autoclave and heated at 175°C for 7 days while stirring at 100 rpm.

[0051] Thereafter, it was filtered with distilled water, the white solid was recovered, and then dried at room temperature to produce the B-MWW precursor [B-MWW(P)].

[0052] b) Production of Ni-DML (Delaminated MWW layers) The as-prepared B-MWW(P) was added to an aqueous solution of nickel(II) nitrate hexahydrate at a concentration of 0.25 - 1 M at a rate of 0.02 g / mL and mixed. The mixed solution was placed in a hydrothermal synthesis apparatus (Teflon-lined stainless autoclaves, PARR Instrument Company), heated at 100 - 160 °C for 1 - 4 days while stirring at 0 - 100 rpm.

[0053] Subsequently, it was washed and filtered with deionized water, dried at room temperature (RT), and then calcined at 550 °C for 8 hours.

[0054] Thereby, Ni-DML-X-Y-Z was produced, where X, Y, and Z respectively represent the temperature, hydrothermal treatment time, and molar concentration of nickel nitrate during hydrothermal synthesis, and were produced in Examples 1 - 9 according to the values of X, Y, and Z.

[0055] (2) Preparation of Comparative Example 1: Ni / γ-Al2O3 The carrier was γ-Al2O3, the precursor of the active metal was nickel(II) nitrate hexahydrate, and Ni / γ-Al2O3 impregnated with 5 wt% nickel was produced by the initial wet impregnation method. The synthesized Ni / γ-Al2O3 was dried at 100 °C overnight and then calcined at 550 °C for 3 hours.

[0056] (3) Preparation of Comparative Example 2: Ni / B-MWW Although the same method as that for Ni / γ-Al2O3 was applied, Ni / B-MWW was produced using B-MWW as the carrier.

[0057] (4) Control group: B-MWW The B-MWW precursor produced in the above examples was used as the control group.

[0058] The nickel silicate catalysts for the dry reforming reaction of methane produced by the above respective methods are shown in Table 1 below.

[0059]

Table 1

[0060] 3. Catalyst Physical Property Analysis (1) ICP Analysis Figure 2(a) is a graph showing the elemental analysis of the compositions of the manufactured Examples 1 to 4 (Ni-DML-X-4-1) by ICP to measure the content. The following Table 2 shows the framework compositions of Examples 1 to 4 calculated based on the elemental analysis, assuming 72 T-atoms in the MWW unit cell, with the molar ratio as the reference. Here, □ means a defect site. Nickel

[0061]

Table 2

[0062] In Figure 2(a) and Table 2, the Ni content of Examples 1 to 4 (Ni-DML-X-4-1) increased proportionally with the increase in the hydrothermal synthesis temperature during the catalyst production.

[0063] This is because during the production of Examples 1 to 4 (Ni-DML-X-4-1), when the interlayer delamination and nickel substitution mechanism are carried out in a single step by hydrothermal synthesis, at relatively low temperatures of 100 °C and 120 °C, some nickel atoms are replaced in the framework space where boron atoms are removed, while some remain as defect sites. On the other hand, at relatively high temperatures of 140 °C and 160 °C, there may be additional frameworks per nickel framework atom substituted by one or more nickel atoms.

[0064] As a result, the catalyst of Example 4 (Ni-DML-160-4-1) contains the most nickel in the framework, and the ratio of Si / Ni Framework was 10.4.

[0065] (2) N2 Adsorption Isotherm Analysis Figure 2(b) is a diagram showing the N2 adsorption isotherm morphology according to the hydrothermal treatment temperature during the production of the produced Examples 1 to 4 catalysts (Ni-DML-X-4-1). As the hydrothermal treatment temperature increased, the characteristics changed from a Type I microporous structure to a Type IV mesoporous structure. Through this, it can be seen that the three-dimensional B-MWW precursor was successfully changed to a two-dimensional layered structure.

[0066] Also, the hysteresis of the adsorption-desorption isotherm for Example 4 (Ni-DML-160-4-1) shown in Figure 2(b) has the characteristics of typical parallel plate-like pores and shows the characteristics of an interlayer exfoliated substance.

[0067] (3) BET analysis Figure 2(c) is a diagram showing the BET analysis results of the catalysts of Examples 1 to 4 (Ni-DML-X-4-1). Through this, it can be seen that as the exfoliation of B-MWW(P) proceeds at a higher hydrothermal temperature, the external surface areas of Ni-DML increase.

[0068] 4. Analysis of dry reforming reaction (DRM) of methane over the catalyst The dry reforming reaction (DRM) experiment of methane over the catalyst was carried out under atmospheric pressure in a continuous flow apparatus having a fixed-bed microreactor, and the products were analyzed by gas chromatography (GC) equipped with a thermal conductivity detector (TCD). Prior to the experiment, the catalyst was activated under pure H2 (50 mL min -1 ) flowing at 700 °C for 3 hours and was flushed with N2 (60 mL min -1 ) at the same temperature for 0.5 hours (however, the reaction was carried out without H2 pretreatment if necessary).

[0069] A feed gas stream (balanced with N2) of 40 vol.% CH4 and 40 vol.% CO2 was fed at a gas hourly space velocity (GHSV) of 30,000 mL g cat -1 h -1 (to a reactor containing 0.1 g of the catalyst activated by the above process at a rate of 20, 20, and 10 mL min -1 each for the feed gas stream composed of CH4, CO2, and N2), and the DRM catalyst activity was measured. The inert gas N2 was used as an internal standard during GC-TCD analysis to correct for the change in concentration due to the increase in gas volume after the DRM reaction.

[0070] Also, the CH4 conversion rate, CO2 conversion rate, and H2 / CO ratio were calculated by the following formulas.

[0071] CH4 conversion rate (%) = {[(CH4)in - (CH4)out] / (CH4)in} × 100 CO2 conversion rate (%) = {[(CO2)in - (CO2)out] / (CO2)in} × 100 H2 / CO ratio = {[(H2)out / 2(CH4)in]} / [(CO)out / {(CH4)in + (CO2)in}] Deactivation rate = (10 Day conversion - 12 h conversion) / 10 Day conversion × 100

[0072] (1) Catalyst activity depending on reaction temperature Figure 3 is a diagram showing the catalyst activities of Examples 1 to 4 (Ni-DML-X-4-1), Comparative Example 1 (Ni / γ-Al2O3), and Comparative Example 2 (Ni / B-MWW) depending on the DRM measurement temperature and usage time, and Table 3 below summarizes these results.

[0073] First, FIGS. 3(a)-(c) show the comparison of CH4 conversion rate, CO2 conversion rate, and H2 / CO ratio for Examples 1-4 (Ni-DML-X-4-1), Comparative Example 1 (Ni / γ-Al2O3), and Comparative Example 2 (Ni / B-MWW) respectively, when measuring DRM at 700 °C. Through FIGS. 3(a), (b) and Table 3, it can be seen that Examples 1-4 (Ni-DML-X-4-1) having a similar amount of nickel at 700 °C show higher and more stable conversion of CH4 and CO2 compared to Comparative Example 1 (Ni / γ-Al2O3) and Comparative Example 2 (Ni / B-MWW). This is because catalyst deactivation due to coke deposition appears at a significantly faster rate in Comparative Examples 1 and 2 compared to the Examples.

[0074] Generally, during the DRM reaction, coke formation is very rapidly formed at low reaction temperatures due to an increase in the Boudouard reaction (2CO⇔C + CO2).

[0075] Also, the deactivation rate of the CO2 conversion rate for Examples 1-4 (Ni-DML-X-4-1) during 12 hours was 0-1%, while the deactivation rates of Comparative Example 1 (Ni / γ-Al2O3) and Comparative Example 2 (Ni / B-MWW) were 10% and 45% respectively. This is because in the case of Examples 1-4 (Ni-DML-X-4-1), high activity and excellent stability can be maintained by highly dispersed nickel sites located on the external surface area.

[0076] Also, in Examples 1-4, the higher the hydrothermal treatment temperature, the more the nickel active sites increased, and the CH4 conversion rate and CO2 conversion rate increased.

[0077] In Fig. 3(c), the H2 / CO ratios of Example 1 ((Ni-DML100-4-1) to Example 3 (Ni-DML-140-4-1) were approximately 0.89, and they appeared close to the thermodynamic equilibrium values at the experimental temperature. On the other hand, both the CH4 conversion rate and the H2 / CO ratio of Example 4 (Ni-DML-160-4-1) appeared higher than the thermodynamic equilibrium values. Such results are due to the generation of H2 and molecular carbon by catalytic methane cracking under high-temperature DRM conditions.

[0078] Figs. 3(d) to (f) are diagrams showing the CH4 conversion rate, CO2 conversion rate, and H2 / CO ratio for Examples 1 to 4 (Ni-DML-X-4-1), Comparative Example 1 (Ni / γ-Al2O3), and Comparative Example 2 (Ni / B-MWW) respectively, when measuring DRM at 750°C. The catalytic activity of Examples 1 to 4 appeared 8 to 18% higher than when the reaction conditions were 700°C.

[0079] Also, in Figs. 3(a) to (f), the fact that the H2 / CO ratios of Comparative Example 1 (Ni / γ-Al2O3) and Comparative Example 2 (Ni / B-MWW) are lower than those of Examples 1 to 4 (Ni-DML-X-4-1) can be explained by the influence of the reverse water gas shift (RWGS) under DRM conditions. That is, the RWGS reaction is CO 2 reacts with Hydrogen and CO and Water are generated. A lower H2 / CO ratio means that the RWGS reaction occurs actively, which is further supported by a relatively higher CO2 conversion rate compared to the CH4 conversion rate.

[0080] Figures 3(g) and (h) show the conversion rates of CH4 and CO2 and the Raman spectra for Example 3 (Ni-DML-140-4-1) when undergoing the DRM reaction at 750 °C for 10 days (marked with * in Table 3), 12 hours, and when fresh. Through this, it was found that Example 3 maintained remarkable stability and activity over 10 days, with no measured catalyst deactivation. Instead, the conversion rates of CH4 and CO2 increased by 1% or 2% during TOS (Time on stream) (Figure 3(g)). Such results are due to the occurrence of endothermic side reactions such as methane cracking or RWGS at high temperatures. The influence of the methane cracking is more prominent at high temperatures. As a result, the H2 / CO ratio gradually increased over time.

[0081] In the Raman spectrum of Figure 3(h), when the catalyst of Example 3 was used for the DRM reaction for 12 hours and 10 Day days, different from the fresh catalyst, signals corresponding to disordered graphite crystals and aligned graphite crystals were measured, indicating that coke was formed.

[0082] [Table 3]

[0083] (2) Catalytic activity depending on the hydrothermal treatment time and the concentration of the nickel precursor Figure 4 and Table 4 below show the catalytic activity depending on the hydrothermal treatment time and the concentration of the nickel precursor.

[0084] Figures 4(a) to (c) are diagrams showing the CH4 conversion rate, CO2 conversion rate, and H2 / CO ratio depending on the hydrothermal treatment time for Examples 4 to 7 (Ni-DML-160-Y-1) during the DRM reaction at 750 °C. It was found that the difference in catalytic activity depending on the hydrothermal treatment time was not significant.

[0085] On the one hand, Figs. 4(d)-(f) are diagrams showing the CH4 conversion rate, CO2 conversion rate, and H2 / CO ratio according to the concentration of the nickel precursor in Examples 4, 8, and 9 (Ni-DML-160-4-Z) during the DRM reaction at 750 °C. When the concentration of the nickel precursor was low (0.25-0.5 M), the catalytic activity appeared to be relatively low.

[0086]

Table 4

Claims

**Claim 1** (a) synthesizing a layered borosilicate MWW zeolite framework precursor [B-MWW(P)]; and (b) adding a nickel precursor to the B-MWW(P) and performing hydrothermal treatment, a method for producing a two-dimensional nickel silicate molecular sieve catalyst for dry reforming of methane. **Claim 2** The method for producing a two-dimensional nickel silicate molecular sieve catalyst for dry reforming of methane according to claim 1, wherein in the step (a), B-MWW(P) with a Si / B molar ratio of 5.0 to 20.0 is synthesized. **Claim 3** The method for producing a two-dimensional nickel silicate molecular sieve catalyst for dry reforming of methane according to claim 1, wherein the concentration of the nickel precursor in the step (b) is 0.25 to 1 M. **Claim 4** The method for producing a two-dimensional nickel silicate molecular sieve catalyst for dry reforming of methane according to claim 1, wherein the hydrothermal treatment temperature in the step (b) is 100 to 160°C.

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