Zeolite-supported catalyst and manufacturing method thereof

Abstract

Provided are a zeolite-supported catalyst and a manufacturing method thereof. The zeolite-supported catalyst comprises zeolite and a metal catalyst supported on the zeolite. The zeolite is treated with quaternary ammonium hydroxide before supporting the metal catalyst, and thus has an increase in mesopores and a reduction in Al sites on the outer surface. The manufacturing method of the zeolite-supported catalyst comprises the steps of: preparing zeolite; base-treating the zeolite with quaternary ammonium hydroxide; and supporting a metal catalyst on the base-treated zeolite.

Description

Zeolite-supported catalyst and method for producing the same

[0001] The present invention relates to a zeolite-supported catalyst and a method for producing the same.

[0002] Shale gas aromatization can produce the high-value-added compound BTX without the naphtha process by conducting the reaction under oxygen-free conditions. However, the shale gas aromatization reaction presents a problem: significant carbon deposition occurs on the catalyst's outer surface, clogging its pores and ultimately deactivating the catalyst before all active sites within the catalyst are utilized.

[0003] The present invention provides a zeolite-supported catalyst having excellent performance.

[0004] The present invention provides a method for producing the above zeolite-supported catalyst.

[0005] Other objects of the present invention will become apparent from the following detailed description and the accompanying drawings.

[0006] In embodiments of the present invention, a zeolite-supported catalyst comprises a zeolite and a metal catalyst supported on the zeolite. The zeolite is treated with quaternary ammonium hydroxide prior to supporting the metal catalyst, thereby increasing mesopores and reducing Al sites on the outer surface.

[0007] In embodiments of the present invention, a method for producing a zeolite-supported catalyst includes the steps of preparing a zeolite, treating the zeolite with a base using quaternary ammonium hydroxide, and supporting a metal catalyst on the base-treated zeolite.

[0008] Zeolite-supported catalysts according to embodiments of the present invention can exhibit excellent performance. For example, the zeolite-supported catalyst exhibits excellent activity and stability in shale gas aromatization reactions. The reduced content of metal catalyst on the external surface of the zeolite reduces external coke formation, thereby suppressing catalyst deactivation caused by blockage of the external pores of the zeolite. The activity of the zeolite-supported catalyst is enhanced and its service life is increased. The amount of light coke formation predominantly present on the external surface of the zeolite after use is reduced, thereby maintaining catalytic activity even after catalyst regeneration.

[0009] Figure 1 shows the PXRD patterns of the raw ZSM-5 sample and the base-treated ZSM-5 sample.

[0010] Figure 2 shows TEM images of a pristine ZSM-5 sample and a base-treated ZSM-5 sample.

[0011] Figure 3 shows FFT patterns obtained from the inner and outer domains of a crystal of ZSM-5 treated with CTAOH.

[0012] Figure 4 shows the adsorption-desorption isotherms of the raw ZSM-5 sample and the base-treated ZSM-5 sample according to the N2 physical adsorption experiment.

[0013] Figure 5 shows the BJH pore size distribution of the raw ZSM-5 sample and the base-treated ZSM-5 sample according to the N2 physical adsorption experiment.

[0014] Figure 6 shows the results of the raw ZSM-5 sample and the base-treated ZSM-5 sample. 27 Al MAS NMR spectrum is shown.

[0015] Figure 7 shows the NH3-TPD profiles of the raw ZSM-5 sample and the base-treated ZSM-5 sample.

[0016] Figure 8 shows the FT-IR spectra of the pristine ZSM-5 sample and the base-treated ZSM-5 sample adsorbed with pyridine (Py).

[0017] Figure 9 shows the FT-IR spectra of the pristine ZSM-5 sample and the base-treated ZSM-5 sample adsorbed with 2,6-di-tert-butylpyridine (2,6-DTBPy).

[0018] Figure 10 shows the H2-TPR profiles of the pristine ZSM-5 sample loaded with molybdenum (Mo) and the base-treated ZSM-5 sample.

[0019] Figure 11 shows UV-Vis DRS spectra of pristine ZSM-5 samples loaded with molybdenum (Mo) and base-treated ZSM-5 samples.

[0020] Figure 12 shows the PXRD patterns of the molybdenum (Mo) loaded raw ZSM-5 sample and the base-treated ZSM-5 sample.

[0021] Figure 13 shows the Mo 3d XPS spectra of the pristine ZSM-5 sample loaded with molybdenum (Mo) and the base-treated ZSM-5 sample.

[0022] Figure 14 shows the conversion of each reactant in the shale gas feed of a raw ZSM-5 sample loaded with molybdenum (Mo) and a base-treated ZSM-5 sample.

[0023] Figure 15 shows the BTX yields of molybdenum (Mo) loaded raw ZSM-5 samples and base-treated ZSM-5 samples.

[0024] Figure 16 shows the mole fraction of the product of the Mo / Z catalyst.

[0025] Figure 17 shows the mole fraction of the product of the Mo / Z-CTAOH catalyst.

[0026] Figure 18 shows the TGA profiles of the pristine ZSM-5 sample loaded with molybdenum (Mo) and the base-treated ZSM-5 sample after 15 hours of reaction.

[0027] Figure 19 shows the DTG curves of the molybdenum (Mo)-loaded raw ZSM-5 sample and the base-treated ZSM-5 sample after 15 hours of reaction.

[0028] Figure 20 shows the BTX yield according to the base treatment temperature of a base-treated ZSM-5 sample loaded with molybdenum (Mo) at low temperature (65°C) and high temperature (160°C).

[0029] Figure 21 shows the DTG analysis results of the Mo / Z-CTAOH sample and the Mo / Z-CTAOH-LT sample after 15 hours of reaction.

[0030] Figure 22 shows the BTX yield when using the raw ZSM-5 sample, Z-CTAOH sample, and Z-NaOH sample loaded with molybdenum (Mo) for regeneration.

[0031] Hereinafter, the present invention will be described in detail through examples. The objectives, features, and advantages of the present invention will be readily understood through the following examples. The present invention is not limited to the examples described herein and may be embodied in other forms. The examples introduced herein are provided to ensure that the disclosure is thorough and complete and to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention should not be limited by the following examples.

[0032]

[0033] In embodiments of the present invention, a zeolite-supported catalyst comprises a zeolite and a metal catalyst supported on the zeolite. The zeolite is treated with quaternary ammonium hydroxide prior to supporting the metal catalyst, thereby increasing mesopores and reducing Al sites on the outer surface.

[0034] In embodiments of the present invention, a method for producing a zeolite-supported catalyst includes the steps of preparing a zeolite, treating the zeolite with a base using quaternary ammonium hydroxide, and supporting a metal catalyst on the base-treated zeolite.

[0035] The zeolite may comprise ZSM-5. The metal catalyst may comprise molybdenum. The quaternary ammonium hydroxide may comprise at least one of cetyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, and tetramethylammonium hydroxide.

[0036] The base treatment may reduce Al sites on the surface of the zeolite. The base treatment may cause the surface of the zeolite to be dealuminate and then recrystallize. The base treatment may increase the mesopores of the zeolite and decrease the micropores.

[0037] The above zeolite can be hydrothermally treated after the base treatment. The Brønsted acid sites of the zeolite can be reduced by the hydrothermal treatment after the base treatment.

[0038] The zeolite may comprise ZSM-5. The metal catalyst may comprise molybdenum. The quaternary ammonium hydroxide may comprise at least one of cetyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, and tetramethylammonium hydroxide.

[0039]

[0040] [Example of manufacturing a zeolite-supported catalyst]

[0041]

[0042] Zeolite post-treatment

[0043] Quaternary ammonium hydroxide (QAH) used in the post-treatment of ZSM-5 according to embodiments of the present invention includes CTAOH (cetyltrimethylammonium hydroxide), TPAOH (tetrapropylammonium hydroxide), and TMAOH (tetramethylammonium hydroxide).

[0044] Pristine ZSM-5 (NH4-form, nominal Si / Al2 ratio = 23) was dispersed in an aqueous base solution (0.2 mol / L QAH or NaOH) at a solid-to-liquid ratio of 1 g:15 mL and stirred at room temperature for 2 h. After stirring, the dispersion was transferred to a PTFE-lined autoclave (40 mL) and placed in a preheated convection oven, where it was hydrothermally treated at 160 °C for 24 h. The post-treated ZSM-5 was washed four times with deionized water and then dispersed in a 1 M ammonium nitrate (NH4NO3) solution at a solid-to-liquid ratio of 1 g:50 mL for subsequent ion-exchange processing. The ion-exchange process was repeated 2–3 times at 80 °C. The sample was transformed into the H-form by calcination at 580 °C for 6 h.

[0045] The ZSM-5 samples used in the examples and comparative examples of the present invention are denoted as “Z-base name” by applying the name of the base used in the post-treatment. For example, “Z-CTAOH” represents ZSM-5 treated with CTAOH according to the procedure described above. Samples using raw ZSM-5 without any post-treatment are denoted simply as “Z”. To investigate the influence of hydrothermal post-treatment conditions, a separate sample was prepared under milder conditions. This sample was hydrothermally treated at 65°C for only 1 hour while all other conditions were kept constant. This sample is denoted as “Z-base name-LT”.

[0046]

[0047] Metal impregnation of post-treated zeolite

[0048] ZSM-5 was post-treated with quaternary ammonium hydroxide and then Mo was loaded onto the ZSM-5 using a wet impregnation process. The post-treated ZSM-5 was dispersed in an aqueous ammonium heptamolybdate tetrahydroxide solution at a mixing ratio designed to achieve a nominal Mo loading of 10 wt%. The dispersion was stirred for 1 h, then excess water was removed from the dispersion using a rotary evaporator, and the formed solid product was dried overnight in a heated oven at 105°C. The sample was heated in air at a heating rate of 5°C / min and then calcined at 500°C for 5 h. The product is designated as Mo / (zeolite sample name) (e.g., Mo / Z-CTAOH).

[0049]

[0050] [Evaluation method of zeolite-supported catalysts]

[0051]

[0052] Zeolite-supported Mo catalyst samples (pelletized and sieved to 425–850 μm) were introduced into a continuous-flow fixed-bed quartz reactor with an inner diameter of 1.2 cm and a length of 33 cm. Prior to the catalytic reaction, the catalyst samples were pre-carburized. The reactor was heated to 650°C under a N2 stream, and then a mixed flow of shale (composed of 85% CH4, 10% C2H6, and 5% C3H8) and N2 (volume ratio 9:11, total gas hourly space velocity (GHSV) 6,000 mL / h·gcat) was applied. This pre-carburization stream was applied for 6 min to allow the catalyst sample to undergo aromatization through the in situ formation of MoCx (Mo carbide) sites. After the pre-carburization, the reactor was purged with a N2 flow and the temperature was raised to 700°C for 30 min. When the temperature reached 700°C, a reactant consisting of shale and N2 (volume ratio 1:1, GHSV 3,000 mL / h·gcat) was supplied. The product was analyzed by an online gas chromatograph (GC) equipped with a GS-gaspro capillary column aligned with a flame ionization detector (FID) and a Carboxen-1000 packed column aligned with a thermal conductivity detector (TCD).

[0053] The reactant conversion, product selectivity, and product yield were determined based on the carbon balance using N2 as an internal standard. After 15 h of reaction, the used zeolite-supported Mo catalyst sample was regenerated by a 10% O2 / N2 stream at 550°C, and the total GHSV was 6,000 mL / h·g. cat After regeneration, the catalytic performance of the regenerated sample was evaluated using the method described above.

[0054]

[0055] [Zeolite Analysis]

[0056]

[0057] The elemental composition (Si / Al ratio) of zeolites can be changed through hydrothermal post-treatment under basic conditions. Under these conditions, either dealumination or desilication can occur depending on the initial Si / Al ratio and the basicity of the solution phase. In the embodiments of the present invention, the spatial distribution of Al sites was modified by treating pristine ZSM-5 with various quaternary ammonium hydroxides, and the results were compared with those obtained by treating with NaOH. To investigate the changes in the chemical composition of ZSM-5 zeolites post-treated with various bases, XPS (surface, <10 nm depth) and ICP-OES (bulk) elemental analyses were performed before and after post-treatment and Mo loading, and the results are shown in Table 1.

[0058] [Table 1]

[0059]

[0060] The two analytical techniques yield data within a closely aligned range, so any errors arising from differences between the two techniques can be ignored. Pristine ZSM-5 exhibited heterogeneity in the Si / Al ratio between the outer surface and the bulk phase. The surface Si / Al ratio of pristine ZSM-5 (10.0) was lower than that of the bulk (11.7), suggesting a relative Al-enrichment of the outer surface, a phenomenon commonly referred to as Al zoning.

[0061] Hydrothermal post-treatment of ZSM-5 with various quaternary ammonium hydroxide solutions tested at 160°C generally resulted in net dealumination of the samples, except for the NaOH treatment, where net desilication was observed. When the base used in the post-treatment was quaternary ammonium hydroxide, the bulk Si / Al ratio (11.7) increased moderately to a range of Si / Al = 11.8–12.6. The surface Si / Al ratio also generally increased as a result of quaternary ammonium hydroxide treatments, except for the CTAOH treatment. The Z-TPAOH and Z-TMAOH samples showed surface Si / Al ratios similar to or even higher than the bulk Si / Al ratio, indicating that net dealumination occurred primarily at the surface. However, the CTAOH treatment slightly decreased the surface Si / Al ratio values. This result suggests that the amphiphilic CTA on the surface of the pure Z-CTAOH sample may be due to the presence of amphiphilic CTA on the surface of the pure Z-CTAOH sample. + Anionic extraframework Al species with a negative charge stabilized by molecules (e.g., Al(OH)4(Nu)2) - , where Nu = H2O or a nucleophile in the system such as surface silanols) is believed to be due to re-adsorption. During base treatment, the pH of the solution phase exceeds 13, which indicates that the extraframework Al species prefer the anionic form.

[0062] After Mo impregnation, the low surface Si / Al ratio of the Z-CTAOH sample increased to 12.4, indicating that the re-adsorbed extraframework Al species were removed. Considering that the Mo precursor (ammonium heptamolybdate) solution was slightly acidic (pH approximately 4) during impregnation, this Al(OH)4 - The species is available Al during Mo loading 3+It may have been converted to cations and removed from the surface. In contrast, TMAOH and TPAOH did not show any discernible resorption of available Al species after treatment, directly demonstrating their net dealumination ability under hydrothermal treatment conditions at 160°C. This is an amphiphilic CTA. + Unlike the case of cations, TPA for Al species + and TMA + This may be due to a lack of stabilizing ability of cations.

[0063] In the case of NaOH treatment, the bulk Si / Al ratio decreased from 11.7 to 10.3. This is because Na + This means that the NaOH treatment at 160°C, which exhibits the effect of quaternary ammonium cations, differs from the treatment under test conditions. The surface Si / Al ratio also decreased from 10.0 to 8.1 after the NaOH treatment at 160°C, indicating that net desilication occurred indiscriminately in both the external and internal regions of the ZSM-5 crystals when NaOH was used. Post-treatment with a strong base at 160°C did not significantly damage the crystal structure of ZSM-5.

[0064]

[0065] Figure 1 shows the PXRD patterns of the pristine ZSM-5 sample and the base-treated ZSM-5 sample. Referring to Figure 1, all diffraction peaks corresponding to the MFI framework remained clearly identifiable even after the post-treatment, although their intensities were slightly reduced. Although not shown in the figure, a similar observation was made for ZSM-5 samples exposed to much milder hydrothermal conditions, particularly the LT series samples. This indicates that a complete loss of the MFI crystal structure was not observed in any of the samples presented in the examples of the present invention.

[0066]

[0067] Figure 2 shows TEM images of the pristine ZSM-5 sample and the base-treated ZSM-5 sample. Referring to Figure 2, the pristine ZSM-5 exhibited well-defined crystalline planes characteristic of the orthorhombic MFI type crystal structure. The CTAOH, TMAOH, and TPAOH treatments did not cause serious damage to the crystal structure of ZSM-5. However, the Z-NaOH sample exhibited a highly destroyed structure. This indiscriminately destroyed Z-NaOH structure is likely to be responsible for the increased adsorption of probe molecules such as NH3, Py, and N2 in the NH3-TPD, FT-IR, and physisorption experiments. In general, the alkali treatment mainly causes the cleavage of Si-O-Si bonds rather than Si-O-Al bonds, which leads to the cleavage of OH - Hydrolysis of Si-O-Al bonds through attack yields negatively charged AlO4 - This is because it is hindered by tetrahedral and hydroxyl groups. This leads to net desilication of zeolites under typical basic conditions, which is manifested by NaOH treatment.

[0068] Na +The main difference between the tested quaternary ammonium hydroxide and other quaternary ammonium cations is their ability to recrystallize ZSM-5 under the tested hydrothermal conditions. TPAOH is a well-known OSDA for MFI synthesis, and TMAOH and CTAOH can also crystallize MFI frameworks, although with less structure-directing ability than TPAOH. Based on the fact that the tested quaternary ammonium hydroxide can crystallize ZSM-5 without the assistance of seeds, and if we acknowledge that NaOH can be used for seed-assisted crystallization of MFI frameworks, we can say that quaternary ammonium hydroxide has a stronger structure-directing ability for MFI frameworks than NaOH. The Z-QAH sample exhibits non-straight edges of the crystals, indicating that a reversible recrystallization process can occur on the surface of ZSM-5. Unlike the Z-NaOH sample, the Z-QAH sample did not show extensive defects within the crystals.

[0069] Recrystallization of the MFI framework can occur outside the ZSM-5 crystal in the presence of quaternary ammonium cations and leached Al and Si species. The kinetics associated with the incorporation of Si and Al can influence the Si / Al ratio of the recrystallized phase of ZSM-5. The reintroduction of leached Al into the recrystallized phase depends on the treatment duration. The observed increases in the surface and bulk Si / Al ratios of the Z-QAH samples according to the embodiments of the present invention may indicate that the hydrothermal treatment duration may not be long enough to ensure Al incorporation within the framework.

[0070]

[0071] Figure 3 shows the Fast-Fourier-transform (FFT) patterns obtained from the inner and outer domains of the crystals of ZSM-5 treated with CTAOH. Referring to Figure 3, the Z-CTAOH sample revealed a mesoporous microstructure in the outermost region of the crystals. This surface microstructure was found to be unique to the Z-CTAOH sample and was observed during the post-treatment with CTA. + This is likely a result of the formation of a superstructure associated with cations. The reconstructed fast-Fourier transform (FFT) patterns from both the inner and outermost regions of the Z-CTAOH crystals were found to be compatible with each other. This observation suggests that the mesoporous architecture in the outer region of the Z-CTAOH crystals is also composed of the MFI framework. Although not depicted in the figure, the FFT patterns of the Z-TPAOH and Z-TMAOH samples showed consistent outer and inner crystal structures, excluding the surface mesoporosity.

[0072]

[0073] Figure 4 shows the adsorption-desorption isotherms of the pristine ZSM-5 sample and the base-treated ZSM-5 sample according to the N2 physisorption experiment, and Figure 5 shows the BJH pore size distribution of the pristine ZSM-5 sample and the base-treated ZSM-5 sample according to the N2 physisorption experiment. Table 2 shows the micropore and mesopore sizes of the pristine ZSM-5 sample and the base-treated ZSM-5 sample.

[0074] [Table 2]

[0075]

[0076] Referring to Figures 4, 5, and Table 2, the trends observed in the porosity modification generally included an increase in mesoporosity and a decrease in microporosity. The decrease in microporosity appears to be due to an overall weakening of the zeolite crystal structure due to hydroxide attack during the post-synthetic process. This weakening was significantly observed when TPAOH, TMAOH, or NaOH was used. Conversely, the decrease in microporosity was minimal when CTAOH was used as the treating base. The Z-CTAOH sample exhibited unique pore characteristics, manifested by a pronounced adsorption-desorption hysteresis and increased mesoporosity with a size of 5–10 nm. CTA + Due to their unique properties as surfactants, cations can be used as mesoporogens in the synthesis or post-treatment of zeolites. The emergence of mesoporosity after post-treatment with CTAOH is believed to be due to CTAOH's unique ability to form micellar or lamellar structures, which can provide a soft template during post-treatment, unlike other bases tested in the examples of the present invention. The Z-NaOH sample also exhibited an increased mesopore volume. Unlike the case with CTAOH, this increase is likely due to structural disruption due to hydroxide attack both inside and outside the crystals, as observed in the TEM image of Figure 2.

[0077]

[0078] Figure 6 shows the results of the raw ZSM-5 sample and the base-treated ZSM-5 sample. 27 Al MAS NMR spectra are shown, and Fig. 7 shows the NH3-TPD profiles of the pristine ZSM-5 sample and the base-treated ZSM-5 sample. Table 3 shows the NH3-TPD profiles of the pristine ZSM-5 sample and the base-treated ZSM-5 sample. 27 Al MAS NMR analysis and NH3-TPD analysis values ​​are shown.

[0079] [Table 3]

[0080]

[0081] Referring to Figures 6, 7, and Table 3, two resonance signals are present at +55 ppm and about 0 ppm. 27 Al were observed in the Al spectrum and were assigned to the tetrahedral framework Al (FAl) site and the octahedral framework Al site (EFAl), respectively. The area ratio of the two signals (FAl / EFAl) was used as an indicator to estimate the relative amounts of FAl and EFAl sites. The FAl / EFAl ratio was observed to decrease as a result of hydrothermal treatment under basic conditions, indicating that dealumination of FAl sites occurred. The extent of dealumination varied depending on the type of base used. The FAl / EFAl ratio of ZSM-5 treated with quaternary ammonium hydroxide was lower than that of ZSM-5 treated with NaOH, indicating that ZSM-5 treated with quaternary ammonium hydroxide had fewer FAl sites that functioned as strong Brønsted acid sites (BAS).

[0082] The NH3-TPD profile of the ZSM-5 sample exhibited two distinct desorption signals at 150–300°C and 350–500°C, which were assigned to the weakly acid and strongly acid sites, respectively. The NaOH treatment at 160°C did not significantly alter the specific molar density of the strong Brønsted acid sites in ZSM-5.

[0083] The overall increase in NH3 adsorption in the NaOH-treated ZSM-5 samples is probably due to the presence of intracrystalline defects generated by hydroxide attack, as also observed in the TEM images. In contrast, the quaternary ammonium hydroxide treatment was observed to remove 15–23% of the strong Brønsted acid sites in the pure ZSM-5 samples. 27Al NMR and NH3-TPD experiments indicate that quaternary ammonium hydroxide leaches framework Al sites more effectively than NaOH in hydrothermal post-treatment at 160°C.

[0084]

[0085] Figure 8 shows the FT-IR spectra of the pristine ZSM-5 sample and the base-treated ZSM-5 sample adsorbed with pyridine (Py), and Figure 9 shows the FT-IR spectra of the pristine ZSM-5 sample and the base-treated ZSM-5 sample adsorbed with 2,6-di-tert-butylpyridine (2,6-DTBPy). Table 4 shows the amounts of pyridine (Py) and 2,6-DTBPy adsorbed on the Brønsted acid site (BAS) and Lewis acid site (LAS) of the pristine ZSM-5 sample and the base-treated ZSM-5 sample.

[0086] [Table 4]

[0087]

[0088] While regular pyridine (Py) molecules can diffuse within the micropore system of the MFI framework (5.5–6.0 Å), bulky DTBPy molecules cannot enter the 10MR micropore openings and can only adsorb on acidic sites in the outer region of the zeolite crystallites. Therefore, the amounts of regular pyridine (Py) and DTBPy adsorbed on zeolite Brønsted acid sites can serve as indicators for determining the spatial distribution of strong Brønsted acid sites within the ZSM-5 sample.

[0089] Referring to Figures 8, 9, and Table 4, the characteristic IR bands of a typical pyridine (Py) molecule interacting with the Bronsted acid site and Lewis acid site of the zeolite are 1545 and 1455 cm, respectively. -1was observed. The specific amount of pyridine (Py) molecules adsorbed on the ZSM-5 Brønsted acid sites showed a slight decrease after hydrothermal quaternary ammonium hydroxide treatment. This decrease indicates a net removal of framework Al sites. 27 This is consistent with the results of Al NMR and NH3-TPD experiments. Conversely, the amount of pyridine (Py) adsorbed on Lewis acid sites shows a significant increase as a result of the post-treatment, regardless of the type of base used in the hydrothermal treatment. Considering that the dealuminate EFAl species in the framework can exhibit Lewis acidity, this observation is consistent with the results shown above. 27 This is consistent with the decrease in the FAl / EFAl ratio observed in Al NMR experiments.

[0090] Unlike the adsorption of general pyridine (Py), the adsorption of bulky DTBPy showed considerable variability depending on the type of base used in the hydrothermal post-treatment. The adsorption of DTBPy on the external Brønsted acid sites of zeolites was detected at approximately 1615±50 cm in the FT-IR spectrum. -1 This was evident by the broad IR absorption band observed in the pristine ZSM-5 sample. For the pristine ZSM-5 sample, the estimated amount of adsorbed DTBPy was 32.4 μmol probe / g cat These values ​​were 27.9 and 23.1 μmol, respectively, after hydrothermal treatment using NaOH and TPAOH. probe / g cat was reduced to . The reduction difference between the two bases is TPA + The cation is Na + Indicates that the CTAOH-treated ZSM-5 provided higher regioselectivity for dealumination in the outer region of the ZSM-5 crystallites compared to the CTAOH-treated ZSM-5. In particular, the CTAOH-treated ZSM-5 showed 5.3 μmol probe / g catshowed a significantly low value of , indicating that CTAOH showed the most effective surface-selective removal of Brønsted acid sites among the bases tested. Despite the significant removal of external Brønsted acid sites (approximately 84% reduction), the density of bulk Brønsted acid sites characterized based on the generic pyridine (Py) probe remained virtually unchanged (approximately 0.4% reduction).

[0091]

[0092] [Analysis of Zeolite-Supported Catalysts]

[0093]

[0094] To test the catalytic activity of shale gas dehydroaromatization, 10 wt% nominal Mo was impregnated into both pristine and base-treated ZSM-5 samples using ammonium heptamolybdate as a precursor. Considering that differences in the acidic properties and porosity of base-treated zeolites can lead to distinct behaviors of impregnated Mo sites, the chemical states of the Mo / zeolite samples and the impregnated Mo were investigated using various techniques.

[0095]

[0096] Figures 10 to 13 show the H2-TPR profiles, UV-Vis DRS spectra, PXRD patterns, and Mo 3d XPS spectra of the molybdenum (Mo)-loaded pristine ZSM-5 sample and the base-treated ZSM-5 sample, respectively. Table 5 shows the elemental analysis results of the Mo-loaded base-treated ZSM-5 sample.

[0097] [Table 5]

[0098]

[0099] Referring to Figs. 10 to 13 and Table 5, the H2-TPR profiles show two main reduction reactions in the temperature ranges of 500 to 650°C and 650 to 800°C, which can be attributed to the sequential reduction of Mo(+6) to Mo(+4) and Mo(+4) to Mo(0). Upon calcination, Mo oxide is preferentially fixed on the Brønsted acid sites of the zeolite framework in the form of monomers or dimers. The Mo / Al molar ratio of the Mo-impregnated ZSM-5 samples was obtained in the range of 0.81 < Mo / Al < 1.01.

[0100] Considering that a certain portion of Al exists as extraframework species in bare zeolites, the value of the Mo / FAl ratio (the molar ratio between Mo and framework Al) is estimated to be close to or greater than 1. This value represents the maximum stoichiometry of Mo species fixed on Brønsted acid sites. Furthermore, considering that approximately 30–40% of the framework Al consists of isolated Al sites in ZSM-5 with a similar Si / Al ratio, it can be predicted that some amount of Mo should exist as unfixed Mo species.

[0101] These unanchored Mo species may not be completely dispersed due to a lack of anchoring sites. Comparison with the reduction profile of unsupported MoO3 reveals the absence of crystalline MoO3 bulk species. This absence is further supported by the lack of UV-vis DRS absorption bands in the range of 325–350 nm, unlike the spectrum observed for MoO3. Furthermore, a physical mixture of MoO3 and Z (MoO3 + Z(PM)) was investigated, and a significant diffraction peak at approximately 25.6° attributed to crystalline MoO3 was observed. However, no peak representing crystalline MoO3 was detected in the Mo / zeolite sample, and only the characteristics of the zeolite MFI structure were observed.

[0102] These results indicate that most of the Mo in the tested impregnated samples is well dispersed and exists as a combination of monomers, dimers, or small Mo oxide particles. 27 The presence of a signal at -14 ppm in the Al MAS NMR spectrum, which is absent in the NMR spectrum of the bare zeolite, also indicates the presence of unhydrated aluminum molybdate (Al2(MoO4)3). These compounds are formed by the interaction between Mo and extraframework Al species.

[0103] The complexity of the H2-TPR profiles, as evidenced by the appearance of multiple shoulder peaks, limits the clear identification of the exact chemical composition of the Mo oxide species and indicates the heterogeneity of the Mo species. Nevertheless, the similarity in peak positions in both the H2-TPR and UV-vis DRS profiles between different samples indicates that there is no dominant difference in the chemical state of Mo in the tested Mo / zeolite samples.

[0104] Meanwhile, significant differences in the Mo distribution within the zeolite particles were observed between the Mo / zeolite samples. The data presented in Table 5 clearly indicate a marked decrease in the Mo amount in the Mo / Z-QAH sample, as determined by XPS. This observation suggests a lower amount of Mo species very close to the zeolite surface (within approximately 10 nm depth). This finding resulted in a decrease in the Mo on the external surface for the Mo-Z / QAH sample, despite the similar bulk Mo content determined by ICP-OES analysis (approximately 10 wt%). In contrast, the Mo / Z and NaOH or LT treated samples exhibited a higher distribution of Mo on the external surface.

[0105] The relative lack of Brønsted acid sites beneath the zeolite surface of the Z-QAH sample may be responsible for this characteristic Mo distribution. Furthermore, the enhanced mesoporosity within the sample may have contributed to the reduction in surface Mo by facilitating the introduction of Mo precursors into the zeolite pore system. This is confirmed by the significantly lower Mo at the external surface observed for Mo / Z-CTAOH. The support of the Z-CTAOH sample exhibited a 50% increase in specific mesopore volume compared to pristine ZSM-5, with a predominant pore size distribution within the 2–10 nm range. However, this effect is contradicted by the fact that the highest amount of surface Mo is observed for Mo / Z-NaOH despite its significant mesoporosity. This observation implies that the distribution of Brønsted acid sites (i.e., framework Al) is the primary factor governing the Mo distribution at the external surface. Meanwhile, the similarity of the Mo 3d binding energy values ​​of each sample obtained within the range of 232–233 eV is consistent with the typical value of Mo(VI).

[0106]

[0107] [Shale Gas Aromaticization and Coke Analysis]

[0108]

[0109] Figure 14 shows the conversion of each reactant in the shale gas feed of the raw ZSM-5 sample loaded with molybdenum (Mo) and the base-treated ZSM-5 sample, and Figure 15 shows the BTX yield of the raw ZSM-5 sample loaded with molybdenum (Mo) and the base-treated ZSM-5 sample. Figure 16 shows the mole fraction of the product of the Mo / Z catalyst, and Figure 17 shows the mole fraction of the product of the Mo / Z-CTAOH catalyst. In Figures 16 and 17, C2= represents ethylene, C3= represents propylene, B represents benzene, T represents toluene, X represents xylene, and N represents naphthalene.

[0110] Referring to Figures 14-17, each catalyst sample exhibited high initial conversions of ethane and propane, while the methane conversion remained consistently negative throughout the 15-h reaction period. This negative methane conversion was due to the strict formation of methane from ethane and propane, resulting in a total carbon conversion in the range of 10-20%. Despite the negative methane conversion, which indicates production rather than consumption, techno-economic analysis suggests that the overall efficiency of the process (when integrated with an additional methane utilization process) could benefit from this methane production if the ethane and propane in the feed were strictly converted. A consistent decrease in conversion due to catalyst deactivation was observed throughout the reaction, accompanied by a shift in the product distribution from aromatics to olefins (ethylene and propylene).

[0111] Clearly, the Mo / Z-QAH catalyst sample exhibited improved catalytic stability compared to the Mo / Z catalyst sample, as evidenced by a slower deactivation rate in terms of conversion and BTX yield. The olefin-to-aromatic ratio increased rapidly after 12 h of reaction for Mo / Z, whereas the major products for the quaternary ammonium hydroxide sample remained aromatic even after 15 h of reaction. The performance of the Mo / Z-NaOH catalyst did not differ significantly from that of the Mo / Z catalyst.

[0112]

[0113] Figures 18 and 19 show the TGA profile and DTG curve of the pristine ZSM-5 sample loaded with molybdenum (Mo) and the base-treated ZSM-5 sample after 15 hours of reaction, respectively.

[0114] Referring to Figures 18 and 19, the total amount of deposited coke was confirmed to be similar among the samples, but most of the coke in the quaternary ammonium hydroxide sample was composed of soft coke burned below 500°C. This type of coke is associated with Mo sites and is reactive. According to the widely proposed hydrocarbon pool mechanism for the dehydroaromatization reaction on Mo / ZSM-5, these reactive coke species can participate in the reaction and therefore contribute less to deactivation. The predominant formation of soft coke in the quaternary ammonium hydroxide sample explains the enhanced catalytic stability under the reaction conditions. In contrast, most of the coke deposited in the Mo / Z and Mo / Z-NaOH samples was confirmed to be hard coke oxidized above 500°C. This type of coke, which is typically polyaromatic, blocks the pore system of the zeolite, inhibiting access to the active MoCx sites and resulting in catalyst deactivation.

[0115] The sharp increase in olefin selectivity combined with the decrease in low-molecular-weight aromatic selectivity is also associated with the pore-blocking effect of hard coke, as the release of aromatic molecules from the zeolite structure is hindered by the reduced pore diameter. Consequently, the predominance of hard coke in the Mo / Z and Mo / Z-NaOH samples is consistent with poor catalyst stability. The coke properties in the catalytic system of Mo / ZSM-5 are strongly dependent on the spatial distribution of MoCx within the zeolite particles. The 10MR structure of the MFI pore system provides adequate morphoselectivity for preferential production of low-molecular-weight aromatics from activated carbon species (also known as the hydrocarbon pool, which includes the concept of reactive soft coke). In contrast, carbon intermediates generated by MoCx located near the zeolite surface hardly benefit from the confinement effect of the MFI channel system. This indicates a higher selectivity for hard coke generated through further condensation of aromatic rings. Differences in the spatial distribution of Mo sites between ZSM-5 samples are considered to be a direct cause of the differences in coke properties. These differences ultimately result in catalytic stability.

[0116]

[0117] Figure 20 shows the BTX yield according to the base treatment temperature of the base-treated ZSM-5 sample loaded with molybdenum (Mo) at low temperature (65°C) and high temperature (160°C), and Figure 21 shows the DTG analysis results of the Mo / Z-CTAOH sample and the Mo / Z-CTAOH-LT sample after 15 hours of reaction.

[0118] Referring to Figures 20 and 21, the correlation between coke characteristics and catalytic performance was further confirmed through the catalytic activity of LT samples containing ZSM-5 treated under mild conditions at a lower temperature (65°C). Higher Mo composition values ​​in the outer region of Mo / Z-CTAOH-LT and Mo / Z-TPAOH-LT indicate preferential formation of light coke and poor long-term performance.

[0119] The similar coke characteristics observed in the Mo / Z-NaOH and LT samples were reflected in comparable activity profiles, consistent with the higher elemental composition of surface Mo species in the samples. These results ultimately indicate that manipulation of the spatial distribution of acid sites within zeolite particles via DRP can be effectively utilized to control the catalytic performance of Mo / ZSM-5 by modifying the spatial distribution of active Mo species.

[0120] Meanwhile, it should be noted that several additional factors may have influenced the activity of the samples. The low acidity of the Z-QAH samples may have reduced the selectivity for light coke formation. Additionally, the increased mesoporosity of these samples facilitated mass transport within the zeolite, preventing coke condensation within the zeolite pores. This observation explains the remarkable stability of Mo / Z-CTAOH compared to other Mo / QAH samples, as the long hydrocarbon chains of CTAOH contributed to the significant development of mesopores. However, the poor stability of the Mo / Z-NaOH sample, which exhibited the second-largest characteristic mesopore volume among the tested catalyst samples, indicates that this improvement in mass transport was minimal compared to the effect of Mo distribution in this system.

[0121]

[0122] Figure 22 shows the BTX yield when using the raw ZSM-5 sample, Z-CTAOH sample, and Z-NaOH sample loaded with molybdenum (Mo) for regeneration.

[0123] Considering that the industrial application of shale gas aromatization is significantly hampered by the limited regeneration of the catalyst, regeneration experiments were conducted to elucidate the effect of coke type on catalyst regeneration. While a higher regeneration temperature effectively removes precipitated coke from the deactivated catalyst, the use of temperatures exceeding 550°C is limited due to structural changes in the catalyst under harsh oxidation conditions. Therefore, 550°C was selected as the regeneration temperature in the embodiments of the present invention.

[0124] Referring to Figure 22, the regeneration potential of Mo / Z-CTAOH is superior to that of other catalysts in terms of BTX production capacity per 15-hour reaction cycle. This difference in regeneration potential is not due to differences in the degree of MoOx sublimation during oxidation regeneration, as the sample regenerated once after three consecutive reaction regeneration cycles did not show any loss of Mo content.

[0125]

[0126] We have discussed specific embodiments of the present invention. Those skilled in the art will appreciate that the present invention can be implemented in modified forms without departing from its essential characteristics. Therefore, the disclosed embodiments should be considered illustrative rather than restrictive. The scope of the present invention is set forth in the claims, not the foregoing description, and all differences within the scope equivalent thereto should be construed as being encompassed by the present invention.

[0127] Zeolite-supported catalysts according to embodiments of the present invention can exhibit excellent performance. For example, the zeolite-supported catalyst exhibits excellent activity and stability in shale gas aromatization reactions. The reduced content of metal catalyst on the external surface of the zeolite reduces external coke formation, thereby suppressing catalyst deactivation caused by blockage of the external pores of the zeolite. The activity of the zeolite-supported catalyst is enhanced and its service life is increased. The amount of light coke formation predominantly present on the external surface of the zeolite after use is reduced, thereby maintaining catalytic activity even after catalyst regeneration.

Claims

1. Zeolite; and Comprising a metal catalyst supported on the above zeolite, A zeolite-supported catalyst characterized in that the zeolite is treated with quaternary ammonium hydroxide before supporting the metal catalyst, thereby increasing mesopores and reducing Al sites on the outer surface.

2. In paragraph 1, A zeolite supported catalyst, characterized in that the zeolite comprises ZSM-5.

3. In paragraph 1, A zeolite-supported catalyst, characterized in that the metal catalyst comprises molybdenum.

4. In paragraph 1, A zeolite-supported catalyst, characterized in that the quaternary ammonium hydroxide comprises at least one of cetyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, and tetramethylammonium hydroxide.

5. Step for preparing zeolite; A step of treating the above zeolite with quaternary ammonium hydroxide; and A method for producing a zeolite-supported catalyst, comprising the step of supporting a metal catalyst on the above-mentioned base-treated zeolite.

6. In paragraph 5, A method for producing a zeolite-supported catalyst, characterized in that the Al site on the surface of the zeolite is reduced by the above-mentioned base treatment.

7. In paragraph 5, A method for producing a zeolite-supported catalyst, characterized in that the zeolite surface is de-aluminated and then recrystallized by the above-mentioned base treatment.

8. In paragraph 5, A method for producing a zeolite-supported catalyst, characterized in that the mesopores of the zeolite increase and the micropores decrease by the above-mentioned base treatment.

9. In paragraph 5, A method for producing a zeolite-supported catalyst, characterized in that the zeolite is hydrothermally treated after the base treatment.

10. In paragraph 9, A method for producing a zeolite-supported catalyst, characterized in that the Bronsted acid site of the zeolite is reduced by hydrothermal treatment after the above-mentioned basic treatment.

11. In paragraph 5, A method for producing a zeolite supported catalyst, characterized in that the zeolite comprises ZSM-5.

12. In paragraph 5, A method for producing a zeolite supported catalyst, characterized in that the metal catalyst comprises molybdenum.

13. In paragraph 5, A method for producing a zeolite-supported catalyst, characterized in that the quaternary ammonium hydroxide comprises at least one of cetyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, and tetramethylammonium hydroxide.

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