C / ZSM-5 zeolite molecular sieve, and preparation method therefor and use thereof

Abstract

Provided in the present invention are a C / ZSM-5 zeolite molecular sieve, and a preparation method therefor and the use thereof. The molecular sieve comprises an HZSM-5 zeolite molecular sieve and amorphous carbon compounded on the HZSM-5 zeolite molecular sieve, wherein the mass percent of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 0.4-3%. In the present invention, amorphous C is used for the first time to control the acid sites of the HZSM-5 zeolite molecular sieve, and it is found that after the introduction of the amorphous C into the single HZSM-5 zeolite molecular sieve, the amorphous C can exist both in the internal channels and on the outer surface of the HZSM-5 zeolite molecular sieve and cover part of the acid sites, thereby exerting an impact on the number of the acid sites on the surface and improving the catalytic performance. In the present invention, when the C / ZSM-5 zeolite molecular sieve and a ZrCr catalyst are compounded and then applied to a reaction system for directly converting carbon dioxide into benzene-toluene-xylene (BTX), it is found that the selectivity of BTX is significantly improved.

Description

A C / ZSM-5 zeolite molecular sieve, and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on February 23, 2024, with application number 202410205658.X and invention name “A C / ZSM-5 zeolite molecular sieve, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of catalyst technology, and in particular to a C / ZSM-5 zeolite molecular sieve, and a preparation method and application thereof. Background Art

[0003] Light aromatics (Benzene-Toluene-Xylene, or BTX), generally including benzene, toluene, and xylene, are irreplaceable raw materials for the petrochemical industry in the production of plastics, polymers, and other products. Global demand for commercial aromatic monomers, particularly BTX, exceeds 140 million tons annually, growing by approximately 2-6% annually. Traditionally, BTX is produced through the catalytic reforming of naphtha. However, the decline in petroleum resources will not keep pace with the future growth in BTX demand, necessitating the development of non-petroleum-based BTX synthesis technologies.

[0004] In recent years, the efficient utilization of non-petroleum energy resources (such as coal, natural gas, biomass, and organic waste) has attracted considerable attention. Among these, the direct conversion of CO2 to BTX has become a hot topic of research for many scholars. This approach not only partially alleviates CO2 emissions and addresses environmental concerns, but also opens up new avenues for the non-petroleum synthesis of BTX. Generally, there are two pathways for the hydrogenation of CO2 to BTX: the modified Fischer-Tropsch synthesis (FTS) pathway and the methanol pathway. The modified FTS pathway first converts CO2 to CO via the reverse water-gas shift (RWGS) reaction, followed by the conversion of CO to BTX via the classic FTS reaction. While the modified FTS pathway offers high CO2 conversion rates, the resulting products are complex and widely distributed. The methanol pathway, which first converts CO2 to methanol, followed by the conversion of methanol to BTX via the classic methanol-aromatics reaction, has become the mainstream method for the direct conversion of CO2 to BTX. In this catalytic system, zeolite catalysts play a crucial role due to their excellent hydrocarbon oligomerization and aromatization capabilities.

[0005] CN110743606A discloses a method for preparing a carbon dioxide to aromatics catalyst and a method for synthesizing aromatics. The catalyst combines one or two metal oxides, such as Ga, In, Zn, or Zr, with a molecular sieve catalyst, such as ZSM-5 or MCM-22, through coprecipitation, stepwise precipitation, sedimentation, or mechanical mixing, to directly catalyze the hydrogenation of CO2 to produce aromatics.

[0006] CN110694673A discloses a method for preparing a catalyst for the efficient aromatization of waste cooking oil to produce light aromatic hydrocarbons. The method involves first treating a ZSM-5 carrier with one or more of an acid, base, and water vapor to produce hierarchical HZSM-5. An aromatization-active metal oxide is then loaded onto the hierarchical HZSM-5 by impregnation to produce M / HZSM-5. A thin film of metal oxide with aromatization catalytic activity is then layered onto the inside and outside of the M / HZSM-5 pores using atomic layer deposition. Finally, a SiO2 film is introduced by atomic layer deposition to selectively passivate the pore openings and non-selective acidic sites on the outer surface of the M / HZSM-5@N. The catalyst prepared in this patent effectively improves the reactivity, selectivity, and stability of the aromatization of waste cooking oil to produce light aromatic hydrocarbons.

[0007] At present, HZSM-5 zeolite molecular sieve has become the best zeolite catalyst candidate for the synthesis of BTX due to its suitable pore size. In the methanol to aromatics reaction process, BTX is first formed in the micropores of HZSM-5 zeolite molecular sieve, and then alkylated to heavy aromatics (C 9+ Aromatic hydrocarbons). Studies have shown that the key to improving BTX selectivity lies in precisely controlling the acidity of HZSM-5 zeolite molecular sieves, but it is difficult to precisely control the acidity and acid sites of HZSM-5 zeolite molecular sieves in existing technologies.

[0008] Summary of the Invention

[0009] In view of this, the present application provides a C / ZSM-5 zeolite molecular sieve, a preparation method, and an application thereof. The C / ZSM-5 molecular sieve catalyst uses amorphous carbon to cover some of the acid sites of the HZSM-5 molecular sieve, which can significantly improve the selectivity of BTX while maintaining stable BTX selectivity.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a C / ZSM-5 zeolite molecular sieve, comprising a HZSM-5 zeolite molecular sieve and amorphous carbon (hereinafter referred to as amorphous C) composited on the HZSM-5 zeolite molecular sieve;

[0012] The mass percentage of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 0.4-3%.

[0013] Preferably, the mass percentage of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 1.45-2.8%.

[0014] Preferably, the amorphous carbon is distributed on the outer surface and in the inner pores of the HZSM-5 zeolite molecular sieve.

[0015] Preferably, the silicon-aluminum ratio of the HZSM-5 zeolite molecular sieve is (25-1500):1.

[0016] In a second aspect, the present invention provides a method for preparing the above-mentioned C / ZSM-5 zeolite molecular sieve, comprising:

[0017] The carbon source and the HZSM-5 zeolite molecular sieve are mixed in the presence of a dispersant, dried, and calcined under an inert atmosphere to obtain the C / ZSM-5 zeolite molecular sieve.

[0018] Preferably, the carbon source is selected from any one or more of carboxymethyl cellulose, amino acids or sugars.

[0019] Preferably, the dispersant is selected from any one or more of water, alcohols or n-hexane.

[0020] Preferably, the mixing is performed under ultrasonic conditions.

[0021] Preferably, the drying temperature is 80-100° C. and the drying time is 8-15 hours.

[0022] Preferably, the calcination temperature is 600-800° C. and the calcination time is 2-5 hours.

[0023] In a third aspect, the present invention provides an application of the C / ZSM-5 zeolite molecular sieve involved in the above technical solution in the preparation of light aromatics by hydrogenation of carbon dioxide.

[0024] Preferably, the C / ZSM-5 zeolite molecular sieve is composited with a ZrCr catalyst to catalyze the hydrogenation of carbon dioxide to produce light aromatics.

[0025] Preferably, the mass ratio of the C / ZSM-5 zeolite molecular sieve to the ZrCr catalyst is 1:(1-1.5).

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a C / ZSM-5 zeolite molecular sieve that, for the first time, utilizes amorphous carbon to control the acid sites of HZSM-5 zeolite molecular sieve. Research has found that the introduction of amorphous carbon into a single HZSM-5 zeolite molecular sieve allows it to coexist within the internal channels and external surface of the HZSM-5 zeolite, covering some of the acid sites. This, in turn, affects the number of acid sites on the surface of the C / ZSM-5 zeolite molecular sieve and improves its catalytic performance. The present invention combines the C / ZSM-5 zeolite molecular sieve with a ZrCr catalyst and applies it to a reaction system for the direct conversion of carbon dioxide to light aromatics. Compared to the original single HZSM-5 zeolite molecular sieve, the selectivity for the direct conversion of carbon dioxide to BTX is significantly improved.

[0028] Testing has shown that the highest aromatics selectivity and BTX selectivity are achieved when the mass fraction of carbon in the C / ZSM-5 zeolite is 1.45wt%. Furthermore, compared to the original single HZSM-5 zeolite, the 1.45C / ZSM-5 zeolite maintains a stable CO2 conversion rate and increases the BTX selectivity from 36.2% to 45.4%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is an XRD spectrum of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1;

[0030] FIG2 is a graph showing N2 adsorption / desorption isotherms of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1;

[0031] FIG3 is an SEM image of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1;

[0032] Among them, a is single HZSM-5, b is 0.44C / ZSM-5, c is 0.74C / ZSM-5, d is 1.45C / ZSM-5, e is 2.13C / ZSM-5, and f is 0.81C / ZSM-5;

[0033] FIG4 is a graph showing the results of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve tested using the NH3-TPD method;

[0034] FIG5 is a graph showing the results of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained by Py-FTIR spectroscopy;

[0035] FIG6 is a graph showing the results of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained by DTBPy-FTIR detection;

[0036] FIG7 is an Al2p XPS spectra of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1;

[0037] FIG8 is a graph showing the results of CO2 hydrogenation performance tests of a series of C / ZSM-5 zeolite molecular sieves obtained in Example 1 and a single HZSM-5 zeolite molecular sieve composited with a ZrCr catalyst. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] Efficient catalysts are key to improving the selectivity of CO2 conversion to BTX. Existing technologies mostly construct core-shell catalysts using HZSM-5 as the core and a non-acidic membrane as the shell. For non-acidic membranes, silicate-1 and amorphous SiO2 have been extensively studied. As an Al-free molecular sieve, silicate-1 not only lacks acid sites but also has the same pore size as HZSM-5, which facilitates the diffusion of BTX. Traditionally, HZSM-5@Silicate-1 core-shell zeolites are prepared via a hydrothermal method. However, this method not only produces large amounts of wastewater but is also time-consuming to prepare. Compared to the HZSM-5@Silicate-1 core-shell molecular sieve, the HZSM-5@SiO2 core-shell molecular sieve is a simpler and more time-efficient chemical liquid deposition method. However, the size of the amorphous SiO2 molecules is larger than the pore size of the HZSM-5, causing the amorphous SiO2 to block the channels of the HZSM-5 zeolite, hindering the diffusion of BTX.

[0040] In view of the difficulty in accurately controlling the acidity and acid sites of HZSM-5 zeolite molecular sieve in the prior art, the present invention provides a C / ZSM-5 zeolite molecular sieve, which includes HZSM-5 zeolite molecular sieve and amorphous carbon composited on the HZSM-5 zeolite molecular sieve.

[0041] In the present invention, the HZSM-5 zeolite molecular sieve is obtained by calcining ZSM-5 zeolite molecular sieve after 2 to 4 ammonium ion exchange treatments. The present invention has no particular restrictions on the source of the ZSM-5 zeolite molecular sieve, and it can be a general commercial product. In some specific embodiments of the present invention, the HZSM-5 zeolite molecular sieve is prepared by the following steps:

[0042] ZSM-5 zeolite molecular sieve (SiO2 / Al2O3=105) was calcined at 550°C for 6 h. 2 g of ZSM-5 zeolite molecular sieve was then dispersed in 100 mL of 1 M NH4NO3 aqueous solution and stirred at 80°C for 5 h. This ion exchange process was repeated twice. The sample was filtered and washed with deionized water, dried at 100°C overnight, and calcined at 550°C for 5 h. The resulting sample was labeled HZSM-5 zeolite molecular sieve.

[0043] In the present invention, the pore size of the HZSM-5 zeolite molecular sieve is the pore size of ordinary ZSM-5 molecular sieve. The present invention has no particular restrictions on the ZSM-5 molecular sieve and its source, and it can be a common commercial product. In some embodiments of the present invention, the ZSM-5 molecular sieve has straight through channels along the crystal b axis. and the sinusoidal channel along the ac plane Two pore structures; the silicon-aluminum ratio of the HZSM-5 zeolite molecular sieve is (25-1500):1, preferably (50-1000):1, and more preferably 105:1.

[0044] In the present invention, the amorphous C is distributed on the outer surface and in the internal pores of the HZSM-5 zeolite molecular sieve. The mass percentage of the amorphous C in the C / ZSM-5 zeolite molecular sieve is 0.4-3%, preferably 1.45-2.8%, and most preferably 1.45%.

[0045] The above-mentioned C / ZSM-5 zeolite molecular sieve provided by the present invention uses amorphous C to control the acid sites of HZSM-5 zeolite molecular sieve for the first time. The study found that after introducing amorphous C into a single HZSM-5 zeolite molecular sieve, it can exist simultaneously in the internal channels and outer surface of the HZSM-5 zeolite molecular sieve and cover some of the acid sites, thereby affecting the number of acid sites on the surface of the C / ZSM-5 zeolite molecular sieve, which can effectively improve its catalytic performance. The present invention composites the C / ZSM-5 zeolite molecular sieve with a ZrCr catalyst and applies it to a reaction system for the direct conversion of carbon dioxide into light aromatics. Compared with the original single HZSM-5 zeolite molecular sieve, the selectivity of directly converting carbon dioxide into BTX is significantly improved.

[0046] The present invention also provides a method for preparing the above-mentioned C / ZSM-5 zeolite molecular sieve, which adopts an improved impregnation method and specifically comprises:

[0047] The carbon source and the HZSM-5 zeolite molecular sieve are mixed in the presence of a dispersant, dried, and calcined under an inert atmosphere to obtain the C / ZSM-5 zeolite molecular sieve.

[0048] According to the present invention, a carbon source and HZSM-5 zeolite molecular sieve are first mixed in the presence of a dispersant. In some preferred embodiments of the present invention, the carbon source and HZSM-5 zeolite molecular sieve are first mixed, and then the dispersant is slowly added dropwise to the resulting mixture under ultrasonic conditions for 1-2 hours. The carbon source is preferably selected from any one or more of carboxymethyl cellulose, amino acids, or sugars, preferably carboxymethyl cellulose; the dispersant is any one or more of water, an alcohol, or n-hexane, preferably water, and more preferably deionized water.

[0049] Then, the obtained product is dried at a temperature of 80 to 100° C., preferably 90 to 100° C., for a time of 8 to 15 hours, preferably 10 to 12 hours.

[0050] Finally, the dried product is calcined under an inert atmosphere. The inert atmosphere is an atmosphere familiar to those skilled in the art, and nitrogen is preferred in the present invention. The nitrogen flow rate is preferably 30 to 60 mL / min, more preferably 40 mL / min. The calcination temperature is 600 to 800°C, preferably 650 to 700°C, and the calcination time is 2 to 5 hours, preferably 3 to 4 hours.

[0051] After the above calcination is completed, the final product can be obtained, which can be recorded as x C / ZSM-5 zeolite molecular sieve (x represents the mass percentage of C in the C / ZSM-5 zeolite molecular sieve).

[0052] The preparation method provided by the present invention is an improved impregnation method, which has simpler steps compared with the traditional hydrothermal precipitation method and liquid phase precipitation method.

[0053] The present invention also provides an application of the C / ZSM-5 zeolite molecular sieve in the preparation of light aromatic hydrocarbons by hydrogenation of carbon dioxide.

[0054] In the present invention, the C / ZSM-5 zeolite molecular sieve and the ZrCr catalyst are composited and can be used as a composite catalyst to catalyze the hydrogenation of carbon dioxide to directly produce light aromatics. The ZrCr catalyst can be purchased directly or prepared according to methods well known to those skilled in the art. In some embodiments of the present invention, the mass ratio of the C / ZSM-5 zeolite molecular sieve to the ZrCr catalyst is preferably 1: (1 to 1.5), more preferably 1: 1.

[0055] In summary, this invention, for the first time, prepares C / ZSM-5 zeolite molecular sieves via a simple modified impregnation method. It then prepares a ZrCr-C / ZSM-5 composite catalyst via a physical mixing method and applies it to the direct conversion of CO2 to light aromatics. Unlike traditional hydrothermal precipitation and liquid-phase precipitation methods, amorphous C can partially cover the acidic sites of HZSM-5. Introducing 1.45 wt% C onto a single HZSM-5 zeolite molecular sieve increases the BTX selectivity from 39.6% to 45.4%. Under conditions of 5.0 MPa, 360°C, and 4800 mL / gcat / h, the ZrCr-1.45C / ZSM-5 composite catalyst achieves a BTX selectivity of 46.9% and a CO2 conversion of 13.5%. Furthermore, the preparation method for the C / ZSM-5 molecular sieve in this invention is simpler than that for HZSM-5@Silicate-1 and HZSM-5@SiO2 core-shell molecular sieves.

[0056] The present invention not only opens up a way for the modification of HZSM-5 zeolite molecular sieve, but also provides a powerful molecular sieve for the high-selective synthesis of BTX from CO2.

[0057] In order to further illustrate the present invention, the following examples are provided for detailed description. The experimental raw materials used in the following examples of the present invention are all commonly available commercial products.

[0058] Example 1

[0059] This embodiment provides a series of C / ZSM-5 zeolite molecular sieves, and the specific preparation method is as follows:

[0060] First, HZSM-5 zeolite molecular sieve was prepared: ZSM-5 zeolite molecular sieve (SiO2 / Al2O3=105) was calcined at 550°C for 6 hours, then 2g of ZSM-5 zeolite was dispersed in 100mL of 1M NH4NO3 aqueous solution and stirred at 80°C for 5 hours. This ion exchange process was repeated twice. The sample was filtered and washed with deionized water, dried at 100°C overnight, and calcined at 550°C for 5 hours. The resulting sample was labeled HZSM-5 zeolite molecular sieve.

[0061] 0.1g, 0.3g, 0.6g, 1.0g, and 1.5g of carboxymethyl cellulose were mixed with 1.5g of HZSM-5 zeolite, and deionized water was slowly added dropwise to the mixture under ultrasound assistance for 1 hour. After drying at 100°C overnight, the resulting product was calcined at 650°C under a nitrogen flow rate of 40mL / min for 3 hours. The calcined product is labeled xC / ZSM-5 (x represents the mass percentage of carbon in the total C / ZSM-5 zeolite).

[0062] After analysis, 0.44C / ZSM-5 zeolite molecular sieve, 0.74C / ZSM-5 zeolite molecular sieve, 1.45C / ZSM-5 zeolite molecular sieve, 2.13C / ZSM-5 zeolite molecular sieve, and 2.81C / ZSM-5 zeolite molecular sieve were finally obtained.

[0063] XRD tests were performed on a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1. The results are shown in Figure 1. It can be seen that the C / ZSM-5 zeolite molecular sieves with different carbon contents and the single HZSM-5 zeolite molecular sieve all exhibit typical characteristic peaks, which are related to the MFI (Mobil Five) structure of the molecular sieve. For the C / ZSM-5 zeolite molecular sieves with different carbon contents, no characteristic peaks of amorphous carbon were observed, indicating that the amorphous carbon is well dispersed on the HZSM-5 zeolite.

[0064] A series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1 were tested for N2 adsorption / desorption. The test results are shown in FIG2 .

[0065] Elemental analysis was used to determine the weight percentage of carbon in C / ZSM-5 zeolite molecular sieves with varying carbon contents. The carbon loading was calculated using thermogravimetric (TG) analysis. Based on the N adsorption / desorption isotherms shown in Figure 2, the total surface area, micropore surface area, external surface area, total pore volume, micropore volume, and mesopore volume of the C / ZSM-5 zeolite molecular sieves with varying carbon contents and the HZSM-5 zeolite alone were calculated. The results are shown in Table 1.

[0066] Table 1

[0067] In the above Table 1, C loading (wt%) a Indicates the weight percentage of C; C loss (wt%) b : C content measured by TG method; S BET (m 2 / g) c : total surface area calculated using the BET method; S micro (m 2 / g) d : Micropore surface area was determined by t-Plot method; S ext (m 2 / g) e : External surface area, i.e. S BET -smmicro;V total (cm 3 / g) f : Total pore volume estimated using nitrogen adsorption p / p0=0.99; V micro (cm3 / g) g : Micropore volume measured by t-Plot method; V meso (cm 3 / g) h : Mesopore volume, that is, Vtotal-Vmicro.

[0068] The surface morphologies of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1 were observed using a scanning electron microscope, as shown in FIG3 . The results show that the introduction of amorphous C did not change the shape of the HZSM-5 molecular sieve.

[0069] The acid sites of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1 were tested using the NH3-TPD method. The test results are shown in Figure 4. It can be seen that the single HZSM-5 zeolite molecular sieve exhibits two obvious NH3 desorption peaks: the peak at around 148°C belongs to the weak acid site, and the peak at around 385°C belongs to the medium-strong acid site. It can be clearly seen that as the C content in the C / ZSM-5 zeolite molecular sieve increases, these two peaks shift to lower temperatures, indicating that the area of ​​the medium-strong acid site decreases. The above results show that the introduction of C reduces the acidity of the HZSM-5 zeolite molecular sieve and reduces the number of medium-strong acid sites.

[0070] The acid site types of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1 were detected by Py-FTIR spectroscopy. The test results are shown in FIG5 . In particular, the acid site types at 1452 cm -1 and 1541cm -1 The peaks near the Acid sites. With the increase of C content in C / ZSM-5 zeolite molecular sieve, the peak areas of the two peaks decrease, indicating that the Lewis acid sites and The number of acid sites is reduced. This indicates that the introduction of C reduces both Lewis acid sites and Acid position.

[0071] Furthermore, DTBPy-FTIR spectra were used to identify the external surface acid sites of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1. The test results are shown in Figure 6. It can be seen that the signal of the external acid sites decreases with increasing carbon content in the C / ZSM-5 zeolite molecular sieve. However, some external acid sites were still detected in the HZSM-5 molecular sieve, indicating that amorphous carbon shields some of the acid sites on the external surface of the HZSM-5 molecular sieve.

[0072] It should be noted that since the color of the 2.81C / ZSM-5 zeolite molecular sieve sample is too dark, the corresponding test results cannot be displayed in Figures 5 and 6.

[0073] In order to study the outer surface information of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1, the present invention further adopts XPS method to detect. The Al 2p XPS spectrum of different zeolite molecular sieves is as shown in Figure 7, and it can be seen that the Al characteristic peak of the outer surface of zeolite appears at about 75.0eV in C / ZSM-5 zeolite molecular sieve and a single HZSM-5 zeolite molecular sieve. In summary, it is proved that the C / ZSM-5 zeolite molecular sieve prepared by modified impregnation method can not be coated with amorphous C as a shell on the outer surface of HZSM-5 zeolite molecular sieve, and the reason is: the amorphous C content introduced is few, and amorphous C can enter the endoporus of HZSM-5 zeolite molecular sieve.

[0074] CO2 hydrogenation performance test

[0075] ZrCr catalyst preparation:

[0076] The ZrCr catalyst was prepared using a sol-gel method combined with CO2 supercritical drying. Typically, 8.56 g of ZrO(NO3)2·2H2O and 1.61 g of Cr(NO3)3·9H2O were dissolved in 75 mL of deionized water and 225 mL of ethanol. The mixed solution was stirred at room temperature for 0.5 h. Then, 1.95 g of formamide and 30.2 g of 1,2-propylene oxide were added to the aqueous solution. After stirring at the same temperature for 1 h, the precursor was transferred to a 70°C water bath for gelation for 2 h. The gel was then washed with ethanol and placed in an autoclave. Carbon dioxide gas was pumped into the autoclave via a high-pressure pump. After reaching a pressure of 7.5 MPa, the temperature was gradually increased to 260°C and maintained for 1 h. Finally, the ZrCr catalyst was calcined at 500°C for 3 h.

[0077] The composite catalyst is prepared by physical mixing method:

[0078] The ZrCr catalyst with a mass ratio of 1:1 and the different C / ZSM-5 zeolite catalysts obtained in Example 1 (or a single HZSM-5 zeolite molecular sieve) were mixed in agate mortar for 3 minutes, and then pressed, crushed, and sieved to 20-40 mesh to obtain a composite catalyst.

[0079] CO2 hydrogenation performance was tested on the various composite catalysts obtained. The results are shown in Figure 8. Calculation and analysis show that the ZrCr-HZSM-5 zeolite catalyst achieved a CO2 conversion of 16.6%, an aromatics selectivity of 66.2%, a BTX selectivity of 36.2%, and a CO selectivity of 64.5%. After impregnation of the HZSM-5 zeolite with 0.44 wt% carbon, the CO2 conversion dropped to 16.3%, while the aromatics selectivity increased to 72.2%. Analysis suggests that the introduction of amorphous carbon reduces the acidity and number of medium- and strong-acid sites in the HZSM-5 zeolite, inhibiting the hydrogenation of light olefins.

[0080] In addition, increasing the weight percentage of C from 0.44 wt% to 2.81 wt% did not significantly change the CO2 conversion. The aromatics selectivity first increased from 72.2% to 75.8% and then decreased to 72.2%. 2-4 The selectivity of olefins gradually increased from 3.0% to 6.6%. 2-4 Alkane selectivity and aromatic selectivity exhibited opposite trends. BTX selectivity first increased from 43.4% to 45.4% before decreasing to 41.0%. This is attributed to the infiltration of amorphous carbon into the micropores of the HZSM-5 zeolite, which partially suppresses acid sites. The highest aromatics and BTX selectivities were achieved when the carbon mass fraction was 1.45 wt%. Furthermore, compared with the 1.45 wt% C / ZSM-5 zeolite alone, CO2 conversion remained stable, BTX selectivity increased from 36.2% to 45.4%, and CH4 was controlled within 2%. These results demonstrate that appropriate amorphous carbon can partially cover the acid sites of the HZSM-5 zeolite, effectively improving BTX selectivity.

[0081] The CO2 hydrogenation performance test was carried out using different composite catalysts, and the product distribution obtained is shown in Table 2 below:

[0082] Table 2

[0083] As shown in Table 2, the selectivity of HZSM-5 zeolite alone for PX is 6.7%. After impregnation of the HZSM-5 zeolite with amorphous carbon, the PX selectivity initially slightly increased to 8.8% and then decreased to 7.9%. The highest selectivity for PX was achieved when the carbon mass fraction was 1.45 wt%. As the carbon mass percentage increases, excess carbon enters the micropores of the HZSM-5 zeolite, covering some of its internal acid sites and reducing PX selectivity. However, the C / ZSM-5 zeolite exhibits a clear advantage in maintaining stable aromatics selectivity while significantly improving BTX selectivity.

[0084] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A C / ZSM-5 zeolite molecular sieve, characterized in that: Comprising HZSM-5 zeolite molecular sieve and amorphous carbon composited on the HZSM-5 zeolite molecular sieve; The mass percentage of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 0.4-3%.

2. The C / ZSM-5 zeolite molecular sieve according to claim 1, characterized in that The mass percentage of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 1.45-2.8%.

3. The C / ZSM-5 zeolite molecular sieve according to claim 1 or 2, characterized in that The amorphous carbon is distributed on the outer surface and in the inner pores of the HZSM-5 zeolite molecular sieve.

4. The C / ZSM-5 zeolite molecular sieve according to claim 1 or 2, characterized in that The silicon-aluminum ratio of the HZSM-5 zeolite molecular sieve is (25-1500):

1.

5. A method for preparing the C / ZSM-5 zeolite molecular sieve according to any one of claims 1 to 4, characterized in that: include: The carbon source and the HZSM-5 zeolite molecular sieve are mixed in the presence of a dispersant, dried, and calcined under an inert atmosphere to obtain the C / ZSM-5 zeolite molecular sieve.

6. The method according to claim 5, characterized in that The carbon source is selected from any one or more of carboxymethyl cellulose, amino acids or sugars; The dispersant is selected from any one or more of water, alcohols or n-hexane.

7. The method according to claim 5, characterized in that The mixing is performed under ultrasonic conditions; The drying temperature is 80-100°C and the drying time is 8-15 hours; The calcination temperature is 600-800° C. and the calcination time is 2-5 hours.

8. Use of the C / ZSM-5 zeolite molecular sieve according to any one of claims 1 to 4 or the C / ZSM-5 zeolite molecular sieve prepared according to the preparation method according to any one of claims 5 to 7 in the preparation of light aromatic hydrocarbons by hydrogenation of carbon dioxide.

9. The use according to claim 8, characterized in that The C / ZSM-5 zeolite molecular sieve is composited with a ZrCr catalyst to catalyze the hydrogenation of carbon dioxide to prepare light aromatics.

10. The use according to claim 9, characterized in that The mass ratio of the C / ZSM-5 zeolite molecular sieve to the ZrCr catalyst is 1:(1-1.5).

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