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

Abstract

The present invention provides a C / ZSM-5 zeolite molecular sieve, and its preparation method and application. The molecular sieve includes HZSM-5 zeolite molecular sieve and amorphous carbon composited on the HZSM-5 zeolite molecular sieve, and the mass percentage of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 0.4-3%. The present invention uses amorphous C to control the acid sites of HZSM-5 zeolite molecular sieve for the first time. It is found that after introducing amorphous C in a single HZSM-5 zeolite molecular sieve, it can be present in the internal channel and outer surface of the HZSM-5 zeolite molecular sieve at the same time, and covers part of the acid sites, thereby affecting the number of surface acid sites and improving catalytic performance. After the present invention composites the C / ZSM-5 zeolite molecular sieve with a ZrCr catalyst, it is applied to the reaction system of direct conversion of carbon dioxide into light aromatics, and it is found that the selectivity of BTX is significantly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a C / ZSM-5 zeolite molecular sieve, and a preparation method and application thereof. Background Art

[0002] Light aromatics (Benzene-Toluene-Xylene, referred to as BTX), generally including benzene, toluene, and xylene, are irreplaceable raw materials for the production of plastics, polymers, etc. in the petrochemical industry. The global demand for commodity aromatic monomers (especially BTX) exceeds 140 million tons per year, with an annual growth of about 2-6%. Traditionally, BTX is generally prepared by catalytic reforming of naphtha. However, the reduction of petroleum resources cannot keep up with the growth of BTX demand in the future, so it is urgent to develop some non-petroleum synthesis technologies for BTX.

[0003] In recent years, the efficient utilization of non-petroleum energy resources (such as coal, natural gas, biomass, organic waste, etc.) has attracted much attention. 2 The method of direct conversion to BTX has become a hot topic for many scholars. This method not only partially alleviates the CO 2 The emission of CO2 solves the environmental problem and opens up new ideas for the synthesis of BTX through non-petroleum pathways. 2 There are two ways to prepare BTX by hydrogenation: modified Fischer-Tropsch synthesis (FTS) and methanol. In the improved FTS route, CO is first converted to 2 The improved FTS route has a higher CO 2 The conversion rate is high, but the products are complex and widely distributed. 2 Converted into methanol, and then converted into BTX through a typical methanol-aromatic reaction, currently becoming CO 2 The mainstream means of direct conversion to BTX. In this catalytic system, zeolite catalyst plays a vital role due to its excellent hydrocarbon oligomerization and aromatization reaction ability.

[0004] CN110743606A discloses a method for preparing a catalyst for preparing aromatic hydrocarbons from carbon dioxide and a method for synthesizing aromatic hydrocarbons. The catalyst is prepared by combining one or two metal oxides such as Ga, In, Zn, Zr and molecular sieve catalysts such as ZSM-5 and MCM-22 by coprecipitation, step-by-step precipitation, deposition precipitation or mechanical mixing, thereby achieving direct catalysis of CO 2 Hydrogenation to produce aromatics.

[0005] CN110694673A discloses a catalyst preparation method for high-efficiency aromatization of waste edible oil to prepare light aromatic hydrocarbons. First, the carrier ZSM-5 is treated with one or more of acid, alkali and water vapor to obtain multi-level pore HZSM-5, and then the aromatization active metal oxide is loaded on the multi-level pore HZSM-5 by impregnation to obtain M / HZSM-5, and then the metal oxide film with aromatization catalytic activity is coated layer by layer inside and outside the pores of M / HZSM-5 by atomic layer deposition, and then SiO is introduced by atomic layer deposition. 2 The membrane selectively passivates the pores and non-selective acid sites on the outer surface of M / HZSM-5@N. The catalyst prepared by this patent effectively improves the reaction activity, selectivity and stability of aromatization of waste cooking oil to produce light aromatics.

[0006] At present, HZSM-5 zeolite molecular sieve has become the best candidate for zeolite catalyst for synthesizing BTX because of 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 the precise control of 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 the prior art. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a C / ZSM-5 zeolite molecular sieve, and a preparation method and application thereof. The C / ZSM-5 molecular sieve catalyst uses amorphous C to cover part of the acid sites of the HZSM-5 molecular sieve, which can significantly improve the selectivity of BTX while maintaining the selectivity of BTX stable.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] 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;

[0010] The mass percentage of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 0.4-3%.

[0011] Preferably, the mass percentage of the amorphous carbon in the C / ZSM-5 zeolite molecular sieve is 1.45-2.8%.

[0012] Preferably, the amorphous carbon is distributed on the outer surface and in the inner pores of the HZSM-5 zeolite molecular sieve.

[0013] Preferably, the silicon-aluminum ratio of the HZSM-5 zeolite molecular sieve is (25-1500):1.

[0014] In a second aspect, the present invention provides a method for preparing the above-mentioned C / ZSM-5 zeolite molecular sieve, comprising:

[0015] The carbon source and the HZSM-5 zeolite molecular sieve are mixed in the presence of a dispersant, dried, and calcined in an inert atmosphere to obtain a C / ZSM-5 zeolite molecular sieve.

[0016] Preferably, the carbon source is selected from any one or more of carboxymethyl cellulose, amino acids or sugars.

[0017] Preferably, the dispersant is selected from any one or more of water, alcohols or n-hexane.

[0018] Preferably, the mixing is performed under ultrasonic conditions.

[0019] Preferably, the drying temperature is 80-100° C. and the drying time is 8-15 hours.

[0020] Preferably, the calcination temperature is 600-800° C. and the calcination time is 2-5 hours.

[0021] 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.

[0022] 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.

[0023] Preferably, the mass ratio of the C / ZSM-5 zeolite molecular sieve to the ZrCr catalyst is 1:(1-1.5).

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a C / ZSM-5 zeolite molecular sieve, which uses amorphous C to control the acid sites of HZSM-5 zeolite molecular sieve for the first time. Studies have found that after introducing amorphous C into a single HZSM-5 zeolite molecular sieve, it can exist simultaneously in the internal channel and the outer surface of the HZSM-5 zeolite molecular sieve, and cover part of the acid sites, thereby affecting the number of acid sites on the surface of the C / ZSM-5 zeolite molecular sieve and improving the 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 directly converting 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.

[0026] The test shows that when the mass fraction of C in C / ZSM-5 zeolite is 1.45wt%, the highest aromatics selectivity and BTX selectivity can be obtained. At the same time, compared with the original single HZSM-5 zeolite, 1.45C / ZSM-5 zeolite has a higher CO 2 The conversion rate remained stable and the BTX selectivity increased from 36.2% to 45.4%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 XRD spectra of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1;

[0028] Figure 2 The N of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1 is 2 Adsorption / desorption isotherm plots;

[0029] Figure 3 The SEM images of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1;

[0030] 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 .81C / ZSM-5;

[0031] Figure 4 To adopt NH 3 -The results of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained by TPD method testing;

[0032] Figure 5 The results of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained by Py-FTIR spectrum detection;

[0033] Figure 6 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;

[0034] Figure 7 Al 2p XPS spectra of a series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1;

[0035] Figure 8A series of C / ZSM-5 zeolite molecular sieves obtained in Example 1 and a single HZSM-5 zeolite molecular sieve were composited with a ZrCr catalyst and used for CO 2 Results of hydrogenation performance test. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Efficient catalysts are important for improving CO 2 The key to converting to BTX selectivity is that most existing technologies use HZSM-5 as the core and non-acidic membrane as the shell to construct a core-shell catalyst. For non-acidic membrane, Silicate-1 and amorphous SiO 2 It has been widely studied. As an Al-free molecular sieve, Silicate-1 not only has no acid sites, but also has the same pore size as HZSM-5. These characteristics are conducive to the diffusion of BTX. Traditionally, HZSM-5@Silicate-1 core-shell zeolite is prepared by hydrothermal method. However, this method not only produces a lot of wastewater, but also takes a long time to prepare. Compared with HZSM-5@Silicate-1 core-shell molecular sieve, HZSM-5@SiO 2 Core-shell molecular sieve is a simple and time-saving chemical liquid deposition method, but amorphous SiO 2 The size of the molecule is larger than the pore size of HZSM-5, which results in the amorphous SiO 2 It will block the channels of HZSM-5 zeolite and prevent the diffusion of BTX.

[0038] 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.

[0039] In the present invention, the HZSM-5 zeolite molecular sieve is obtained by calcining the 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:

[0040] ZSM-5 zeolite molecular sieve (SiO 2 / Al 2 O3 =105) was calcined at 550°C for 6 h, and then 2 g of ZSM-5 zeolite molecular sieve was dispersed in 100 mL of NH 4 NO 3 The ion exchange process was repeated twice in an aqueous solution (1M) at 80°C for 5 hours. The sample was filtered and washed with deionized water, dried at 100°C overnight, and calcined at 550°C for 5 hours. The obtained sample was labeled as HZSM-5 zeolite molecular sieve.

[0041] In the present invention, the pore size of the HZSM-5 zeolite molecular sieve is the pore size of a common 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 general 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.

[0042] 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, and 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%.

[0043] 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. Studies have found that after introducing amorphous C into a single HZSM-5 zeolite molecular sieve, it can exist simultaneously in the internal channel and the outer surface of the HZSM-5 zeolite molecular sieve, and cover part of the acid sites, thereby affecting the number of acid sites on the surface of the C / ZSM-5 zeolite molecular sieve, and can effectively improve its catalytic performance. After the C / ZSM-5 zeolite molecular sieve is composited with a ZrCr catalyst, it is applied to a reaction system for directly converting 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.

[0044] The present invention also provides a method for preparing the above C / ZSM-5 zeolite molecular sieve, which adopts an improved impregnation method and specifically comprises:

[0045] The carbon source and the HZSM-5 zeolite molecular sieve are mixed in the presence of a dispersant, dried, and calcined in an inert atmosphere to obtain a C / ZSM-5 zeolite molecular sieve.

[0046] According to the present invention, the carbon source and the 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 the HZSM-5 zeolite molecular sieve are first mixed, and then the dispersant is slowly dripped into the obtained mixture under ultrasonic conditions for 1 to 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, alcohols or n-hexane, preferably water, and more preferably deionized water.

[0047] 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.

[0048] Finally, the dried product is calcined under an inert atmosphere. The inert atmosphere is an atmosphere well known to those skilled in the art, and nitrogen is preferred in the present invention. The flow rate of the nitrogen 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.

[0049] 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).

[0050] The preparation method provided by the present invention is an improved impregnation method, and compared with the traditional hydrothermal precipitation method and liquid phase precipitation method, the steps are simpler.

[0051] 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.

[0052] In the present invention, the C / ZSM-5 zeolite molecular sieve can be used as a composite catalyst to catalyze the hydrogenation of carbon dioxide to directly prepare light aromatics after being composited with the ZrCr catalyst. Wherein, 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.

[0053] In summary, the present invention prepares C / ZSM-5 zeolite molecular sieve for the first time through a simple modified impregnation method, and then prepares ZrCr-C / ZSM-5 composite catalyst through a physical mixing method, and applies it to the reaction of direct conversion of carbon dioxide into light aromatics. Unlike the traditional hydrothermal precipitation method and liquid phase precipitation method, amorphous C can cover some acid sites of HZSM-5. After introducing 1.45wt% C on a single HZSM-5 zeolite molecular sieve, the selectivity of BTX increased from 39.6% to 45.4%. Under the conditions of 5.0MPa, 360℃, and 4800mL / gcat / h, the BTX selectivity of ZrCr-1.45C / ZSM-5 composite catalyst is 46.9%, CO 2 The conversion rate was 13.5%. In addition, it is worth noting that the preparation method of C / ZSM-5 molecular sieve in the present invention is better than that of HZSM-5@Silicate-1 and HZSM-5@SiO 2 The preparation method of core-shell molecular sieves is simpler.

[0054] The present invention not only opens up a way for the modification of HZSM-5 zeolite molecular sieve, but also provides a new way for CO 2 The highly selective synthesis of BTX provides a powerful molecular sieve.

[0055] 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 common commercially available products.

[0056] Example 1

[0057] This embodiment provides a series of C / ZSM-5 zeolite molecular sieves, and the specific preparation method is as follows:

[0058] First, HZSM-5 zeolite molecular sieve was prepared: ZSM-5 zeolite molecular sieve (SiO 2 / Al 2 O 3 =105) was calcined at 550°C for 6 h, and then 2 g of ZSM-5 zeolite molecular sieve was dispersed in 100 mL of NH 4 NO 3 The ion exchange process was repeated twice in an aqueous solution (1M) at 80°C for 5 h. The sample was filtered and washed with deionized water, dried at 100°C overnight, and calcined at 550°C for 5 h. The obtained sample was labeled as HZSM-5 zeolite molecular sieve;

[0059] 0.1g, 0.3g, 0.6g, 1.0g, 1.5g carboxymethyl cellulose and 1.5g HZSM-5 zeolite were mixed respectively, and deionized water was slowly dripped into the mixture for 1h under the assistance of ultrasound. After drying at 100°C overnight, the obtained product was calcined at 650°C and nitrogen flow rate (40mL / min) for 3h. The product obtained after calcination was marked as xC / ZSM-5 (x represents the mass percentage of C in the whole C / ZSM-5 zeolite molecular sieve).

[0060] 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.

[0061] 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 as follows: Figure 1 As shown, it can be seen that C / ZSM-5 zeolite molecular sieves with different C contents and single HZSM-5 zeolite molecular sieves all show typical characteristic peaks, which are related to the MFI (MobilFive) structure of the molecular sieve. For C / ZSM-5 zeolite molecular sieves with different C contents, no characteristic peaks of amorphous C were observed, indicating that amorphous C is well dispersed on HZSM-5 zeolite.

[0062] A series of C / ZSM-5 zeolite molecular sieves and a single HZSM-5 zeolite molecular sieve obtained in Example 1 were subjected to N 2 Adsorption / desorption test, the test results are as follows Figure 2 shown.

[0063] The weight percentage of C in C / ZSM-5 zeolite molecular sieves with different C contents was detected by elemental analysis, and the C loading was calculated by thermogravimetric (TG) analysis. Figure 2 N 2 The total surface area, micropore surface area, external surface area, total pore volume, micropore volume and mesopore volume of C / ZSM-5 zeolite molecular sieves with different C contents and single HZSM-5 zeolite molecular sieve were calculated by adsorption / desorption isotherms. The results are shown in Table 1.

[0064] Table 1

[0065]

[0066] 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; SBET (m 2 / g) c : total surface area calculated by BET method; S micro (m 2 / g) d : The 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 :Adsorption with nitrogen p / p 0 = 0.99 estimated total pore volume; V micro (cm 3 / g) g : Micropore volume measured by t-Plot method; V meso (cm 3 / g) h : Mesopore volume, that is, Vtotal-Vmicro.

[0067] 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. Figure 3 As shown, it was found that the introduction of amorphous C did not change the shape of the HZSM-5 molecular sieve.

[0068] Using NH 3 -TPD method was used to test 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. The test results are as follows: Figure 4 As shown, it can be seen that a single HZSM-5 zeolite molecular sieve exhibits two obvious NH 3 Desorption peak: The peak around 148℃ belongs to the weak acid site, and the peak around 385℃ belongs to the medium-strong acid site. It can be clearly seen that with the increase of C content in C / ZSM-5 zeolite molecular sieve, these two peaks move to lower temperatures, indicating that the area of ​​medium-strong acid sites decreases. The above results show that the introduction of C reduces the acidity of HZSM-5 zeolite molecular sieve and reduces the number of medium-strong acid sites.

[0069] 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 as follows: Figure 5 As shown, among them, 1452cm -1 and 1541cm -1 The peaks near the Acid site. 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 site and The number of acid sites decreased. This indicates that the introduction of C simultaneously reduced the Lewis acid sites and Acid position.

[0070] Furthermore, the DTBPy-FTIR spectrum was used to determine 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 as follows: Figure 6 As shown, it can be seen that with the increase of C content in C / ZSM-5 zeolite molecular sieve, the signal of external acid sites weakens. However, some external acid sites are still detected in HZM-5 molecular sieve, indicating that amorphous C shields some acid sites on the outer surface of HZM-5 molecular sieve.

[0071] It should be noted that the color of the 2.81C / ZSM-5 zeolite molecular sieve sample is too dark. Figure 5 and Figure 6 The corresponding test results cannot be displayed.

[0072] In order to study the external 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 the XPS method for detection. The Al2p XPS spectra of different zeolite molecular sieves are as follows: Figure 7 As shown, it can be seen that the Al characteristic peak of the outer surface of the zeolite appears at about 75.0 eV for both the C / ZSM-5 zeolite molecular sieve and the single HZSM-5 zeolite molecular sieve. In summary, it is proved that the C / ZSM-5 zeolite molecular sieve prepared by the modified impregnation method cannot coat the amorphous C as a shell on the outer surface of the HZSM-5 zeolite molecular sieve. The reason is that the content of the introduced amorphous C is small, and the amorphous C can enter the inner pores of the HZSM-5 zeolite molecular sieve.

[0073] CO 2 Hydrogenation performance test

[0074] ZrCr catalyst preparation:

[0075] Sol-gel combined with CO 2 The ZrCr catalyst was prepared by supercritical drying. Usually, 8.56 g ZrO(NO 3 ) 2 ·2H 2 O and 1.61 g Cr(NO 3 ) 3 9H 2O was dissolved in 75 mL of deionized water and 225 mL of ethanol. The mixed solution was stirred at room temperature for 0.5 h, and then 1.95 g of formamide and 30.2 g of 1,2-propylene oxide were added to the above aqueous solution. After stirring at the same temperature for 1 hour, the precursor was moved to a 70 ° C water bath for gelation for 2 hours, and then the gel was washed with ethanol and converted into an autoclave. Carbon dioxide gas was sent into the autoclave by a high-pressure pump. After the pressure reached 7.5 MPa, the temperature was gradually increased to 260 ° C, maintained for 1 hour, and finally calcined at 500 ° C for 3 hours to obtain the ZrCr catalyst.

[0076] Preparation of composite catalyst by physical mixing method:

[0077] 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 an agate mortar for 3 minutes, and then pressed, crushed, and sieved to 20-40 mesh to obtain a composite catalyst.

[0078] The different composite catalysts were subjected to CO 2 Hydrogenation performance test, test results such as Figure 8 As shown in the figure, after calculation and analysis, the CO 2 The conversion rate was 16.6%, the aromatics selectivity was 66.2%, the BTX selectivity was 36.2%, and the CO selectivity was 64.5%. After impregnation of 0.44 wt% C on HZSM-5 zeolite, CO 2 The conversion rate dropped to 16.3%, and the aromatic selectivity increased to 72.2%. After analysis, it was found that the introduction of amorphous C reduced the acidity and the number of medium-strong acid sites of HZSM-5 molecular sieve, inhibiting the hydrogenation reaction of light olefins.

[0079] In addition, increasing the weight percentage of C from 0.44 wt% to 2.81 wt%, CO 2 The conversion rate did not change significantly. The aromatic 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 The selectivity of alkanes and aromatics showed an opposite trend. The selectivity of BTX first increased from 43.4% to 45.4%, and then decreased to 41.0%. The reason is that amorphous C enters the micropores of HZSM-5 zeolite molecular sieve, inhibiting some acid sites. When the mass fraction of C is 1.45wt%, the highest selectivity of aromatics and BTX is obtained. In addition, compared with the single HZSM-5 zeolite molecular sieve and the 1.45C / ZSM-5 zeolite molecular sieve, CO 2The conversion rate remained stable, and the BTX selectivity increased from 36.2% to 45.4%, and CH 4 The results show that appropriate amorphous C can cover some acid sites of HZSM-5 molecular sieve and effectively improve the selectivity of BTX.

[0080] Using different composite catalysts to 2 The product distribution obtained from the hydrogenation performance test is shown in Table 2 below:

[0081] Table 2

[0082]

[0083]

[0084] As can be seen from Table 2, the selectivity of a single HZSM-5 zeolite molecular sieve for PX is 6.7%. After impregnation of amorphous C on the HZSM-5 zeolite molecular sieve, the selectivity of PX first slightly increased to 8.8%, and then decreased to 7.9%. When the mass fraction of C is 1.45wt%, the selectivity for PX is the highest. As the mass percentage of C increases, excess carbon will enter the micropores of the HZSM-5 zeolite molecular sieve, covering part of its internal acid sites and reducing the selectivity of PX. However, the C / ZSM-5 zeolite molecular sieve shows a clear advantage in that it can maintain the stability of aromatic selectivity while significantly improving the selectivity of BTX.

[0085] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those 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 will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a C / ZSM-5 zeolite molecular sieve, 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 in an inert atmosphere to obtain a C / ZSM-5 zeolite molecular sieve; The carbon source is selected from any one or more of carboxymethyl cellulose, amino acids or sugars; The C / ZSM-5 zeolite molecular sieve comprises 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 preparation method 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 preparation method 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 preparation method 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. The preparation method according to claim 1, characterized in that: The dispersant is selected from any one or more of water, alcohols or n-hexane.

6. The preparation method according to claim 1, 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 h.

7. Use of the C / ZSM-5 zeolite molecular sieve prepared by the preparation method according to any one of claims 1 to 6 in the preparation of light aromatics by hydrogenation of carbon dioxide.

8. The use according to claim 7, characterized in that: The C / ZSM-5 zeolite molecular sieve is composited with the ZrCr catalyst to catalyze the hydrogenation of carbon dioxide to prepare light aromatics.

9. The use according to claim 8, 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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