CuO-CdO / OH-H beta acid catalyst and preparation method and application thereof

Abstract

The invention discloses a CuO-CdO / OH-H [beta] acidic catalyst and a preparation method and application thereof. The catalyst comprises an OH-H [beta] molecular sieve carrier with hierarchical pores, and CuO and CdO are loaded on the OH-H [beta] molecular sieve carrier; cuO accounts for 1-10 wt% of the total mass of the catalyst, and CdO accounts for 1-10 wt% of the total mass of the catalyst. The preparation method comprises the following steps: carrying out calcination treatment, alkali treatment and ion exchange on an H beta molecular sieve to prepare an OH-H beta molecular sieve carrier with hierarchical pores; dipping the OH-H beta molecular sieve carrier in a mixed solution of copper salt and cadmium salt, taking out the OH-H beta molecular sieve carrier, drying, grinding, and calcining to obtain the CuO-CdO / OH-H beta acidic catalyst. The catalyst provided by the invention not only has higher stability and anti-coking performance, but also has the advantages of higher conversion rate, long service life and the like, the formaldehyde conversion rate reaches 99.9%, and the imidazole content in a reaction product reaches up to 72.1%.

Description

Technical Field

[0001] The present invention relates to an acid catalyst and a preparation method and application thereof, in particular to a CuO-CdO / OH-Hβ acid catalyst and a preparation method and application thereof Background Art

[0002] Imidazole is one of the most important five-membered heterocyclic rings with a variety of functions and applications, such as drugs, bioactive natural products, and acylating agents. In addition, imidazolium salts are used as precursors of ionic liquids and stable carbene ligands in organometallic chemistry. Imidazole has also been suggested as an absorbent for improving current carbon dioxide capture and storage (CCS) technology. Imidazole is an important pharmaceutical and pesticide intermediate and chemical raw material, widely used as a curing agent for epoxy resins, pharmaceutical antifungal and pesticide insecticides, etc. Imidazole can be used as a curing agent for epoxy resins, can improve the mechanical properties of products such as bending, stretching, and compression, improve the electrical properties of insulation, and improve the chemical resistance to chemical agents. It is widely used in computers and electrical appliances; imidazole is the main raw material for the preparation of antifungal drugs such as dichlorobenzazole, econazole, ketoconazole and clotrimazole, and is of great significance in production and manufacturing.

[0003] Acidic media inhibit the rearrangement of 1-alkyl and the hydrolysis of azomethylene back to the starting amine and aldehyde species. The stability of glyoxal is also improved under acidic conditions. Therefore, the addition of acidic copper nitrate and acidic cadmium nitrate is extremely important for improving the reaction yield.

[0004] Common imidazole synthesis methods include the Radziszewski method, the Phillips method, the bromoacetaldehyde method, and the like. Initially, ammonia water was added to the reactor, glyoxal was added dropwise, and the reaction temperature was controlled at 60-70°C. After two hours of reaction, a new compound imidazole was generated, but the yield was only about 12%. In 1882, Radziszewski and others improved this method and successfully synthesized imidazole using ammonia water, glyoxal, and formaldehyde. Radziszewski's method for synthesizing imidazole has become a commonly used method for preparing imidazole in industry because of its readily available raw materials and simple operation.

[0005] Among the molecular sieves with a large number of acidic sites, Hβ molecular sieves show relatively high catalytic performance, but they are accompanied by the production of a large number of by-products, which leads to rapid coking and deactivation of the catalyst, limiting its further application in industry. Therefore, the development of micro-mesoporous molecular sieves with higher conversion rate and anti-coking ability and extended catalyst life has important industrial application value. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a CuO-CdO / OH-Hβ acidic catalyst with higher conversion rate, anti-coking ability and long catalyst life;

[0007] The second object of the present invention is to provide a method for preparing the above-mentioned CuO-CdO / OH-Hβ acidic catalyst;

[0008] The third object of the present invention is to provide the application of the above-mentioned CuO-CdO / OH-Hβ acidic catalyst.

[0009] Technical solution: The CuO-CdO / OH-Hβ acidic catalyst of the present invention comprises an OH-Hβ molecular sieve carrier with multi-level pores, on which CuO and CdO are loaded; wherein CuO accounts for 1 to 10 wt% of the total mass of the catalyst, and CdO accounts for 1 to 10 wt% of the total mass of the catalyst.

[0010] Wherein, the silicon-aluminum ratio of the Hβ molecular sieve carrier is 25-40.

[0011] The preparation method of the above-mentioned CuO-CdO / OH-Hβ acid catalyst comprises the following steps:

[0012] (1) calcining, alkali treating and ion exchanging Hβ molecular sieve to obtain an OH-Hβ molecular sieve carrier with multi-level pores;

[0013] (2) The OH-Hβ molecular sieve carrier is immersed in a mixed solution of copper salt and cadmium salt, and then taken out, dried, ground, and calcined to obtain a CuO-CdO / OH-Hβ acidic catalyst.

[0014] Wherein, in step (2), preferably, the copper salt and the cadmium salt are dissolved in deionized water to form a mixed aqueous solution; and the volume ratio of the OH-Hβ molecular sieve carrier to the mixed aqueous solution is 1:1 to 1:10.

[0015] Wherein, in step (2), in the CuO-CdO / OH-Hβ acidic catalyst obtained after calcination, the loading amounts of CuO and CdO are 1-10wt% and 1-10wt% respectively.

[0016] Wherein, in step (2), the mass ratios of the copper salt and the cadmium salt to the mass ratio of the OH-Hβ molecular sieve carrier are 1:1 to 1:10 and 1:1 to 1:10, respectively.

[0017] Wherein, in step (2), the immersion time is 10 to 24 hours.

[0018] The calcination temperature in step (1) and step (2) is 450-650° C., and the calcination time is 3-5 hours. The OH-Hβ molecular sieve carrier with multi-level pores in step (1) can be obtained using the existing method.

[0019] The application of the above-mentioned CuO-CdO / OH-Hβ acidic catalyst in the catalytic synthesis of imidazole.

[0020] The above-mentioned CuO-CdO / OH-Hβ is used as a catalyst, mixed aldehydes and ammonia water are used as reaction raw materials, and imidazole is prepared through an amine-aldehyde condensation ring reaction; the volume ratio of the mixed aldehyde and ammonia water is 0.5:1 to 2:1; the mixed aldehyde includes formaldehyde and glyoxal; the volume ratio of formaldehyde to glyoxal in the mixed aldehyde is 0.4:1 to 0.7:1.

[0021] The reaction conditions are as follows: normal pressure, reaction temperature of 100-150°C, mass space velocity of the reaction raw materials of 0.7-1.8h -1 .

[0022] Principle of the invention: During the preparation process of the catalyst of the present invention, the original Hβ is transformed with a base, the purpose of which is to make the molecular sieve have mesopores in the original microporous structure at the same time, and to increase the specific surface area that can be loaded by the metal salt. Since the reaction involves the rearrangement of 1-alkyl and the hydrolysis of azomethylene, adding an acidic medium will greatly inhibit its occurrence, thereby reducing the formation of by-products and making the reaction proceed in the forward direction, so an acidic metal salt is selected for loading. Under copper catalysis, the condensation reaction of aldehyde and amino groups is faster, and the reaction conditions are milder. The ketone or alcohol generated in the reaction is not further reduced, which is conducive to the forward reaction. Under cadmium catalysis, the intermediate generated by the aldehyde reaction has a higher electrophilicity, so that the molecule is easy to attack the aldehyde molecule and form an imine intermediate, which promotes the forward reaction, not only reducing the temperature required for the reaction, but also greatly accelerating the reaction rate.

[0023] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0024] (1) The CuO-CdO / OH-Hβ acidic catalyst not only has high stability and anti-coking performance, but also has the advantages of high conversion rate and service life. This is mainly because the catalyst retains the high stability of the original microporous molecular sieve. (2) The continuous tubular gas phase catalytic reaction is used to prepare imidazole. Due to the loading of bimetallic, the catalyst performance is improved. Under the catalysis of the CuO-CdO / OH-Hβ acidic catalyst, the formaldehyde conversion rate reached 99.9%, and the imidazole content in the reaction product was as high as 72.1% (excluding water content). BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 XRD diagrams of Hβ and CuO-CdO / OH-Hβ in Comparative Example 1 and Example 1 of the present invention;

[0026] Figure 2 The SEM images of Hβ and CuO-CdO / OH-Hβ in Comparative Example 1 and Example 1 of the present invention are shown;

[0027] Figure 3It is a N2 absorption and desorption diagram of Hβ and CuO-CdO / OH-Hβ in Comparative Example 1 and Example 1 of the present invention;

[0028] Figure 4 The pore size distribution diagram of Hβ and CuO-CdO / OH-Hβ in Comparative Example 1 and Example 1 of the present invention;

[0029] Figure 5 It is a comparison chart of the catalytic performance of Hβ and CuO-CdO / OH-Hβ in Comparative Example 1 and Example 1 of the present invention;

[0030] Figure 6 This is a trend diagram of the life investigation experimental results of CuO-CdO / OH-Hβ in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The present invention is described in further detail below.

[0032] Example 1

[0033] A method for preparing a CuO-CdO / OH-Hβ acidic catalyst, comprising the following steps:

[0034] (1) Preparation of NaOH-Hβ molecular sieve carrier:

[0035] The Hβ molecular sieve raw powder was calcined at 550°C for 5h; the calcined Hβ molecular sieve was mixed with 0.5mol / L NaOH solution at a solid-liquid ratio (g / mL) of 1:20, and stirred in a round-bottom flask at 65°C for 0.5h, and then the round-bottom flask was placed in water and cooled to room temperature, washed with water and filtered to pH=7, and dried at 110°C for 10h, and the obtained solid was ground into powder; the powder was added to 0.5mol / LNH4Cl solution at a solid-liquid ratio (g / mL) of 1:20, ion exchange was performed at 60°C for 1h and filtered, and the above operation was repeated four times, and then washed with deionized water until the filtrate did not contain chloride ions, placed in an oven at 110°C for 10h, and then ground into powder and placed in a muffle furnace, and calcined at 550°C for 5h to obtain a micro-mesoporous Hβ molecular sieve, which was recorded as a multi-level pore NaOH-Hβ molecular sieve;

[0036] (2) Preparation of CuO-CdO / OH-Hβ Metal Acid Catalyst

[0037] 1.215 g of copper nitrate trihydrate and 0.961 g of cadmium nitrate tetrahydrate were dissolved in 40 ml of deionized water to obtain a brine solution. 8 g of a NaOH-Hβ molecular sieve carrier and the brine solution were mixed in a round-bottom flask and stirred. The mixture was stirred at 800 rpm at 65° C. for 18 h. The mixture was filtered and then dried in an oven at 105° C. for 13 h to obtain a solid, which was ground into powder. The solid was placed in a muffle furnace and heated to 500° C. at 2° C. / min in an air atmosphere. The powder was calcined for 5 h to obtain a CuO-CdO / OH-Hβ metal acid catalyst.

[0038] Example 2

[0039] The CuO-CdO / OH-Hβ modified molecular sieve material prepared in Example 1 was used as a catalyst to synthesize imidazole, and the specific steps were as follows:

[0040] 5 g of catalyst was loaded into the reaction tube, and ammonia, formaldehyde and glyoxal were used as the reaction raw materials. Ammonia and mixed aldehyde were fed into the tubular reactor in two streams. The reaction conditions were: normal pressure, reaction temperature of 120 °C, mass space velocity of 1.2 h -1 The volume ratio of formaldehyde to glyoxal is 0.61:1.0. The raw materials are cooled after the reaction, and the products are collected and detected by a thermal conductivity detector, a moisture meter and titration.

[0041] Comparative Example 1

[0042] On the basis of Example 2, the difference from Example 2 is that the Hβ molecular sieve in Example 1 is used as a catalyst to synthesize imidazole.

[0043] Figure 1 The XRD spectra of the two catalysts Hβ and CuO-CdO / OH-Hβ are shown in Figure 2. Figure 1 It can be seen that both samples have Hβ characteristic diffraction peaks at diffraction angles of 2θ=7.8° and 22.4°, indicating that the crystal structure of Hβ molecular sieve has not been changed during strong stirring, heating, ion exchange, loading of CuO and CdO, and alkali treatment. The intensity of the diffraction peak reflects the integrity of the molecular sieve crystal structure. Compared with Hβ, the diffraction peak intensity of CuO-CdO / OH-Hβ decreases, indicating that the NaOH solution has a desiliconization effect after treatment, which has a certain destructive effect on the skeleton silicon, resulting in a decrease in the crystallinity of the sample. No obvious diffraction peaks of CuO and CdO were found in the spectrum, indicating that the content of the loaded metal is low, resulting in no corresponding signal detected during the XRD measurement, or because the CuO and CdO loaded on NaOH-Hβ are evenly distributed on the catalyst surface and no obvious metal clusters are formed.

[0044] Figure 2 (a) is the SEM image of Hβ catalyst. Figure 2(b) is the SEM image of CuO-CdO / OH-Hβ catalyst. Figure 2 It can be seen that before alkali treatment, the surface of Hβ molecular sieve is relatively neat and flat, and the crystal morphology is mostly cubic; after alkali treatment, the molecular sieve has changed, the crystal has many pores, becomes rough and uneven, and the edges and corners disappear; this is mainly attributed to the alkaline solution dissolving the silicon species in the molecular sieve, generating holes in the molecular sieve skeleton, thus forming a micro-mesoporous structure. In addition, it can be seen that the molecular sieve particles after alkali treatment are more uniform in size, which is conducive to the amine-aldehyde condensation reaction.

[0045] Figure 3 and Figure 4 The N2 adsorption-desorption curves and pore size distribution curves of the two catalysts Hβ and CuO-CdO / OH-Hβ are shown in Figure 2. Figure 3 It can be seen that the isotherm of Hβ rises rapidly in the low pressure region, and adsorption occurs in the micropores, showing a typical type I isotherm, proving the microporous structure of the Hβ sample. At the same time, the H4 type hysteresis loop belonging to the narrow slit pores can be observed at P / P0>0.5, which indicates that there are irregular pore gaps between Hβ particles. The CuO-CdO / OH-Hβ sample still maintains similar characteristics to the Hβ sample, due to Figure 4 The pore size distribution diagram also shows that the CuO-CdO / OH-Hβ sample has more mesopores than the Hβ molecular sieve, and the mesopore size range is concentrated between 2 and 6 nm. However, the loading of CuO and CdO may have a certain influence on the pore size and pore volume of the sample, resulting in the pore size and pore volume being slightly smaller than those of the Hβ sample.

[0046] The formaldehyde conversion rate of imidazole synthesized by Hβ molecular sieve and CuO-CdO / OH-Hβ was compared with that of imidazole without considering the water content. The results are shown in Table 1 and Figure 5 shown.

[0047] Table 1 Performance comparison of Hβ and CuO-CdO / OH-Hβ

[0048] catalyst Excluding water content / wt% Conversion Rate % Hβ 58 86.5 CuO-CdO / OH-Hβ 72.1 99.9

[0049] From Table 1 and Figure 5 It can be seen that the catalytic activity of CuO-CdO / OH-Hβ is significantly improved compared with Hβ, and the content of imidazole in organic matter is increased by 14.1% (excluding water content); the conversion rate of imidazole is increased by 13.4% (excluding water content) compared with Hβ molecular sieve. The reason is that copper and cadmium catalysis not only accelerates the rate of condensation of reactants into imidazole rings, but also reduces the energy required for the reaction, making the reaction proceed more quickly and accurately in the forward direction.

[0050] The life test of the CuO-CdO / OH-Hβ catalyst prepared in Example 1 was carried out. The results are as follows: Figure 6 As shown. Figure 6 It can be seen that throughout the experiment, as time goes by, the activity and selectivity of the CuO-CdO / OH-Hβ catalyst are relatively stable, which means that the catalyst has a relatively long catalyst life of 720 hours while having a high catalytic activity.

[0051] Example 3

[0052] This example investigates the effect of CuO and CdO loading on the catalytic performance of the metal acid catalyst CuO-CdO / OH-Hβ. The effects of different CuO and CdO loadings on the conversion rate and content of imidazole synthesis are shown in Table 2.

[0053] Table 2 Effect of different metal loadings on formaldehyde conversion and imidazole excluding water content

[0054] CuO content / wt% CdO content / wt% Conversion rate / % Content / wt% 0.0 10.0 91.0 62.3 2.5 7.5 96.0 69.5 5.0 5.0 99.9 72.1 7.5 2.5 95.0 70.2 10.0 0.0 92.0 69.1

[0055] It can be seen from Table 2 that when the CuO content is 5wt% and the CdO content is 5wt%, using CuO-CdO / OH-Hβ as a catalyst can achieve a formaldehyde conversion rate of 99.9% and an imidazole content of 72.1% (excluding water content).

[0056] Example 4

[0057] This example investigates the effect of the solid-to-liquid ratio (g / ml) of the carrier and the metal salt solution in the metal acid catalyst CuO-CdO / OH-Hβ on the formaldehyde conversion rate and the imidazole excluding water content, as shown in Table 3.

[0058] Table 3 Effect of different metal loadings on formaldehyde conversion and imidazole excluding water content

[0059] Solid-liquid ratio (g / ml) CuO content / wt% CdO content / wt% Conversion rate / % Content / wt% 1:3 5.0 5.0 99.2 69.2 1:4 5.0 5.0 99.6 71.8 1:5 5.0 5.0 99.9 72.1 1；6 5.0 5.0 99.5 71.3 1；7 5.0 5.0 99.3 69.4

[0060] It can be seen from Table 3 that when the solid-liquid ratio is 1:5, the metal salt can be most effectively loaded on the carrier. The reason is that too low a solid-liquid ratio will greatly increase the concentration of the metal salt, thereby blocking the micropores on the surface of the molecular sieve, while too high a solid-liquid ratio will make the metal salt concentration too low, resulting in insufficient loading in the molecular sieve.

[0061] Example 5

[0062] The basic steps are the same as those in Example 2, except that the reaction temperatures are different. The reaction temperatures are 100°C, 110°C, 120°C, 130°C, and 140°C, respectively. The experimental results are shown in Table 4. This example is a single-dimensional experiment of reaction temperature in imidazole synthesis.

[0063] Table 4 Effect of reaction temperature on formaldehyde conversion and imidazole excluding water content

[0064] Reaction temperature / ℃ Ammonia-aldehyde ratio (ml / ml) <![CDATA[Feed space velocity / h -1 > Mixed aldehyde ratio (ml / ml) Conversion rate / % Content / wt% 100 3：3 1.2 0.61:1 97.0 68.4 110 3：3 1.2 0.61:1 98.2 70.4 120 3：3 1.2 0.61:1 99.9 72.1 130 3：3 1.2 0.61:1 98.5 63.5 140 3：3 1.2 0.61:1 98.0 62.9

[0065] Note: The solution ratios in this table and the following tables are all volume ratios, and the mixed aldehyde ratio is the ratio of formaldehyde to glyoxal.

[0066] It can be seen from Table 4 that different reaction temperatures have a great influence on the catalytic activity of the CuO-CdO / OH-Hβ catalyst. As the reaction temperature increases, the conversion rates of formaldehyde and imidazole increase first and then decrease. This is because too low a temperature is not conducive to the conversion of formaldehyde, glyoxal, and ammonia water into imidazole, resulting in a decrease in the conversion rate of imidazole; too high a temperature easily generates high-boiling point byproducts that block the catalyst pores, resulting in a decrease in catalyst activity and a decrease in imidazole content. Therefore, considering all factors, the most suitable reaction temperature for this reaction is 120°C.

[0067] Example 6

[0068] The basic steps are the same as those in Example 2, except that the mass air velocity is different. The mass air velocity is 0.72h -1 , 0.96h -1 , 1.2h -1 , 1.44h -1 , 1.68h -1 This example is a single-dimensional experiment on mass space velocity in imidazole synthesis. The results are shown in Table 5.

[0069] Table 5 Effect of mass space velocity on formaldehyde conversion and imidazole excluding water content

[0070] Reaction temperature / ℃ Ammonia-aldehyde ratio (ml / ml) <![CDATA[Feed space velocity / h -1 > Mixed aldehyde ratio (ml / ml) Conversion rate / % Content / wt% 120 3：3 0.72 0.61:1 97.0 68.4 120 3：3 0.96 0.61:1 98.2 70.4 120 3：3 1.20 0.61:1 99.9 72.1 120 3：3 1.44 0.61:1 98.5 63.5 120 3：3 1.68 0.61:1 98.0 63.2

[0071] It can be seen from Table 5 that different mass space velocities have little effect on the catalytic activity of the CuO-CdO / OH-Hβ catalyst. When the space velocity is low, the reactants stay in the system for a long time, and excessively high temperatures are more likely to cause reactants to coke and increase side reactions; when the space velocity is too high, the reactants stay for a short time, the reaction is not complete, and the imidazole content and yield are reduced accordingly. Therefore, considering all factors, the most suitable mass space velocity for this reaction is 1.2h -1 .

[0072] Example 7

[0073] The basic steps are the same as those in Example 2, except that the ammonia-aldehyde ratio is different. The volume ratios of aqueous ammonia and mixed aldehyde in the raw materials are 4.2:1.8, 3.6:2.4, 3.0:3.0, 2.4:3.6, and 1.8:4.2, respectively. Ammonia and mixed aldehyde are fed in two streams, and the optimal reaction conditions are achieved when the feed rates of aqueous ammonia and mixed aldehyde are 3 ml / h respectively. This embodiment is a single-dimensional experiment on the ammonia-aldehyde ratio in imidazole synthesis, and the results are shown in Table 6.

[0074] Table 6 Effect of ammonia-formaldehyde ratio on formaldehyde conversion rate and imidazole excluding water content

[0075] Reaction temperature / ℃ Ammonia-aldehyde ratio (ml / ml) <![CDATA[Feed space velocity / h -1 > Mixed aldehyde ratio (ml / ml) Conversion rate / % Content / wt% 120 4.2：1.8 1.2 0.61:1 96.0 67.8 120 3.6：2.4 1.2 0.61:1 98.2 68.7 120 3.0：3.0 1.2 0.61:1 99.9 72.1 120 2.4：3.6 1.2 0.61:1 98.2 71.7 120 1.8：4.2 1.2 0.61:1 98.0 70.2

[0076] It can be seen from Table 6 that when the amount of ammonia water is insufficient, the formaldehyde conversion rate is low due to incomplete reaction, while when the amount of ammonia water is large, glyoxal is consumed excessively, resulting in a decrease in the cyclization reaction rate and incomplete reaction. Therefore, the optimal amount of ammonia water in this reaction should be controlled at V (ammonia): V (mixed aldehyde) = 3:3.

[0077] Example 8

[0078] The basic steps are the same as those in Example 2, except that the ratio of formaldehyde to glyoxal is different. The volume ratios of formaldehyde to glyoxal in the raw materials are 0.67:1, 0.64:1, 0.61:1, 0.58:1, and 0.55:1, respectively. This example is a single-dimensional experiment on the ratio of mixed aldehydes in the synthesis of imidazoles, and the results are shown in Table 7.

[0079] Table 7 Effect of mixed aldehyde ratio on formaldehyde conversion rate and imidazole content

[0080] Reaction temperature / ℃ Ammonia-aldehyde ratio (ml / ml) <![CDATA[Feed space velocity / h ～1 > Mixed aldehyde ratio (ml / ml) Conversion rate / % Content / wt% 120 3：3 1.2 0.67:1 97.5 67.2 120 3：3 1.2 0.64:1 99.0 68.7 120 3：3 1.2 0.61:1 99.9 72.1 120 3：3 1.2 0.58:1 98.7 66.5 120 3：3 1.2 0.55:1 98.6 66.2

[0081] It can be seen from Table 7 that under the condition of excess glyoxal, the content and yield of imidazole in the reaction solution gradually increase. With the increase of the proportion of formaldehyde in the mixed aldehydes, the content and yield of imidazole tend to decrease again. When V (formaldehyde): V (glyoxal) = 0.61: 1.00, the effect is best.

Claims

1. A CuO-CdO / OH-Hβ acidic catalyst, characterized in that: The invention comprises an OH-Hβ molecular sieve carrier with multi-level pores, on which CuO and CdO are loaded; wherein CuO accounts for 1-10wt% of the total mass of the catalyst, and CdO accounts for 1-10wt% of the total mass of the catalyst.

2. The CuO-CdO / OH-Hβ acidic catalyst according to claim 1, characterized in that: The silicon-aluminum ratio of the Hβ molecular sieve carrier is 25-40.

3. A method for preparing the CuO-CdO / OH-Hβ acidic catalyst according to claim 1, characterized in that: The following steps are involved: (1) The Hβ molecular sieve is subjected to calcination, alkali treatment and ion exchange to obtain an OH-Hβ molecular sieve carrier with multi-level pores; (2) The OH-Hβ molecular sieve carrier is immersed in a mixed solution of copper salt and cadmium salt, and then taken out, dried, ground, and calcined to obtain a CuO-CdO / OH-Hβ acidic catalyst.

4. The method for preparing the CuO-CdO / OH-Hβ acidic catalyst according to claim 3, characterized in that: In step (2), the volume ratio of the OH-Hβ molecular sieve carrier to the mixed solution is 1:1 to 1:

10.

5. The method for preparing the CuO-CdO / OH-Hβ acidic catalyst according to claim 3, characterized in that: In step (2), in the CuO-CdO / OH-Hβ acidic catalyst obtained after calcination, CuO accounts for 1 to 10 wt% of the total mass of the catalyst, and CdO accounts for 1 to 10 wt% of the total mass of the catalyst.

6. The method for preparing the CuO-CdO / OH-Hβ acidic catalyst according to claim 3, characterized in that: In step (2), the mass ratio of copper salt to OH-Hβ molecular sieve is 1:1 to 1:10, and the mass ratio of cadmium salt to OH-Hβ molecular sieve is 1:1 to 1:

10.

7. The method for preparing the CuO-CdO / OH-Hβ acidic catalyst according to claim 3, characterized in that: In step (2), the immersion time is 12 to 24 hours.

8. The method for preparing the CuO-CdO / OH-Hβ acidic catalyst according to claim 3, characterized in that: The calcination temperature in step (1) and step (2) is 450-650° C., and the calcination time is 3-5 hours.

9. Use of the CuO-CdO / OH-Hβ acid catalyst according to claim 1 in catalytic synthesis of imidazole.

10. Use of the CuO-CdO / OH-Hβ acidic catalyst according to claim 9 in catalytic synthesis of imidazole, characterized in that: The method comprises taking the CuO-CdO / OH-Hβ of claim 1 as a catalyst, taking a mixed aldehyde and ammonia water as reaction raw materials, and subjecting imidazole to an amine-aldehyde condensation ring reaction; the volume ratio of the mixed aldehyde and ammonia water is 0.5:1-2:1; the mixed aldehyde comprises formaldehyde and glyoxal; the volume ratio of formaldehyde to glyoxal in the mixed aldehyde is 0.4:1-0.7:1; the reaction temperature is 100-150°C; the mass space velocity of the reaction raw materials is 0.7-1.8h -1 .

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