CN111389460A - Copper-silicon catalyst modified by silanization and preparation method and application thereof - Google Patents

Abstract

The invention discloses a silanization modified copper-silicon catalyst, which comprises a copper species, silicon dioxide and silicon dioxide modified by silanization of a silane coupling agent; the copper species accounts for 10-30 wt.% of the weight of the copper-silicon catalyst, the silicon dioxide accounts for 60-85 wt.% of the weight of the copper-silicon catalyst, and the carbon element accounts for 1-10 wt.% of the weight of the copper-silicon catalyst in the silicon dioxide modified by silanization. The invention also discloses a preparation method of the catalyst and application of the catalyst in preparation of ethylene glycol by hydrogenation of dimethyl oxalate. After the silicon hydroxyl in the copper-silicon catalyst is covered by alkyl, the alkaline sites on the surface of the catalyst are reduced, and the generation of byproducts is inhibited, so that the selectivity of the byproducts is reduced, and the energy consumption and the cost for separating the byproducts 1, 2-butanediol and ethylene glycol can be further reduced. Compared with the unmodified copper-silicon catalyst, the copper-silicon catalyst provided by the invention has excellent reaction activity on the basis of ensuring economic cost and environmental friendliness, and has excellent performances of high selectivity and high stability.

Description

A kind of copper-silicon catalyst modified by silanization and its preparation method and use

technical field

The invention belongs to the technical field of catalysts, and relates to a gas-phase ester hydrogenation catalyst, in particular to a silanization-modified copper-silicon catalyst and a preparation method and application thereof.

Background technique

Ethylene glycol (EG) is an essential chemical product that is widely used as a solvent, antifreeze, PET raw material, etc. Compared with petroleum-derived routes, the process of producing ethylene glycol from coal has become increasingly attractive, which consists of three steps: coal gasification to syngas, and carbon monoxide to obtain dimethyl oxalate through a catalytic coupling reaction Esters (DMO), and dimethyl oxalate are hydrogenated to ethylene glycol. Due to the abundant syngas resources, short process flow and low cost, this process has become one of the main development directions of coal chemical industry in my country. The hydrogenation reaction of dimethyl oxalate, as one of the key steps, has received extensive attention at home and abroad.

Copper-silicon catalysts are widely used in the hydrogenation of dimethyl oxalate due to their good performance in the selective hydrogenation of carbon-oxygen double bonds. It is generally believed that copper active species with different valences on the surface of the copper-silicon catalyst have a synergistic catalytic effect in the hydrogenation of dimethyl oxalate, wherein the zero-valent copper species catalyzes the dissociation of hydrogen gas, and the monovalent copper species activates the acyl group or methoxy group. At present, there are a series of preparation methods for copper-silicon catalysts, such as ammonia evaporation method (AE), sol-gel method, deposition precipitation method, impregnation method and ion exchange method. Among them, the ammonia evaporation method is beneficial to the formation of layered copper silicate, promotes the high dispersion of active copper species on the silica support, and improves the strong interaction between the metal and the support to form and stabilize more monovalent copper species, Therefore, it has become a commonly used method for preparing copper-silicon catalysts and is used in industrial production.

However, the catalyst still has the following problems to be solved: the silyl hydroxyl group on the surface of the copper-silicon catalyst has a certain basicity, and the side reaction Guerbet reaction generates alcohol substances containing three or four carbon atoms as by-products on the basic site (later It is also represented by C _3,4 -OH in the text), such as 1,2-butanediol and 1,2-propanediol, and the reaction by-products 1,2-butanediol and ethylene glycol have close boiling points, resulting in large separation costs and energy consumption. Increase.

In order to solve the above problems, the present invention has been proposed.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a silylation-modified copper-silicon catalyst for ester hydrogenation, wherein the copper-silicon catalyst modified with functional group alkyl not only reduces the selectivity of reaction by-products, but also improves the catalyst stability.

A first aspect of the present invention provides a silylation-modified copper-silicon catalyst, which includes copper species, silica, and silylation-modified silica with a silane coupling agent; the copper species accounts for the silane-modified copper species. 10-30 wt.% of the weight of the silylation-modified copper-silicon catalyst, the silica accounts for 60-85 wt.% of the weight of the silylated-modified copper-silicon catalyst, and the silane coupling agent silylation-modified The carbon element in the silica with the silane coupling agent accounts for 1-10 wt.% of the weight of the copper-silicon catalyst; preferably, the carbon element in the silica modified by silanization with a silane coupling agent accounts for the weight of the copper-silicon catalyst 2-8 wt.%; more preferably, the carbon element in the silanized silica modified by the silane coupling agent accounts for 2.6-7.6 wt.% of the weight of the copper-silicon catalyst. The above mass percentages are all based on the copper-silicon catalyst product after silanization modification.

Preferably, the particle size of copper species in the copper-silicon catalyst is 1.5-4.5 nm, the specific surface area of the copper-silicon catalyst is 200-500 m ² /g, the average pore volume is 0.4-0.9 cm ³ /g, and the average pore diameter is 5 -12nm.

Preferably, the silane coupling agent is n-propyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane.

The second aspect of the present invention provides a preparation method of the copper-silicon catalyst described in the first aspect of the present invention, comprising the following steps:

(1) after the mixed solution of copper salt and ammoniacal liquor is stirred, add silicon source, stir at room temperature, obtain the first mixed solution;

(2) heating the first mixed solution obtained in step (1), carrying out ammonia distillation, until the pH value is 6-7, ending the ammonia distillation to obtain the second mixed solution;

(3) the second mixed solution obtained in step (2) is filtered and washed, dried, and calcined to obtain a copper-silicon catalyst by steaming ammonia;

(4) The copper-silicon catalyst obtained in step (3) is mixed and stirred with the silane coupling agent in an organic solvent, then filtered, washed or centrifuged, and dried to obtain a silanized-modified copper-silicon catalyst. Preferably, centrifugation washes. The organic solvent is selected from anhydrous methanol, anhydrous ethanol, isopropanol, toluene, etc., preferably anhydrous methanol.

Preferably, in step (1), the copper salt is copper nitrate, copper acetate or copper chloride; the silicon source is silica sol, sodium silicate solution, ethyl orthosilicate or propyl orthosilicate; adding silicon source, the dropping speed is 1-3 seconds per drop, and the stirring time after adding the silicon source is 0.5-24h. The addition amount of copper salt and silicon source is determined according to the copper metal loading in the copper-silicon catalyst, wherein the copper metal loading is preferably 20 wt.%.

Preferably, in the step (2), the first mixed solution obtained in the step (1) is heated to 70-90° C. for ammonia distillation.

Preferably, in step (3), the second mixed solution obtained in step (2) is directly filtered and washed, or the second mixed solution is first cooled to room temperature, and then filtered and washed, and the calcination temperature is 350-450 ° C, The roasting time is 4-6h.

Preferably, in step (4), the copper-silicon catalyst obtained in step (3) and the silane coupling agent are mixed and stirred in an organic solvent, the temperature is raised to 70-100° C., and refluxed and stirred for 4-8 hours; The linking agent is n-propyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane. The organic solvent is selected from anhydrous methanol, anhydrous ethanol, isopropanol, toluene, etc., preferably anhydrous methanol.

The third aspect of the present invention provides a use of the copper-silicon catalyst described in the first aspect of the present invention for ester hydrogenation.

Preferably, the copper-silicon catalyst is used as the reaction of dimethyl oxalate hydrogenation to produce ethylene glycol, which is used to reduce the generation of by-products and improve the selectivity of the main product, ethylene glycol.

Preferably, the copper-silicon catalyst is used in the reaction of dimethyl oxalate hydrogenation to produce ethylene glycol after hydrogen reduction; Under the pressure of 3MPa, hydrogen was introduced to carry out temperature-programmed heating. After reduction at 220-350°C for 2-6h, the temperature was lowered to 180-220°C, and then dimethyl oxalate was introduced for the reaction. The reaction pressure was 2-3MPa. 70-100.

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

1. The silanized-modified copper-silicon catalyst of the present invention uses copper species as the active component, and has the characteristics of mild reaction conditions, excellent catalytic reaction performance, simple preparation process, and low cost.

2. When used in the heterogeneous hydrogenation of dimethyl oxalate, compared with the unmodified copper-silicon catalyst, the silylated-modified copper-silicon catalyst of the present invention has high activity, high selectivity and high stability sex. At the same time, compared with traditional precious metal catalysts, the silylation-modified copper-silicon catalyst of the present invention obtains excellent reactivity and selectivity on the basis of ensuring economic cost and environmental friendliness.

3. After the silyl hydroxyl group of the silanized modified copper-silicon catalyst of the present invention is covered by an alkyl group, the surface basic position of the catalyst is reduced to some extent, and by-products such as 1,2-butanediol and 1,2-propanediol are suppressed. The generation of alcohol substances containing three or four carbon atoms can reduce the selectivity of by-products, and can further reduce the energy consumption and cost of separation of by-products 1,2-butanediol and ethylene glycol in industry.

4. In addition to the hydrogenation reaction of dimethyl oxalate, the catalyst involved in the present invention can also be applied to other ester hydrogenation reactions.

Description of drawings

Fig. 1 is the in-situ infrared spectrogram of the copper-silicon catalyst in the present invention after reduction, including catalyst samples 20Cu/SiO ₂ and 20Cu/SiO ₂ -4.6CH ₃ ;

Figure 2 is the X-ray diffraction (XRD) pattern of the copper-silicon catalyst in the present invention after reduction, including catalyst samples 20Cu/SiO ₂ , 20Cu/SiO ₂ -2.6CH ₃ , 20Cu/SiO ₂ -4.6CH ₃ , 20Cu/SiO _{2 -6.2CH3} ;

Fig. 3 is the temperature programmed desorption mass spectrometry (MG-TPD-MS) of methyl glycolate after reduction of the copper-silicon catalyst in the present invention, including catalyst samples 20Cu/SiO ₂ and 20Cu/SiO ₂ -4.6CH ₃ ;

Fig. 4 is the CO ₂ temperature programmed desorption (CO ₂ -TPD) diagram of the copper-silicon catalyst in the present invention, including catalyst samples 20Cu/SiO ₂ and 20Cu/SiO ₂ -4.6CH ₃ ;

Fig. 5 is the stability test result of the copper-silicon catalyst in the present invention, including catalyst samples 20Cu/SiO ₂ and 20Cu/SiO ₂ -4.6CH ₃ ;

Figure 6 is the structural formula and name of the silane coupling agent used in the modification of the copper-silicon catalyst in the present invention.

Detailed ways

The present invention is further described below through examples, but is not limited to this example. The experimental methods for which specific conditions are not indicated in the examples are usually in accordance with the conventional conditions and the conditions described in the manual, or the general equipment, materials, reagents, etc. used in accordance with the conditions suggested by the manufacturer, unless otherwise specified. commercially available. The raw materials required in the following examples and comparative examples are all commercially available. Among them, copper nitrate, ammonia water and silane coupling agent are all commercially purchased products.

In the present embodiment and the comparative example, the catalyst on-line reduction and catalytic effect evaluation method are as follows:

In the present invention, the hydrogenation reaction of dimethyl oxalate is carried out in a fixed bed reactor. Load 0.5g of catalyst, reduce at 300℃ in a pure _H2 atmosphere of 2.5MPa, the gas flow is 80mL/min, keep for 4h, cool down to the reaction temperature of 200℃, vaporize dimethyl oxalate and mix it with hydrogen and then enter the reaction system Among them, the mass space velocity of dimethyl oxalate is 1.5h ^-1 , the hydrogen ester ratio is 80, and the hydrogenation reaction is carried out at 2.5MPa. The reaction products were analyzed by gas chromatography, and the conversion of dimethyl oxalate and the selectivity of methyl glycolate, ethylene glycol, ethanol and by-products were calculated. Wherein, the stability test was carried out under the condition that the reaction temperature was 190° C., and dimethyl oxalate and methyl glycolate were mixed and fed at a ratio of 1:1.

Comparative Examples 1-3: 10Cu/SiO ₂ , 20Cu/SiO ₂ , 30Cu/SiO ₂

Comparative Examples 1-3 are the preparation of 10Cu/SiO ₂ , 20Cu/SiO ₂ , and 30Cu/SiO ₂ , wherein 10Cu/SiO ₂ refers to the copper metal loading in the copper-silicon catalyst of the steam ammonia method being 10wt.%, 20Cu/SiO ₂ The copper metal loadings in 30Cu/SiO ₂ are 20wt.% and 30wt.%, respectively.

The specific preparation method is as follows: Weigh 7.9140g, 15.2259g, 18.1920g of copper nitrate and dissolve them in 100mL of distilled water, add 52mL of ammonia water, and after stirring for a period of time, dropwise add 45mL of 30wt% silica sol, and keep the dripping speed for 1-2 seconds One drop, after the dropwise addition was completed, the mixture was stirred at room temperature for 4 h. Raise the temperature to 80°C, open the stopper to conduct ammonia distillation, the initial pH is 11-12, and continue to steam ammonia until the pH reaches between 6-7, and the ammonia steaming ends. After filtration and washing, the filter cake was placed in an oven for drying, and the dried samples were placed in a muffle furnace, roasted in an air atmosphere for 4 hours, and the temperature was controlled at about 400 °C. The catalyst was pressed into tablets and sieved to obtain 40-60 mesh particles, namely 10Cu/SiO ₂ , 20Cu/SiO ₂ and 30Cu/SiO ₂ catalysts for the ammonia evaporation method.

The online reduction of the catalyst and the evaluation of the catalytic effect are shown above, and the results of the evaluation of the catalyst performance are shown in Table 1.

Example _1-3 : 10Cu/ _SiO2-4.6CH3 , _20Cu / _SiO2-4.6CH3 , _30Cu / _SiO2-4.6CH3

Example 1-3 is the preparation of 10Cu/SiO ₂ -4.6CH ₃ , 20Cu/SiO ₂ -4.6CH ₃ , and 30Cu/SiO ₂ -4.6CH ₃ , wherein 10Cu/SiO ₂ -4.6CH ₃ refers to ammonia steam copper The copper metal loading in the silicon catalyst is 10wt.%, the carbon element accounts for 4.6wt.% of the catalyst weight, and the copper metal loading in 20Cu/SiO ₂ -4.6CH ₃ and 30Cu/SiO ₂ -4.6CH ₃ is 20wt.% respectively , 30wt.%, and the carbon element accounts for 4.6wt.% of the catalyst weight. The active species copper loading and carbon content in the catalyst of the present invention are both characterized by using an inductively coupled plasma emission spectrometer and an elemental analyzer.

The specific preparation method is as follows: Weigh 1g of 10Cu/SiO ₂ , 20Cu/SiO ₂ and 30Cu/SiO ₂ respectively, dissolve them in 125mL of anhydrous methanol, add 0.0605g of n-propyltrimethoxysilane dropwise at 30°C, dropwise After the addition was completed, the temperature was raised to 80 °C, and the mixture was refluxed and stirred for 6 h. The cooled solution was washed by centrifugation, and dried at 80° C. overnight to obtain a silylation-modified copper-silicon catalyst. Press the catalyst into tablets and sieve to obtain 40-60 mesh particles, which are the silanized modified copper-silicon catalysts 10Cu/SiO ₂ -4.6CH ₃ , 20Cu/SiO ₂ -4.6CH ₃ , 30Cu/SiO ₂ -4.6 _CH3 .

The online reduction of the catalyst and the evaluation of the catalytic effect are shown above, and the results of the evaluation of the catalyst performance are shown in Table 1.

Example 4-5: 20Cu/SiO ₂ -2.6CH ₃ , 20Cu/SiO ₂ -6.2CH ₃

Embodiment 4-5 is the preparation of 20Cu/SiO ₂ -2.6CH ₃ and 20Cu/SiO ₂ -6.2CH ₃ , wherein 20Cu/SiO ₂ -2.6CH ₃ means that the copper metal loading in the copper-silicon catalyst of the ammonia evaporation method is 20wt .%, the addition amount of silane coupling agent is 0.0121g n-propyltrimethoxysilane, the carbon element accounts for 2.6wt.% of the catalyst weight, and the copper metal loading in 20Cu/SiO ₂ -6.2CH ₃ is 20 wt.% respectively , the addition amount of the silane coupling agent is 0.1209g n-propyltrimethoxysilane, and the carbon element accounts for 6.2wt.% of the catalyst weight.

The specific preparation method is as follows: 1 g of 20Cu/SiO ₂ was dissolved in 125 mL of anhydrous methanol, 0.0121 g and 0.1209 g of n-propyltrimethoxysilane were added dropwise at 30 °C, and the temperature was raised to 80 °C after the dropwise addition, and refluxed and stirred 6h. The cooled solution was washed by centrifugation, and dried at 80° C. overnight to obtain a silylation-modified copper-silicon catalyst. Press the catalyst into tablets and sieve to obtain 40-60 mesh particles, which are the silanized-modified copper-silicon catalysts 20Cu/SiO ₂ -2.6CH ₃ and 20Cu/SiO ₂ -6.2CH ₃ .

The reduced 20Cu/SiO ₂ and 20Cu/SiO ₂ -4.6CH ₃ were characterized by in-situ infrared spectroscopy, and the results are shown in FIG. 1 . The peak (I ₁ ) at 3740 cm ^-1 is attributed to the stretching vibration peak of the silanol group isolated on the surface of the copper-silicon catalyst, and the peak (I ₂ ) at 3675 cm ^-1 is attributed to the stretching vibration peak of the silanol group inside the silica support, The peaks at 2860-2960 cm ^-1 and 1391 cm- ¹ represent CH vibration peaks introduced by the coupling agent. Comparing the 20Cu/SiO ₂ and 20Cu/SiO ₂ -4.6CH ₃ catalysts, it is found that after the silane coupling agent is modified, the stretching vibration peak of CH can be clearly observed, indicating that the silane coupling agent is successfully grafted onto the catalyst surface; The relative peak intensities of s were significantly weakened, indicating that the silane coupling agent successfully covered the silyl hydroxyl groups on the catalyst surface. The peak intensity ratio of I ₁ /I ₂ in the infrared spectrum can represent the relative content of isolated silanols on the catalyst surface. Taking the ratio of I ₁ /I ₂ in the unmodified copper-silicon catalyst as the standard, it can be calculated. 59.8% of the silanols on the surface of the catalyst after the modification of the linker were covered, and the carbon element accounted for 4.6% of the weight of the catalyst.

20Cu/SiO ₂ , 20Cu/SiO ₂ -2.6CH ₃ , 20Cu/SiO ₂ -4.6CH ₃ , 20Cu/SiO ₂ -6.2CH ₃ after the reduction of the present invention were characterized by XRD, and the results are shown in FIG. 2 . The peak at about 22° 2θ is the peak of amorphous silica, the characteristic diffraction peak at 2θ at 43.3° is the diffraction peak of metal Cu (JCPDS 65-9743), and the characteristic peak at 2θ at 36.4° is attributed to Cu The characteristic diffraction peaks of ₂ O (JCPDS05-0667) indicate that the active species after reduction of different catalysts of the present invention are mainly metallic copper and monovalent copper species, and the particle size range calculated according to the Scherrer formula is about 1.5-4.5 nm.

MG-TPD-MS was used to investigate the desorption ability of 20Cu/SiO ₂ and its surface modified 20Cu/SiO ₂ -4.6CH ₃ catalyst for methyl glycolate, and the results are shown in Figure 3. As can be seen from Figure ₃ , compared with the copper-silicon catalyst 20Cu/ _SiO2 by the steaming ammonia method, the desorption temperature of the silylation-modified copper-silicon catalyst 20Cu/ _SiO2-4.6CH3 to methyl glycolate is reduced to some extent, It shows that covering silanol can achieve the effect of promoting the desorption of methyl glycolate.

CO ₂ -TPD was used to explore the number and strength of basic sites on the surface of 20Cu/SiO ₂ and its surface modified 20Cu/SiO ₂ -4.6CH ₃ catalyst. The results are shown in Figure 4. As can be seen from accompanying drawing 4, 1. The peak area of the silanized-modified copper-silicon catalyst is smaller than that of the ammonia-steaming catalyst, indicating that the alkyl-modified copper-silicon catalyst has the effect of reducing the number of basic sites; 2. The copper-silicon catalyst of steam ammonia method has an obvious carbon dioxide desorption peak at high temperature, which corresponds to the existence of medium and strong basic sites, while the alkyl-modified catalyst has no obvious desorption peak at high temperature, indicating that after alkyl modification, The basic strength of the catalyst surface is reduced, thereby reducing the formation of by-products.

The stability results of the 20Cu/ _SiO2 catalyst and the _20Cu / _SiO2-4.6CH3 catalyst are shown in Figure 5. It can be seen from Figure 5 that the stability of the silanized modified copper-silicon catalyst is improved. The ethylene glycol selectivity of the 20Cu/SiO ₂ -4.6CH 3 catalyst began to decline after 20 h of reaction, while the activity and ethylene glycol selectivity of the 20Cu/SiO ₂ -4.6CH ₃ catalyst did not decrease significantly within the same time period, indicating that the passivating silicon Hydroxyl groups can play a role in improving stability.

After analysis of BET characterization results, the copper-silicon catalyst has a specific surface area of 200-500 m ² /g, an average pore volume of 0.4-0.9 cm ³ /g, and an average pore diameter of 5-12 nm.

The on-line reduction and catalytic effects of 10Cu/SiO ₂ , 20Cu/SiO ₂ , 30Cu/SiO ₂ , 10Cu/SiO ₂ -4.6CH ₃ , 20Cu/SiO ₂ -4.6CH ₃ , 30Cu/SiO ₂ -4.6CH ₃ are as described above The performance evaluation results of the catalysts are shown in Table 1.

Table 1 Performance evaluation of different catalyst samples for dimethyl oxalate hydrogenation

It can be seen from Table 1 that the silanized-modified copper-silicon catalyst has an inhibitory effect on by-products, indicating that passivation of silanol groups can inhibit the occurrence of side reactions, and when the copper loading is 20wt.%, the catalyst Best performance. The by-products mentioned herein refer to alcohols containing three or four carbon atoms (C _3,4 -OH), specifically 1,2-butanediol, 1,2-propanediol and the like.

On-line reduction and catalytic effect evaluation of 20Cu/SiO ₂ , 20Cu/SiO ₂ -2.6CH ₃ , 20Cu/SiO ₂ -4.6CH ₃ , 20Cu/SiO ₂ -6.2CH ₃ catalysts are as described above, and the performance evaluation results of the catalysts are shown in Table 2.

Table 2 Performance evaluation of different catalyst samples for dimethyl oxalate hydrogenation

It can be seen from Table 2 that the selectivity of the by-products of the catalyst after silylation modification is significantly reduced compared with the catalyst of the steaming ammonia method, and with the increase of the amount of silane coupling agent added, the selectivity of the catalyst to by-products It shows a decreasing trend, which indicates that proper passivation of silanol groups can play a role in inhibiting the occurrence of side reactions. However, with the increase of the amount of silane coupling agent added, more silane coupling agent covers part of the active sites, resulting in a decrease in the hydrogenation performance of the catalyst, an increase in the selectivity of methyl glycolate, and a decrease in the selectivity of the target product ethylene glycol. , the catalyst (20Cu/SiO ₂ -4.6CH ₃ ) when the copper metal loading is 20wt.% and the carbon element accounts for 4.6wt.% of the catalyst weight has the best performance in catalyzing the hydrogenation of dimethyl oxalate to ethylene glycol.

Examples 6-8

Embodiment 6-8 is the preparation of 20Cu/SiO ₂ -3.8CH ₂ , 20Cu/SiO ₂ -6.1CH ₂ -2, 20Cu/SiO ₂ -7.6CH ₃ (CO), wherein 20Cu/SiO ₂ -3.8CH ₂ , In 20Cu/SiO ₂ -6.1CH ₂ -2 and 20Cu/SiO ₂ -7.6CH ₃ (CO), the copper metal loading was 20wt.%, and the carbon element accounted for 3.8wt.%, 6.1wt.%, 7.6 wt%.

The specific preparation method is as follows: respectively weigh 1g of 20Cu/ _SiO2 and dissolve it in 125mL of anhydrous methanol, and add 0.368mmol of silane coupling agent dropwise at 30°C, namely, add 0.0546g of vinyltrimethoxysilane, 0.0546g of vinyltrimethoxysilane, 0.0701 g of vinyltriethoxysilane and 0.0914 g of γ-methacryloyloxypropyltrimethoxysilane were added dropwise, and the temperature was raised to 80° C., and the mixture was refluxed and stirred for 6 hours. The cooled solution was washed by centrifugation, and dried at 80° C. overnight to obtain a silylation-modified copper-silicon catalyst. Press the catalyst into tablets and sieve to obtain 40-60 mesh particles, which are the silanized modified copper-silicon catalysts 20Cu/SiO ₂ -3.8CH ₂ , 20Cu/SiO ₂ -6.1CH ₂ -2, 20Cu/SiO _{2 -7.6CH3} (CO).

On-line reduction and catalytic effect evaluation of 20Cu/SiO ₂ , 20Cu/SiO ₂ -3.8CH ₂ , 20Cu/SiO ₂ -6.1CH ₂ -2, 20Cu/SiO ₂ -7.6CH ₃ (CO) catalysts The performance evaluation results are shown in Table 3.

Table 3 Performance evaluation of different catalyst samples for dimethyl oxalate hydrogenation

It can be seen from Table 3 that the selectivity of by-products of the catalyst after silylation modification is significantly reduced compared with the catalyst of steaming ammonia method, indicating that the modification of silane coupling agent can reduce the generation of by-products and improve oxalic acid. The effect of ester hydrogenation to ethylene glycol performance, and the group grafted with the silyl hydroxyl group on the catalyst surface after the dissociation of the silane coupling agent affects the oxalate hydrogenation performance of the catalyst to a certain extent.

In addition to the hydrogenation reaction of dimethyl oxalate, the catalyst involved in the present invention can also be applied to other ester hydrogenation reactions, such as the hydrogenation reaction of ethylene carbonate, the hydrogenation reaction of diethyl oxalate, and the like. For example, in the hydrogenation of ethylene carbonate to methanol and ethylene glycol, the silanols on the surface of the copper-silicon catalyst will promote the occurrence of side reactions, resulting in high selectivity of by-products such as 1,2-butanediol. After the modification treatment of silane coupling agent, the selectivity of the catalyst to by-products decreased obviously, which indicated that covering silanols played a role in suppressing by-products.

The present invention has been exemplarily described above. It should be noted that, without departing from the core of the present invention, any simple deformation, modification, or other equivalent replacements that can be performed by those skilled in the art without any creative effort fall into the scope of the present invention. the scope of protection of the invention.

Claims (10)

1. A silanization-modified copper-silicon catalyst, characterized in that it comprises a copper species, silica and silica modified by silanization with a silane coupling agent; the copper species accounts for 10-30 wt.% of the weight of the copper silicon catalyst, the silicon dioxide accounts for 60-85 wt.% of the weight of the copper silicon catalyst, and carbon element accounts for 1-10 wt.% of the weight of the copper silicon catalyst in the silicon dioxide modified by silanization of a silane coupling agent.

2. According to claim1, the copper-silicon catalyst is characterized in that the particle size of the copper species in the copper-silicon catalyst is 1.5-4.5nm, and the specific surface area of the copper-silicon catalyst is 200-500m²Per g, average pore volume of 0.4-0.9cm³(ii)/g, the average pore diameter is 5-12 nm.

3. The copper-silicon catalyst according to claim 1, wherein the silane coupling agent is n-propyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, or gamma-methacryloxypropyltrimethoxysilane.

4. A method for preparing the copper silicon catalyst according to claim 1, comprising the steps of:

(1) stirring a mixed solution of copper salt and ammonia water, adding a silicon source, and stirring at room temperature to obtain a first mixed solution;

(2) heating the first mixed solution obtained in the step (1), carrying out ammonia distillation until the pH value is 6-7, and ending the ammonia distillation to obtain a second mixed solution;

(3) filtering and washing, drying and roasting the second mixed solution obtained in the step (2) to obtain an ammonia distillation method copper-silicon catalyst;

(4) and (4) mixing and stirring the ammonia distillation copper-silicon catalyst obtained in the step (3) and a silane coupling agent in an organic solvent, and then washing and drying to obtain the silanization modified copper-silicon catalyst.

5. The method according to claim 4, wherein the copper salt in the step (1) is copper nitrate, copper acetate or copper chloride; the silicon source is silica sol, sodium silicate solution, ethyl orthosilicate or propyl orthosilicate; adding a silicon source in a dropping mode, wherein the dropping speed is 1-3 seconds, and the stirring time is 0.5-24 hours after the silicon source is added.

6. The production method according to claim 4, wherein the first mixed solution obtained in the step (1) is heated to 70 to 90 ℃ in the step (2) to perform ammonia distillation.

7. The preparation method according to claim 4, wherein in the step (3), the second mixed solution obtained in the step (2) is filtered and washed, the roasting temperature is 350-450 ℃, and the roasting time is 4-6 h.

8. The preparation method according to claim 4, characterized in that in the step (4), the ammonia evaporation method copper-silicon catalyst obtained in the step (3) and the silane coupling agent are mixed and stirred in the organic solvent, the temperature is raised to 70-100 ℃, and the reflux stirring is carried out for 4-8 hours; the silane coupling agent is n-propyl trimethoxy silane, vinyl triethoxy silane and gamma-methacryloxy propyl trimethoxy silane.

9. Use of the copper silicon catalyst of claim 1 in ester hydrogenation reactions, wherein the copper silicon catalyst is used in the reaction of dimethyl oxalate hydrogenation to ethylene glycol, to reduce the formation of by-products and to increase the selectivity of the main product ethylene glycol.

10. The use of claim 9, wherein the copper-silicon catalyst is used for the reaction of preparing ethylene glycol by hydrogenation of dimethyl oxalate after hydrogen reduction; firstly, the copper-silicon catalyst is loaded in a constant temperature section of a fixed bed reactor, hydrogen is introduced under the pressure of 2-3MPa for temperature programming, the temperature is reduced to the reaction temperature of 180-220 ℃ after reduction is carried out for 2-6h under the temperature of 220-350 ℃, and then dimethyl oxalate is introduced for reaction, the reaction pressure is 2-3MPa, and the hydrogen-ester ratio is 70-100.

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