阅读说明：本技术 一种碳化硅基银纳米催化剂的制备方法及在环氧乙烷合成中的应用 (Preparation method of silicon carbide-based silver nano catalyst and application of silicon carbide-based silver nano catalyst in synthesis of ethylene oxide ) 是由 郭向云 焦志锋 赵吉晓 于 2021-08-02 设计创作，主要内容包括：本发明涉及一种碳化硅基银纳米催化剂的制备方法及在环氧乙烷合成中的应用,包括SiC载体的修饰改性和银纳米颗粒的尺寸调控,首先在SiC前驱体制备过程中,加入适量的硼源、磷源对SiC进行B、P体相掺杂；然后采用CeO-(2)、ZrO-(2)、Al-(2)O-(3)等含氧空位的氧化物对SiC表面进行修饰；最后以不同量的硝酸银为前驱体,采用液相还原法在SiC载体表面负载金属银,抽滤、干燥后得到负载型碳化硅基银纳米催化剂。本发明通过优化催化剂载体性质和金属负载条件制备的催化剂具有银颗粒尺寸可控、分散均匀、导热性好以及稳定性好等特点。将该催化剂用于乙烯环氧化制备环氧乙烷反应中,能够表现出优异的催化活性、产物选择性及稳定性。(The invention relates to a preparation method of a silicon carbide-based silver nano catalyst and application thereof in ethylene oxide synthesis, comprising modification of SiC carrier and size regulation of silver nano particles, firstly, in the preparation process of SiC precursor, adding a proper amount of boron source and phosphorus source to carry out B, P bulk phase doping on SiC; then using CeO 2 、ZrO 2 、Al 2 O 3 Modifying the SiC surface by oxide containing oxygen vacancy; finally, loading metallic silver on the surface of the SiC carrier by using different amounts of silver nitrate as a precursor by adopting a liquid phase reduction method, performing suction filtration,Drying to obtain the supported silicon carbide-based silver nano catalyst. The catalyst prepared by optimizing the property of the catalyst carrier and the metal loading condition has the characteristics of controllable silver particle size, uniform dispersion, good thermal conductivity, good stability and the like. The catalyst is used in the reaction of preparing ethylene oxide by ethylene epoxidation, and can show excellent catalytic activity, product selectivity and stability.)

1. A preparation method of silicon carbide based silver nano catalyst is characterized by comprising the following steps: the preparation method comprises the following steps: and (3) taking SiC/modified SiC as a carrier and silver salt as a metal precursor, loading metal silver by adopting a low-temperature liquid phase reduction method, and performing suction filtration and drying to obtain the silicon carbide-based silver nano catalyst.

2. The method for preparing silicon carbide-based silver nanocatalyst according to claim 1, wherein: the SiC is high-surface-area SiC with the specific surface area of 30-200 m²(ii)/g; the SiC carrier is pure SiC or SiC which is subjected to surface modification or bulk phase doping treatment.

3. The method for preparing silicon carbide-based silver nanocatalyst according to claim 2, wherein: the surface modification of SiC adopts oxide CeO with oxygen-containing vacancy₂、ZrO₂Or Al₂O₃Or the mixture of the oxides and the mixture modifies the surface of the SiC, and the content of the oxides or the mixture is 0.1 to 20 percent of the weight fraction of the silicon carbide.

4. The method for preparing silicon carbide-based silver nanocatalyst according to claim 3, wherein: the SiC modification method of the oxide is characterized by adopting an impregnation method for preparation, adding a proper amount of SiC powder into a solution of which the precursor is cerium salt, zirconium salt or mixed salt, stirring for a certain time, drying at 110 ℃ for 12-24h, and calcining at 400-600 ℃ in a muffle furnace for 4-10 h to obtain the oxide-modified SiC.

5. The method for preparing silicon carbide-based silver nanocatalyst according to claim 2, wherein: and in the bulk phase doping, a boron source and a phosphorus source are added to carry out B, P bulk phase doping on SiC in the preparation process of the SiC precursor, wherein the molar ratio of B/Si or P/Si is 0.01-1, and then the bulk phase B, P doped SiC is obtained through carbothermal reduction.

6. The method for preparing silicon carbide-based silver nanocatalyst according to claim 5, wherein: the phosphorus source is phosphoric acid, phosphorous acid, sodium phosphate, ammonium phosphate, diammonium phosphate, ammonium dihydrogen phosphate, calcium hydrogen phosphate, calcium pyrophosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium acid pyrophosphate, sodium dihydrogen phosphate or sodium pyrophosphate; the boron source is boric acid, borane, boron trichloride or boron trifluoride.

7. The method for preparing silicon carbide-based silver nanocatalyst according to claim 1, wherein: the liquid phase reduction comprises the following steps: mixing a certain amount of silver salt solution and SiC/modified SiC carrier, stirring for 0.5-2 h, then dropwise adding 0.1M lysine solution into the reaction solution, continuously stirring for 0.5-2 h, finally dropwise adding a proper amount of 0.1M sodium borohydride solution and 0.1M hydrochloric acid solution into the reaction solution in sequence, and continuously stirring for 1-48 h.

8. The method for preparing silicon carbide-based silver nanocatalyst according to claim 7, wherein: in the liquid phase reduction process, the amount of the added silver salt solution is controlled as follows: the content of silver is 0.1-30% of the mass fraction of silicon carbide, and the particle size range of the prepared silver nanoparticles is 5-50 nanometers.

9. The use of the silicon carbide-based silver nanocatalyst prepared by the preparation method of claim 1 in ethylene oxide synthesis, which is characterized in that: the catalyst is applied to the reaction of preparing ethylene oxide by ethylene epoxidation, and the specific reaction conditions are as follows: 1-200 g of silicon carbide-based silver nano catalyst is filled into a fixed bed reactor, and the raw material gas comprises the following components: 25-30% of ethylene, 6-9% of oxygen and the balance of nitrogen; the airspeed is 800-10000 h^-1The reaction pressure is 0-5 MPa, and the reaction temperature is 150-250 ℃.

10. The use of the silicon carbide-based silver nanocatalyst of claim 9 in ethylene oxide synthesis, wherein: the selectivity of the ethylene oxide reaches more than 80 percent.

Technical Field

The invention relates to the technical field of catalyst preparation, in particular to a preparation method of a silicon carbide-based silver nano catalyst and application of the silicon carbide-based silver nano catalyst in synthesis of ethylene oxide.

Background

Ethylene oxide is an important organic chemical raw material and is widely used in washing, pharmacy, printing and dyeing and other industries. Conventional methods for producing ethylene oxide include chlorohydrin processes and oxidation processes. The chlorohydrin method mainly comprises two steps: the first step is that ethylene and chlorine are introduced into water to react to generate 2-chloroethanol; the second step is to react 2-chloroethanol with alkali (common lime milk) to produce ethylene oxide product. However, the ethylene unit consumption is high and the environmental pollution is serious in the production process of the chlorohydrin method, and the ethylene unit consumption is gradually stopped.

Currently, the industrial production of ethylene oxide is mainly carried out by the direct oxidation process, i.e. the epoxidation of ethylene based on oxygen to produce ethylene oxide. The existing ethylene oxide industrial production device mostly adopts an Ag-based nano catalyst, and the Ag-based nano catalyst has certain defects after years of development although the catalytic performance is improved. Firstly, the selectivity of the catalyst is a problem, and one of the main reasons that the selectivity of the product is difficult to improve at present is that oxidation reaction releases a large amount of heat, and the heat removal rate has a bottleneck, and the core factor of the catalyst is that the heat conduction rate of the traditional carrier material alpha-alumina is low; secondly, the specific surface area of the alpha-alumina carrier material adopted by the traditional technology is small, the dispersity of the loaded Ag is poor, and the Ag is easy to agglomerate; to ensure activity, high loadings of Ag are required. In addition, if a material with acid sites on the surface is used as a catalyst carrier, the reaction network is easier to proceed to the route of ethylene oxide isomerization to acetaldehyde, and the EO selectivity is seriously reduced, so that a surface inert material is required as the carrier. Therefore, an inert inorganic material with a high specific surface area and good thermal conductivity is developed to be used as a carrier, so that the selectivity and the stability of the Ag-based catalyst can be effectively improved.

Silicon carbide is a semiconductor material, has high temperature resistance, corrosion resistance, high mechanical strength and good chemical stability, and particularly has good electric conductivity and heat conductivity. In addition, when a metal is loaded on the surface of the SiC, electron transfer can occur between the metal and the SiC carrier, so that the metal and the SiC carrier can show unique activity and selectivity in catalytic reaction. High specific surface area silicon carbide as oneThe novel supports have shown significant advantages in the fields of catalysis, photocatalysis and electrocatalysis. Therefore, SiC is used as the carrier of the ethylene epoxidation catalyst, and the existing Ag/alpha-Al can be broken through₂O₃The catalytic system faces the technical bottlenecks of low product selectivity and high Ag loading, thereby generating a subversive effect on the epoxidation reaction.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: in order to overcome the defects in the prior art, the invention provides a preparation method of a silicon carbide-based silver nano catalyst and application of the silicon carbide-based silver nano catalyst in ethylene oxide synthesis, so that the nano catalyst with uniform metal dispersion, good stability and good thermal conductivity is obtained and is used for preparing ethylene oxide by ethylene epoxidation.

The technical scheme adopted by the invention for solving the technical problems is as follows: a preparation method of silicon carbide based silver nano-catalyst comprises the following steps:

(1) during the preparation of SiC precursor, adding boron source and phosphorus source to carry out B, P bulk phase doping on SiC, and then adopting CeO₂、ZrO₂、Al₂O₃And modifying the SiC surface by oxide containing oxygen vacancy or mixture thereof to obtain the modified SiC carrier.

(2) Mixing and stirring a certain amount of silver nitrate solution and the SiC carrier for a period of time, then dropwise adding a quantitative 0.1M lysine solution, continuously stirring, finally dropwise adding a proper amount of 0.1M sodium borohydride solution and a proper amount of 0.1M hydrochloric acid solution into the reaction solution in sequence, continuously stirring for reaction, performing suction filtration, washing and drying to obtain the high-efficiency silicon carbide-based silver catalyst.

Preferably, the content of the bulk phase doping B, P in the carrier is controlled to be B/Si or the molar ratio of P/Si is 0.01-1; surface modification of CeO₂、ZrO₂、Al₂O₃The content of the oxygen-containing vacancy oxide is 0.1-20% of the mass fraction of the silicon carbide.

Preferably, the phosphorus source is phosphoric acid, phosphorous acid, sodium phosphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, calcium hydrogen phosphate, calcium pyrophosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium acid pyrophosphate, sodium dihydrogen phosphate or sodium pyrophosphate; the boron source is boric acid, borane, boron trichloride or boron trifluoride.

Preferably, the carrier in the metal loading process is an optimally screened SiC carrier.

Preferably, the content of silver in the catalyst is 0.1-80% of the weight fraction of the silicon carbide, and the particle size of the prepared silver nanoparticles is less than 5-50 nm.

Preferably, the added lysine accounts for 0.1-80% of the weight fraction of the silicon carbide.

Preferably, the amount of the sodium borohydride reducing agent added is 0.1-80% of the weight fraction of the silicon carbide.

Preferably, the amount of the added hydrochloric acid solution is controlled to keep the pH value of the reaction solution between 9 and 10.

Preferably, the temperature in the preparation process of the catalyst is controlled to be 20-50 ℃.

Preferably, after each drop of the solution is added, the stirring is continued for 0.5-2 hours; and stirring and reacting for 1-48 h after all the dropwise adding is finished.

Preferably, the catalyst preparation process agitation is magnetic agitation.

Preferably, the catalyst wash is a wash with deionized water.

Preferably, the drying temperature of the catalyst is 50-80 ℃, and the drying time is 6-18 h.

The silicon carbide-based silver nano-catalyst prepared by the method is applied to the reaction of preparing ethylene oxide by ethylene epoxidation, and the specific reaction conditions are as follows: filling 0.05-50 g of silicon carbide-based silver nano catalyst on a fixed bed reactor, wherein the raw materials comprise ethylene and oxygen, and the balance is nitrogen; the airspeed is 800-10000 h^-1The reaction pressure is 0-5 MPa, the reaction temperature is 100-300 ℃, the selectivity of the catalyst to ethylene oxide reaches over 80 percent, and the service life of the catalyst reaches over 800 hours.

The invention has the beneficial effects that: the invention uses silicon carbide as a catalyst carrier and utilizes a liquid phase reduction method to load active silver nano particles. The silicon carbide-based silver nanocatalyst with uniform metal dispersion, good thermal conductivity and high stability is prepared by optimizing the property of the silicon carbide carrier and a metal loading process, the preparation process has universality and simplicity, and the industrial synthesis is easy to realize; the catalyst can show higher activity, selectivity and cycling stability when being applied to the preparation of ethylene oxide by ethylene epoxidation.

Detailed Description

Specific examples of the present invention are described in further detail below. It should be understood that the specific embodiments described herein are only for illustrating and explaining the technical solutions of the present invention, and are not used to limit the technical solutions of the present invention.

Example one

High surface silicon carbide was used directly as support: 1854mL of AgNO₃Uniformly mixing and stirring an aqueous solution (0.01M) and 18g of silicon carbide, adding 200mL of 0.1M lysine, stirring for 1h, then adding 100mL of 0.1M sodium borohydride aqueous solution, stirring for 0.5h, finally adding 100mL of 0.1M HCl to keep the pH of the solution between 9 and 10, then continuing stirring for 24h at room temperature, centrifuging, washing and drying to obtain the Ag/SiC catalyst with the loading of 10 wt%, wherein the average particle size of silver particles is about 20 nm.

5g of the catalyst is filled into a fixed bed reactor, and the volume of raw material gas comprises 25 percent of ethylene, 7 percent of oxygen and the balance of nitrogen; the space velocity is 5000h^-1The reaction pressure is 1.5MPa, and the reaction temperature is 200 ℃. The gas chromatography quantitative detection of the outlet gas and the feed gas of the reactor shows that the ethylene conversion rate is 5 percent and the selectivity of the ethylene oxide is 82.5 percent.

Example two

Directly using high-surface silicon carbide as a carrier, then using aluminum nitrate as a precursor, and modifying Al on the surface of the silicon carbide₂O₃The content is 5 percent of the mass fraction of the silicon carbide.

1854mL of AgNO₃Mixing and stirring uniformly an aqueous solution (0.01M) and 18g of modified silicon carbide, adding 200mL of 0.1M lysine, stirring for 1h, then adding 100mL of 0.1M sodium borohydride aqueous solution, stirring for 0.5h, finally adding 100mL of 0.1M HCl to keep the pH of the solution between 9 and 10, then continuing stirring for 30h at room temperature, centrifuging, washingWashing and drying to obtain Ag/Al with the loading of 10 wt%₂O₃-SiC catalyst, in which the silver particles have an average particle size of about 13 nm.

Filling 8g of the catalyst into a fixed bed reactor, wherein the volume of raw material gas comprises 25% of ethylene, 8% of oxygen and the balance of nitrogen; space velocity is 5500h^-1The reaction pressure is 1.5MPa, and the reaction temperature is 200 ℃. The gas chromatography quantitative detection of the outlet gas and the feed gas of the reactor shows that the ethylene conversion rate is 5.9 percent and the selectivity of the ethylene oxide is 85 percent.

EXAMPLE III

In the preparation process of the silicon carbide precursor, adding a proper amount of boric acid to enable the molar ratio of B/Si to be 0.1, and preparing a B-doped silicon carbide carrier (B-SiC); then with Ce (NO)₃)₂·6H₂O is used as a precursor, and a single-layer CeO is modified on the surface of the B-SiC₂(CeO₂2 percent of the mass fraction of B-SiC) to obtain the modified silicon carbide carrier.

2224.9mL of AgNO₃Uniformly mixing and stirring an aqueous solution (0.01M) and 17.6g of modified silicon carbide, adding 250mL of 0.1M lysine, stirring for 1h, then adding 130mL of 0.1M sodium borohydride aqueous solution, stirring for 0.5h, and finally adding 130mL of 0.1M HCl to keep the pH value of the solution between 9 and 10; then continuously stirring for 24 hours at room temperature, centrifuging, washing and drying to obtain Ag/CeO with the load of 12 wt%₂-B-SiC catalyst, wherein the silver particles have an average particle size of about 15 nm.

5g of the catalyst is filled into a fixed bed reactor, and the volume of raw material gas comprises 25 percent of ethylene, 8 percent of oxygen and the balance of nitrogen; the space velocity is 5000h^-1The reaction pressure is 2MPa, and the reaction temperature is 190 ℃. The gas chromatography quantitative detection of the reactor outlet gas and the feed gas shows that the ethylene conversion rate is 7 percent and the selectivity of the ethylene oxide is 884 percent.

Example four

In the preparation process of the silicon carbide precursor, adding a proper amount of ammonium phosphate to ensure that the molar ratio of P/Si is 0.5, and preparing a P-doped silicon carbide carrier (P-SiC); then, taking zirconium oxychloride as a precursor to modify ZrO on the surface of the P-SiC₂(ZrO₂1 percent of P-SiC mass fraction) to obtain the modified silicon carbide carrier.

927mL of AgNO₃Uniformly mixing and stirring an aqueous solution (0.01mol/L) and 19g of silicon carbide, adding 150mL of 0.1M lysine, stirring for 1h, then adding 50mL of 0.1M sodium borohydride aqueous solution, stirring for 0.5h, and finally adding 50mL of 0.1M HCl to keep the pH of the solution between 9 and 10; then continuously stirring for 24 hours at room temperature, centrifuging, washing and drying to obtain Ag/ZrO with the load of 5 wt%₂-P-SiC catalyst, in which the silver particles have an average particle size of about 15 nm.

3g of the catalyst is filled into a fixed bed reactor, and the volume of raw material gas comprises 26 percent of ethylene, 8 percent of oxygen and the balance of nitrogen; the space velocity is 4000h^-1The reaction pressure is 2.5MPa, and the reaction temperature is 200 ℃. The gas chromatography quantitative detection of the outlet gas and the feed gas of the reactor shows that the ethylene conversion rate is 6.3 percent and the selectivity of the ethylene oxide is 87.4 percent.

After the catalyst is used for 800 hours, the conversion rate of ethylene is 5.9 percent, and the selectivity of ethylene oxide is 80 percent.

EXAMPLE five

In the preparation process of the silicon carbide precursor, a proper amount of boric acid is added to ensure that the molar ratio of B/Si is 0.3, and the B-doped silicon carbide carrier (B-SiC) is prepared. Then cerium nitrate and aluminum nitrate are taken as precursors to modify CeO on the surface of B-SiC₂And Al₂O₃(the content of the oxide is 3 percent of the mass fraction of the B-SiC) to obtain the modified silicon carbide carrier.

1483mL of AgNO₃Uniformly mixing and stirring an aqueous solution (0.01mol/L) and 18.4g of silicon carbide, adding 180mL of 0.1M lysine, stirring for 1h, then adding 70mL of 0.1M sodium borohydride aqueous solution, stirring for 0.5h, and finally adding 70mL of 0.1M HCl to keep the pH value of the solution between 9 and 10; then continuously stirring for 24 hours at room temperature, centrifuging, washing and drying to obtain Ag/CeO with the load of 8 wt%₂-Al₂O₃-B-SiC catalyst, wherein the silver particles have an average particle size of about 15 nm.

6g of the catalyst is filled into a fixed bed reactor, and the volume composition of raw material gas is 28 percent of ethylene and oxygen9 percent of nitrogen and the balance of nitrogen; the space velocity is 8000h^-1The reaction pressure is 2MPa, and the reaction temperature is 210 ℃. The gas chromatography quantitative detection of the outlet gas and the feed gas of the reactor shows that the ethylene conversion rate is 7.2 percent and the selectivity of the ethylene oxide is 84.0 percent.

After the catalyst is used for 500 hours, the conversion rate of ethylene is 6.8 percent, and the selectivity of ethylene oxide is 80 percent.

EXAMPLE six

In the preparation process of the silicon carbide precursor, adding a proper amount of boric acid to enable the molar ratio of B/Si to be 0.25, and preparing a B-doped silicon carbide carrier (B-SiC); then cerium nitrate and zirconium nitrate are used as precursors to modify CeO on the surface of B-SiC₂And ZrO₂(the content of the oxide is 4 percent of the mass fraction of the B-SiC) to obtain the modified silicon carbide carrier.

742mL of AgNO₃Uniformly mixing and stirring an aqueous solution (0.01M) and 19.2g of silicon carbide, adding 100mL of 0.1M lysine, stirring for 2h, then adding 50mL of 0.1M sodium borohydride aqueous solution, stirring for 1h, and finally adding 30mL of 0.1M HCl to keep the pH of the solution between 9 and 10; then continuously stirring for 48 hours at room temperature, centrifuging, washing and drying to obtain Ag/CeO with the load of 4 wt%₂-ZrO₂-B-SiC catalyst, wherein the silver particles have an average particle size of about 10 nm.

10g of the catalyst is filled into a fixed bed reactor, and the volume of raw material gas comprises 28 percent of ethylene, 8 percent of oxygen and the balance of nitrogen; space velocity of 7000h^-1The reaction pressure is 2.3MPa, and the reaction temperature is 200 ℃. The gas chromatography quantitative detection of the outlet gas and the feed gas of the reactor shows that the ethylene conversion rate is 6.5 percent and the selectivity of the ethylene oxide is 88 percent.

After the catalyst is used for 200 hours, the conversion rate of ethylene is 6.1 percent, and the selectivity of ethylene oxide is 80 percent.

EXAMPLE seven

Adding a proper amount of phosphoric acid in the preparation process of the silicon carbide precursor to enable the molar ratio of P/Si to be 0.19, and preparing a P-doped silicon carbide carrier (P-SiC); then, cerium nitrate and zirconium nitrate are used as precursors to modify CeO on the surface of P-SiC₂And ZrO₂(the oxide content is B-SiC by mass)Fraction 10%) to yield a modified silicon carbide support.

5562mL of AgNO₃Uniformly mixing and stirring an aqueous solution (0.0mol/L) and 34g of silicon carbide, adding 600mL of 0.1M lysine, stirring for 1h, then adding 350mL of 0.1M sodium borohydride aqueous solution, stirring for 2h, and finally adding 350mL of 0.1M HCl to keep the pH of the solution between 9 and 10; then continuously stirring for 48 hours at room temperature, centrifuging, washing and drying to obtain Ag/CeO with 15 wt% of loading capacity₂-ZrO₂-B-SiC catalyst, wherein the silver particles have an average particle size of about 25 nm.

Filling 30g of the catalyst into a fixed bed reactor, wherein the volume of raw material gas comprises 30% of ethylene, 9% of oxygen and the balance of nitrogen; space velocity of 10000h^-1The reaction pressure is 1.5MPa, and the reaction temperature is 180 ℃. The gas chromatography quantitative detection of the outlet gas and the feed gas of the reactor shows that the ethylene conversion rate is 6.8 percent and the selectivity of the ethylene oxide is 85.3 percent.

After 800h of use, the catalyst had an ethylene conversion of 6.5% and an ethylene oxide selectivity of 82%.

According to the invention, P, B is doped in the silicon carbide carrier to increase the thermal conductivity of the carrier, accelerate the heat removal rate of the catalyst and effectively improve the selectivity of ethylene epoxidation to ethylene oxide; the oxygen vacancy on the surface of the catalyst is increased by modifying the oxide on the surface of the catalyst, so that the loaded silver nano particles are effectively stabilized, and the stability of the catalyst is improved; the catalyst prepared by optimizing the properties of the silicon carbide carrier and the metal loading process has the advantages of uniform metal dispersion, good thermal conductivity and good stability; the preparation process of the catalyst has universality and simplicity and is easy for industrial synthesis; the prepared silicon carbide-based silver nano-catalyst has higher activity, selectivity and cycling stability for preparing ethylene oxide by ethylene epoxidation.

In light of the foregoing description of the preferred embodiment of the present invention, many modifications and variations will be apparent to those skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.