WO2022134675A1

WO2022134675A1 - Zirconium-based gold catalyst for propylene epoxidation reaction and preparation method therefor

Info

Publication number: WO2022134675A1
Application number: PCT/CN2021/118910
Authority: WO
Inventors: 祁彩霞; 郑玉华; 苏慧娟; 孙逊; 孙立波
Original assignee: 烟台大学
Priority date: 2020-12-24
Filing date: 2021-09-17
Publication date: 2022-06-30
Also published as: CN112495359A

Abstract

Disclosed are a zirconium-based gold catalyst for a propylene epoxidation reaction and a preparation method therefor. The catalyst uses zirconium-based materials as the support, including ZrO₂and a zirconium silicon molecular sieve. After obtaining a zirconium-containing precursor by precipitation, ZrO₂ supports of different crystalline phases are obtained by means of changing the calcination temperature. The zirconium silicon molecular sieve is obtained by using Tween as a template and subjecting zirconium n-butoxide and tetraethyl orthosilicate to hydrolysis, crystallization, and calcination. The gold-supporting mode is selected from an equal volume impregnation or deposition-precipitation process. The catalyst is used for the propylene epoxidation reaction, can ensure high selectivity of propylene oxide at low temperatures, and avoids complete oxidation of propylene. After appropriate addition of auxiliaries, the catalyst is desirable to increase the conversion rate of propylene, and at the same time, improves the high temperature selectivity of propylene oxide. Thus, the present invention expands the type of catalyst support used for the reaction, having a broader application prospect.

Description

Zirconium-based catalyst for propylene epoxidation reaction and preparation method thereof

technical field

The invention relates to a gold catalyst and a preparation method thereof, in particular to a supported nano-gold catalyst used for propylene epoxidation to synthesize propylene oxide and a preparation method thereof.

Background technique

Propylene oxide (PO) is the third largest propylene derivative after polypropylene and acrylonitrile, and is mainly used in the production of polyether, propylene glycol, etc. It is the main raw material of the fourth-generation detergent, non-ionic surfactant, oil field demulsifier, pesticide emulsifier, etc. It is also an important raw material for fine chemical products. Nearly 100 kinds of downstream products have been produced.

At present, the production methods of propylene oxide mainly include chlorohydrin method and co-oxidation method. Both methods account for 99% of the world's total production capacity. The chlorohydrin process is divided into two steps. In the first step, chlorine and propylene are introduced into the water, and the chlorine and propylene undergo a chlorohydrin reaction to generate the intermediate chloropropanol. In the second step, chloropropanol is saponified under the action of lye to obtain propylene oxide. This method is the earliest method used to produce propylene oxide. The technology is relatively mature, the operation load is flexible, the raw material purity requirements are not high, and the construction investment is low, but the atomic utilization rate of the chlorohydrin method is low (w=27.35%), and In the reaction process, a large amount of chlorine gas is required, which seriously corrodes the equipment, and the discharged waste water and slag bring serious harm to the environment. The co-oxidation method, also known as the Haakon method, overcomes the problems of serious pollution and equipment corrosion in the chlorohydrin method, but has the disadvantages of high propylene purity requirements, long process flow, many types of raw materials, many co-products, and high requirements for equipment materials. The direct gas-phase catalytic oxidation of propylene to propylene oxide has always been the most ideal way, but it is also considered to be one of the most challenging subjects.

Since Haruta et al. found that gold nanoparticles supported on anatase _TiO2 can selectively oxidize propylene to PO in _H2 and _O2 atmospheres (Res Chem Intermed, 1998, 24, 329-336), more and more His work focuses on the development of gold catalysts for this type of reaction. In addition to clarifying the effects of gold particle size, gold nanoparticle loading site and loading amount on catalytic activity in this reaction, the influence of carrier acidity, carrier surface pore size distribution, hydrophilicity and hydrophobicity, and additives have also become research hotspots. Up to now, the supports of such catalysts are mainly concentrated in titanium-based materials, such as titanium dioxide with different crystal phases and porous silica materials containing titanium.

The catalysts prepared with gold nanoparticles supported on anatase _TiO2 showed high selectivity to propylene oxide, while the catalysts prepared on amorphous and rutile _TiO2 could not show this performance (Journal of Catalysis , 1998, 178: 566-575; Research on chemical intermediates, 1998, 24: 329-336). Qi et al. found that isolated tetrahedral TiO ₂ has an important effect on the activity and selectivity of PO (Applied Catalysis A: General, 2001, 218: 81-89.).

Uphade et al. found that the performance of the catalyst prepared by gold supported on the two-dimensional structure Ti-MCM-41 was inferior to the catalyst prepared by the gold supported on the three-dimensional structure Ti-MCM-48 (Journal of Catalysis, 2002, 209(2): 331-340 .) . Delgass et al. found that the morphology of TS-1 is very important for the epoxidation activity of Au catalysts (Catalysis today, 2007, 123(1): 50-58). The gold catalyst prepared by using TS-1 with poor crystallinity as the carrier has higher catalytic activity, indicating that a certain defect in the carrier structure plays a key role in the activity of the Au/TS-1 catalyst. The research team also found that the preparation attaches Cs to the catalyst. In the pores of the carrier, gold has a strong interaction with cesium, so that more gold nanoparticles are attached to the pores of the catalyst, which improves the activity of the catalyst. Huang's group recently reported the research on Ti-MCM-41, TS-1 and Ti-MCM-41 gold-supported catalysts. By studying the effect of pore structure and propylene adsorption capacity on the catalytic activity, the microstructure of the three types of supports was elucidated in detail. Pore, mesopore distribution, Ti coordination defects and the correlation between propylene conversion and selectivity to PO formation.

It can be seen from the literature survey that propylene epoxidation under _H2 and _O2 atmosphere is the research trend of this reaction. However, the current work focuses on the preparation and modification of titanium-based material-supported gold catalysts, and there are only a few reports of non-titanium-supported catalysts for this reaction, such as Su Weiguang et al. reported that ZnO-CuOx/ _SiO2 was used for this reaction, However, at a high temperature of 260 ^o C, the conversion rate of propylene is less than 1%, and the selectivity of PO of the target product is less than 20%. Even after modification with Na, the conversion rate of propylene can be improved to 2%, but the selectivity of PO is still not obvious. improvement, and the catalyst preparation method is complicated.

technical problem

The technical problem to be solved by the present invention is to provide a zirconium-based catalyst for propylene epoxidation reaction and a preparation method thereof, aiming at expanding the catalyst types for propylene epoxidation reaction and further improving the conversion rate of propylene.

technical solutions

A zirconium-based catalyst for propylene epoxidation is characterized in that it is a nano-gold catalyst supported by zirconium-silicon molecular sieve as a zirconium-based material or a nano-gold catalyst supported by ZrO ₂ as a zirconium-based material.

The gold loadings ranged from 0.05 wt% to 3 wt%.

The preparation method of zirconium-silicon molecular sieve is as follows: dissolving the template agent Tween 20 in water, adding 10-50wt% tetrapropylammonium hydroxide (TPAOH), adding tetraethyl orthosilicate dropwise under stirring, and continuing to stir for 0.5-24 wt% h; then add zirconium-containing raw materials dropwise to the solution, stir for 0.5-24 h, crystallize at 160-180 ^o C for 10-80 h, and finally obtain zirconium-silicon molecular sieve by calcining at 400-650 ^o C.

The zirconium-containing raw material is tetrabutyl zirconate or zirconium ethoxide dissolved in isopropanol.

The amount of added tetraethyl orthosilicate and zirconium-containing raw material satisfies n(Si) : n(Zr) = 10~90; the molar ratio of (zirconium + silicon) to TPAOH is 1~5; the molar ratio of (zirconium + silicon) to Tween 20 is 50~150.

The preparation method of ZrO ₂ is as follows: dissolving the template agent and the soluble zirconium salt in water, and adding the precipitant dropwise with stirring; after the precipitation is complete, continue stirring for 0.5-24 h, and then stand for 0.5-24 h; The precipitate was washed by centrifugation, dried at 60-100 ℃, and then calcined to obtain ZrO ₂ .

The template is selected from one of cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG); the soluble zirconium salt is Zr(NO ₃ ) ₃ solution, ZrOCl ₂ One of the solution and ZrCl ₄ solution (mass concentration 0.05%~2%), the molar ratio of the template agent to the amount of soluble zirconium salt is 0.1~10; the precipitating agent is ammonia water, KOH solution, NaOH solution, K ₂ CO ₃ solution and one of Na ₂ CO ₃ solutions, wherein the mass concentration of ammonia water is 5%~25%, and the concentration of the last four solutions is 0.5~5.0 mol/L.

The calcination temperature is 400~1200 ^o C, and the calcination time is 1~10 h.

The first method for preparing the catalyst for propylene epoxidation is characterized in that the catalyst is prepared according to the following steps:

(1) Adjust the pH of the HAuCl ₄ solution to 6~10 with alkaline solution, add deionized water to make the total volume of the solution equal to the maximum water absorption of the catalyst carrier, and then impregnate the catalyst carrier for 1~8 h after adding it;

(2), centrifugal washing, drying at 60~120 ^o C to obtain the catalyst precursor;

(3) The catalyst precursor is slowly heated up to 100-500 ^o C under a hydrogen atmosphere and maintained for 0.5-4 h to obtain the desired catalyst.

The second method for preparing the catalyst for propylene epoxidation is characterized in that the catalyst is prepared according to the following steps:

(1) Take the HAuCl ₄ solution, add an appropriate amount of deionized water, add the catalyst carrier and stir for 0.5~1h;

(2) Adjust the pH value to 6~10 with lye, and continue stirring for 2~5 h;

(3), centrifugal washing, drying at 60~120 ^o C to obtain the catalyst precursor;

beneficial effect

The invention aims to expand the range of catalysts used in the propylene epoxidation reaction and obtain higher PO selectivity, select two types of materials containing zirconium, covering oxides and porous materials, and obtain two types of different gold loading methods. Zirconium-based catalysts suitable for propylene epoxidation. Among them, zirconium-containing molecular sieve adopts a new preparation method, which is easy to operate; zirconium dioxide with different crystal phases is prepared by changing the calcination temperature of the same precursor. Both types of carriers are environmentally friendly and the process is simple. If the conversion rate of propylene is improved through continuous improvement in the later stage, it will have a very broad market application prospect.

The present invention includes two types of zirconium-based supported gold catalysts for propylene epoxidation. Zirconium _- containing molecular sieves are prepared by hydrothermal crystallization, and ZrO2 with different crystal phases can be obtained only by calcining the same precursor. The gold nanoparticles are supported on the above two types of carriers by two mature preparation methods, and then a gold catalyst is prepared, which is used to catalyze the epoxidation of propylene to generate propylene oxide. After testing, the selectivity of propylene oxide at low temperature (<150 ^o C) can be maintained above 80%, and the conversion rate is about 0.1%. This result confirms that propylene oxide can still be obtained by expanding the support types of the gold catalyst used in this reaction, and the high selectivity at low temperature can be maintained. At the same time, this type of catalyst can effectively inhibit the complete oxidation of propylene, and it can be expected to achieve high conversion while keeping the selectivity of propylene oxide unchanged after selecting appropriate additives and gold loading conditions.

Description of drawings

Fig. 1 is the XRD spectrum of the zirconium-containing molecular sieve prepared in Example 1;

Fig. ₂ is the XRD spectrum of ZrO prepared in Example 4 and Example 5;

Fig. ₃ is the TEM image of catalyst 0.5%Au/m-ZrO prepared in Example 5;

4 is a particle size distribution diagram of the gold nanoparticles of the catalyst 0.5% Au/m-ZrO ₂ prepared in Example 5.

Fig. ₅ is the N adsorption _- desorption isotherms of ZrO carriers obtained at different calcination temperatures;

Embodiments of the present invention

The present invention will be further described below in conjunction with the embodiments.

Example 1 : 1.0% Au/Zr-MFI-35 catalyst was prepared by DP method, and the preparation steps were as follows:

Weigh 2 g of Tween 20 (Tween 20, CP) and dissolve it in deionized water, add an appropriate amount of tetrapropylammonium hydroxide (TPAOH, 25%wt%) under stirring conditions, and measure 38.6 mL of ethyl orthosilicate (TEOS, AR) was slowly added to the above solution, stirred vigorously for 1 h, 2.3 g of tetrabutyl zirconate was dissolved in 20 mL of isopropanol (IPA), added dropwise to the above solution, and vigorously stirred for 1 h. Crystallize under normal pressure at 170 ^o C for 18 h, cooled to room temperature, centrifugally washed with deionized water and ethanol for several times, vacuum dried at 60 ^o C, and calcined at 550 ^o C, and the obtained molecular sieve is denoted as Zr-MFI-35 carrier.

Add 0.02 g HAuCl ₄ ^. 4H ₂ O to 5 mL of distilled water, add 1 g of the Zr-MFI-35 carrier prepared above, stir for 30 min, adjust the pH of the solution to 9 with Na ₂ CO ₃ solution, and continue stirring for 5 h ; centrifuged and washed with distilled water once (5000 r/min), the samples were dried in a 60 ℃ oven, and reduced at 300 ℃ for 1 h under a H ₂ atmosphere to obtain 1.0% Au/Zr-MFI-35(DP) catalyst .

It can be seen from the XRD pattern in Figure 1 that strong characteristic diffraction peaks appear at 2θ=7.8°, 8.8°, 23.1°, 23.8° and 24.3°, indicating that the synthesized molecular sieves have MFI topology and good crystallinity. . Compared with the all-silicon molecular sieve, the diffraction peaks of the synthesized Zr-MFI molecular sieve samples at 2θ=24.3° and 29.3° are both single peaks, which is due to the change of crystal symmetry.

0.15 g of the above catalyst was added to the fixed-bed micro-reaction device at atmospheric pressure, the reaction gas composition was C ₃ H ₆ /H ₂ /O ₂ /Ar= 1/1/1/7 (volume ratio), and the space velocity was 8000 mL·h ^-1 ·g ^-1 _cat , the reaction temperature is RT~340 ^o C. The catalytic reaction results are shown in Table 1.

Example 2 : 0.5% Au/Zr-MFI-35 catalyst was prepared by IMP method, and the preparation steps were as follows:

Calculate the gold solution, KOH solution and the amount of distilled water to be added for the theoretical gold loading of 1.0%. Measure a certain amount of HAuCl ₄ ·3H ₂ O solution into a clean small beaker, add an appropriate amount of distilled water, use KOH solution to adjust the pH of the gold solution to 9, add Zr-MFI-35 carrier, shake evenly, stand for 4 h, distilled water After washing, the samples were dried in an oven at 60 ^o C and reduced in H ₂ atmosphere at 300 ^o C for 1 h to obtain 1.0% Au/Zr-MFI-35(IMP) catalyst.

0.15 g of the above catalyst was added to the fixed-bed micro-reaction device at atmospheric pressure, the reaction gas composition was C ₃ H ₆ /H ₂ /O ₂ /Ar= 1/1/1/7 (volume ratio), and the space velocity was 8000 mL·h ^-1 ·g ^-1 _cat , the reaction temperature is RT~340 ^o C. The catalytic reaction results are shown in Table 2.

Example 3 : 1.0% Au/Zr-MFI-60 catalyst was prepared by IMP method, and the preparation steps were as follows:

Weigh 1.5 g of Tween 20 (Tween 20, CP) and dissolve it in deionized water, add 42.5 g of tetrapropylammonium hydroxide (TPAOH, 25% wt%) into the flask, and weigh 38.6 mL of ethyl orthosilicate ( TEOS, AR) was slowly added to the above solution, stirred vigorously for 1 h, and 0.8869 g of zirconium ethoxide was added dropwise to the above solution slowly and uniformly, and stirred vigorously for 1 h. Crystallize at 170 ^o C for 18 h, cool to room temperature, wash with deionized water and ethanol for several times, vacuum dry at 60 ^o C, and calcine at 550 ^o C for 3 h to obtain Zr with n(Si/Zr)=60 -MFI-60 carrier.

Take 0.02 g HAuCl ₄ ^. 4H ₂ O and add it to 0.12 mL of distilled water, adjust the pH to 9 with KOH solution, then add the ZS(60) carrier prepared above, shake evenly, and let stand for 4 h; wash with distilled water once, The samples were dried in a 60 ^o C oven, and reduced at 300 ^o C for 1 h in a H ₂ atmosphere to obtain a 1.0% Au/Zr-MFI-60(IMP) catalyst.

0.15 g of the above catalyst was added to the fixed-bed micro-reaction device at atmospheric pressure, the reaction gas composition was C ₃ H ₆ /H ₂ /O ₂ /Ar = 1/1/1/7 (volume ratio), and the space velocity was 4000 mL·h ^{− 1} ·g ^-1 _cat , the reaction temperature is RT~340 ^o C. The catalytic reaction results are shown in Table 3.

Example 4 : 0.2%Au/t-ZrO ₂ catalyst was prepared by IMP method, and the preparation steps were as follows:

Weigh 8.58 g Zr(NO ₃ ) ₃ ^. 5H ₂ O into 100 mL of distilled water, heat it in a 60 ^o C water bath, add 2.7 g CTAB under stirring, and slowly add 1 mol/L KOH to complete the precipitation after stirring for 30 min. Continue to stir for 30 min, centrifuge, wash, dry at 60 ^o C, and bake in air at 400 ^o C for 2 h. Through XRD test (Fig. 2), the prepared support is tetragonal ZrO ₂ (t-ZrO ₂ ).

Take 0.004 g HAuCl ₄ solution, add 0.8 mL deionized water, adjust pH = 6 with KOH solution, then add 1 g t-ZrO ₂ carrier, mix by ultrasonic, let stand for 4 h at room temperature, centrifuge, wash, and dry at 60 ^oC . The N adsorption _- desorption isotherms of the obtained ZrO supports (Fig. ₅ ), it can be seen that the samples show obvious type IV isotherms and H1 hysteresis loops, indicating the existence of a large number of columnar channels.

0.15 g of the above catalyst was added to the fixed-bed micro-reaction device at atmospheric pressure, the reaction gas composition was C ₃ H ₆ /H ₂ /O ₂ /Ar= 1/1/1/7 (volume ratio), and the space velocity was 8000 mL·h ^-1 ·g ^-1 _cat , the reaction temperature is RT~340 ^o C. The catalytic reaction results are shown in Table 4.

Example 5 : 0.5%Au/m-ZrO ₂ catalyst was prepared by IMP method, and the preparation steps were as follows:

Weigh 3.56 g of ZrOCl ₂ ^. 8H ₂ O into 100 mL of distilled water, heat it in a 60 ^o C water bath, add 2.7 g of CTAB under stirring, slowly add 1 mol/L KOH to complete the precipitation after stirring for 30 min, and continue stirring for 30 min. Centrifuge, wash, dry at 60 ^o C, and bake in air at 1000 ^o C for 2 h. Through XRD test (Fig. 2), the prepared carrier is monoclinic ZrO ₂ (m-ZrO ₂ ).

Take 0.01 g HAuCl ₄ solution, add 0.8 mL deionized water, adjust pH = 6 with KOH solution, then add 1 g m-ZrO ₂ carrier, mix by ultrasonic, let stand for 4 h at room temperature, centrifuge, wash, and dry at 60 ^oC . The structure of the obtained sample is shown in the TEM image in Figure 3. The carrier is micron-sized ZrO ₂ particles. The gold nanoparticles are uniformly dispersed on the surface of the carrier, and the particle size of the gold nanoparticles is concentrated at 2-6 nm (Figure 5). The N adsorption _- desorption isotherm of the obtained ZrO carrier (Fig. ₅ ), it can be seen that the isotherm of the sample does not belong to a clear type, indicating that the sample belongs to the accumulation of irregular particles, which is consistent with the results of transmission electron microscopy.

0.15 g of the above catalyst was added to the fixed-bed micro-reaction device at atmospheric pressure, the reaction gas composition was C ₃ H ₆ /H ₂ /O ₂ /Ar= 1/1/1/7 (volume ratio), and the space velocity was 8000 mL·h ^{− 1} ·g ^-1 _cat , the reaction temperature is RT~340 ^o C. The catalytic reaction results are shown in Table 5.

The zirconium-silicon molecular sieve prepared by the invention is a molecular sieve with an MFI structure, and its XRD spectrum peak is consistent with that of the TS-1 molecular sieve.

The ZrO ₂ carrier prepared by the invention can realize the transformation from the tetragonal phase (t-ZrO 2 ) to the monoclinic phase (m-ZrO ₂ ) according to the different calcination temperature.

Claims

A zirconium-based catalyst for propylene epoxidation is characterized in that it is a nano-gold catalyst supported by zirconium-silicon molecular sieve as a zirconium-based material or a nano-gold catalyst supported by ZrO 2 as a zirconium-based material.
The zirconium-based catalyst for propylene epoxidation according to claim 1, wherein the gold loading is 0.05 wt% to 3 wt%.
The zirconium-based catalyst for propylene epoxidation according to claim 1 or 2, wherein the preparation method of zirconium-silicon molecular sieve is as follows: the template agent Tween 20 is dissolved in water, and 10～50wt% tetrapropyl hydroxide is added. ammonium (TPAOH), add tetraethyl orthosilicate dropwise with stirring, continue stirring for 0.5~24 h; then add zirconium-containing raw materials dropwise to the solution, stir for 0.5~24 h, and crystallize at 160-180 o C for 10~80 h h, and finally calcined at 400-650 o C to obtain zirconium-silicon molecular sieves.
The zirconium-based catalyst for propylene epoxidation according to claim 3 is characterized in that the zirconium-containing raw material is tetrabutyl zirconate or zirconium ethoxide dissolved in isopropanol.
According to the zirconium fund catalyst for propylene epoxidation reaction according to claim 3, it is characterized in that the amount of added tetraethyl orthosilicate and zirconium-containing raw material satisfies n(Si): n(Zr)=10～90; The molar ratio of (zirconium + silicon) to TPAOH is 1~5; the molar ratio of (zirconium + silicon) to Tween 20 is 50~150.
According to the zirconium-based catalyst for propylene epoxidation according to claim 1 or 2 , it is characterized in that the preparation method of described ZrO is as follows: the template agent and the soluble zirconium salt are dissolved in water, and the precipitant is added dropwise with stirring; After the precipitation is complete, continue stirring for 0.5-24 h, and then stand for 0.5-24 h; then the precipitate is washed by centrifugation, dried at 60-100 ℃, and then calcined to obtain ZrO 2 .
The zirconium-based catalyst for propylene epoxidation according to claim 6, wherein the template is selected from cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG). ); soluble zirconium salt is one of Zr(NO 3 ) 3 solution, ZrOCl 2 solution and ZrCl 4 solution (mass concentration 0.05%~2%), and the molar ratio of template agent to soluble zirconium salt dosage is 0.1~10; the precipitating agent selects one of ammonia water, KOH solution, NaOH solution, K 2 CO 3 solution and Na 2 CO 3 solution, wherein the mass concentration of ammonia water is 5% to 25%, and the concentrations of the latter four solutions are 0.5~5.0 mol/L.
The zirconium-based catalyst for propylene epoxidation reaction according to claim 6, characterized in that the calcination temperature is selected from 400 to 1200 ° C, and the calcination time is 1 to 10 h.
The preparation method of the catalyst for propylene epoxidation according to any one of claims 1 to 8, wherein the catalyst is prepared according to the following steps:

(1) Adjust the pH of the HAuCl 4 solution to 6~10 with alkaline solution, add deionized water to make the total volume of the solution equal to the maximum water absorption of the catalyst carrier, and then impregnate the catalyst carrier for 1~8 h after adding it;

(2), centrifugal washing, drying at 60~120 o C to obtain the catalyst precursor;

(3) The catalyst precursor is slowly heated up to 100-500 o C under a hydrogen atmosphere and maintained for 0.5-4 h to obtain the desired catalyst.
The preparation method of the catalyst for propylene epoxidation according to any one of claims 1 to 8, wherein the catalyst is prepared according to the following steps:

(1) Take the HAuCl 4 solution, add an appropriate amount of deionized water, add the catalyst carrier and stir for 0.5~1h;

(2) Adjust the pH value to 6~10 with lye, and continue stirring for 2~5 h;

(3), centrifugal washing, drying at 60~120 o C to obtain the catalyst precursor;

(3) The catalyst precursor is slowly heated up to 100-500 o C under a hydrogen atmosphere and maintained for 0.5-4 h to obtain the desired catalyst.