Preparation method and application of zirconium dioxide catalyst with different crystal phases

Abstract

The invention relates to the field of catalyst preparation and application thereof, in particular to a preparation method and application of zirconium dioxide catalysts with different crystal phases, a zirconium precursor and P123 are dissolved in deionized water, then ammonia water is added, and then the mixture is subjected to oil bath, product filtering and washing; and drying and then roasting to obtain tetragonal phase ZrO2. The preparation method comprises the following steps: dissolving a zirconium precursor and yttrium nitrate in deionized water, adding citric acid, adding ammonia water, carrying out oil bath, drying, and roasting to obtain cubic phase ZrO2; the preparation method comprises the following steps: dissolving a zirconium precursor in deionized water, adding ammonium fluoride, stirring, carrying out a hydrothermal reaction, cooling, carrying out centrifugal washing, drying, and roasting in a muffle to obtain the monoclinic phase ZrO2. Compared with a traditional metal supported catalyst, the problems of metal sintering, agglomeration, loss and the like are avoided. Therefore, the prepared ZrO2 catalyst with different crystal phases is an effective catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalyst preparation and its application, in particular to a preparation method and application of a zirconium dioxide catalyst with different crystal phases. BACKGROUND

[0002] With the rapid development of the global economy, the demand for energy is growing explosively. The reserves of oil, coal, natural gas and other non-renewable resources are limited and face an increasingly severe depletion crisis. In the face of the energy crisis, countries around the world have recognized the urgency of energy transformation and are actively seeking renewable, clean and sustainable energy alternatives to achieve stable energy supply and sustainable development of the environment. Biomass is a widely available and renewable resource, mainly including plants, animals, microorganisms and their waste, etc. Compared with traditional fossil energy, biomass has the advantages of wide source, strong renewability, environmental friendliness, etc.

[0003] Gamma-valerolactone (GVL) is a compound with unique chemical structure and excellent performance, which has low toxicity, low odor, high boiling point, good solubility and biodegradability, etc. It has wide application prospects in many fields, such as being used as an organic solvent in the paint, ink, perfume and other industries; being used as a chemical intermediate to synthesize fine chemicals such as drugs, perfumes and pesticides; and being used as a plasticizer for bio-based plastics, etc., and its market demand is increasing year by year. There are two ways to convert lignocellulosic biomass into GVL. One is to use cellulose as raw material. First, hydrolysis generates glucose, which is then isomerized to fructose, and fructose is further dehydrated to 5-hydroxymethylfurfural, which is then converted to levulinic acid and its esters, and finally synthesized into GVL through hydrogenation-cyclization tandem reaction. However, if cellulose or hemicellulose is used as raw material to directly synthesize GVL, there are great challenges, mainly due to the numerous reaction steps and extremely harsh process conditions. At present, a large number of literatures have reported the process of preparing GVL from biomass platform molecules through two-step method: first hydrolysis to levulinic acid or its ester, and then conversion to GVL. However, this process generally has limited GVL yield and poor reaction selectivity. In summary, although there are many routes to synthesize GVL, due to the harsh reaction conditions, complex reaction process and poor selectivity, etc. Therefore, it is urgent to develop environmentally friendly, efficient and low-pollution GVL synthesis technology.

[0004] In recent years, the reaction of preparing gamma-valerolactone by catalytic transfer hydrogenation of ethyl levulinate (EL) has attracted extensive attention. EL is a key biomass-derived compound, which has abundant chemical functional groups in the molecule and can be obtained from biomass through pyrolysis, hydrolysis or esterification, etc. Therefore, it is quite attractive. Catalytic transfer hydrogenation (CTH) is considered as an efficient and green approach. This process meets the economic and environmental development route. In addition, the traditional metal-supported catalysts have problems such as easy sintering, agglomeration and loss of metal, therefore, it is crucial to develop non-supported catalysts. SUMMARY

[0005] In order to solve the problems of easy sintering, agglomeration and loss of metal of the traditional metal-supported catalysts, the application provides a preparation method and application of a different crystal phase zirconium dioxide catalyst.

[0006] The application is implemented by the following technical scheme: In a first aspect, a preparation method of a different crystal phase zirconium dioxide catalyst comprises the following steps: (1) Preparation of tetragonal ZrO2: Dissolve the precursor of zirconium and P123 in deionized water, then adjust the pH to 11 with ammonia water, then oil bath at 88 ℃ for 40 h, filter the product and wash with water and acetone; dry, then calcine at 700 ℃ in a muffle furnace for 4 h to obtain tetragonal ZrO2; (2) Preparation of cubic ZrO2: Dissolve the precursor of zirconium and yttrium nitrate in deionized water, add citric acid under stirring, the solution becomes turbid quickly, then adjust the pH to 7 with ammonia water, then oil bath at 110 ℃ for 24 h. Dry overnight in an oven at 110 ℃, then calcine at 800 ℃ in a muffle furnace for 4 h to obtain cubic ZrO2; (3) Preparation of monoclinic ZrO2: Dissolve the precursor of zirconium in deionized water, then add ammonium fluoride, stir at room temperature for 1 h, then transfer the solution to a stainless steel autoclave with a polytetrafluoroethylene liner, hydrothermal at 105 ℃ for 24 h, wash by centrifugation after cooling; dry overnight in an oven at 105 ℃, then calcine at 550 ℃ in a muffle furnace for 5 h to obtain monoclinic ZrO2.

[0007] As a further improvement of the technical scheme of the application, the precursor of zirconium is one of zirconium oxynitrate and zirconium nitrate.

[0008] As a further improvement of the technical scheme of the application, n （P123 / Zr） =0.03.

[0009] As a further improvement of the technical scheme of the present application, n （Y / Zr） =0.18.

[0010] As a further improvement of the technical scheme of the present application, n （F / Zr） =1.5.

[0011] In a second aspect, the method is used to prepare the different crystal phase zirconium dioxide catalyst.

[0012] In a third aspect, the different crystal phase zirconium dioxide catalyst is used in the reaction of preparing gamma-valerolactone by hydrogenation of ethyl levulinate.

[0013] Preferably, the hydrogenation reaction conditions of ethyl levulinate are as follows: the reaction temperature is 170℃, the reaction pressure is 0.8 MPa of nitrogen, and the reaction time is 7 h.

[0014] The present application provides a preparation method and application of a different crystal phase zirconium dioxide catalyst, which has the following advantages compared with the prior art: The different crystal phase ZrO2 catalysts prepared by the reflux and hydrothermal methods respectively provided by the present application directly determine the properties and quantity of the surface active sites. The different crystal phase ZrO2 has different surface areas and acid site contents, and the selectivity of GVL can be improved by adjusting the crystal phase. Compared with the traditional metal-supported catalysts, the present application avoids the problems of metal sintering, agglomeration, and loss. Therefore, the prepared different crystal phase ZrO2 catalyst is an effective catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0017] Figure 1 The XRD and Raman spectra of the three different crystal phase ZrO2 catalysts are obtained. It can be seen from the XRD graph that the XRD spectra of the three different crystal phase ZrO2 catalysts correspond to the standard PDF card. Since the peak positions of t-ZrO2 and c-ZrO2 are close, combined with the Raman spectrum, the c-ZrO2 only shows a broad peak at 600 cm -1 , which is obviously different from t-ZrO2, indicating that the three different crystal phase ZrO2 catalysts are successfully synthesized.

[0018] Figure 2 The N2-adsorption-desorption curves of the three different crystal phase ZrO2 catalysts are obtained. The results show that t-ZrO2 has the largest specific surface area, which is about 10 times of c-ZrO2 and m-ZrO2, indicating that the synthesized t-ZrO2 has a larger specific surface area.

[0019] Figure 3 The SEM spectra of the three different crystal phase ZrO2 catalysts are obtained. The results show that t-ZrO2 has an irregular small particle aggregate structure, and c-ZrO2 has a block structure. Interestingly, m-ZrO2 has a lamellar structure with a layer thickness of about 20 nm, and the number of layers is relatively large, up to about 800 nm.

[0020] Figure 4 The TEM spectra of the three different crystal phase ZrO2 catalysts are obtained. The results show that the fringe spacings of the (112) and (101) crystal planes of t-ZrO2 are 0.183 nm and 0.292 nm, the lattice spacings of the (220) and (111) crystal planes of c-ZrO2 are 0.191 nm and 0.309 nm, and the lattice spacings of the (111) and ( ) crystal planes of m-ZrO2 are 0.286 nm and 0.316 nm. Through the control of the preparation process, pure ZrO2 of three different phases is successfully obtained.

[0021] Figure 5 The NH3-TPD spectra of the three different crystal phase ZrO2 catalysts are obtained. The desorption peaks below 200℃ in the curve correspond to the weak acid sites on the surface of the catalyst, the desorption peaks between 200-400℃ correspond to the medium-strong acid centers, and the desorption peaks above 400℃ correspond to the strong acid centers. Through curve fitting integration, five similar overlapping peaks and proportions are obtained, and the total acidity of the three catalysts is in the order of t-ZrO2 > c-ZrO2 > m-ZrO2, which may be due to the fact that t-ZrO2 has an irregular small particle aggregate structure with the smallest particle size, thereby providing the largest specific surface area and surface acid sites.

[0022] Figure 6 A process flow diagram for separating and purifying γ-valerolactone is shown. In the figure: 1 - filter; 2 - rectification tower; 3 - first condenser; 4 - first reboiler; 5 - γ-valerolactone separation tower; 6 - second condenser; 7 - ethyl levulinate rectification tower; 8 - γ-valerolactone rectification tower; 9 - second reboiler; 10 - 4-hydroxyvaleric acid ethyl ester storage tank; 11 - third condenser; 12 - γ-valerolactone storage tank; 13 - third reboiler; 14 - mixture storage tank; 15 - fourth condenser; 16 - fourth reboiler; 17 - ethyl levulinate raw material tank. DETAILED DESCRIPTION

[0023] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the following will further describe the solutions of the present application. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0024] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other manners different from those described herein; obviously, the embodiments described in the specification are only a part of the embodiments of the present application, and not all the embodiments.

[0025] A preparation method of a different crystal phase zirconium dioxide catalyst, characterized in that it comprises the following steps: (1) Preparation of tetragonal phase ZrO2: Dissolve the precursor of zirconium and P123 in deionized water, then adjust the pH to 11 with ammonia water, and then oil bath at 88 ℃ for 40 h. Filter the product and wash with water and acetone; dry, and then calcine at 700 ℃ in a muffle furnace for 4 h to obtain tetragonal phase ZrO2; (2) Preparation of cubic phase ZrO2: Dissolve the precursor of zirconium and yttrium nitrate in deionized water, and add citric acid under stirring. The solution becomes turbid quickly, and then adjust the pH to 7 with ammonia water. Then oil bath at 110 ℃ for 24 h. Dry overnight in an oven at 110 ℃, and then calcine at 800 ℃ in a muffle furnace for 4 h to obtain cubic phase ZrO2; (3) Preparation of monoclinic phase ZrO2: Dissolve the precursor of zirconium in deionized water, and then add ammonium fluoride. Stir at room temperature for 1 h, and then transfer the solution to a stainless steel autoclave with a polytetrafluoroethylene liner. Hydrothermal treatment at 105 ℃ for 24 h, and then wash by centrifugation after cooling. Dry overnight in an oven at 105 ℃, and then calcine at 550 ℃ in a muffle furnace for 5 h to obtain monoclinic phase ZrO2.

[0026] In specific implementation, the precursor of zirconium is one of zirconium oxynitrate and zirconium nitrate.

[0027] Preferably, in the preparation of tetragonal phase ZrO2, the molar ratio of the precursor of zirconium to P123 is 33.28. In the tetragonal phase ZrO2, n （P123 / Zr） =0.03.

[0028] In the preparation of cubic phase ZrO2, the molar ratio of the precursor of zirconium to yttrium nitrate is 5.67. In the cubic phase ZrO2, n （Y / Zr） =0.18.

[0029] In the preparation of monoclinic ZrO2, the molar ratio of zirconium precursor to ammonium fluoride was 0.67. The n in the monoclinic ZrO2... （F / Zr） =1.5.

[0030] This invention also provides zirconium dioxide catalysts with different crystalline phases prepared by the above method.

[0031] Furthermore, the application of the different crystalline phase zirconium dioxide catalysts in the hydrogenation of ethyl levulinate to prepare γ-valerolactone.

[0032] Preferred conditions for the hydrogenation reaction of ethyl levulinate are: reaction temperature 170 °C, reaction pressure of nitrogen 0.8 MPa, and reaction time 7 h.

[0033] The specific embodiments of the present invention will be described in detail below. Example 1

[0034] 6.9 g of zirconium oxynitrate and 5.2 g of P123 were dissolved in 200 mL of deionized water. After complete dissolution, the pH was adjusted to 11 with ammonia. The solution was then in an oil bath at 88 °C for 40 h. The product was filtered and washed three times with water and acetone. After drying in an oven at 110 °C overnight, the product was ground into powder and then calcined in a muffle furnace at a rate of 5 °C / min to 700 °C for 4 h. The resulting sample (tetragonal ZrO2) is t-ZrO2. For its specific properties, please refer to [link to relevant documentation]. Figures 1 to 5 . Example 2

[0035] 4.7170 g of zirconium oxynitrate and 1.3788 g of yttrium nitrate were dissolved in 60 mL of deionized water. 6.07 g of citric acid was added with stirring, and the solution quickly became turbid. Ammonia was then added to adjust the pH to 7, followed by oil bath treatment at 110 °C for 24 h. After drying in an oven at 110 °C overnight, the solution was ground into powder and then calcined in a muffle furnace at a rate of 5 °C / min to 800 °C for 4 h. The resulting sample (cubic ZrO2) is designated c-ZrO2. For its specific properties, please refer to [link to relevant documentation]. Figures 1 to 5 . Example 3

[0036] 3.22 g of nitric acid was dissolved in 150 mL of deionized water, followed by the addition of 0.4167 g of ammonium fluoride. The mixture was stirred at room temperature for 1 h, then transferred to a PTFE-lined stainless steel autoclave and hydrothermally heated at 105 °C for 24 h. After cooling, the solution was washed by centrifugation. The powder was then dried overnight at 105 °C in an oven and ground into powder. The powder was then calcined in a muffle furnace at a rate of 5 °C / min to 550 °C for 5 h. The resulting sample (monoclinic ZrO2) was named m-ZrO2. For its specific properties, please refer to [link to relevant documentation]. Figures 1 to 5 . Test Examples

[0037] The catalysts of Examples 1-3 were evaluated, and the catalytic performance evaluation was performed on a liquid phase reactor-chromatograph device (0.8 MPa, 170°C). The specific method is as follows: 0.1 g of the catalyst, 1 mmole of EL, 7.3 g of isopropyl alcohol, and 0.5 mL of dodecane as an internal standard were added to the liquid phase reactor. The reactor was sealed, purged with N2 three times to replace the air, pressurized to 0.8 MPa, stirred at 900 rpm, heated to the reaction temperature, and after the reaction, the finished product was centrifuged, and the clear liquid obtained was injected into a gas chromatograph (GC-950, Haixin, Shanghai, China) equipped with a PEG-20M capillary column to analyze the products.

[0038] The conversion of ethyl levulinate and the selectivity of the product γ-valerolactone were calculated using the following equation.

[0039]

[0040]

[0041] Table 1 Catalytic performance evaluation results of the catalysts of the embodiments

[0042] The above table is the catalytic performance evaluation results of the three different crystal phase ZrO2 catalysts prepared in Examples 1-3. The catalytic performance of GVL in ELCTH at 170°C for 7 h, although the EL conversion is basically at the same level, at 94.9% ~96.9%, but the GVL selectivity is significantly different. In terms of GVL yield, the activity order of the catalysts is t-ZrO2 (92.7%) > c-ZrO2 (85.4%) > m-ZrO2 (79.2%), and the different crystal phase ZrO2 has different specific surface area and acid content, thereby affecting the selection, which shows that the different crystal phase ZrO2 catalysts have obvious influence on the EL hydrogenation activity. Separation process

[0043] The present application provides a process for generating γ-valerolactone by hydrogenation of ethyl levulinate. The process flow is as follows: (1) Product pretreatment stage The mixed liquid after the reaction is subjected to initial separation of the catalyst and the reaction product through filter 1. The pretreated reaction liquid is pumped into rectification column 2, heated to an appropriate temperature by a feed preheater, and then enters the middle part of the light component removal column. In the column, mass transfer and heat transfer are carried out on the column plates. The light components are enriched at the top of the column, and the heavy components are enriched at the bottom of the column.

[0044] (2) Product initial separation stage Vapor rich in light components (unreacted isopropanol, byproduct 2-methyltetrahydrofuran, and a small amount of ethyl levulinate) enters the first condenser 3 at the top of the column and is completely condensed into liquid. Part of the liquid is refluxed back into the column, and the other part flows into the ethyl levulinate distillation column 7. Ethyl levulinate is obtained from the bottom of the column. Part of it is heated and vaporized in the fourth reboiler 16 and returned to the ethyl levulinate distillation column 7, while the other part is sent to the ethyl levulinate feed tank 18. The light components at the top of the column, including unreacted isopropanol and byproduct 2-methyltetrahydrofuran, are condensed in the fourth condenser 15. Part of the condensate is refluxed back to the ethyl levulinate distillation column 7, and the other part is discharged to the storage tank 17. The heavy components in distillation column 2 (γ-valerol, unreacted ethyl levulinate, ethyl 4-hydroxyvalerate, and water) are partially refluxed and vaporized in the first reboiler 4 and returned to distillation column 2. The other part is depressurized by a pressure reducing valve and sent to the γ-valerol separation column 5. The light components (γ-valerol, unreacted ethyl levulinate, and water) of the γ-valerol distillation column 5 are discharged from the top of the column. After being condensed in the second condenser 6, part of the liquid is returned to the γ-valerol separation column 5, and the other part flows into the γ-valerol distillation column 8. Ethyl 4-hydroxyvalerate is discharged from the bottom of the γ-valerol separation column 5. Part of it is heated and vaporized in the second reboiler 9 and returned to the γ-valerol separation column 5, while the other part is sent to the storage tank 10.

[0045] (3) Purification of γ-valerol The γ-valerol distillation column 8 yields a light component product containing ethyl levulinate and water. After condensation in the third condenser 11, a portion of the feed is refluxed back into the γ-valerol distillation column 8, while the remaining portion is sent to the storage tank 12 for storage. A portion of the γ-valerol obtained at the bottom of the γ-valerol distillation column 8 is heated and vaporized in the third reboiler 13 and returned to the distillation column 8, while the remaining portion is discharged to the γ-valerol storage tank 14.

[0046] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A method for preparing a different crystalline phase zirconium dioxide catalyst, characterized by, The method comprises the following steps: (1) Preparation of tetragonal phase ZrO2: Dissolve the precursor of zirconium and P123 in deionized water, then adjust the pH to 11 with ammonia water, then oil bath at 88 ℃ for 40 h, filter the product, and wash with water and acetone; Dry, then calcine at 700 ℃ in a muffle furnace for 4 h to obtain tetragonal phase ZrO2; (2) Preparation of cubic phase ZrO2: Dissolve the precursor of zirconium and yttrium nitrate in deionized water, add citric acid under stirring, the solution becomes turbid quickly, then adjust the pH to 7 with ammonia water, then oil bath at 110 ℃ for 24 h, dry, then calcine at 800 ℃ in a muffle furnace for 4 h to obtain cubic phase ZrO2; (3) Preparation of monoclinic phase ZrO2: Dissolve the precursor of zirconium in deionized water, then add ammonium fluoride, stir at room temperature for 1 h, then transfer the solution to a stainless steel autoclave with a polytetrafluoroethylene liner, hydrothermal at 105 ℃ for 24 h, wash by centrifugation after cooling; dry, then calcine at 550 ℃ in a muffle furnace for 5 h to obtain monoclinic phase ZrO2.

2. The method of claim 1, wherein the method is characterized by: The precursor of zirconium is one of zirconium oxynitrate and zirconium nitrate.

3. The method of claim 1, wherein the method is characterized by: n = 0.03 in the tetragonal ZrO2 （P123 / Zr） =0.

03.

4. The method of claim 1, wherein the method is characterized by: n in the cubic ZrO2 （Y / Zr） = 0.

18.

5. The method of claim 1, wherein the method is characterized by: n in the monoclinic phase ZrO2 （F / Zr） = 1.

5.

6. A different crystal phase zirconium dioxide catalyst prepared by the method of any one of claims 1 to 5.

7. Application of the different crystal phase zirconium dioxide catalyst of claim 6 in the reaction of preparing γ-valerolactone by hydrogenation of ethyl levulinate.

8. Use according to claim 7, characterized in that, The reaction conditions of ethyl levulinate hydrogenation reaction are as follows: reaction temperature 170 ℃, reaction pressure 0.8 MPa of nitrogen, and reaction time 7 h.

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