Niobium oxide-based bimetallic oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a bimetallic oxide catalyst based on niobium oxide and a preparation method and application thereof, the molecular formula of the bimetallic oxide catalyst is MxNb (10-nx) / 5O5, M is one metal element of Ti, Y, Zr, Al, Cu, P and W, n is the valence of the metal element M, and x is the molar ratio of the metal element M to Nb. The bimetallic oxide catalyst based on niobium oxide is obtained through hydrolysis, the preparation method is simple, green and environment-friendly, the reaction process is controllable, the preparation repeatability is good, and the bimetallic oxide catalyst based on niobium oxide can be applied to the reaction for preparing levulinic acid by catalyzing cellulose hydrolysis. The bimetallic oxide catalyst based on niobium oxide has the advantages of strong stability, high product selectivity, high yield of levulinic acid, no toxicity and no pollution, and can efficiently promote the reaction in the process of preparing levulinic acid by catalyzing cellulose hydrolysis through niobium oxide. The problems that a traditional high-activity catalyst is low in product selectivity and a common catalyst is low in yield are solved.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic technology, and particularly relates to a bimetallic oxide catalyst based on acidic niobium oxide, a preparation method thereof, and an application thereof. Background Art

[0002] As the most abundant renewable biomass resource in nature, cellulose is widely present in agricultural wastes, forestry residues, and energy crops. Its efficient conversion into high-value-added organic compounds (such as hexose, levulinic acid, etc.) is the core direction of biomass resource utilization. However, the highly crystalline structure of cellulose and the complex cross-linked network of lignin - hemicellulose lead to significant technical bottlenecks in its conversion. Existing technologies generally have problems such as low conversion efficiency, poor product selectivity, and high process costs.

[0003] With the increasing global attention to sustainable development and green chemistry, finding renewable resources to replace traditional fossil raw materials has become an important research direction in the chemical field. As one of the most abundant renewable biomass resources on earth, the efficient utilization of cellulose is of great significance.

[0004] Cellulose is a high molecular polymer formed by glucose units connected by β-1,4-glycosidic bonds and is widely present in plant cell walls. However, due to the crystalline structure of cellulose and the strong intermolecular hydrogen bond interaction, it is difficult to be effectively degraded and converted. Converting cellulose into high-value-added chemicals can not only achieve the full utilization of biomass resources but also reduce the environmental pressure.

[0005] Levulinic acid is an important platform compound with broad application prospects. It can be used to synthesize various products such as biofuels, pharmaceuticals, spices, plastics, etc. Currently, levulinic acid is mainly prepared by acid-catalyzed hydrolysis of cellulose or hemicellulose. In common processes, strong acids such as sulfuric acid and hydrochloric acid are used as catalysts. Under high temperature (usually 160 - 20 °C) and high pressure (2 - 5 MPa) conditions, cellulose or hemicellulose is first hydrolyzed into monosaccharides such as glucose and xylose, and these monosaccharides further undergo dehydration and rearrangement reactions to form levulinic acid. Although this method can obtain levulinic acid to a certain extent, its drawbacks are significant. On the one hand, the strong corrosiveness of strong acids requires extremely high material requirements for reaction equipment, and special corrosion-resistant alloy materials are needed, which greatly increases the equipment purchase cost. At the same time, during long-term use, the maintenance and replacement frequency of the equipment is also relatively high, further increasing the operating cost. On the other hand, during the reaction process, due to the severe reaction conditions and lack of high selectivity, in addition to the target product levulinic acid, a large number of by-products such as furfural and humus are also generated. These by-products not only affect the purity of levulinic acid, but also require complex separation techniques such as distillation, extraction, and chromatographic separation during the subsequent separation and purification process, which greatly increases the separation cost and reduces the production efficiency. In addition, the waste acid solution generated after a large amount of strong acid use will cause serious pollution to the ecological environment such as soil and water bodies, which does not conform to the concepts of green chemistry and sustainable development.

[0006] Therefore, developing a mild, efficient, and green method for the conversion of cellulose to levulinic acid has important practical significance and economic value. The present invention aims to provide a new technical solution to solve the above problems existing in the prior art. Summary of the Invention

[0007] The present invention aims to solve the deficiencies existing in the prior art and provides a niobia-based double metal oxide catalyst, its preparation method, and application. Compared with the prior art, this niobia-based double metal oxide catalyst has significant advantages. It not only has strong stability and high product selectivity, but also has a simple and convenient preparation process, and can be effectively applied to catalytically convert cellulose into levulinic acid efficiently, providing a new solution for the technical development in related fields.

[0008] The technical solution adopted by the present invention to solve the above technical problems is: a double metal oxide catalyst based on niobic acid, and the molecular formula of this double metal oxide catalyst is M x Nb (10-nx) / 5 O 5 , where M is a metal element among Ti, Y, Zr, Al, Cu, P, and W, n is the valence of the metal element M, and x is the molar ratio of the metal element M to Nb.

[0009] Preferably, M is one of tetravalent Ti, trivalent Y, tetravalent Zr, trivalent Al, divalent Cu, pentavalent P, and hexavalent W.

[0010] Preferably, when M is tetravalent Ti, the value of x is 0.01, 0.1, or 0.15.

[0011] The preparation method of the above-mentioned niobium-based bimetallic oxide catalyst includes the following steps: according to the molar ratio of metal element M to Nb, an aqueous solution of a metal salt of M and a metal salt of Nb is mixed and hydrolyzed to obtain a powder material. After washing and drying the powder material, the niobium-based bimetallic oxide catalyst is obtained.

[0012] Preferably, the metal salt of Nb is niobium chloride, the metal salt of Ti is titanium sulfate, the metal salt of Y is yttrium acetate, the metal salt of Zr is zirconium sulfate, the metal salt of Al is aluminum acetate, the metal salt of Cu is copper sulfate, the compound of P is phosphoric acid, and the metal salt of W is ammonium metatungstate.

[0013] The application of the above-mentioned niobium-based bimetallic oxide catalyst in the reaction of catalyzing cellulose to levulinic acid.

[0014] Preferably, the niobium-based bimetallic oxide catalyst and cellulose are mixed and dispersed in water, and the reaction of catalyzing cellulose to levulinic acid is carried out in a closed hydrothermal autoclave.

[0015] Preferably, the reaction temperature is 100 - 200 °C.

[0016] Preferably, the dosage of the niobium-based bimetallic oxide catalyst is 0.1 - 0.5 g, the dosage of cellulose is 0.1 - 0.5 g, and the dosage of water is 2 - 10 mL.

[0017] Compared with the prior art, the present invention has the following remarkable advantages: the niobium-based bimetallic oxide catalyst of the present invention has strong stability, high product selectivity, high levulinic acid yield, and is non-toxic and pollution-free. In the process of catalyzing cellulose to levulinic acid by niobium oxide, this catalyst effectively solves the problem of low product selectivity of traditional catalysts. In addition, the niobium-based bimetallic oxide catalyst of the present invention is synthesized by physical grinding, the preparation method is simple, green and environmentally friendly, the reaction process is easy to control, the preparation reproducibility is good, and it has great potential in industrial applications. Description of the Drawings

[0018] Figure 1 XRD powder diffraction patterns of the catalysts prepared in Examples 1 - 7 and Comparative Example 1;

[0019] Figure 2 For the catalysts in Example 1 and Comparative Example 1, N2 Adsorption - desorption isotherm;

[0020] Figure 3 For the NH of the catalysts in Example 1 and Comparative Example 1 3 -TPD spectrum; Detailed implementation manners

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and examples. The raw materials used in the following examples are all commercially available products.

[0022] Example 1: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula Ti 0.05 Nb 1.96 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to Ti of 0.05, 0.01 - 0.02 g of titanium sulfate and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, the powder is obtained after centrifugation, and then the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain the Ti 0.05 Nb 1.96 O 5 catalyst.

[0023] Example 2: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula Y 0.05 Nb 1.97 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to Y of 0.05, 0.01 - 0.04 g of yttrium acetate and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, the powder is obtained after centrifugation, and then the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain the synthesized Y 0.05 Nb 1.97 O 5 catalyst.

[0024] Example 3: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula Zr 0.05 Nb 1.96 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to Zr of 0.05, 0.01 - 0.02 g of zirconium sulfate and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, the powder is obtained after centrifugation, and then the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain the synthesized Zr 0.05 Nb 1.96 O5 Catalyst

[0025] Example 4: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula Al 0.05 Nb 1.97 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to Al of 0.05, 0.01 - 0.02 g of aluminum chloride and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, and after centrifugation, a powder is obtained. Then, the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain the synthesized Al 0.05 Nb 1.97 O 5 catalyst

[0026] Example 5: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula Cu 0.05 Nb 1.98 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to Cu of 0.05, 0.01 - 0.02 g of copper sulfate and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, and after centrifugation, a powder is obtained. Then, the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain the synthesized Cu 0.05 Nb 1.98 O 5 catalyst

[0027] Example 6: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula P 0.05 Nb 1.95 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to P of 0.05, 0.005 - 0.01 g of phosphoric acid and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, and after centrifugation, a powder is obtained. Then, the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain the synthesized P 0.05 Nb 1.95 O 5 catalyst

[0028] Example 7: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula W 0.05 Nb 1.94 O 5, where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to W of 0.05, 0.02 - 0.05 g of ammonium metatungstate and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, and after centrifugation, a powder is obtained. Then the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain the synthesized W 0.05 Nb 1.94 O 5 catalyst.

[0029] Example 8: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula Ti 0.1 Nb 1.92 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to Ti of 0.1, 0.02 - 0.04 g of titanium sulfate and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, and after centrifugation, a powder is obtained. Then the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain Ti 0.1 Nb 1.92 O 5 catalyst.

[0030] Example 9: A bimetallic oxide catalyst based on niobium oxide, with the molecular formula Ti 0.15 Nb 1.88 O 5 , where Nb is pentavalent Nb. The preparation method of this catalyst includes the following steps: According to the molar ratio of metal element Nb to Ti of 0.15, 0.03 - 0.06 g of titanium sulfate and 2 - 3 g of niobium chloride are mixed in 50 - 100 mL of water, stirred for 12 - 24 hours, and after centrifugation, a powder is obtained. Then the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain Ti 0.15 Nb 1.88 O 5 catalyst.

[0031] Comparative Example 1: Nb 2 O 5 catalyst, and its preparation method includes the following steps: Dissolve 2 - 3 g of niobium chloride in 50 - 100 mL of water, stir for 12 - 24 hours, and after centrifugation, a powder is obtained. Then the powder is washed 3 times with distilled water and dried at 80 °C for 12 - 24 h to obtain Nb 2 O 5 catalyst.

[0032] Figure 1 are the XRD powder diffraction patterns of the catalysts prepared in Examples 1 - 7 and Comparative Example 1. From Figure 1It can be seen that there are no characteristic diffraction peaks in the range of 5 - 60° for Examples 1 - 7 and Comparative Example 1. There is only a broad diffraction peak at 20 - 30°.

[0033] The catalysts prepared in the above Examples 1 - 9 and Comparative Example 1 were applied to Application Examples 1 - 10 for the catalytic conversion of cellulose to levulinic acid. Among them, in Application Examples 1 - 9, the catalysts prepared in Examples 1 - 9 were used respectively, and in Application Example 10, the catalyst prepared in Comparative Example 1 was used.

[0034] Application Examples 1 - 10: The dosage of the catalyst was 0.2 g, the dosage of cellulose was 0.4 g, the dosage of water was 5 mL, the reaction temperature was 160 °C, and the reaction time was 2 hours. The reaction was carried out in a closed hydrothermal autoclave. After the reaction, the generated gas was introduced into a Shimadzu HPLC - LC20 high - performance liquid chromatograph for analysis, and the yields of levulinic acid of the 10 catalysts were analyzed and compared. The results are shown in Table 1.

[0035] Figure 2 For the N of Example 1 and Comparative Example 1 2 adsorption - desorption isotherm, it can be seen that the catalysts in Example 1 and Comparative Example 1 are both microporous materials, and the specific surface areas are 326 m 2 / g and 137 m 2 / g respectively.

[0036] Figure 3 For the NH of Example 1 and Comparative Example 1 3 -TPD spectra, it can be seen that the acid amounts of the catalysts in Example 1 and Comparative Example 1 are 1.21 mmol / g and 0.97 mmol / g respectively.

[0037] By comparing Application Examples 1 - 10 in Table 1, it can be found that the yield of levulinic acid of the catalyst Ti 0.05 Nb 1.96 O 5 is the best.

[0038] Table 1

[0039]

Claims

1. A bimetallic oxide catalyst based on niobium oxide, characterized in that The molecular formula of the bimetallic oxide catalyst is M x Nb (10-nx) / 5 O5, wherein M is a metal element selected from Ti, Y, Zr, Al, Cu, P, and W, n is the valence of the metal element M, and x is the molar ratio of the metal element M to Nb.

2. The bimetallic oxide catalyst based on niobium oxide according to claim 1, characterized in that M is one of tetravalent Ti, trivalent Y, tetravalent Zr, trivalent Al, divalent Cu, pentavalent P, and hexavalent W.

3. The bimetallic oxide catalyst based on niobium oxide according to claim 2, characterized in that When M is tetravalent Ti, the value of x is 0.05, 0.1 or 0.

15.

4. The bimetallic oxide catalyst based on niobium oxide according to claim 2, characterized in that When M is one of tetravalent Ti, trivalent Y, tetravalent Zr, trivalent Al, divalent Cu, pentavalent P, and hexavalent W, the value of x is 0.

01.

5. The method for preparing a bimetallic oxide catalyst based on niobium oxide according to any one of claims 1 to 4, characterized in that: The following steps are involved: According to the molar ratio of metal elements M to Nb, aqueous solutions of metal salts of M and Nb are mixed and hydrolyzed to obtain powders. After washing and drying the powders, a bimetallic oxide catalyst based on niobium oxide is obtained.

6. The method for preparing a bimetallic oxide catalyst based on niobium oxide according to claim 5, characterized in that: The metal salt of Nb is niobium chloride, the metal salt of Ti is titanium sulfate, the metal salt of Y is yttrium acetate, the metal salt of Zr is zirconium sulfate, the metal salt of Al is aluminum acetate, the metal salt of Cu is copper sulfate, the compound of P is phosphoric acid, and the metal salt of W is ammonium metatungstate.

7. Use of the niobium oxide-based bimetallic oxide catalyst according to any one of claims 1 to 4 in catalyzing the conversion of cellulose into levulinic acid.

8. The use according to claim 7, characterized in that: The niobium oxide-based bimetallic oxide is used in a closed hydrothermal autoclave to catalyze the conversion of cellulose into levulinic acid.

9. The use according to claim 8, characterized in that: The reaction temperature of the niobium oxide-based bimetallic oxide catalyst for catalyzing the conversion of cellulose into levulinic acid is 160°C.

10. The use according to claim 8, characterized in that: The amount of the bimetallic oxide catalyst based on niobium oxide is 0.2 g, the amount of cellulose is 0.4 g, and the amount of water is 5 mL.

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