A catalyst for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium, and a preparation method and application thereof

Abstract

The present invention belongs to the field of photocatalysis, and discloses a catalyst for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium, its preparation method and application. The catalyst has a hollow structure, ZnSe particles are on the inner wall of the hollow structure, and TiO2 is wrapped outside the ZnSe particles as the outer wall of the hollow structure. The preparation method comprises the following operating steps: reacting 2-methylimidazole with zinc acetate to prepare ZIF-8 particles; reacting the obtained ZIF-8 particles with tetrabutyl titanate to obtain ZIF-8@TiO2 particles; calcining the obtained ZIF-8@TiO2 particles in air, then adding selenium powder and calcining in an argon-hydrogen mixed gas to obtain h-ZnSe / TiO2 particles, which are the catalyst for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium. The catalyst can continuously work for 300 hours at an efficiency of 1500 μmol / g in a neutral aqueous medium without obvious efficiency reduction.

Description

Technical Field

[0001] The present invention belongs to the field of photocatalysis, and particularly relates to a catalyst for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium, a preparation method thereof, and an application thereof. Background Art

[0002] As a clean energy, hydrogen energy is a potential alternative to solve the current environmental and energy problems, and is expected to replace current fossil fuels in the future. However, the current hydrogen production methods still mainly rely on the reforming / gasification of fossil coal, natural gas or petroleum. Considering the soaring prices of fossil fuels, hydrogen production by biomass reforming is a more green and sustainable way. Using solar energy as an energy source, photocatalytic reforming of cellulose to produce hydrogen is obviously more environmentally friendly and sustainable, and has received extensive attention in recent years. However, current photocatalytic cellulose reforming often needs to be carried out under relatively harsh conditions, and toxic catalysts or photosensitizers are required for the pretreatment of cellulose and photocatalytic reaction in a strong alkaline environment. This method has a high cost and causes great pollution to the environment. Therefore, it is particularly important to develop a new photocatalyst for photocatalytic cellulose reforming to produce hydrogen in a neutral aqueous medium. Summary of the Invention

[0003] In order to overcome the limitations of the photocatalyst for cellulose reforming to produce hydrogen in the prior art, the primary object of the present invention is to provide a catalyst for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium. The catalyst is a h-ZnSe / TiO2 photocatalyst with a hollow structure, where ZnSe particles are on the inner wall of the hollow structure, and TiO2 wraps around the ZnSe particles as the outer wall of the hollow structure. With Pt as a co-catalyst, the catalyst can continuously work for 300 hours at an efficiency of 1500 μmol / g in a neutral aqueous medium without obvious efficiency reduction.

[0004] Another object of the present invention is to provide a preparation method for the above catalyst; the method prepares the h-ZnSe / TiO2 photocatalyst with a hollow structure through stepwise synthesis and by using a template method, and controls the spatial distribution of the two materials ZnSe and TiO2.

[0005] Another object of the present invention is to provide an application of the above catalyst.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A catalyst for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium, wherein the catalyst has a hollow structure, ZnSe particles are on the inner wall of the hollow structure, and TiO2 wraps around the ZnSe particles as the outer wall of the hollow structure.

[0008] The preparation method of the above-mentioned catalyst for highly efficient photocatalytic reforming of cellulose to hydrogen in a neutral aqueous medium comprises the following operating steps:

[0009] (1) Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution with a concentration of 2 - 10 mol / L; mix the obtained 2-methylimidazole solution with a zinc acetate solution for reaction. After centrifuging the obtained reaction product, disperse the precipitate in water to obtain a colloidal dispersion, and dry it to obtain metal-organic framework ZIF-8 particles; the molar ratio of 2-methylimidazole in the 2-methylimidazole solution to zinc acetate in the zinc acetate solution is 25:3.

[0010] (2) Disperse the ZIF-8 particles obtained in step (1) in ethanol, and add tetrabutyl titanate to the obtained ethanol dispersion to obtain ZIF-8 particles coated with a layer of titanium dioxide, namely ZIF-8@TiO2 particles; the mass ratio of the ZIF-8 particles to tetrabutyl titanate is 1:(0.3 - 0.9).

[0011] (3) Calcinate the ZIF-8@TiO2 particles obtained in step (2) in air, with a calcination temperature of 400 - 550 °C and a calcination time of 1 - 6 hours to obtain ZnO@TiO2 particles.

[0012] (4) Add 2 - 10 times the stoichiometric ratio of selenium powder to the ZnO@TiO2 particles obtained in step (3), and calcine in an argon-hydrogen mixed gas, with a calcination temperature of 400 - 550 °C and a calcination time of 4 - 8 hours to obtain h-ZnSe / TiO2 particles, which are the catalysts for highly efficient photocatalytic reforming of cellulose to hydrogen in a neutral aqueous medium.

[0013] The application of the above-mentioned catalyst in highly efficient photocatalytic reforming of cellulose to hydrogen in a neutral aqueous medium.

[0014] The said application comprises the following steps: mix the catalyst with cellulose powder, add water, introduce argon, and irradiate under a xenon lamp, and hydrogen can be prepared in a neutral environment.

[0015] The present invention has the following advantages and beneficial effects compared with the prior art:

[0016] (1) The photocatalytic reaction using the catalyst of the present invention can occur in a neutral aqueous medium, without the need for toxic organic solvents or strong acid or strong base environments, with low cost and environmental friendliness.

[0017] (2) The catalyst of the present invention is non-toxic itself, without heavy metals and toxic photosensitizers.

[0018] (3) The catalyst of the present invention has high stability and high hydrogen production efficiency, and can continuously work for 300 hours at an efficiency of 1500 μmol / g in a neutral water medium without obvious efficiency reduction. Description of the Drawings

[0019] Figure 1 Schematic diagram of the particle structure of h-ZnSe / TiO2 synthesized in Example 1.

[0020] Figure 2 Transmission electron microscope image of the h-ZnSe / TiO2 particles synthesized in Example 1.

[0021] Figure 3 X-ray diffraction comparison chart of the h-ZnSe / TiO2 particles synthesized in Example 1 with ZnSe and TiO2 powders.

[0022] Figure 4 Hydrogen production performance chart of the h-ZnSe / TiO2 particles synthesized in Example 1.

[0023] Figure 5 Hydrogen production performance chart of the h-ZnSe / TiO2 particles obtained by the present invention for the reforming of different cellulose raw materials. Detailed Embodiments

[0024] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0025] Example 1: Steps for synthesizing h-ZnSe / TiO2 particles

[0026] The synthesis steps are as follows: Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution with a concentration of 10 mol / L; mix the obtained 2-methylimidazole solution with a zinc acetate solution for reaction. After centrifuging the obtained reaction product, disperse the precipitate in water to obtain a colloidal dispersion, and dry it to obtain metal-organic framework ZIF-8 particles; the molar ratio of 2-methylimidazole in the 2-methylimidazole solution to zinc acetate in the zinc acetate solution is 25:3. Disperse the obtained ZIF-8 particles in ethanol to obtain an ethanol dispersion, and then add tetrabutyl titanate. The mass ratio of ZIF-8 particles to tetrabutyl titanate is 1:0.9 to obtain ZIF-8 particles coated with a layer of titanium dioxide, namely ZIF-8@TiO2. Calcinate the obtained ZIF-8@TiO2 in air at a temperature of 500 °C for 4 hours to obtain ZnO@TiO2 particles. Add 2 times the stoichiometric ratio of selenium powder to the obtained ZnO@TiO2 particles, and calcinate in an argon-hydrogen mixed gas at a temperature of 500 °C for 6 hours to obtain h-ZnSe / TiO2 particles, which are the catalysts for highly efficient photocatalytic cellulose reforming to produce hydrogen in a neutral water medium.

[0027] Figure 2 The transmission electron microscope image of the obtained h-ZnSe / TiO2 particles is as follows. As Figure 2 shown, these particles have a hollow structure. It can be seen from the elemental distribution map that the outer layer is TiO2 and the inner layer is ZnSe. Figure 3 The X-ray diffraction comparison diagram of the obtained h-ZnSe / TiO2 particles with ZnSe and TiO2 powders is as follows. As Figure 3 shown, the characteristic peaks of the X-ray diffraction of ZnSe and TiO2 powders can be seen, which proves that these particles contain two materials, ZnSe and TiO2. Thus, the structural schematic diagram of the h-ZnSe / TiO2 particles is as Figure 1 shown.

[0028] The performance of the above h-ZnSe / TiO2 particles was obtained by testing with a gas chromatograph under the irradiation of a 300W xenon lamp using a Beijing Perfectlight SolarLab-6A photocatalytic system. The specific method is to disperse the h-ZnSe / TiO2 particles in water to obtain a catalyst aqueous dispersion, and add this dispersion to the reactor of the above photocatalytic system. Connect the reactor to the photocatalytic system, introduce argon gas, turn on the condensed water, and control the temperature at 5 degrees Celsius. Turn on the xenon lamp and turn on the automatic test function of the photocatalytic system. As Figure 4 shown, it can continuously work for 300 hours at an efficiency of 1500 μmol / g in a neutral water medium without obvious efficiency reduction. For celluloses from different sources, including microcrystalline cellulose, paper, branches, and straws, the h-ZnSe / TiO2 particle photocatalyst obtained in the present invention can achieve photocatalytic hydrogen production from cellulose and shows an efficiency comparable to that of photocatalytic hydrogen production from microcrystalline cellulose. As Figure 5 shown.

[0029] Example 2: Synthesis of h-ZnSe / TiO2 particles in different amounts of tetrabutyl titanate

[0030] The synthesis steps are as follows: Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution with a concentration of 10 mol / L; mix the solution with a zinc acetate solution and carry out a reaction. After centrifuging the reaction product, disperse the precipitate with water to obtain a colloidal dispersion, and obtain metal-organic framework ZIF-8 particles after drying; the molar ratio of 2-methylimidazole in the 2-methylimidazole solution to zinc acetate in the zinc acetate solution is 25:3. Disperse the obtained ZIF-8 particles in ethanol to obtain an ethanol dispersion, and then add tetrabutyl titanate. The mass ratio of ZIF-8 particles to tetrabutyl titanate is 1:0.7 to obtain ZIF-8 particles coated with a layer of titanium dioxide, namely ZIF-8@TiO2. Calcinate the obtained ZIF-8@TiO2 in air at a temperature of 500 °C for 4 hours to obtain ZnO@TiO2 particles. Add 5 times the stoichiometric ratio of selenium powder to the obtained ZnO@TiO2 particles and calcinate in an argon-hydrogen mixed gas at a temperature of 500 °C for 6 hours to obtain h-ZnSe / TiO2 particles, which are the catalysts for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium.

[0031] Example 3: Synthesis of h-ZnSe / TiO2 particles at different calcination times

[0032] The synthesis steps are as follows: Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution with a concentration of 8 mol / L; mix the solution with a zinc acetate solution and carry out a reaction. After centrifuging the reaction product, disperse the precipitate with water to obtain a colloidal dispersion, and obtain metal-organic framework ZIF-8 particles after drying; the molar ratio of 2-methylimidazole in the 2-methylimidazole solution to zinc acetate in the zinc acetate solution is 2500:300. Disperse the obtained ZIF-8 particles in ethanol to obtain an ethanol dispersion, and then add tetrabutyl titanate. The mass ratio of ZIF-8 particles to tetrabutyl titanate is 1:0.7 to obtain ZIF-8 particles coated with a layer of titanium dioxide, namely ZIF-8@TiO2. Calcinate the obtained ZIF-8@TiO2 in air at a temperature of 550 °C for 4 hours to obtain ZnO@TiO2 particles. Add 10 times the stoichiometric ratio of selenium powder to the obtained ZnO@TiO2 particles and calcinate in an argon-hydrogen mixed gas at a temperature of 500 °C for 6 hours to obtain h-ZnSe / TiO2 particles, which are the catalysts for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral aqueous medium.

[0033] Example 4: Synthesis of h-ZnSe / TiO2 particles at different selenization temperatures

[0034] The synthesis steps are as follows: Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution with a concentration of 5 mol / L; mix the solution with a zinc acetate solution and carry out a reaction. After centrifuging the reaction product, disperse the precipitate in water to obtain a colloidal dispersion, and obtain metal-organic framework ZIF-8 particles after drying; the molar ratio of 2-methylimidazole in the 2-methylimidazole solution to zinc acetate in the zinc acetate solution is 2500:300. Disperse the obtained ZIF-8 particles in ethanol to obtain an ethanol dispersion, and then add tetrabutyl titanate. The mass ratio of ZIF-8 particles to tetrabutyl titanate is 1:0.3 to obtain ZIF-8 particles coated with a layer of titanium dioxide, namely ZIF-8@TiO2. Calcinate the obtained ZIF-8@TiO2 in air at a temperature of 500 °C for 4 hours to obtain ZnO@TiO2 particles. Add 8 times the stoichiometric ratio of selenium powder to the obtained ZnO@TiO2 particles, and calcine in an argon-hydrogen mixed gas at a temperature of 450 °C for 6 hours to obtain h-ZnSe / TiO2 particles, which are the catalysts for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral water medium.

[0035] Example 5: Synthesis of h-ZnSe / TiO2 particles at different selenization times

[0036] The synthesis steps are as follows: Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution with a concentration of 6 mol / L; mix the solution with a zinc acetate solution and carry out a reaction. After centrifuging the reaction product, disperse the precipitate in water to obtain a colloidal dispersion, and obtain metal-organic framework ZIF-8 particles after drying; the molar ratio of 2-methylimidazole in the 2-methylimidazole solution to zinc acetate in the zinc acetate solution is 2500:300. Disperse the obtained ZIF-8 particles in ethanol to obtain an ethanol dispersion, and then add tetrabutyl titanate. The mass ratio of ZIF-8 particles to tetrabutyl titanate is 1:0.5 to obtain ZIF-8 particles coated with a layer of titanium dioxide, namely ZIF-8@TiO2. Calcinate the obtained ZIF-8@TiO2 in air at a temperature of 500 °C for 4 hours to obtain ZnO@TiO2 particles. Add 5 times the stoichiometric ratio of selenium powder to the obtained ZnO@TiO2 particles, and calcine in an argon-hydrogen mixed gas at a temperature of 500 °C for 4 hours to obtain h-ZnSe / TiO2 particles, which are the catalysts for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral water medium.

[0037] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and shall all be included in the protection scope of the present invention.

Claims

1. Application of a catalyst in highly efficient photocatalytic reforming of cellulose to hydrogen in neutral aqueous medium, characterized in that: The catalyst has a hollow structure, with ZnSe particles on the inner wall of the hollow structure, and TiO2 as the outer wall of the hollow structure wrapping around the ZnSe particles.

2. Use of a catalyst according to claim 1 in highly efficient photocatalytic reforming of cellulose to hydrogen in a neutral aqueous medium, characterized in that: The catalyst is prepared according to the following steps: (1) Dissolve 2-methylimidazole in water to obtain a 2-methylimidazole solution with a concentration of 2-10 mol / L; mix the obtained 2-methylimidazole solution with a zinc acetate solution and react. After centrifuging the obtained reaction product, disperse the precipitate in water to obtain a colloidal dispersion, and dry it to obtain metal-organic framework ZIF-8 particles; the molar ratio of 2-methylimidazole in the 2-methylimidazole solution to zinc acetate in the zinc acetate solution is 25:3; (2) Disperse the ZIF-8 particles obtained in step (1) in ethanol, and add tetrabutyl titanate to the obtained ethanol dispersion to obtain ZIF-8 particles wrapped with a layer of titanium dioxide, namely ZIF-8@TiO2 particles; the mass ratio of the ZIF-8 particles to tetrabutyl titanate is 1:(0.3-0.9); (3) Calcinate the ZIF-8@TiO2 particles obtained in step (2) in air, with a calcination temperature of 400-550 °C and a calcination time of 1-6 hours to obtain ZnO@TiO2 particles; (4) Add 2-10 times the stoichiometric ratio of selenium powder to the ZnO@TiO2 particles obtained in step (3), and calcinate in an argon-hydrogen mixed gas, with a calcination temperature of 400-550 °C and a calcination time of 4-8 hours to obtain h-ZnSe / TiO2 particles, which are the catalyst for efficiently photocatalytically reforming cellulose to produce hydrogen in a neutral water medium.

3. Use of a catalyst according to claim 1 in highly efficient photocatalytic reforming of cellulose to hydrogen in a neutral aqueous medium, characterized in that: The application is carried out according to the following steps: mix the catalyst with cellulose powder, add water, introduce argon, and irradiate under a xenon lamp to produce hydrogen in a neutral environment.

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