阅读说明：本技术 一种乌洛托品的制备方法 (Preparation method of urotropine ) 是由 袁友珠 陈伟坤 付肖 柳晓英 叶林敏 段新平 于 2021-08-20 设计创作，主要内容包括：本发明涉及有机合成技术领域,提供了一种乌洛托品的制备方法,将甲醇-氨混合溶液和光催化剂混合,进行光催化反应,得到乌洛托品和氢气；所述光催化剂包括光响应半导体载体和负载在所述光响应半导体上的过渡金属。本发明采用的光催化剂中光响应半导体载体具有较宽的禁带宽度,空穴的氧化性较强,有利于甲醇脱氢,过渡金属由于其具有较大的功函,对光生电子的捕获能力较强,促进了光生电子和空穴的分离,具有优异的光催化活性或光催化循环稳定性。本发明提供的制备方法,利用廉价、丰富的太阳能资源,在同一个反应器中、光催化剂存在条件下合成乌洛托品,反应条件温和,大大降低了能耗；同时脱氢的产生氢气可作为原料进一步利用,提升了经济效益。(The invention relates to the technical field of organic synthesis, and provides a preparation method of urotropine, which comprises the steps of mixing a methanol-ammonia mixed solution with a photocatalyst, and carrying out photocatalytic reaction to obtain urotropine and hydrogen; the photocatalyst includes a photoresponsive semiconductor support and a transition metal supported on the photoresponsive semiconductor. The photoresponse semiconductor carrier in the photocatalyst adopted by the invention has wider forbidden bandwidth and stronger hole oxidability, is beneficial to methanol dehydrogenation, and the transition metal has stronger capture capability to photo-generated electrons due to the larger work function, promotes the separation of the photo-generated electrons and the holes, and has excellent photocatalytic activity or photocatalytic cycle stability. The preparation method provided by the invention utilizes cheap and abundant solar energy resources to synthesize the urotropine in the same reactor in the presence of the photocatalyst, the reaction condition is mild, and the energy consumption is greatly reduced; meanwhile, hydrogen generated by dehydrogenation can be further utilized as a raw material, so that the economic benefit is improved.)

1. A preparation method of urotropine is characterized by comprising the following steps:

mixing the methanol-ammonia mixed solution with a photocatalyst, and carrying out photocatalytic reaction to obtain urotropine and hydrogen;

the photocatalyst includes a photoresponsive semiconductor support and a transition metal supported on the photoresponsive semiconductor.

2. The production method according to claim 1, wherein the photoresponsive semiconductor support comprises one or more of titanium dioxide, carbon nitride, cadmium sulfide, zinc indium sulfide, bismuth tungstate and bismuth molybdate;

the transition metal comprises one or more of platinum, palladium, gold, silver, copper, cobalt, nickel and manganese;

the content of the transition metal in the photocatalyst is 0.1-1.0 wt%.

3. The preparation method according to claim 1 or 2, wherein the photocatalyst is prepared by a photo-deposition method, an impregnation reduction method or a chemical reduction method;

the photo-deposition method comprises the following steps: mixing a photoresponse semiconductor carrier, a solvent and a water-soluble transition metal source, and carrying out illumination deposition under a protective atmosphere to obtain a photocatalyst;

the impregnation reduction method comprises the following steps: mixing a water-soluble transition metal source, a photoresponse semiconductor carrier and water, and carrying out reduction reaction in a reducing atmosphere to obtain a photocatalyst;

the chemical reduction method comprises the following steps: and mixing the photoresponse semiconductor carrier, the water-soluble transition metal source, the reducing agent and water to carry out chemical reduction reaction to obtain the photocatalyst.

4. The production method according to claim 3, wherein in the photo-deposition method, the immersion reduction method, and the chemical reduction method, the mass ratio of the transition metal in the photoresponsive semiconductor support and the water-soluble transition metal source is independently 1: 0.001 to 0.01.

5. The method according to claim 3 or 4, wherein the light deposition method comprises the steps of depositing light with a wavelength of 300-1100 nm and an intensity of 500-900 mW/cm²The time is 0.5-4 h.

6. The production method according to claim 3 or 4, wherein in the immersion reduction method, a reducing atmosphere is a hydrogen-containing gas;

the temperature of the reduction reaction is 300-400 ℃, and the time is 1-4 h.

7. The production method according to claim 3 or 4, wherein in the chemical reduction method, the chemical reducing agent comprises sodium borohydride;

the temperature of the chemical reduction reaction is room temperature, and the time is 30-60 min.

8. The production method according to claim 1, wherein the methanol-ammonia mixed solution is a mixed solution of methanol and concentrated aqueous ammonia; the mass concentration of the strong ammonia water is 25-28%;

the volume fraction of concentrated ammonia water in the methanol-ammonia mixed solution is 1-10%;

the ratio of the volume of the methanol-ammonia mixed solution to the mass of the photocatalyst is 2-10 mL: 5-20 mg.

9. The method according to claim 1 or 8, wherein the photocatalytic reaction has a light wavelength of 300 to 1100nm and a light intensity of 500 to 900mW/cm²The temperature is 25-65 ℃, and the time is 1-4 h.

10. The production method according to claim 1, 2, 4, or 8, characterized in that the ratio of the amount of the substance of ammonia in the methanol-ammonia mixed solution to the mass of the photocatalyst is 1.0 mol: 0.5 to 3.0 g.

Technical Field

The invention relates to the technical field of organic synthesis, and particularly relates to a preparation method of urotropine.

Background

Urotropine, known as hexamethylenetetramine, is an important chemical raw material, is widely applied to industrial production and medical medicine, and can be used as a curing agent for resin and plastics and a medicine raw material for producing chloramphenicol, nitrated synthetic cyclone explosive and the like. Currently, the production and synthesis of urotropine are mature, and formaldehyde and ammonia are generally used as raw materials for condensation to prepare urotropine. The conventional industrial synthesis method can be divided into a liquid phase method and a gas phase method, wherein the liquid phase method is generally to place a formaldehyde aqueous solution into a reactor, introduce ammonia gas or ammonia water, keep the solution alkaline, and condense to obtain urotropine; the gas phase method is that formaldehyde gas and ammonia gas are introduced into a reactor filled with urotropine mother liquor, a large amount of heat is released by reaction, partial water is taken away by evaporation, and supersaturated solution is formed to promote precipitation of urotropine. However, formaldehyde is a known human carcinogen and is highly polluting to human and the environment.

Methanol and ammonia are used as raw materials to synthesize urotropine, the methanol is firstly catalyzed and oxidized into formaldehyde under the conditions of high temperature (300-700 ℃), catalyst (iron, molybdenum or silver catalyst) or hydrogen peroxide oxidant, and then the formaldehyde is transferred to another reactor to be condensed with ammonia gas to prepare the urotropine. However, the above synthetic method has a low yield of urotropin.

Disclosure of Invention

In view of the above, the present invention aims to provide a method for preparing urotropin, which has high yield.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of urotropine, which comprises the following steps:

mixing the methanol-ammonia mixed solution with a photocatalyst, and carrying out photocatalytic reaction to obtain urotropine and hydrogen;

the photocatalyst includes a photoresponsive semiconductor support and a transition metal supported on the photoresponsive semiconductor.

Preferably, the photoresponse semiconductor carrier comprises one or more of titanium dioxide, carbon nitride, cadmium sulfide, zinc indium sulfide, bismuth tungstate and bismuth molybdate;

the transition metal comprises one or more of platinum, palladium, gold, silver, copper, cobalt, nickel and manganese;

the content of the transition metal in the photocatalyst is 0.1-1.0 wt%.

Preferably, the photocatalyst is prepared by a photo-deposition method, a dipping reduction method or a chemical reduction method;

the photo-deposition method comprises the following steps: mixing a photoresponse semiconductor carrier, a solvent and a water-soluble transition metal source, and carrying out illumination deposition under a protective atmosphere to obtain a photocatalyst;

the impregnation reduction method comprises the following steps: mixing a water-soluble transition metal source, a photoresponse semiconductor carrier and water, and carrying out reduction reaction in a reducing atmosphere to obtain a photocatalyst;

the chemical reduction method comprises the following steps: and mixing the photoresponse semiconductor carrier, the water-soluble transition metal source, the reducing agent and water to carry out chemical reduction reaction to obtain the photocatalyst.

Preferably, in the photo deposition method, the immersion reduction method, and the chemical reduction method, the mass ratio of the transition metal in the photoresponsive semiconductor support and the water-soluble transition metal source is independently 1: 0.001 to 0.01.

Preferably, in the photo-deposition method, the light wavelength of the illumination deposition is 300-1100 nm, and the illumination intensity is 500-900 mW/cm²The time is 0.5-4 h.

Preferably, in the immersion reduction method, the reducing atmosphere is a hydrogen-containing gas;

the temperature of the reduction reaction is 300-400 ℃, and the time is 1-4 h.

Preferably, in the chemical reduction method, the chemical reducing agent comprises sodium borohydride;

the temperature of the chemical reduction reaction is room temperature, and the time is 30-60 min.

Preferably, the methanol-ammonia mixed solution is a mixed solution of methanol and concentrated ammonia water; the mass concentration of the strong ammonia water is 25-28%;

the volume fraction of concentrated ammonia water in the methanol-ammonia mixed solution is 1-10%;

the ratio of the volume of the methanol-ammonia mixed solution to the mass of the photocatalyst is 2-10 mL: 5-20 mg.

Preferably, the light wavelength of the photocatalytic reaction is 300-1100 nm, and the illumination intensity is 500-900 mW/cm²The temperature is 25-65 ℃, and the time is 1-4 h.

Preferably, the mass ratio of the amount of ammonia in the methanol-ammonia mixed solution to the photocatalyst is 1.0 mol: 0.5 to 3.0 g.

The invention provides a preparation method of urotropine, which comprises the following steps: mixing the methanol-ammonia mixed solution with a photocatalyst, and carrying out photocatalytic reaction to obtain urotropine and hydrogen; the photocatalyst includes a photoresponsive semiconductor support and a transition metal supported on the photoresponsive semiconductor. In the photocatalyst adopted by the invention, the photoresponse semiconductor carrier has wider forbidden bandwidth, the oxidability of a hole is stronger, and the methanol dehydrogenation is facilitated. According to the preparation method provided by the invention, cheap and abundant solar energy resources are utilized, the methanol is dehydrogenated into formaldehyde and the formaldehyde and ammonia are aminated to prepare urotropine in the same reactor in the presence of a photocatalyst, the reaction condition is mild, and the energy consumption is greatly reduced; because the reaction is carried out in the solution mainly containing methanol, the boiling point of the methanol is lower, and the subsequent mother liquor concentration can be carried out at a lower temperature, the energy consumption is saved; meanwhile, dehydrogenation generates hydrogen, which is an important chemical product, and the hydrogen can be further utilized as a raw material after purification, so that the economic benefit is improved.

Drawings

FIG. 1 is an X-ray powder diffraction pattern of the photocatalysts of example 1 and comparative example 1;

FIG. 2 is a graph of the results of the cyclic catalytic stability test of 0.5Pt/P25 prepared in example 1.

Detailed Description

The invention provides a preparation method of urotropine, which is characterized by comprising the following steps:

and mixing the methanol-ammonia mixed solution with a photocatalyst, and carrying out photocatalytic reaction to obtain urotropine and hydrogen.

In the present invention, all the raw material components are commercially available products well known to those skilled in the art unless otherwise specified.

In the present invention, the photocatalyst includes a photoresponsive semiconductor support and a transition metal supported on the photoresponsive semiconductor. In the present invention, the photo-responsive semiconductor support preferably comprises titanium dioxide, carbon nitride (C)₃N₄) Cadmium sulfide (CdS), zinc indium sulfide (ZnIn)₂S₄) Bismuth tungstate (Bi)₂WO₆) And bismuth molybdate (Bi)₂MoO₆) One or more of them. In the present invention, the transition metal preferably includes one or more of platinum, palladium, gold, silver, copper, cobalt, nickel and manganese. In the present invention, the content of the transition metal in the photocatalyst is preferably 0.1 to 1.0 wt%, more preferably 0.2 to 0.8 wt%, and further preferably 0.5 to 0.6 wt%.

In the present invention, the carbon nitride is preferably obtained by baking dicyanodiamine; the roasting temperature is preferably 500-600 ℃, and more preferably 550 ℃; the temperature rise rate from room temperature to the roasting temperature is preferably 2-5 ℃/min, and more preferably 3 ℃/min; starting timing by raising the temperature to the roasting temperature, wherein the roasting heat preservation time is preferably 3-6 h, and more preferably 4 h; the calcination is preferably carried out in a muffle furnace with dicyanodiamine placed in a crucible.

In the present invention, the preparation method of cadmium sulfide preferably comprises the following steps: mixing ethylenediamine, cadmium chloride and thiourea, and carrying out a solvothermal reaction to obtain cadmium sulfide. In the present invention, the usage ratio of ethylenediamine (as solvent), cadmium chloride and thiourea is preferably 1.0mL: 0.05-0.1 g: 0.05-0.1 g, more preferably 1.0mL: 0.07-0.08 g: 0.07-0.08 g. In the invention, the temperature of the solvothermal reaction is preferably 100-180 ℃, and more preferably 160 ℃; the solvothermal reaction time is preferably 8-60 h, and more preferably 48 h. After the solvothermal reaction, the method preferably further comprises the steps of carrying out solid-liquid separation on the solvothermal reaction system, washing the obtained solid product with water and then drying to obtain cadmium sulfide; the solid-liquid separation mode is not particularly limited, and a solid-liquid separation mode known to those skilled in the art can be adopted, specifically, filtration or centrifugal separation; the washing is preferably centrifugal washing, the centrifugal washing is not particularly limited, and the washing liquor is neutral; the drying temperature is preferably 40-60 ℃, and more preferably 60 ℃; the drying time is preferably 8-12 h, and more preferably 10 h; the drying mode is preferably vacuum drying.

In the present invention, the method for preparing zinc indium sulfide preferably comprises the following steps: mixing indium chloride, zinc acetate, thioacetamide and water, and carrying out water bath reaction to obtain the sulfur indium zinc. In the present invention, the amount ratio of water, indium chloride, zinc acetate and thioacetamide is preferably 1.0mL: 2.0-5.0 mg: 1.0-5.0 mg: 1.0-3.0 mg, more preferably 1.0mL: 3.5-4.0 mg: 1.5-2.0 mg: 1.5-2.0 mg. In the invention, the temperature of the water bath reaction is preferably 80-90 ℃, and more preferably 90 ℃; the water bath reaction time is 4-8 h, and more preferably 5 h. After the water bath reaction, the method preferably further comprises the steps of carrying out solid-liquid separation on a system of the water bath reaction, and drying the obtained solid to obtain the sulfur indium zinc. The solid-liquid separation mode is not particularly limited, and a solid-liquid separation mode known to those skilled in the art can be adopted, specifically, filtration or centrifugal separation; the washing is preferably centrifugal washing, the centrifugal washing is not particularly limited, and the washing liquor is neutral; the drying temperature is preferably 40-60 ℃, and more preferably 60 ℃; the drying time is preferably 8-12 h, and more preferably 10 h; the drying mode is preferably vacuum drying.

In the present invention, the preparation method of bismuth tungstate preferably comprises the following steps: dissolving bismuth nitrate and sodium tungstate in glycol, and heating the solvent for a period of time. In the invention, the dosage ratio of the ethylene glycol, the bismuth nitrate and the sodium tungstate is preferably 1.0mL to 20.0-80.0 mg: 10.0-30.0 mg, more preferably 1.0mL, 40.0-50.0 mg: 20.0-25.0 mg, in the invention, the solvothermal reaction temperature is preferably 160-180 ℃, and more preferably 160 ℃; the hydrothermal reaction time is 10-16 h, and more preferably 12 h. After the solvent thermal reaction, the solid-liquid separation adopts the centrifugal water washing mode which is optimized above; the drying temperature is preferably 40-60 ℃, and more preferably 60 ℃; the drying time is preferably 8-12 h, and more preferably 10 h; the drying mode is preferably vacuum drying.

In the present invention, the photocatalyst is preferably prepared by a photo-deposition method, a dipping reduction method or a chemical reduction method.

In the present invention, the preparation of the photocatalyst using the photo-deposition method preferably comprises the steps of: mixing the photoresponse semiconductor carrier, the solvent and the water-soluble transition metal source, and carrying out illumination deposition under a protective atmosphere to obtain the photocatalyst. In the invention, the water-soluble transition metal source preferably comprises one or more of a water-soluble platinum source, a water-soluble palladium source, a water-soluble gold source, a water-soluble silver source, a water-soluble copper source, a water-soluble cobalt source, a water-soluble nickel source and a water-soluble manganese source; the water-soluble platinum source preferably comprises chloroplatinic acid; the water-soluble palladium source preferably comprises chloropalladite; the water-soluble gold source preferably comprises chloroauric acid; the water soluble silver source preferably comprises silver nitrate; the water-soluble copper source preferably comprises one or more of copper chloride, copper nitrate and copper sulfate; the water-soluble cobalt source preferably comprises one or more of cobalt chloride, cobalt nitrate and cobalt sulfate; the water-soluble nickel source preferably comprises one or more of nickel chloride, nickel nitrate and nickel sulfate; the water-soluble manganese source preferably comprises one or more of manganese chloride, manganese nitrate and manganese sulfate. In the present invention, the mass ratio of the photoresponsive semiconductor carrier to the transition metal in the water-soluble transition metal source is preferably 1: 0.001 to 0.01, more preferably 1: 0.003 to 0.005. In the present invention, the solvent preferably includes an alcohol solvent, water or an alcohol aqueous solution; the alcohol in the alcohol solvent or the alcohol aqueous solution preferably comprises one or more of methanol, ethanol, isopropanol and glycerol; hair brushIt is to be noted that the volume ratio of the alcohol to the water in the alcohol aqueous solution is not particularly limited, and may be any ratio. In the present invention, the ratio of the mass of the photoresponsive semiconductor carrier to the volume of the solvent is preferably 1.0 g: 200-600 mL, more preferably 1.0 g: 400-500 mL. In the invention, the photoresponse semiconductor carrier, the solvent and the water-soluble transition metal source are mixed, preferably, the photoresponse semiconductor carrier is ultrasonically dispersed in the solvent to obtain carrier dispersion liquid; adding a water-soluble transition metal source to the obtained carrier dispersion liquid under stirring; the power of the ultrasonic dispersion is preferably 120-200W, and more preferably 180-200W; the ultrasonic dispersion time is preferably 5-30 min, and more preferably 10 min; the stirring speed and time are not particularly limited, and the transition metal ions can be sufficiently adsorbed in the photoresponsive semiconductor carrier. In the present invention, the protective atmosphere preferably includes an inert gas or nitrogen, and the inert gas preferably includes at least one of helium, argon, and argon. In the invention, the light wavelength of the illumination deposition is preferably 300-1100 nm; the illumination intensity of the illumination deposition is preferably 500-900 mW/cm²More preferably 600-700 mW/cm²(ii) a The illumination deposition time is preferably 0.5-4 h, and more preferably 0.5-1 h. After the illumination deposition, the invention preferably further comprises the steps of carrying out solid-liquid separation on the illumination deposition system, washing the obtained solid product with water and then drying to obtain the photocatalyst; the solid-liquid separation mode is not particularly limited, and the solid-liquid separation mode known to those skilled in the art can be adopted, such as filtration; the water washing is preferably distilled water pumping washing; the drying temperature is preferably 40-80 ℃, and more preferably 60 ℃; the drying time is preferably 10-12 h, and more preferably 10 h; the drying mode is preferably vacuum drying.

In the present invention, the preparation of the photocatalyst by the dipping reduction method preferably comprises the steps of: and mixing the water-soluble transition metal source, the photoresponse semiconductor carrier and water, and carrying out reduction reaction in a reducing atmosphere to obtain the photocatalyst. In the present invention, the kind of the water-soluble transition metal source and the mass ratio of the photoresponsive semiconductor carrier to the transition metal in the water-soluble transition metal source are preferably the same as those of the photocatalyst prepared by the photo-deposition method, and are not described in detail herein. In the invention, the mass ratio of the photoresponsive semiconductor carrier to water is preferably 0.1-0.5: 2 to 10, more preferably 0.2 to 0.5: 3 to 5. In the invention, the mixing is preferably that after a water-soluble transition metal source is dissolved in water, a photoresponse semiconductor carrier is added under the stirring condition for ultrasonic mixing; the invention has no special limit on the dosage of the water, and can dissolve the water-soluble transition metal source and successfully prepare the photocatalyst; the stirring speed is not particularly limited, and the raw materials can be uniformly mixed; the power of the ultrasonic mixing is preferably 120-200W, and more preferably 180-200W; the ultrasonic treatment time is preferably 5-30 min, and more preferably 10 min. According to the invention, the mixed system is preferably dried and then subjected to reduction reaction; the drying temperature is preferably 60-100 ℃, and more preferably 70-80 ℃; the drying time is preferably 10-24 hours, and more preferably 12-16 hours. In the invention, the reducing atmosphere is preferably hydrogen-containing gas, and the volume fraction of hydrogen in the hydrogen-containing gas is preferably 5-100%, and more preferably 10-20%; when the hydrogen-containing gas is not pure hydrogen, the hydrogen-containing gas is preferably hydrogen-argon gas or a mixed gas of hydrogen and nitrogen. In the invention, the temperature of the reduction reaction is preferably 300-400 ℃, and more preferably 350-380 ℃; the heating rate is preferably 1-10 ℃/min, and more preferably 2-5 ℃/min; the time of the reduction reaction is preferably 1-4 h, and more preferably 2-3 h.

In the present invention, the preparation of the photocatalyst by the chemical reduction method preferably comprises the steps of: and mixing the photoresponse semiconductor carrier, the water-soluble transition metal source, the reducing agent and water to carry out chemical reduction reaction to obtain the photocatalyst. In the present invention, the kind of the water-soluble transition metal source and the mass ratio of the photoresponsive semiconductor carrier to the transition metal in the water-soluble transition metal source are preferably the same as those of the photocatalyst prepared by the photo-deposition method, and are not described in detail herein. In the invention, the mass ratio of the photoresponsive semiconductor carrier to water is preferably 0.1-0.5: 50 to 250, more preferably 0.3 to 0.4: 50 to 100. In the present invention, the reducing agent preferably includes sodium borohydride; the sodium borohydride is preferably realized in the form of an aqueous sodium borohydride solution, and the concentration of the aqueous sodium borohydride solution is preferably 0.5-2.0 mol/L, and more preferably 1.0-1.5 mol/L; the molar ratio of the transition metal and the reducing agent in the water-soluble transition metal source is preferably 1: 10-100, more preferably 1: 30 to 50. In the invention, the mixing is preferably that the photoresponse semiconductor carrier is dispersed in water by ultrasound, a water-soluble transition metal source is added and then stirred, and then a reducing agent is added and mixed; the power of the ultrasonic dispersion is preferably 120-200W, and more preferably 150-180W; the time for ultrasonic dispersion is preferably 5-30 min, and more preferably 10-20 min; the stirring temperature is preferably room temperature, and the stirring time is preferably 1-4 h, and more preferably 2-3 h; when the reducing agent is used in the form of an aqueous reducing agent solution, the aqueous reducing agent solution is preferably added dropwise with stirring; the dropping speed is not specially limited, and the dropping can be carried out dropwise; the stirring speed is not particularly limited, and the raw materials can be uniformly mixed.

The photocatalyst prepared by adopting the photo-deposition method, the dipping reduction method or the chemical reduction method has the advantages of stable structure, high photocatalytic activity, good catalytic stability and simple and convenient operation of the preparation method.

In the present invention, the molar ratio of methanol to ammonia in the methanol-ammonia mixed solution is 1: 0.1 to 0.15, more preferably 1: 0.13 to 0.14. In the present invention, the methanol-ammonia mixed solution is preferably obtained by mixing methanol and concentrated aqueous ammonia; the mass fraction of the strong ammonia water is preferably 25-28%; the volume fraction of the concentrated ammonia water in the methanol-ammonia mixed solution is preferably 1-10%, more preferably 2-8%, and further preferably 5-7%; the concentration of ammonia in the methanol-ammonia mixed solution is preferably 0.1-1.0 mol/L, and more preferably 0.5-1.0 mol/L. In the present invention, the ratio of the volume of the methanol-ammonia mixed solution to the mass of the photocatalyst is preferably 2 to 10 mL: 5-20 mg, more preferably 5-8 mL: 5-10 mg.

In the invention, the optical wavelength of the photocatalytic reaction is preferably 300-1100nm; the illumination intensity is 500-900 mW/cm²Preferably 600-700 mW/cm²(ii) a The temperature of the photocatalytic reaction is preferably 25-65 ℃, and more preferably 30-55 ℃; the time of the photocatalytic reaction is preferably 1-4 h, and more preferably 2-3 h; the pressure of the photocatalytic reaction is preferably normal pressure; the photocatalytic reaction is preferably carried out in a jacketed quartz reaction tube, and the reaction atmosphere is preferably an inert gas, preferably comprising helium, argon or nitrogen. In the invention, in the photocatalytic reaction process, methanol is dehydrogenated under the photocatalytic condition to generate formaldehyde, and the formaldehyde and ammonia in the solution are condensed to form urotropine.

According to the preparation method provided by the invention, cheap and abundant solar energy resources are utilized, the methanol dehydrogenation is realized to formaldehyde and the formaldehyde and ammonia are aminated to prepare the urotropine by a one-step method in the same reactor under the mild condition of 25-65 ℃, the reaction condition is mild, and the energy consumption is greatly reduced; because the reaction is carried out in the solution mainly containing methanol, the boiling point of the methanol is lower, and the subsequent mother liquor concentration can be carried out at a lower temperature, the energy consumption is saved; meanwhile, hydrogen generated by dehydrogenation can be further utilized as a raw material after purification, and the economic benefit is improved.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Adding 0.1g of titanium dioxide (Degussa, P25) into 50mL of methanol aqueous solution (the volume fraction of methanol is 20%), carrying out ultrasonic treatment for 10min, adding 0.105mL of chloroplatinic acid solution with the concentration of 10g/L, introducing argon to remove air in a system, stirring for 1h, starting a xenon lamp, and carrying out ultraviolet irradiation at the wavelength of 300-1100 nm and the illumination intensity of 700mW/cm²Depositing under illumination for 1h, filtering, suction-filtering and washing the obtained solid product with distilled water, and vacuum-drying at 60 deg.C for 10h to obtain photocatalyst (recorded as 0.5 Pt-P25)。

Example 2

A photocatalyst was prepared in the same manner as in example 1 except that 0.105mL of a chloroplatinic acid solution having a concentration of 10g/L was replaced with 0.280mL of a chloropalladate solution having a concentration of 3g/L to obtain a photocatalyst (described as 0.5 Pd/P25).

Example 3

A photocatalyst was prepared in the same manner as in example 1 except that 0.105mL of a chloroplatinic acid solution having a concentration of 10g/L was replaced with 1.330mL of a copper chloride solution having a concentration of 1g/L to obtain a photocatalyst (described as 0.5 Cu/P25).

Example 4

Placing 10.0g dicyanodiamine in a crucible, covering the crucible, placing the crucible in a muffle furnace, heating to 550 ℃ at a heating rate of 3 ℃/min, and then carrying out heat preservation roasting for 4h to obtain C₃N₄. A photocatalyst was then prepared in the same manner as in example 1, except that P25 was replaced with C₃N₄To obtain a photocatalyst (noted as 0.5 Pt/C)₃N₄)。

Example 5

Adding 4.62g of cadmium chloride and 4.62g of thiourea into 60mL of ethylenediamine, uniformly mixing, carrying out hydrothermal reaction for 48h at 160 ℃, carrying out centrifugal separation, carrying out centrifugal washing on the obtained solid product to neutrality, and carrying out vacuum drying for 10h at 60 ℃ to obtain the CdS. A photocatalyst was then prepared as in example 1, except that P25 was replaced with CdS to give a photocatalyst (noted as 0.5Pt/CdS) as in example 1.

Example 6

A photocatalyst was prepared in the same manner as in example 1 except that 0.105mL of a chloroplatinic acid solution having a concentration of 10g/L was replaced with 1.330mL of a copper chloride solution having a concentration of 1g/L and 2.043mL of a nickel chloride solution having a concentration of 1g/L to obtain a photocatalyst (described as 0.5 CuNi/P25).

Example 7

Adding 0.5g of titanium dioxide into 50mL of distilled water, performing ultrasonic treatment for 10min, adding 0.525mL of chloroplatinic acid solution with the concentration of 10g/L, stirring for 1h at room temperature, dropwise adding 5mL of sodium borohydride aqueous solution with the concentration of 0.1mol/L under the stirring condition, performing reduction reaction, continuing stirring for reduction reaction for 30min, performing suction filtration, washing the obtained solid product with water, and performing vacuum drying at 60 ℃ for 10h to obtain the photocatalyst (recorded as 0.5 Pt/P25-C).

Example 8

Adding 0.525mL of chloroplatinic acid solution with concentration of 10g/L into 5mL of distilled water, adding 0.5g of titanium dioxide under stirring, performing ultrasonic treatment for 10min, stirring at room temperature for 1H, transferring into a water bath, stirring at 80 ℃ until the distilled water is completely volatilized, grinding, and reducing in a tubular furnace with reducing gas of 5% H₂and/Ar, the flow rate is 50mL/min, the heating rate is 2 ℃/min, the temperature is increased to 350 ℃, the temperature is kept for 3H, and the photocatalyst (marked as 0.5Pt/P25-H) is obtained after natural cooling.

Comparative example 1

Titanium dioxide (Degussa, P25) is a photocatalyst.

Fig. 1 is an X-ray powder diffraction pattern of the photocatalysts of example 1 and comparative example 1. As can be seen from fig. 1, the XRD test results of the transition metal-unsupported carrier P25 and the photocatalyst after supporting Pt metal are almost the same, which indicates that the transition metal supported does not affect the photoresponsive semiconductor carrier, and no characteristic diffraction peak of the metal is observed because the supported amount of Pt is low and highly dispersed.

Example 8

Respectively mixing 5.0mg of the photocatalyst of examples 1-7 and comparative example 1 and 5mL of methanol-ammonia mixed solution in an interlayer quartz reaction tube, uniformly mixing, and carrying out photocatalytic reaction for 2h under the conditions of argon, normal pressure and 55 ℃ to obtain urotropine and hydrogen, wherein the volume fraction of concentrated ammonia water in the methanol-ammonia mixed solution is 7%, and the mass fraction of the concentrated ammonia water is 25-28%. The production rates of urotropin and hydrogen with different photocatalysts are shown in table 1:

TABLE 1 production rates of urotropin and hydrogen in the presence of different photocatalysts

From Table 1, it can be seen thatDifferent photoresponse semiconductor carriers and photocatalysts loaded with different metals are adopted, and certain activity can be shown in the reaction, wherein the generation rate of the urotropine is 1.30-11.39 mmol · gcat^-1·h^-1The hydrogen generation rate is 10.15 to 71.53 mmol/gcat^-1·h^-1. Among them, the 0.5Pt/P25 catalyst shows the best activity because the titanium dioxide P25 has a wider forbidden bandwidth and stronger hole oxidability, which is beneficial to methanol dehydrogenation, and the Pt has a larger work function and stronger capture capacity for photo-generated electrons, which promotes the separation of photo-generated electrons and holes, thereby showing the best photocatalytic activity.

Example 8

The 0.5Pt/P25 prepared in example 1 was recycled for use in the preparation of urotropin according to the method of example 7, wherein after the completion of the photocatalytic reaction, the photocatalyst was washed with methanol and centrifuged, and a fresh methanol-ammonia mixture was added to again perform the photocatalytic reaction. The results of the cyclic catalytic stability test of 0.5Pt/P25 are shown in FIG. 2 and Table 2.

TABLE 2 results of the cyclic catalytic stability test of 0.5Pt/P25 prepared in example 1

As can be seen from FIG. 2 and Table 2, 0.5Pt/P25 still retains the original catalytic activity after 5 photocatalytic reactions, which indicates that the photocatalyst still retains stable structure and performance after at least 5 reactions. Ratio e of electrons to holes^-/h⁺Approaching to 1, which shows that the photocatalyst adopted by the invention has high cyclic catalysis stability.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.