A method for photocatalytic coupling of carbon monoxide and ammonia to synthesize urea

Abstract

This invention discloses a method for photocatalytic coupling of carbon monoxide and ammonia to synthesize urea. The method involves mixing a photocatalyst and ammonia in a reaction atmosphere containing carbon monoxide, followed by a photocatalytic reaction to obtain the urea. Compared with existing photocatalytic reduction synthesis systems for urea, this invention's method exhibits better selectivity and catalytic performance, avoids the formation of liquid-phase byproducts, and reduces the purification and separation costs of urea. This invention also found that when 20% oxygen is introduced, the method can selectively oxidatively couple carbon monoxide and ammonia to urea, maintaining a catalytic performance of 9290.67 μgh for 4 hours. ‑1 g cat ‑1 The urea production rate has a selectivity of 100%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photochemical synthesis of urea, and particularly relates to a method for synthesizing urea by photocatalytic coupling of carbon monoxide and ammonia. BACKGROUND

[0002] Urea, as a nitrogen-containing fertilizer with a nitrogen content of up to 46%, not only plays an important role in agricultural production, but also is applied in the fields of plastics, medicine and chemical industry. Currently, the two-step synthesis process is mainly used in the industrial production of urea. First, nitrogen and hydrogen are synthesized into ammonia by the Haber-Bosher method, and then ammonia and carbon dioxide are synthesized into urea by the Bosher-Meiser method. It is well known that this process is a high-energy consumption and high-pollution process, which consumes nearly 2% of the global energy consumption and emits a large amount of greenhouse gases under harsh conditions (150-200℃, 150-250bar). Therefore, it is of great significance to develop a sustainable, green and efficient C-N coupling technology for environmentally friendly urea synthesis.

[0003] At present, the electrocatalytic or photocatalytic synthesis of urea can utilize renewable clean energy to couple CO2 and nitrogen-containing compounds (N2, NO2 - , NO3 - , etc.) under mild conditions to achieve decarburization and nitrogen fixation. However, the current photo or electrocatalytic C-N coupling reaction involves a complex multi-electron proton participating reduction process, and thus faces problems such as multiple by-products and low reaction selectivity. In addition, the reduction reaction is usually severely limited by the thermodynamic oxygen reduction reaction, and therefore, the reaction device needs to be sealed to prevent oxygen pollution, which increases the reaction cost and limits the industrial production. SUMMARY

[0004] To improve the above technical problems, the application provides an application of a photocatalyst in photocatalytic coupling of carbon monoxide and ammonia to prepare urea.

[0005] The photocatalyst is at least one selected from the group consisting of rutile titanium dioxide, anatase titanium dioxide, brookite titanium dioxide, P25 type titanium dioxide, graphite phase carbon nitride, indium trioxide, cadmium sulfide and oxygen vacancy titanium dioxide.

[0006] Preferably, the photocatalyst is oxygen vacancy titanium dioxide.

[0007] According to an embodiment of the application, the preparation method of the oxygen vacancy titanium dioxide is as follows:

[0008] The titanium dioxide substrate is calcined in the presence of inert gas to obtain the oxygen vacancy titanium dioxide.

[0009] According to an embodiment of the present application, the titanium dioxide substrate can be obtained from a commercial supplier, such as rutile titanium dioxide, anatase titanium dioxide, brookite titanium dioxide or P25 type titanium dioxide.

[0010] According to an embodiment of the present application, the inert gas is, for example, argon; preferably, the flow rate of the inert gas is 30-50 mL min -1 .

[0011] According to an embodiment of the present application, the calcination temperature is 300-600℃, preferably 300-450℃, and the calcination time can be 1-8h, preferably 1-6h, such as 1h, 2h, 3h, 4h, 5h, 6h.

[0012] According to an embodiment of the present application, the preparation of the oxygen vacancy titanium dioxide further comprises a post-treatment step such as water washing, centrifugation, etc.

[0013] As an exemplary embodiment of the present application, the preparation method of the oxygen vacancy titanium dioxide is as follows:

[0014] The titanium dioxide substrate is laid in an Al2O3 ceramic boat and calcined under argon atmosphere, and the oxygen vacancy titanium dioxide is prepared by washing with water after calcination, and collecting the precipitate by centrifugation.

[0015] The present application also provides a method for photocatalytic coupling of carbon monoxide and ammonia to synthesize urea, which comprises:

[0016] The above photocatalyst and ammonia are mixed in a reaction atmosphere containing carbon monoxide, and urea is prepared after light irradiation.

[0017] According to an embodiment of the present application, oxygen can also be added to the reaction atmosphere.

[0018] According to an embodiment of the present application, the volume ratio of carbon monoxide to oxygen can be (1-0.5):(0-0.5), preferably (0.99-0.5):(0.01-0.5), such as 1:0, 0.9:0.1, 0.8:0.2, 0.7:0.3, 0.6:0.4 or 0.5:0.5.

[0019] According to an embodiment of the present application, the purity of carbon monoxide is 99.99%.

[0020] According to an embodiment of the present application, the purity of oxygen is 99.99%.

[0021] According to an embodiment of the present application, the pressure of the reaction atmosphere can be 0.05-0.2Mpa, such as 0.05Mpa, 0.1Mpa, 0.15Mpa or 0.2Mpa.

[0022] According to an embodiment of the present invention, the mass-to-volume ratio of the photocatalyst and ammonia is 1 mg:(4-12) mL, preferably 1 mg:(4-10) mL.

[0023] According to an embodiment of the present invention, the amount of photocatalyst used can be 5-20 mg, for example 5 mg, 10 mg, 15 mg or 20 mg.

[0024] According to an embodiment of the present invention, the concentration of the ammonia solution can be 0.5-3M, for example, 0.5M, 1M, 2M or 3M. Preferably, the volume of the ammonia solution can be 20-60mL, for example, 20mL, 30mL, 40mL, 50mL or 60mL.

[0025] According to an embodiment of the present invention, the photoreaction is carried out in a photoreactor, which is a sealable quartz reactor with a circulating water glass jacket.

[0026] According to an embodiment of the present invention, the photoreaction is carried out under xenon lamp irradiation; the light intensity of the xenon lamp can be 300-600 mW / cm². -2 For example, 300mW cm -2 400mW cm -2 500mW cm -2 Or 600mW -2 cm.

[0027] According to an embodiment of the present invention, the reaction time of the photoreaction is 1 hour or more, for example, 1-16 hours.

[0028] According to an embodiment of the present invention, the photoreaction is carried out under stirring, preferably at a stirring speed of 500-1000 rpm, more preferably 700 rpm.

[0029] According to an embodiment of the present invention, the pH of the reaction system is 7-11.

[0030] According to an embodiment of the present invention, the main product of the reaction is urea.

[0031] As an exemplary embodiment of the present invention, the method for synthesizing urea specifically includes the following steps:

[0032] The above photocatalyst was added to a glass-jacketed quartz reactor containing ammonia water and ultrasonicated to form a uniform suspension. A mixture of carbon monoxide and oxygen (CO:O2 = 80:20) was introduced into the reactor to make the initial pressure 0.1 MPa. After 30 minutes, the solution reached a state of gas dissolution saturation. Then, a xenon lamp irradiation reaction was carried out to prepare urea.

[0033] Beneficial effects

[0034] 1) Compared with existing photocatalytic reduction synthesis systems for urea, the method of this invention exhibits better selectivity and catalytic performance, and avoids the generation of liquid-phase byproducts, thus reducing the purification and separation cost of urea. This invention also found that when 20% oxygen is introduced, the method can selectively oxidize and couple carbon monoxide and ammonia to urea, maintaining a catalytic performance of 9290.67 μgh for 4 hours. -1 g cat -1 The urea formation rate has a selectivity of 100%.

[0035] 2) The photocatalyst used in the method of the present invention has universality. The photocatalyst can be rutile phase titanium dioxide, anatase phase titanium dioxide, brookite phase titanium dioxide, P25 type titanium dioxide, graphitic phase carbon nitride, indium trioxide or cadmium sulfide, etc., which to a certain extent broadens the path for the development of photocatalytic synthesis of urea.

[0036] 3) This invention can separate urea from volatile ammonia solution by heating and distillation, reducing the steps of liquid product purification and separation, and providing a new approach for the photocatalytic synthesis of urea.

[0037] 4) The oxygen vacancy titanium dioxide photocatalyst provided by the present invention has excellent activity in the above-mentioned photocatalytic oxidation synthesis of urea. The preparation method of the oxygen vacancy titanium dioxide photocatalyst is relatively simple and low in cost, which is of great significance in the field of urea synthesis.

[0038] 5) The method of this invention uses solar energy as the driving force, which reduces reaction costs, avoids secondary pollution and other problems, and solves the problem of difficult urea synthesis. Attached Figure Description

[0039] Figure 1 The images are scanning electron microscope (SEM) images of oxygen-vacancy titanium dioxide P25 (left) and P25-4h (right) from Example 1.

[0040] Figure 2 The images show the transmission electron microscopy (TEM), elemental distribution (top right and bottom left), and high-resolution transmission electron microscopy (HRTEM) images (bottom right) of oxygen-vacancy titanium dioxide P25-4h from Example 1.

[0041] Figure 3 The X-ray diffraction (XRD) patterns of oxygen-vacancy titanium dioxide P25, P25-2h, P25-4h, and P25-6h from Example 1 are shown.

[0042] Figure 4The solid-state diffuse ultraviolet reflectance (DRS) images of oxygen-vacancy titanium dioxide P25, P25-2h, P25-4h and P25-6h from Example 1 are shown.

[0043] Figure 5 This is a comparison chart showing the yield and selectivity of the oxygen vacancy titanium dioxide photocatalyst P25-4h in Example 1, when carbon dioxide and ammonia are coupled together under different oxygen concentrations to form urea.

[0044] Figure 6 The graph shows a comparison of the performance of different oxygen vacancy titanium dioxide photocatalysts (P25, P25-2h, P25-4h, Rutile-4h, Anatase-4h, and Brookite-4h) and photocatalysts rutile TiO2 (Rutile), anatase TiO2 (Anatase), and brookite TiO2 (Brookite) in the oxygen atmosphere for the coupling of carbon dioxide and ammonia to form urea.

[0045] Figure 7 The graph shows a comparison of the performance of the graphitic carbon nitride, indium oxide, and cadmium sulfide photocatalysts in Examples 3, 4, and 5 in the synthesis of urea by coupling carbon oxide and ammonia in oxygen-free and oxygen-containing atmospheres. Detailed Implementation

[0046] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0047] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0048] Example 1

[0049] The preparation of an oxygen-vacancy titanium dioxide photocatalyst is carried out according to the following steps:

[0050] 1) Before use, commercially available P25 TiO2 was washed and filtered with deionized water and ethanol, respectively, and then vacuum-dried at 60℃ for 12h to remove organic and inorganic impurities from its surface. First, 500mg of P25 TiO2 was weighed and placed in an Al2O3 ceramic boat, which was then placed in a tube furnace. A vacuum pump was used to evacuate the furnace, with Ar as the equilibrium gas. This process was repeated three times before the heating program was initiated. The heating program was as follows: heating from room temperature to 350℃ at a rate of 5℃ / min, and then maintaining this temperature at 350℃ for different times: 0h, 2h, 4h, and 6h. After cooling to room temperature, the sample was removed, washed with water, and filtered to obtain oxygen-vacancy titanium dioxide, named P25, P25-2h, P25-4h, and P25-6h, respectively; where P25 refers to commercially available P25 TiO2.

[0051] 2) Based on the above method, rutile phase TiO2, anatase phase TiO2 and brookite phase TiO2 were calcined in the same way to prepare oxygen vacancy titanium dioxide, which were named Rutile-4h, Anatase-4h and Brookite-4h, respectively.

[0052] Figure 1 Scanning electron microscope (SEM) images of P25 (left) and P25-4h (right) prepared in Example 1. A comparison of the images shows that the obtained P25-4h maintains the original nanoparticle shape of P25, with a diameter of approximately 20-50 nm.

[0053] Figure 2 These are transmission electron microscopy (TEM), elemental distribution, and high-resolution transmission electron microscopy (HRTEM) images of P25-4h prepared in Example 1. Figure 2 This indicates that Ti and O elements are uniformly distributed on the catalyst surface.

[0054] Figure 3 X-ray diffraction (XRD) patterns of P25, P25-2h, P25-4h, and P25-6h prepared in Example 1. Figure 3 As can be seen, the crystal form of the synthesized P25 did not change after calcination in an argon atmosphere, and the characteristic peaks corresponding to the standard cards of rutile and anatase phases could be observed, indicating that the synthesis process did not affect the crystal structure of P25-4h.

[0055] To investigate the light absorption of the catalyst, solid-state ultraviolet-visible diffuse reflectance (DRS) measurements were further performed. Figure 4 The solid-state diffuse ultraviolet reflectance (DRS) maps for P25, P25-2h, P25-4h, and P25-6h in Example 1 are obtained from... Figure 4It can be seen that P25-4h shows a slight red shift in the absorption band edge compared to P25, indicating that the introduction of oxygen vacancies gives P25-4h a stronger light absorption capacity.

[0056] Example 2

[0057] Oxygen-vacancy titanium dioxide photocatalysts are used for photocatalytic urea synthesis, comprising the following steps:

[0058] 1) The oxygen vacancy titanium dioxide photocatalysts prepared in Example 1 (including P25, P25-2h, P25-4h, Rutile-4h, Anatase-4h, Brookite-4h) and 10 mg of the photocatalysts rutile TiO2 (Rutile), anatase TiO2 (Anatase), and brookite TiO2 (Brookite) were dispersed in 50 mL of 2M ammonia water and ultrasonically dispersed for 30 min. Then, they were transferred to a quartz reactor with a circulating water glass jacket.

[0059] 2) Before illumination, the reactor was sealed, and an ammonia solution was purged for 30 minutes at a flow rate of 50 mL / min with a mixture of CO and O2 in different proportions (O2 concentrations of 0%, 10v%, 20v%, 40v%, and 50v%; corresponding CO concentrations of 100v%, 90v%, 80v%, 70v%, 60v%, and 50v%). The reactor pressure was 0.1 MPa. The reaction system was then irradiated with a xenon lamp at a light intensity of 300 mW / cm². 2 A rotor was added to the reactor, with a stirring speed of 700 rpm and an illumination time of 4 hours. During the reaction, 2 mL of the reaction solution was collected every 1 hour and filtered through a syringe filter to obtain the liquid product.

[0060] Product detection: Gaseous products were collected using a syringe and analyzed by gas chromatography. Urea was analyzed by colorimetric method using diacetyl monooxime, and other liquid products were detected by ion chromatography.

[0061] Figure 5 The graph shows the yield and selectivity of P25-4h photocatalytic coupling of CO and ammonia to urea at room temperature under different O2 concentrations. Figure 5 It can be seen that when the O2 concentration is 20%, P25-4h can achieve excellent selectivity (100%) for urea and a high urea production rate (9290.67 μgh). -1 g cat -1 ).

[0062] Figure 6The urea production figures for the photocatalysts prepared in Example 1 (P25, P25-2h, P25-4h, Rutile-4h, Anatase-4h, and Brookite-4h, respectively) and the photocatalysts rutile TiO2, anatase TiO2, and Brookite TiO2 during the photocatalytic coupling of CO and NH3 under 20% O2 are shown in the figure. The urea production rates are 3665.68 μgh, respectively. -1 g cat -1 (P25), 5809.44μgh -1 g cat -1 (P25-2h), 9290.67μgh -1 g cat -1 (P25-4h), 4388.36μgh -1 g cat -1 (Rutile-4h), 381.29μgh -1 g cat -1 (Anatase-4h), 165.57 μgh -1 g cat -1 (Brookite-4h) shows that P25-4h has a high urea formation rate. Furthermore, when 20% oxygen is introduced, the method of this invention can selectively oxidize and couple carbon monoxide and ammonia to urea, with a urea selectivity of 100%.

[0063] Example 3

[0064] The preparation of a graphitic carbon nitride photocatalyst is carried out according to the following steps:

[0065] 15g of melamine was weighed and placed in a muffle furnace, heated from room temperature to 500℃ at a rate of 5℃ / min, and then held at 500℃ for 3h to obtain a blocky C3N4 precursor. The C3N4 precursor was weighed and placed in a mortar, then 6.6g of potassium chloride and 5.4g of lithium chloride were added. After thorough grinding, the mixture was transferred to an Al2O3 ceramic boat and placed in a tube furnace. Under Ar conditions, the mixture was heated to 550℃ at 3℃ / min and held for 4h. After cooling to room temperature, the sample was removed, eluted with boiling water, and filtered to obtain graphitic carbon nitride.

[0066] A photocatalyst is used in the photocatalytic synthesis of urea, comprising the following steps:

[0067] 1) 10 mg of the graphitic carbon nitride photocatalyst prepared in Example 3 was dispersed in 50 mL of 2M ammonia water, ultrasonically dispersed for 30 min, and then transferred to a quartz reactor with a circulating water glass jacket.

[0068] 2) Before illumination, seal the reactor and purge it for 30 minutes with an ammonia solution at a flow rate of 50 mL / min with a mixture of CO and O2 (O2 concentration 20 v%; CO concentration 80 v%) or a mixture of CO and Ar (Ar concentration 20 v%; CO concentration 80 v%). The reactor pressure is 0.1 MPa. Irradiate the reaction system with a xenon lamp at a light intensity of 300 mW / cm². 2 A rotor was added to the reactor, the rotor speed was 700 rpm, and the light exposure time was 4 h, to prepare urea.

[0069] Figure 7 The graph shows the urea yield during the photocatalytic coupling of CO and NH3 under anaerobic and aerobic conditions using the photocatalyst prepared in Example 3. The urea yield is 353.09 μgh under anaerobic and aerobic conditions, respectively. -1 g cat -1 11670.87μgh -1 g cat -1 .

[0070] Example 4

[0071] The preparation of an indium trioxide photocatalyst is carried out according to the following steps:

[0072] Weigh 0.3g In(NO3)3·4.5H2O and dissolve it in 30mL ethylene glycol. Slowly add 0.5g / mL NaOH aqueous solution and sonicate for 30min. Transfer the mixed solution to an oven and hydrothermally heat it at 200℃ for 24h. After the oven cools naturally to room temperature, wash it three times with water and ethanol. Then dry the solid product in a vacuum drying oven at 60℃ for more than 12 hours to obtain indium trioxide.

[0073] The preparation of the photocatalyst for photocatalytic urea synthesis is the same as in Example 3, except that indium trioxide is used instead of graphite-phase carbon nitride photocatalyst.

[0074] Figure 7 The graph shows the urea yield during the photocatalytic coupling of CO and NH3 under anaerobic and aerobic conditions using the photocatalyst prepared in Example 4. The urea yield is 434.61 μgh under anaerobic and aerobic conditions, respectively. -1 g cat -1 16100.25μgh -1 g cat-1 .

[0075] Example 5

[0076] The preparation of a photocatalytic cadmium sulfide photocatalyst is carried out according to the following steps:

[0077] Weigh 0.122g CdCl2 and 0.107g sulfur powder and dissolve them in 20mL diethylenetriamine at room temperature. Transfer the solution to an oven and heat it at 80℃ for 3 hours. Then cool it to room temperature at a rate of 5℃ / min. Wash it three times with deionized water. Dry the resulting solid product under vacuum at 80℃ for more than 12 hours to obtain cadmium sulfide.

[0078] The preparation of the photocatalyst for photocatalytic urea synthesis is the same as in Example 3, except that cadmium sulfide is used instead of graphite-phase carbon nitride photocatalyst.

[0079] Figure 7 The graph shows the urea yield during the photocatalytic coupling of CO and NH3 under anaerobic and aerobic conditions using the photocatalyst prepared in Example 5. The urea yield is 461.15 μgh under anaerobic and aerobic conditions, respectively. -1 g cat -1 17332.47μgh -1 g cat -1 .

[0080] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a photocatalyst in the photocatalytic coupling of carbon monoxide and ammonia to prepare urea, characterized in that, The photocatalyst is selected from at least one of rutile phase titanium dioxide, anatase phase titanium dioxide, brookite phase titanium dioxide, P25 type titanium dioxide, graphitic carbon nitride, indium trioxide, cadmium sulfide, and oxygen vacancy titanium dioxide.

2. A method for photocatalytic coupling of carbon monoxide and ammonia to synthesize urea, characterized in that, The method includes: The urea is prepared by mixing the photocatalyst of claim 1 with ammonia water in a reaction atmosphere containing carbon monoxide and then subjecting the mixture to a photocatalytic reaction.

3. The method according to claim 2, characterized in that, Oxygen is also added to the reaction atmosphere.

4. The method according to claim 3, characterized in that, The volume ratio of carbon monoxide to oxygen is (1-0.5):(0-0.5).

5. The method according to claim 2, characterized in that, The pressure of the reaction atmosphere is 0.05–0.2 MPa.

6. The method according to claim 2, characterized in that, The mass-to-volume ratio of the photocatalyst and ammonia water is 1 mg:(4-12) mL.

7. The method according to claim 2, characterized in that, The photoreaction is carried out under xenon lamp irradiation; the light intensity of the xenon lamp is 300–600 mW / cm². -2 .

8. The method according to claim 2, characterized in that, The reaction time of the light-induced reaction is more than 1 hour.

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