Titanium dioxide photocatalyst co-modified by ni monatomic and pd nanoparticles and preparation and application thereof

Abstract

The application discloses a kind of Ni monatomic and Pd nanoparticle co-modified TiO2 Photocatalyst and its preparation method and application in photocatalytic alkane non-oxidative dehydrogenation for olefin.The application first prepares monatomic photocatalyst with organic ligand using surface organometallic chemistry method, then obtains monatomic photocatalyst by calcination, and then prepares photocatalyst containing monatomic and nanoparticle simultaneously by combining with photodeposition method.Ni monatomic in the obtained photocatalyst can make adjacent Pd nanoparticle selectively photocatalyze alkane dehydrogenation for olefin, so that the photocatalyst has excellent dehydrogenation activity, higher product selectivity and carbon deposition resistance in photocatalytic alkane non-oxidative dehydrogenation for olefin.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photocatalysis, and particularly relates to a Ni monatomic and Pd nanoparticle co-modified TiO2 photocatalyst, a preparation method thereof and application of the photocatalyst in photocatalytic non-oxidative dehydrogenation of alkanes to produce alkenes. BACKGROUND

[0002] Ethylene and propylene are one of the largest basic organic chemical raw materials in global production and consumption, are often widely referred to as the cornerstone of petrochemical industry, and the production of ethylene has been considered as one of the important indicators for measuring the development level of a country in the petrochemical industry. With the rapid growth of the demand for alkenes in China, the supply of alkenes has become increasingly tight in recent years. At present, the main method for producing alkenes in industry is through steam cracking of naphtha, but this requires high temperature and high pressure reaction conditions and is accompanied by the generation of other by-products.

[0003] In recent years, with the emergence of shale gas, its development and utilization has become a hot issue in the global energy field. Among them, ethane, as the second most abundant component in shale gas, has attracted widespread attention due to its low cost and low energy consumption in catalytic dehydrogenation to produce ethylene. At present, the reaction of ethane dehydrogenation to produce ethylene is generally divided into two categories: oxidative dehydrogenation of ethane and non-oxidative dehydrogenation of ethane. Although oxidative dehydrogenation of ethane is more thermodynamically favorable, but because the generated ethylene has higher reactivity than the reactant ethane, over-oxidation often occurs, producing CO2 and CO. Compared with oxidative dehydrogenation of ethane, non-oxidative dehydrogenation of ethane has unique advantages in avoiding over-oxidation and producing valuable ethylene and hydrogen fuel. However, whether it is the industrial production of ethylene by cracking naphtha or the production of ethylene by thermal catalytic dehydrogenation of ethane, high temperature reaction conditions are required. Such harsh high temperature conditions can cause metal sintering, resulting in rapid deactivation of the catalyst, poor stability, the need for frequent regeneration, and also reducing the selectivity of the target product. The use of photocatalytic technology to dehydrogenate alkanes to produce alkenes can greatly reduce the sintering of metals at high temperatures, thereby improving the operating cycle of the catalyst. However, most of the current photocatalytic alkanes to produce alkenes are aerobic dehydrogenation, which greatly limits the selectivity of alkenes. SUMMARY

[0004] The purpose of the present application is to provide a Ni monatomic and Pd nanoparticle co-modified TiO2 photocatalyst, a preparation method thereof and application of the photocatalyst in photocatalytic non-oxidative dehydrogenation of alkanes to produce alkenes. The photocatalyst has excellent activity and selectivity of alkenes, and has strong stability and strong anti-coking ability.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] One of the purposes of the present application is to protect a TiO2 photocatalyst co-modified by Ni monomers and Pd nanoparticles, wherein Ni is uniformly distributed on the surface of TiO2 in the form of monomers, and Pd is uniformly distributed on the surface of TiO2 in the form of nanoparticles, thereby forming the TiO2 photocatalyst.

[0007] Further, in the photocatalyst, the content of Ni is 0.4wt%-1wt%, and the content of Pd is 0.2wt%-1.5wt%.

[0008] The second purpose of the present application is to protect the preparation method of the TiO2 photocatalyst co-modified by Ni monomers and Pd nanoparticles, which comprises the following steps:

[0009] 1) After the anatase TiO2 is pressed into a tablet, it is placed in a quartz reaction tube and treated in a flowing oxygen atmosphere at 400℃ for 10h-15h, and then treated at 400℃ under dynamic vacuum conditions for 2h-4h, and then naturally cooled to room temperature;

[0010] 2) The organic transition metal compound is dissolved in n-hexane to form a supersaturated solution, and then the solution is injected into the quartz reaction tube of step 1) in a liquid nitrogen cold trap environment, after which the n-hexane is pumped out under dynamic vacuum conditions, and then calcination is carried out under vacuum conditions, and after the calcination is completed, dynamic vacuum pumping is carried out again;

[0011] 3) The sample obtained in step 2) is calcined in an oxygen atmosphere and ground to obtain a solid powder;

[0012] 4) The solid powder obtained in step 3) is dispersed in deionized water, H2PdCl4 solution is added, and the mixture is irradiated with a 300 mW·cm -2 -2 of xenon lamp light for 5min-30min under stirring conditions, and then the obtained sample is washed with deionized water and dried overnight to obtain the TiO2 photocatalyst.

[0013] Further, the organic transition metal compound in step 2) is nickelocene.

[0014] Further, the temperature of the calcination in step 2) is 100℃-200℃, and the time is 12h-30h.

[0015] Further, the pressure range of the vacuum conditions used in the operation is 10 -2 -10Pa.

[0016] Further, the temperature of the calcination in step 3) is 300℃-400℃, and the time is 10h-16h.

[0017] Further, the concentration of the H2PdCl4 solution in step 4) is 1mg / mL.

[0018] The third object of the present application is to protect the application of the Ni monatomic and Pd nanoparticle co-modified TiO2 photocatalyst in the photocatalytic non-oxidative dehydrogenation of alkanes to produce alkenes.

[0019] Further, the application method is to use a 200 mL reactor in an inert gas atmosphere, using the Ni monatomic and Pd nanoparticle co-modified TiO2 photocatalyst (5-50 mg) to perform non-oxidative dehydrogenation of alkanes under light, normal temperature and pressure.

[0020] Further, the inert gas is argon, and the alkane is one of ethane and propane, and the molar ratio of inert gas to alkane is 9-99:1.

[0021] Further, the intensity of the used light is 300 mW·cm -2 .

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) The present application prepares a highly efficient and stable Ni monatomic and Pd nanoparticle co-modified TiO2 photocatalyst by a method combining surface organometallic chemistry and photodeposition. Compared with other photocatalysts, the photocatalyst of the present application has excellent activity and olefin selectivity.

[0024] (2) In the structure of the prepared photocatalyst, the Ni monatomic can adjust the adsorption and desorption capacity of Pd nanoparticles to alkenes, thereby further improving the selectivity of alkenes and the stability of the catalyst.

[0025] (3) The preparation method of the present application has low energy consumption, the raw materials are easy to obtain, and the production cost is low. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The TEM image of the T-Ni 0.6 Pd 0.24 photocatalyst prepared in Example 1.

[0027] Figure 2 The TEM image of the T-Ni 0.6 Pd 0.24 photocatalyst prepared in Example 1.

[0028] Figure 3 The performance comparison chart of the photocatalytic non-oxidative dehydrogenation of ethane to produce ethylene using the photocatalyst prepared in Examples 1-4. DETAILED DESCRIPTION

[0029] A Ni monatomic and Pd nanoparticle co-modified TiO2 photocatalyst, the preparation method thereof comprises the following steps:

[0030] 1) The anatase TiO2 tablet is placed in a quartz reaction tube, treated in a flowing oxygen atmosphere at 400°C for 10-15h, then treated at 400°C under dynamic vacuum for 2-4h, and then naturally cooled to room temperature;

[0031] 2) The bis(nickelocene) is dissolved in n-hexane to form a supersaturated solution, which is then injected into the quartz reaction tube of step 1) in a liquid nitrogen cold trap environment, after which the n-hexane is pumped out under dynamic vacuum, and then calcined at 100-200°C under vacuum for 12-30h (the heating rate is 1-5°C / min), after which dynamic vacuum is again applied;

[0032] 3) The sample obtained in step 2) is calcined at 300-400°C in an oxygen atmosphere for 10-16h, and then ground to obtain a solid powder;

[0033] 4) The solid powder obtained in step 3) is dispersed in deionized water, 1mg / mL H2PdCl4 solution is added, and the mixture is irradiated with a 300 mW·cm-2 xenon lamp for 5-30min under stirring, after which the sample is washed with deionized water and dried overnight to obtain the TiO2 photocatalyst. -2

[0034] The pressure range of the vacuum conditions used in the operation is 10 -2 -10Pa.

[0035] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0036] Example 1

[0037] 1) 50mg of anatase TiO2 is pressed into a tablet and placed in a quartz reaction tube with a sliding core, treated in a flowing oxygen atmosphere at 400°C for 12h, then treated at 400°C under dynamic vacuum at 10 -2 Pa for 3h, and then naturally cooled to room temperature;

[0038] 2) Bis(nickelocene) is dissolved in n-hexane to form a supersaturated solution, 50μL of which is injected into the reaction tube of step 1) in a liquid nitrogen cold trap environment, after which the n-hexane is pumped out under dynamic vacuum at 10 -2 Pa, then calcined at 130°C under vacuum for 30h, after which the n-hexane is pumped out under dynamic vacuum at 130°C and 10 -2 Pa for 3h;

[0039] 3) The sample obtained in step 2) is calcined at 400°C in an oxygen atmosphere for 12h, and then ground to obtain a solid powder;​

[0040] 4) The solid powder obtained in step 3) was dispersed in 50 mL deionized water, 0.35 mL of 1 mg / mL H2PdCl4 solution was added, and the mixture was irradiated with 300 mW-cm2UV light under stirring for 10 min. -2 Irradiated by xenon lamp for 10 min;

[0041] 5) The sample obtained in step 4) was washed with deionized water for 5 times and dried at 80°C overnight to obtain T-Ni 0.6 Pd 0.24 photocatalyst.

[0042] Figure 1 The spherical aberration transmission electron microscopy image of the T-Ni 0.6 Pd 0.24 photocatalyst prepared in this example. As can be seen from Fig. a, the Ni atoms in the prepared photocatalyst are dispersed on the surface of the catalyst in isolation; as can be seen from Fig. b, the Pd is distributed on the surface of the catalyst in the form of nanoparticles.

[0043] Figure 2 The cyclic stability test graph of the T-Ni 0.6 Pd 0.24 photocatalyst prepared in this example. As can be seen from the graph, the prepared photocatalyst has excellent performance, and the ethylene yield thereof is 956.3 μmol-g -1 ·h -1 , and nearly stoichiometric H2 (890.6 μmol-g -1 ·h -1 ) was also detected; and the photocatalyst still maintains high activity after ten cycles, indicating that the photocatalyst has high activity, stability and anti-carbon deposition capacity.

[0044] Example 2

[0045] The preparation method is the same as that in Example 1, except that 30 μL of the solution was injected into the reaction tube of step 1) in a liquid nitrogen cold trap environment in step 2), thereby obtaining a T-Ni 0.4 Pd 0.24 photocatalyst.

[0046] Example 3

[0047] The preparation method is the same as that in Example 1, except that 70 μL of the solution was injected into the reaction tube of step 1) in a liquid nitrogen cold trap environment in step 2), thereby obtaining a T-Ni 0.8 Pd 0.24 photocatalyst.

[0048] Example 4

[0049] The preparation method is the same as that of Example 1, except that in step 2), 90 μL of the solution is injected into the reaction tube of step 1) in a liquid nitrogen cold trap environment, thereby obtaining T-Ni 1.0 Pd 0.24 photocatalyst.

[0050] Figure 3 The performance of the photocatalysts prepared in Examples 1-4 in photocatalytic non-oxidative dehydrogenation of ethane to ethylene is shown in the figure. As can be seen from the figure, the performance of the photocatalyst is best when the content of Ni in the photocatalyst is 0.6%.

[0051] Comparative Example 1

[0052] 1) 50 mg of anatase TiO2 is placed in a quartz reaction tube with a sliding core after being pressed into a tablet, and is treated at 400°C in a flowing oxygen atmosphere for 12 h, and then is treated at 400°C under a dynamic vacuum of 10 -2 Pa for 3 h, and then is naturally cooled to room temperature;

[0053] 2) Nickelocene is dissolved in n-hexane to form a supersaturated solution, and then 50 μL of the solution is injected into the reaction tube of step 1) in a liquid nitrogen cold trap environment, and then the n-hexane is removed under a dynamic vacuum of 10 -2 Pa, and then is calcined at 130°C under a vacuum for 30 h, and after the calcination is completed, is removed under a dynamic vacuum of 10 -2 Pa for 3 h;

[0054] 3) The sample obtained in step 2) is calcined at 400°C in an oxygen atmosphere for 12 h, and then is ground, thereby obtaining T-Ni 0.6 photocatalyst.

[0055] Comparative Example 2

[0056] 1) 50 mg of anatase TiO2 powder is dispersed in 50 mL of deionized water, and 0.35 mL of a 1 mg / mL H2PdCl4 solution is added, and the mixture is irradiated with 300 mW·cm -2 xenon lamp light for 10 min;

[0057] 2) The sample obtained in step 1) is washed with deionized water 5 times, and is dried at 80°C overnight, thereby obtaining T-Pd 0.24 photocatalyst.

[0058] Comparative Example 3

[0059] 1) 50 mg of anatase TiO2 is placed in a quartz reaction tube with a sliding core after being pressed into a tablet, and is treated at 400°C in a flowing oxygen atmosphere for 12 h, and then is treated at 400°C under a dynamic vacuum of 10 -2 Pa for 3 h, and then is naturally cooled to room temperature;

[0060] 2) Dissolve the Ru-bisphosphine in n-hexane to form a supersaturated solution, then take 70 μL of the solution and inject into the reaction tube of step 1) in a liquid nitrogen cold trap environment, then remove n-hexane under dynamic vacuum condition at 10 -2 Pa under dynamic vacuum condition for 3 h; -2 Pa under dynamic vacuum condition for 3 h;

[0061] 3) Calcine the sample obtained in step 2) at 400°C in oxygen atmosphere for 12 h, then grind to obtain a solid powder;

[0062] 4) Disperse the solid powder obtained in step 3) in 50 mL deionized water, add 0.35 mL of 1 mg / mL H2PdCl4 solution, and stir under the condition of 300 mW·cm -2 Xenon lamp irradiation for 10 min;

[0063] 5) Wash the sample obtained in step 4) with deionized water for 5 times, and dry at 80°C overnight to obtain T-Ru 0.6 Pd 0.24 photocatalyst.

[0064] Comparative Example 4

[0065] The preparation method is the same as that of Comparative Example 3, except that in step 2) the Co-bisphosphine is dissolved in n-hexane to form a supersaturated solution, then 70 μL of the solution is taken and injected into the reaction tube of step 1) in a liquid nitrogen cold trap environment, thereby obtaining T-Co 0.6 Pd 0.24 photocatalyst.

[0066] Performance test of photocatalytic non-oxidative dehydrogenation of alkanes to olefins

[0067] The photocatalytic non-oxidative dehydrogenation of alkanes to olefins is carried out in a glass sealed batch reactor (volume 200 mL) with a quartz window on the top to obtain light irradiation. The specific operation is as follows: 5 mg of catalyst is dispersed in 1 ml of H2O and ultrasonically treated for 5 min to obtain a slurry, then the slurry is coated on a quartz plate and dried to form a catalyst film; then the obtained catalyst film is fixed in the reactor, and all experiments are carried out at normal pressure (101 kPa). Before the reaction, the system is first evacuated by a mechanical pump, then filled with 101 kPa of high-purity Ar (> 99.99%) for 30 min to completely remove O2 in the system; then, 2 ml of C2H6 or C3H8 is injected into the system by a syringe, and then at room temperature, 300 W xenon lamp (300 mW·cm -2) irradiated for 4 h, and 0.5 mL of gas was pumped out every 1 h to detect the product concentration by gas chromatography (GC). The obtained alkanes were analyzed by gas chromatography with a flame ionization detector (FID) on an Agilent 7890A, and the gaseous products were separated by an HP-PLOT Q capillary column. Hydrogen was analyzed by gas chromatography with a thermal conductivity detector (TCD) on an Agilent 7890B, and the product gas was separated by a 5A molecular sieve packed column and a Porapak q packed column.

[0068] Tables 1 and 2 respectively show the photocatalytic activity of the photocatalysts prepared in Example 1 and Comparative Examples 1-4 in the non-oxidative dehydrogenation of ethane and propane to olefins. As can be seen from the tables, the photocatalyst prepared in Example 1 has the highest photocatalytic performance.

[0069] Table 1 Comparison of the photocatalytic activity of different catalysts in the non-oxidative dehydrogenation of ethane to ethylene

[0070]

[0071] Table 2 Comparison of the photocatalytic activity of different catalysts in the non-oxidative dehydrogenation of propane to propylene

[0072]

[0073] Comparative Example 5

[0074] 50 mg of anatase TiO2 was impregnated with an equal volume of a solution of NiCl2·6H2O containing 0.3 mg of metal Ni, then stirred and dried at 80°C, and then calcined in a muffle furnace at 400°C for 12 h to obtain a solid powder. The obtained solid powder was ground and dispersed in 50 mL of deionized water, 0.35 mL of a 1 mg / mL H2PdCl4 solution was added, and the mixture was stirred under 300 mW·cm -2 Irradiated for 10 min with a xenon lamp. The obtained sample was washed with deionized water for 5 times and dried at 80°C overnight to obtain i-T-Ni 0.6 Pd 0.24 photocatalyst.

[0075] Comparative Example 6

[0076] The preparation method was the same as that in Example 1, except that the obtained T-Ni 0.6 Pd 0.24 photocatalyst was calcined at 400°C in an oxygen atmosphere for 12 h to obtain T-Ni 0.6 Pd 0.24 O photocatalyst.

[0077] Table 3 is a comparison of the photocatalytic activity of the photocatalysts prepared in Example 1 and Comparative Examples 5-6 in the photocatalytic non-oxidative dehydrogenation of ethane to ethylene. As can be seen from the table, the photocatalyst prepared in Example 1 has the best performance, which indicates that the synergistic effect of monatomic Ni and Pd nanoparticles is the best.

[0078] Table 3 Comparison of the photocatalytic activity of different catalysts in the photocatalytic non-oxidative dehydrogenation of ethane to ethylene

[0079]

[0080] The above description is merely preferred embodiments of the present application, and any changes and modifications made to the present application within the scope of the patent application should be covered by the present application.

Claims

1. A TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles, characterized in that, Ni is uniformly distributed on the surface of TiO2 in the form of single atoms and Pd is uniformly distributed in the form of nanoparticles, constituting the TiO2 photocatalyst; in the photocatalyst, the content of Ni is 0.4wt%~1wt% and the content of Pd is 0.2wt%~1.5wt%; The preparation method of the TiO2 photocatalyst includes the following steps: 1) After pressing anatase TiO2 tablets, place them in a quartz reaction tube and treat them at 400℃ in a flowing oxygen atmosphere for 10h~15h, then treat them at 400℃ under dynamic vacuum for 2h~4h, and then cool them naturally to room temperature. 2) Dissolve the organic transition metal compound in n-hexane to form a supersaturated solution, and then inject the solution into the quartz reaction tube of step 1) in a liquid nitrogen cold trap environment. Then, remove the n-hexane under dynamic vacuum conditions, and then calcine it under vacuum conditions. After calcineation, remove the solution under dynamic vacuum again. 3) The sample obtained in step 2) was calcined in an oxygen atmosphere and then ground to obtain a solid powder; 4) Disperse the solid powder obtained in step 3) in deionized water, add H2PdCl4 solution, and stir with 300 mW·cm⁻¹ water. -2 Irradiate the sample with a xenon lamp for 5 to 30 minutes, then wash the sample with deionized water and dry it overnight to obtain the TiO2 photocatalyst. The organotransition metal compound mentioned in step 2) is nickel dicerocene.

2. The TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles according to claim 1, characterized in that, The calcination temperature in step 2) is 100℃~200℃, and the time is 12h~30h.

3. The TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles according to claim 1, characterized in that, The pressure range of the vacuum conditions used in the operation is 10. -2 ~10Pa.

4. The TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles according to claim 1, characterized in that, The calcination temperature in step 3) is 300℃~400℃, and the time is 10h~16h.

5. The TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles according to claim 1, characterized in that, The concentration of the H2PdCl4 solution mentioned in step 4) is 1 mg / mL.

6. The application of a TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles as described in claim 1 in the photocatalytic non-oxidative dehydrogenation of alkanes to olefins.

7. The application according to claim 6, characterized in that, Its application method is to use the TiO2 photocatalyst co-modified with Ni single atoms and Pd nanoparticles in an inert gas atmosphere to perform non-oxidative dehydrogenation of alkanes under light irradiation, room temperature and pressure conditions; The inert gas is argon, and the alkane is either ethane or propane, with a molar ratio of inert gas to alkane of 9-99:1; the intensity of the light used is 300 mW·cm. -2 .

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