Preparation method and application of defect-rich metal oxide
Technical Field
The invention relates to the field of preparation of functional catalytic materials, in particular to a preparation method of a defect-rich metal oxide and application of the defect-rich metal oxide to activation of aromatic sulfides in air catalytic oxidation diesel oil.
Background
In recent years, transition metal oxides have attracted attention of many researchers due to their non-stoichiometric forms, and are widely used in hot spot research such as photocatalytic hydrogen generation (j.mater.chem.a., 2017,5,24989), lithium batteries (cat.today, 2014,225,2), and supercapacitors (j.mater.chem.a., 2014,2, 229). In the materials, the crystal lattice disorder and the defects have certain modulation effect on the electronic structure of the metal oxide, which is of great significance for improving the performance of the metal oxide. Common methods for producing defective oxides are: a hydrogen heat treatment method, a hydrogen plasma treatment method, a chemical oxidation method, a chemical reduction method, and the like.
Among them, the hydrogen heat treatment method and the hydrogen plasma treatment method are simple and direct, and utilize the reducibility of hydrogen gas to reduce the metal oxidation state in the metal oxide into the corresponding partial oxidation state, even the reduction state (Science,2011,331,746; adv. funct. mater.,2013,23, 5444). In this process, the lattice structure and other physical/chemical properties of the metal oxide are changed accordingly. Although the process is simple, the size, particle size, morphology and defect content of the metal oxide obtained can vary greatly due to variations in operating conditions such as hydrogen gas pressure, gas flow, reaction time and reaction temperature. The application range of the chemical oxidation method is relatively narrow, and research works indicate that defective titanium dioxide (Nanoscale,2013,5,1870) is prepared by reacting titanium hydride with hydrogen peroxide under certain conditions. The chemical reduction method generally uses the following methods: (1) the reducing metal Al is used as a reducing agent in a dual-temperature-zone vacuum furnace at the temperature of 300-500 ℃. (2) Adopts a zinc-solvent thermal reduction method. (3) Imidazole thermal reduction method. (4) Sodium borohydride reduction method. (5) Calcium hydride reduction method. However, due to the use of hydrogen, metal, reducing agent and oxidizing agent, the safety, economy and environmental protection of the preparation process are all to be improved.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a defective metal oxide obtained without using chemical reagents such as hydrogen, metal, reducibility, strong oxidability and the like and a preparation method thereof. The metal oxide rich in defects prepared by the method is used as a catalyst to activate air for catalytic oxidation to remove aromatic sulfides in the diesel oil, so that the sulfur content in the diesel oil reaches the national V standard.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a defect-rich metal oxide catalyst is prepared without using hydrogen, metal, reductive and strong oxidative chemical reagents. The catalyst is rich in defect structures such as disordered crystal lattices, crystal lattice dislocation, crystal lattice contraction, oxygen vacancies, partially unsaturated metal atoms and the like. The catalyst has rich catalytic active sites, adjustable electronic structure and large specific surface area.
A preparation method of a defect-rich metal oxide comprises the following steps:
(1) the metal oxide and a certain amount of crystal phase transfer auxiliary agent are physically mixed according to a certain proportion, a certain amount of grinding balls are added and uniformly mixed, the mixture is assembled in a planetary ball mill together, and the ball milling treatment is carried out at a certain rotating speed and time.
(2) And (2) carrying out pyrolysis treatment on the solid mixture obtained in the step (1) in an inert gas atmosphere, and keeping the temperature for a period of time to obtain the metal oxide material rich in defects.
In the step (1), the metal oxide is titanium dioxide, cerium oxide, zinc oxide, tin oxide, tungsten oxide or molybdenum oxide.
In the step (1), the crystal phase transfer assistant is: urea, melamine, carbon nitride or dicyanodiamine, preferably urea. The molar ratio of the metal oxide to the crystal phase transfer auxiliary agent is 1: 5-30.
In the step (1), the ball milling tank is made of stainless steel, agate, corundum, zirconia or tungsten carbide, the small balls are made of stainless steel, agate, corundum, zirconia or tungsten carbide, and the diameter of the small balls is 3 mm.
In the step (1), the operating speed of the ball mill is 350-450 rpm/min, the ball milling time is 3-5 h, the ball milling is carried out for every 5-10 min, and the intermittent time is 2.5-5 min each time.
In the step (2), the inert atmosphere is nitrogen or argon, and the gas flow rate range is as follows: 5-10 mL/min.
In the step (2), the heating rate of the high-temperature pyrolysis treatment is 5-10 ℃/min; the high-temperature calcination temperature is 900-1000 ℃; the holding time is 10-90 min.
The defect-rich metal oxides obtained by the above-described process are within the scope of the present invention.
In the preparation of the method, the defect-rich metal oxide refers to the metal oxide containing lattice defects, including lattice disorder, lattice dislocation, lattice contraction effect, oxygen vacancy and unsaturated metal sites.
The application of the defect-rich metal oxide prepared by the method in the removal of aromatic sulfides in diesel oil by activated air catalytic oxidation is also covered by the protection of the invention.
The invention has the beneficial effects that:
(1) the invention enhances the interface interaction between the micromolecules and the metal oxide by the aid of urea, melamine and the like for ball milling. In addition, small molecules such as urea generate a large amount of reducing gases such as NH in situ during the complete decomposition process at high temperature3And CO2And the like, participate in the crystal lattice reconstruction process of the metal oxide at high temperature, and purposefully build crystal lattice defects in the structure.
(2) The defect type metal oxide is prepared under the condition of not using chemical reagents such as hydrogen, metal, reducibility, strong oxidizing property and the like, the safety, the economy and the environmental protection property of the preparation process are fully considered, and the problems of the use of high-risk hydrogen, the waste of metal resources and the post-treatment of the chemical reagents are not involved.
(3) The metal oxide material prepared by the invention has rich catalytic active sites, adjustable electronic structure and large specific surface area, and has better performance when being applied to the sulfur content in the diesel oil of activated air catalytic oxidation. Provides an effective catalyst for the ultra-deep desulfurization of diesel oil.
Drawings
FIGS. 1a and 1b are Transmission Electron Microscope (TEM) photographs of reference example 1 and example 2, respectively, and FIG. 1c is a high-resolution transmission electron microscope (HRTEM) photograph of example 2.
FIG. 2 is an X-ray diffraction (XRD) pattern of examples 1 to 3 and reference example 1.
FIG. 3 is a graph of the ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) of example 2, example 4, example 5, and reference examples 1-3.
Detailed Description
The invention will be better understood from the following examples. However, it is easily understood by those skilled in the art that the contents described in the embodiments are only for illustrating the present invention and should not be limited to the invention described in detail in the claims.
Example 1:
(1) weighing urea and P25 (molar ratio is 5:1) and mixing in a stainless steel ball mill tank, adding zirconia balls (diameter is 3mm,20g), assembling in a planetary ball mill, setting the rotating speed to be 450rpm, and operating the ball mill for 2.5 minutes at intervals of every 5 minutes and 4 hours in total operation.
(2) And (3) placing the ball-milled substances in a tubular electric furnace, heating to 900 ℃ from room temperature at the speed of 5 ℃/min under the protection of nitrogen with the gas flow rate of 5mL/min, keeping for 60min, and cooling to room temperature to obtain gray substances, namely the defective titanium dioxide material.
Example 2:
(1) urea and P25 (molar ratio 15:1) were weighed and mixed in a stainless steel ball mill pot, zirconia balls (diameter 3mm,20g) were added and assembled in a planetary ball mill set at 450rpm with the ball mill running for 2.5 minutes every 5 minutes with a total run time of 4 hours.
(2) And (3) placing the ball-milled substances in a tubular electric furnace, heating to 900 ℃ from room temperature at the speed of 5 ℃/min under the protection of nitrogen with the gas flow rate of 5mL/min, keeping for 60min, and cooling to room temperature to obtain gray substances, namely the defective titanium dioxide material.
Example 3:
(1) weighing urea and P25 (the molar ratio is 30:1) and mixing the urea and the P25 in a stainless steel ball mill pot, adding zirconia balls (the diameter is 3mm and 20g), assembling the mixture in a planetary ball mill, setting the rotating speed to be 450rpm, and operating the ball mill for 2.5 minutes at intervals and 4 hours in total.
(2) And (3) placing the ball-milled substances in a tubular electric furnace, heating to 900 ℃ from room temperature at the speed of 5 ℃/min under the protection of nitrogen with the gas flow rate of 5mL/min, keeping for 60min, and cooling to room temperature to obtain gray substances, namely the defective titanium dioxide material.
Reference example 1: p25 was weighed directly into a stainless steel ball mill jar, zirconia balls (diameter 3mm,20g) were added, and the ball mill was assembled in a planetary ball mill set at 450rpm with a batch time of 2.5 minutes for every 5 minutes and a total run time of 4 hours. The ball-milled material was placed in a tubular electric furnace, heated from room temperature to 900 deg.C at 5 deg.C/min under the protection of nitrogen at a gas flow rate of 5mL/min, held for 60min, and cooled to room temperature, and the resulting white material was compared with example 1 and identified as reference example 1.
Fig. 1a and 1b are Transmission Electron Microscope (TEM) photographs of reference example 1 and example 2, respectively, from which it can be seen that a large number of defects and a pore structure appear on the surface of titanium dioxide subjected to urea-assisted ball milling treatment.
FIG. 1c is a High Resolution Transmission Electron Micrograph (HRTEM) of example 2, which shows that the crystal lattice of the titanium dioxide material obtained in example 1 has a largely disordered and dislocated structure, indicating that the addition of the auxiliary agent is favorable for the formation of lattice defects.
Fig. 2 is an X-ray diffraction (XRD) pattern of examples 1-3 and reference example 1, from which it can be seen that the addition of an adjuvant does not affect the crystal structure of the prepared material, but as the amount of the adjuvant such as urea is increased, the crystallinity of titanium dioxide decreases due to the generation of a large amount of its lattice disorder, further illustrating that this strategy is feasible for introducing defects inside the metal oxide lattice.
Example 4
(1) Weighing urea and commercial grade CeO2(molar ratio 15:1) in a stainless steel ball mill pot, adding zirconia balls (diameter 3mm,20g), assembling in a planetary ball mill, setting the rotation speed at 400rpm, and the ball mill is operated for 5 minutes at intervals of 10 minutes for a total operation time of 5 hours.
(2) Placing the ball-milled material in a tubular electric furnace, heating to 1000 deg.C at 10 deg.C/min under the protection of argon gas at a gas flow rate of 10mL/min, maintaining for 90min, cooling to room temperature to obtain gray material, i.e. defective CeO2A material.
Reference example 2
Directly weighing commercial grade CeO2Zirconia balls (diameter 3mm,20g) were charged into a stainless steel ball mill pot and assembled in a planetary ball mill at a set rotation speed of 400rpm, the ball mill was operated every 10 minutes with an interval of 5 minutes for a total operation time of 5 hours. Placing the ball-milled material in a tubular electric furnace, heating to 1000 ℃ from room temperature at 10 ℃/min under the protection of argon gas at the gas flow rate of 10mL/min, keeping the temperature for 90min, and cooling to room temperature to obtain reference example 2.
Example 5
(1) Weighing urea and ZnO (the molar ratio is 5:1) and mixing the urea and the ZnO in a stainless steel ball mill tank, adding zirconia balls (the diameter is 3mm and the weight is 20g), assembling the mixture in a planetary ball mill, setting the rotating speed to be 350rpm, and intermittently operating the ball mill every 10 minutes for 5 minutes and operating the total time for 3 hours.
(2) And (3) placing the ball-milled substance in a tubular electric furnace, heating the ball-milled substance to 900 ℃ from room temperature at the speed of 5mL/min under the protection of nitrogen at the gas flow rate of 5mL/min, keeping the temperature for 10min, and cooling the ball-milled substance to room temperature to obtain a gray substance, namely the defective ZnO material.
Reference example 3
(1) Directly weighing commercial grade ZnO in a stainless steel ball milling tank, adding zirconia balls (with the diameter of 3mm and the weight of 20g), assembling in a planetary ball mill, setting the rotating speed to be 350rpm, and intermittently operating the ball mill every 10 minutes, wherein the intermittent time is 5 minutes, and the total operating time is 3 hours. Placing the ball-milled material in a tubular electric furnace, heating to 900 ℃ from room temperature at 5 ℃/min under the protection of nitrogen with the gas flow rate of 5mL/min, keeping for 10min, and cooling to room temperature to obtain reference example 3.
FIG. 3 is a graph of the ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) of example 2, example 4, example 5, and reference examples 1-3. As can be seen from the figure, after the auxiliary agent urea is introduced, the examples 2, 4 and 5 generate obvious absorption in the visible light region, which indicates that the electronic structures in the examples 2, 4 and 5 are changed, a large number of oxygen vacancies are generated, and the catalytic performance of the examples is possibly greatly improved.
Examples 6 to 11
The obtained defective metal oxide is used as a catalyst for activating air to oxidize and remove sulfides in oil products. The following are specific experimental details:
preparing model oil: dibenzothiophene (DBT), 4, 6-dimethyldibenzothiophene (4,6-DMDBT), 4-methyldibenzothiophene (4-MDBT) were dissolved in n-dodecane, respectively, and n-hexadecane was added as an internal standard.
Oxidative desulfurization experiment: a certain amount of simulated oil and catalyst are put into a flask, and the flask is placed in a constant-temperature oil bath and condensed and refluxed. Dry air was continuously blown into the system and stirred. During the reaction, the sulfur content in the oil product is quantitatively detected by using a gas chromatograph, and the desulfurization rate is calculated according to the following formula.
Examples the experimental results are as follows:
serial number
|
Type of oil
|
Catalyst number
|
Reaction temperature
|
Reaction time
|
Desulfurization degree%
|
6
|
Model oil (DBT)
|
Example 2
|
120℃
|
4h
|
95.6
|
7
|
Model oil (4,6-DMDBT)
|
Example 2
|
120℃
|
4h
|
92.3
|
8
|
Model oil (DBT)
|
Example 2
|
110℃
|
6h
|
96.4
|
9
|
Model oil (DBT)
|
Example 2
|
105℃
|
6h
|
82.3
|
10
|
Model oil (DBT)
|
Reference example 1
|
120℃
|
4h
|
30.8
|
11
|
Model oil (DBT)
|
Example 1
|
120℃
|
4h
|
92.9 |