CN112777631A - Method for synthesizing cerium-zirconium oxide solid solution hollow spheres by spray combustion - Google Patents

Method for synthesizing cerium-zirconium oxide solid solution hollow spheres by spray combustion Download PDF

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CN112777631A
CN112777631A CN202011520122.5A CN202011520122A CN112777631A CN 112777631 A CN112777631 A CN 112777631A CN 202011520122 A CN202011520122 A CN 202011520122A CN 112777631 A CN112777631 A CN 112777631A
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zirconium oxide
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陈伟凡
王立中
叶剑勇
刘正
张文星
蒋绪川
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Jiangxi Shanna New Material Technology Co Ltd
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Abstract

The invention discloses a method for synthesizing cerium-zirconium oxide solid solution hollow spheres by spray combustion, which is characterized by comprising the following steps of: weighing cerium carbonate, zirconyl nitrate and glycine according to a designed proportion, dissolving and quantifying with nitric acid to obtain a precursor solution I, ultrasonically atomizing the precursor solution I into small drops, loading the small drops into a reaction chamber of a vertical tube furnace by compressed air for reaction, collecting powder, washing with absolute ethyl alcohol and deionized water to remove impurity ions, performing suction filtration, and performing vacuum drying to obtain the final product cerium-zirconium oxide solid solution hollow sphere powder. The method successfully synthesizes the cerium-zirconium solid solution hollow sphere with the nano structure, and the particle size and the sphericity of the product can be adjusted by changing the concentration of cerium-zirconium ions in a precursor solution, the ratio of the cerium-zirconium ions, the reaction temperature and other methods.

Description

Method for synthesizing cerium-zirconium oxide solid solution hollow spheres by spray combustion
Technical Field
The invention relates to the technical field of new materials, in particular to a method for synthesizing cerium-zirconium oxide solid solution hollow spheres by spray combustion.
Background
It is well known that the properties of a material depend primarily on the structure of the material, while the use of a material depends largely on its properties. Since the original report of Caruso et al in 1998 on the fabrication of hollow silica, many hollow nanostructures were developed by a similar templating method. Hollow nanostructures can be divided into different classes from different angles. For example, by reflecting different overall shapes, hollow spheres, hollow tubes, hollow fibers, hollow boxes, etc. may be used. They can be divided into single-layer, double-layer and multi-layer (or walled) hollow structures, depending on the number of shells. They can be classified into organic and inorganic hollow nanostructures, or more specifically into polymer, ceramic, metal and composite hollow structures, taking into account the different composition of the shell structure.
The research community rapidly recognizes the excellent properties of hollow structures, such as large surface area, low density and high loading capacity, and develops a variety of applications, including nanoreactors, catalysts, energy storage, biomedicine, sensors, environmental remediation, and the like. Due to the presence of the cavities, the surface area of the hollow structure is significantly increased and the density is much less than that of a solid of the same composition and size. These properties significantly facilitate the use of hollow nanostructured materials in catalysis, either as support materials or as active catalysts. Since the interior space can serve as a storage space for various substances, they can serve as imaging contrast agents, drug delivery vehicles, and anodes or cathodes for lithium ion batteries. In short, hollow nanostructures can be conveniently engineered to increase structure and composition compared to their solid state, and are therefore well suited for rational design of new functional materials for many desired applications.
The crystal structure employed for the ceria-zirconia solid solution depends on the Zr/Ce ratio and the temperature. At very low Zr concentrations, ceria-zirconia solid solutions are cubic fluorite structures, as are pure ceria and cubic zirconia. However, at higher Zr contents, other crystal structures are formed, including two different tetragonal phases at moderate Zr concentrations and a monoclinic phase with very high Zr concentrations. A zirconia-ceria solid solution (Ce) has been observed by Yashima et al by Raman spectroscopyxZr1-xO2) A structural phase transition between cubic (space group Fm3m) and tetragonal (space group P42/nmc) phases. Sample with uniform composition at room temperature when the composition is X0(0.8<X0<0.9), a cubic-tetragonal phase (c-t ") boundary is present. The axial ratio c/a decreases with increasing ceria concentration and has a composition X at room temperature1(0.65<X1<0.7) becomes 1. Is composed of0And X1The sample in between is t "phase ZrO 2.
One of the many problems facing today's society is the disposal of harmful gases from industrial and automotive vehicles. The problem can be effectively solved by adopting the three-way catalyst. TWC development has been dependent on their ability to remove Hydrocarbons (HC), CO and NO from automobile exhaustxWith simultaneous conversion to H2O，CO2And N2Cerium zirconium solid solutions are widely used in TWCs. The traditional TWC used in the late eighties of the twentieth century used Rh and Pt as the active noble metals, CeO2As an oxygen storage component. In TWCs, the conversion of pollutants is highest when the air/fuel (a/F) ratio is close to the stoichiometric ratio (a/F-14.6), but the efficiency of the TWC is severely reduced due to the change in the a/F ratio under rich or lean conditions. CeO (CeO)2Plays an important role in a three-way catalyst, CeO2The addition of (b) solves this problem because it can act as an oxygen buffer, via Ce4+/Ce3+Storage/release of redox couple
Figure BDA0002849219150000021
The TWC may be operated by storing oxygen under lean conditions and providing oxygen under rich conditionsHas higher conversion rate. Usually CeO2The higher the oxygen storage capacity, the higher the conversion efficiency and the thermal aging resistance. However, one major problem with TWC converters is that only at high temperatures (h>600K) A significant conversion effect is obtained. The amount of pollutants, in particular HC, emitted during a cold start of the engine is therefore very high until the converter reaches the operating temperature. In order to meet the requirements of cold start experiments and low HC emission of the engine, a TWC (two way catalytic converter) is required to be arranged at an exhaust port close to the engine, the TWC is called a close-coupled catalyst, the working temperature can reach 1273-l 373K, and therefore extremely high thermal resistance is required. Furthermore pure CeO2The thermal stability is poor, sintering easily occurs at high temperature, the specific surface area becomes small, and the catalyst is deactivated. It is reported that doping with a suitable cation such as Zr4+,Al3+Or Si4+Can obviously improve the high-temperature stability, in particular to CeO2Middle insert of Zr4+Post-formed CexZr1-xO2Solid solution. And pure CeO2In contrast, CexZr1-xO2The catalyst has good oxygen storage performance and oxidation-reduction performance, excellent low-temperature catalytic performance and higher thermal stability.
Cerium zirconium solid solutions can also be prepared by a variety of methods. Various cerium dioxide nanostructures, such as cubic, rod-like, linear, sheet-like, tubular, polyhedral, plate-like, disk-like, microspheres, etc., have been prepared by various synthetic methods, greatly contributing to the research interest of people in this field. Many groups have produced cerium zirconium solid solutions with varying degrees of homogeneity and crystal properties by different methods. The reported preparation methods include coprecipitation, hydrothermal, sol-gel and other auxiliary methods such as supercritical techniques, surfactants and shape control techniques. In addition, other rare earth elements are also incorporated into the ceria-zirconia solid solution to enhance its structural and chemical properties. Raju et al, having a surface area of 12m, in a cerium-zirconium solid solution prepared by continuous hydrothermal treatment at 1000 deg.C2g-1And Ce0.5Zr0.5O2The maximum oxygen storage capacity of the solid solution after being calcined at 700 ℃ reaches 0.58mmol [ O ]]g-1. Wang et al investigated La incorporationInfluence of impurities on the cerium-zirconium solid solution, the doped La is found to improve the BET specific surface area and the oxygen storage capacity value. Similar conclusions were reported by Yan et al.
The spray combustion method (SCS for short) is a new method for preparing nano material by using comprehensive solution combustion method and spray pyrolysis method. Solution combustion synthesis enables the preparation of ultrafine powders with uniform composition at lower temperatures because of the large amount of heat given off by the redox reaction between metal salts (oxidants, mainly nitrates) and organic fuels (reductants) in aqueous solutions. The method has the following characteristics: (1) the stoichiometric ratio of the components is accurate, and the prepared sample has high uniformity; (2) after low-temperature ignition, the fuel can be combusted in a self-propagating way, a large amount of heat is released, and high temperature can be instantly reached; (3) simple process and equipment, simple and quick synthesis process and energy saving, thus being widely used for synthesizing nano materials.
Disclosure of Invention
The invention aims to provide a method for synthesizing a cerium-zirconium oxide solid solution hollow sphere by spray combustion.
In order to achieve the purpose, the invention adopts the following technical scheme: a method for synthesizing cerium zirconium oxide solid solution hollow spheres by spray combustion is characterized in that an auxiliary agent ammonium nitrate or chloride is added into a precursor solution, an organic fuel is added into the precursor solution, and the precursor solution generates liquid drops under the action of an atomizer, so that the liquid drops generate violent low-temperature self-propagating combustion reaction in a reaction furnace to obtain a product. In the reaction process, after the liquid drop is heated, the moisture on the outer surface is firstly evaporated, so that the solution concentration on the outer surface of the liquid drop is larger than that of the internal solution, the solution on the outer surface reaches a saturation point along with the reaction, crystallization is started to form a shell layer, the internal solution is gradually evaporated, the solution is spread to the outer shell layer and crystallized, and finally a hollow structure is formed.
Specifically, cerium carbonate, zirconyl nitrate and glycine are weighed according to a designed ratio, dissolved and quantified by nitric acid to obtain a precursor solution I, the precursor solution I is ultrasonically atomized into small droplets and then loaded into a reaction chamber of a vertical tube furnace by compressed air to react, powder is collected, the powder is washed by absolute ethyl alcohol and deionized water to remove impurity ions, and after suction filtration and vacuum drying, the final product cerium-zirconium oxide solid solution hollow sphere powder is obtained.
Particularly, the flow rate of carrier gas in the preparation process is 0.5L/min, the atomization frequency is 2.4MHz, the reaction temperature is 800-1000 ℃, and the outer diameter of a quartz tube used in the vertical tube furnace is 20mm and the inner diameter is 16 mm.
In particular, the cerium zirconium solid solution produced is represented by CexZr1-xO2Wherein x is the molar ratio of Ce; the reaction equation for the experiment, which is related to the molar ratio of cerium x and the content of fuel glycine, xCe, is as follows2(CO3)3·+2(1-x)ZrO(NO3)2·+2ψNH2CH2COOH+((9ψ+11x-10)/2)O2＝2CexZr1-xO2+(ψ+2(1-x))N2+(3x+4ψ)CO2+5ψH2O
Here, (Gly: Ce2(CO3)3) 2 psi/x when O2When the index of (b) is "0", the reaction formula is a stoichiometric reaction formula, in which case ψ is (10-11x)/9, Gly is Ce2(CO3)3(20-22x)/9 x; when O is present2When the coefficient of (b) is larger than "0", the reaction is a rich reaction, in which case ψ>(10-11x)/9，Gly:Ce2(CO3)3>(20-22x)/9 x; when O is present2Is less than "0", the reaction is a lean combustion reaction, and in this case, #<(10-11x)/9，Gly:Ce2(CO3)3<(20-22x)/9x。
In particular, the cerium-zirconium solid solution is Ce0.5Zr0.5O2When the reaction formula is a stoichiometric reaction formula, it is represented as:
Ce2(CO3)3+2ZrO(NO3)2+2NH2CH2COOH＝4Ce0.5Zr0.5O2+3N2+7CO2+5H2O。
in particular, the cerium-zirconium solid solution is Ce0.6Zr0.4O2When the reaction formula is a stoichiometric reaction formula, it is represented as:
27Ce2(CO3)3·+36ZrO(NO3)2·+34NH2CH2COOH＝90Ce0.6Zr0.4O2+53N2+149CO2+85H2O。
in particular, the cerium-zirconium solid solution is Ce0.7Zr0.3O2When the reaction formula is a stoichiometric reaction formula, it is represented as:
63Ce2(CO3)3·+54ZrO(NO3)2·+46NH2CH2COOH＝180Ce0.7Zr0.3O2+77N2+281CO2+115H2O。
in particular, the cerium-zirconium solid solution is Ce0.8Zr0.2O2When the reaction formula is a stoichiometric reaction formula, it is represented as:
12Ce2(CO3)3·+6ZrO(NO3)2·+4NH2CH2COOH＝30Ce0.8Zr0.2O2+8N2+44CO2+10H2O。
in particular, the cerium-zirconium solid solution is Ce0.9Zr0.1O2When the reaction formula is a stoichiometric reaction formula, it is represented as:
81Ce2(CO3)3·+18ZrO(NO3)2·+2NH2CH2COOH＝180Ce0.9Zr0.1O2+19N2+247CO2+5H2O。
the invention has the beneficial effects that: the invention adopts a spray combustion method, prepares a precursor solution by taking cerium nitrate, zirconyl nitrate and glycine as raw materials, loads compressed air into a high-temperature tube furnace after atomization to initiate combustion reaction to successfully synthesize the nano-structure cerium-zirconium solid solution hollow sphere, and can adjust the particle size and the sphericity of the product by changing the concentration and the proportion of cerium and zirconium ions, the reaction temperature and other methods of cerium and zirconium ions in the precursor solution.
And by means of characterization means such as X-ray diffraction analysis (XRD), Scanning Electron Microscope (SEM) and specific surface instrument, the influence and related mechanism of the concentration sum, concentration ratio and reaction temperature of cerium nitrate and zirconyl nitrate on the phase and morphology of the product in the process of preparing the nano-structure cerium-zirconium solid solution are researched, and the catalytic oxidation performance of the sample synthesized under different reaction conditions on CO is evaluated. The result shows that under the reaction conditions of the precursor solution in which the concentration sum of cerium nitrate and zirconyl nitrate is 0.05M, the concentration ratio is 6/4, glycine is the stoichiometric ratio and the tube furnace temperature is 800 ℃, cerium-zirconium oxide solid solution hollow spheres with uniform particle size and good sphericity can be prepared, and the specific surface area is only 5.884M because the cerium-zirconium oxide solid solution hollow spheres are not porous structures2(ii) in terms of/g. In addition, the morphology of the nano-structure cerium-zirconium solid solution has obvious influence on the activity of CO catalytic oxidation, and the temperature of the prepared sample with the concentration sum of 0.24M for catalyzing CO is 180 ℃.
Drawings
FIG. 1 is a flow chart of the present invention.
FIG. 2 shows powder Ce with different Ce-Zr ratiosxZr1-xO2XRD of the sample.
Fig. 3 is an SEM photograph of a cerium-zirconium solid solution prepared under the condition that the ratio of cerium ions to zirconium ions in the precursor solution is different.
Figure 4 is an XRD pattern of sample powder at different concentrations.
Fig. 5 is an SEM photograph of cerium-zirconium solid solutions prepared under different conditions and concentrations of cerium and zirconium ions in the precursor solutions.
Figure 6 is an XRD pattern of sample powder prepared at different temperatures.
Fig. 7 is SEM photographs of cerium-zirconium solid solutions prepared from the precursor solutions at different reaction temperatures.
FIG. 8 is Ce0.6Zr0.4O2Catalytic CO oxidation conversion as a function of temperature.
FIG. 9 is a graph of catalytic CO oxidation conversion as a function of temperature.
FIG. 10 is Ce0.5Zr0.5O2Catalytic CO oxidation conversion as a function of temperature.
FIG. 11 shows different Ce concentrations0.6Zr0.4O2Catalytic CO oxidation conversion varies with temperature.
FIG. 12 is Ce at different preparation temperatures0.6Zr0.4O2Catalytic CO oxidation conversion varies with temperature.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
The experimental device for preparing the cerium-zirconium solid solution is a device with the patent number of 2012200942235 and the patent name of 'a reaction device for ultrasonic spray combustion'. Of course, practice of the invention is not limited to this device.
A process for synthesizing hollow spheres of cerium-zirconium oxide solid solution by spray combustion includes such steps as weighing cerium carbonate and zirconyl nitrate, calcining at 1300 deg.C in muffle furnace for 24 hr to decompose them to CeO2And ZrO2And calculating and determining the water content in the raw materials, namely the content of cerium ions and zirconium ions. Weighing cerium carbonate, zirconyl nitrate and glycine according to a designed proportion, dissolving and quantifying with nitric acid to obtain a precursor solution I, ultrasonically atomizing the precursor solution I into small drops, loading the small drops into a reaction chamber of a vertical tube furnace by compressed air for reaction, collecting powder, washing with absolute ethyl alcohol and deionized water to remove impurity ions, performing suction filtration, and performing vacuum drying at 50 ℃ for 2 hours to obtain the final product cerium-zirconium solid solution powder. In the preparation process, the flow rate of carrier gas is 0.5L/min, the atomization frequency is 2.4MHz, the reaction temperature is 800-1000 ℃, and the outer diameter of a quartz tube used in the vertical tube furnace is 20mm and the inner diameter is 16 mm.
Characterization of physicochemical properties of the samples: using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), specific surface area and N2Adsorption-desorption isotherm test, H2-TPR test and CO catalytic activity test the samples were characterized.
X-ray diffractionAnd (3) analysis: x-ray diffraction analysis was carried out using an X-ray diffractometer model Advance D8, Bruker, Germany. Adding Cu target Kα1The wavelength λ of incident light was 0.15406nm, the tube voltage was 40kV, the tube current was 400mA, the divergent slit width was 0.76nm, the scanning range was 10 ° to 90 °, the scanning speed was 18.87 °/min, and the scanning step was 0.013 °.
Environmental scanning electron microscope: working under high vacuum (30kv resolution is less than or equal to 1.2nm) by using an FEI Quanta200F type environment scanning electron microscope.
BET specific surface area test: the specific surface area was obtained under 77K conditions using ASAP2020 specific surface area tester from Micromeritics, USA. Before testing, the samples were degassed under vacuum with heating at 200 ℃ for 4 h. Specific surface area (S) of sampleBET) Using the Barrett-Emmett-Teller (BET) method, according to the relative pressure P/P0The desorption data of the liquid nitrogen is calculated within the range of 0.05-0.2.
H2-TPR test: the temperature programmed reduction was carried out on a pantoea FINESORB-3010C-243 instrument. TCD temperature 60 deg.C, current 30mA, 10% H2The method comprises the following steps of taking an Ar mixed gas as a reducing gas, taking Ar as a carrier gas, taking the carrier gas flow rate as 15ml/min, fixing quartz wool in a quartz tube with the inner diameter of 6mm, pre-treating the sample at 120 ℃ for 60min, purging in a reducing atmosphere for 10min, starting a temperature programming reduction test after a baseline is stable, and carrying out temperature programming to 850 ℃ at the temperature raising rate of 10 ℃/min.
Characterization of the activity of the sample for catalytic oxidation of CO: the CO catalytic activity test was carried out in a continuous reaction apparatus, and the reaction gas composition was examined using GC9310 type gas chromatography. The spectral column is TDX-01, the column length is 2m, the detection is carried out by a thermal conductivity cell (TCD), the column temperature is 80 ℃, the sample injection temperature is 110 ℃, the detection temperature is 80 ℃, and the bridge current is 100 mA. The carrier gas is H2The reaction raw material gas is 1 percent of CO and 20 percent of O2+79％N2The total flow rate of gas was 10ml/min, the catalyst loading was 30mg, and the space velocity was 30000 ml/(g.h). During the experiment, 100mg of the catalyst is weighed and loaded into a U-shaped quartz tube, the catalyst is fixed by quartz wool, and a thermocouple is inserted into a position close to the catalyst. For CO catalytic oxidation reaction, the catalyst is increased at 10 ℃/minThe temperature rate is increased from room temperature to 100 ℃, and the temperature is kept constant for 1h for sampling and analysis.
Example 1
Under the condition of keeping the concentration sum of cerium ions and zirconium ions to be 0.05M, 5 parts of precursor solution with the concentration ratio of the cerium ions to the zirconium ions being 5/5, 6/4, 7/3, 8/2 and 9/1 respectively is prepared, glycine is added according to the stoichiometric ratio, the precursor solution is carried into a reaction cavity of a 800 ℃ vertical tubular furnace by compressed air after being atomized into small liquid drops by ultrasonic, the small liquid drops are reacted, powder is collected, absolute ethyl alcohol and deionized water are used for washing, impurity ions are removed, and the powder is dried for 2 hours in vacuum at 50 ℃ after being filtered, so that products with different cerium-zirconium ratios are obtained.
The complete phase diagram of a cerium-zirconium solid solution generally includes three stable phases (monoclinic (m), tetragonal (t), cubic (c)) and two metastable tetragonal phases (t' and t "phases). Wherein the tetragonal phase (t-phase) is formed by diffusive phase decomposition; the t' phase comes from non-diffuse transformation; and the t "phase is an intermediate phase between t' and the cubic phase, and its structure is similar to the cubic phase. the t 'phase and the t' phase have the same space group symbol P42/nmc。
Figure 2 is an XRD pattern of the sample powder. The diffraction peak was broad, indicating that the sample was low in crystallinity. Since the particle size of the sample is small, the reciprocal sphere becomes large, and the diffraction peak is widened. With Zr content in CeO2The lattice increases and the diffraction peak shifts to the high 2 theta. Because of the broad diffraction peaks observed in the XRD patterns, it is difficult to distinguish between the different equilibrium phases in the nanostructured combustion products. Ce of 0.5 for x0.5Zr0.5O2And x is 0.6 Ce0.6Zr0.4O2The PDF card numbers are 38-1436 and 38-1439 respectively. For the samples with the cerium-zirconium ratios set at 7/3 and 8/2 during the experiment, Ce was formed due to losses during the experiment and the fact that zirconium was not fully doped into the cerium lattice0.75Zr0.25O2The PDF card number is 28-0271, the cerium-zirconium diffraction peak is slightly shifted to higher 2 θ than the sample diffraction peak of 7/3, and the cerium-zirconium diffraction peak is slightly shifted to lower 2 θ than the sample diffraction peak of 8/2. Ce with x equal to 0.90.9Zr0.1O2With pure CeO2The diffraction peak is shifted to higher 2 theta, indicating that there is a trace amount of Zr4+Is doped with CeO2In the crystal lattice.
The properties of the cerium zirconium solid solution particles obtained by the spray combustion method are summarized in table 1.
TABLE 1 properties of particles from cerium zirconium solid solution samples
Figure BDA0002849219150000071
The specific surface area of the sample is determined by BET method, and the specific surface area is 32m because the desorption peak area per gram of powder is in direct proportion to the specific surface area2And taking the/g standard graphite powder as a standard sample, measuring the desorption peak area of each sample, and calculating to obtain the BET specific surface area. The specific surface area is gradually increased with the increase of Zr content, and Ce0.6Zr0.4O2And suddenly decreases. Considering that the sample produced was a hollow nanosphere and was not a porous sphere, the increase in specific surface area was probably due to sphere breakage, and it is presumed that Ce was present0.6Zr0.4O2The sphericity is better.
FIG. 3 is an SEM photograph of cerium-zirconium solid solutions prepared under the conditions of different cerium ion to zirconium ion ratios in the precursor solutions, in which the reaction temperatures were all 800 ℃ and the sum of the cerium-zirconium ion concentrations was 0.05M, glycine was added in a stoichiometric ratio, and (a) the cerium-zirconium ion concentration ratio was 5/5; (b) the concentration ratio of cerium to zirconium ions is 6/4; (c) the concentration ratio of cerium to zirconium ions is 7/3; (d) the concentration ratio of cerium to zirconium ions is 8/2; (e) the cerium-zirconium ion concentration ratio was 9/1. It is very intuitive from the SEM image that the prepared sample is spherical, while it is a hollow structure as seen by some broken particles. (b) The cerium-zirconium solid solution has uniform primary particle size and good sphericity. (a) In the cerium-zirconium solid solution particles in (a), (c), (d) and (e), the particle diameters are not uniform, the sphericity is poor, some secondary particles of nanometer order are present in (a) and (c), and some secondary particles of nanometer order are also present in (d) which forms a structure in which spherical particles are wrapped in spherical particles, but less are present in (a) and (c). An EDS energy spectrum of a cerium-zirconium solid solution with a concentration ratio of 6/4 of cerium-zirconium ions is tested, and the mass percentage of each element can be calculated from the EDS energy spectrum, and the mass percentage is shown in Table 2. The mass percentage of cerium to zirconium was 6.02/3.28, and the equivalent molar ratio was 1.314/1.
TABLE 2.Ce0.6Zr0.4O2Mass percent of medium element
Figure BDA0002849219150000081
Example 2
Under the condition of keeping the concentration ratio of cerium ions to zirconium ions to be 6/4, 3 parts of precursor solution with the concentration ratios of cerium ions to zirconium ions being 0.06M, 0.12M and 0.24M respectively is prepared, glycine is added according to the stoichiometric ratio respectively, the precursor solution is carried into a reaction cavity of a 800 ℃ vertical tubular furnace by compressed air after being atomized into small liquid drops by ultrasonic, the small liquid drops are reacted, powder is collected, absolute ethyl alcohol and deionized water are used for washing, impurity ions are removed, and the powder is dried in vacuum for 2 hours at 50 ℃ after being filtered, so that products with different cerium-zirconium ratios are obtained.
Figure 4 is an XRD pattern of sample powder at different concentrations. (a) The sum of the concentrations of the cerium and zirconium solid solutions in (a) and (b) was 0.06M, and the sum of the concentrations of the cerium and zirconium solid solutions in (c) was 0.24M. Observing FIG. 4, the diffraction peak positions and relative intensities of the (a), (b) and (c) samples are all the same as the cubic phase Ce in PDF (38-1439) card0.6Zr0.4O2The diffraction data were in agreement, and Ce appeared at 29 °, 33 °, 48 °, 57 °, 71 °, and 78 ° of 2 θ, respectively0.6Zr0.4O2Does not have obvious impurity peak, and indicates that the sample is pure cubic phase Ce0.6Zr0.4O2And (3) powder. The diffraction peak intensities of different samples are different, and comparing XRD diffraction patterns of (a), (b) and (c), the concentration sum of cerium nitrate and zirconyl nitrate in the precursor solution is high, and the prepared sample has higher crystallization peak intensity.
FIG. 5 is a SEM photograph of cerium-zirconium solid solutions prepared under different conditions of cerium ion and zirconium ion concentrations in the precursor solutions, both reaction temperatures being 800 ℃ and cerium-zirconium ion concentration ratios being 6/4, glycine was added in stoichiometric ratios, (a) the sum of cerium-zirconium ion concentrations was 0.06M; (b) the sum of the cerium and zirconium ion concentrations is 0.12M; (c) the sum of the cerium zirconium ion concentrations was 0.24M. As the concentration increases, the collapse degree of the hollow sphere structure gradually increases, and the fragments gradually increase. (b) Partial collapse occurred in (a), while most of the spherical structure collapsed in (c), forming a large amount of debris. The reason is that the concentration of the precursor solution is too high, the diffusion speed of the internal solution to the outer layer is too high, and the outer layer has no time to crystallize to form a shell layer, so that the spherical structure collapses. The sum of the concentrations of cerium and zirconium ions thus experimentally formulated thereafter was 0.06M.
Example 3
Preparing 2 parts of precursor solution with the concentration sum of cerium ions and zirconium ions of 0.06M and the concentration ratio of 6/4, adding glycine according to the stoichiometric ratio, carrying the glycine into reaction chambers of a vertical tube furnace at 600 ℃ and 1000 ℃ respectively by compressed air after ultrasonic atomization to form small droplets, reacting, collecting powder, washing by absolute ethyl alcohol and deionized water, removing impurity ions, filtering, and drying in vacuum for 2 hours at 50 ℃ to obtain products with different cerium-zirconium ratios.
Figure 6 is an XRD pattern of sample powder prepared at different temperatures. (a) The preparation temperature is 600 ℃, the preparation temperature is 800 ℃, and the preparation temperature is 1000 ℃. It can be seen from the graph that there is a difference in diffraction peak intensity of each sample, and the higher the temperature, the higher the intensity of the diffraction peak, and the sharper the peak shape, indicating that the higher the preparation temperature, the higher the crystallinity of the sample. In addition, no splitting of diffraction peaks occurs at 1000 ℃, which indicates that the cerium-zirconium solid solution does not have phase separation, i.e. the sample has higher thermal stability.
TABLE 3 specific surface area of samples at different preparation temperatures
Figure BDA0002849219150000091
Table 3 shows the specific surface area of each of the samples prepared at 600 ℃, 800 ℃ and 1000 ℃. The BET specific surface area is the largest at 1000 ℃, but the specific surface area of the sample is more than 800 ℃ at 600 ℃, so that the specific surface area of the sample and the preparation temperature are not necessarily related at the critical temperature, the sample is probably influenced by factors such as preparation environment and the like, and after the critical temperature is exceeded, the sphericity of the sample is poor, fragments are increased, and the specific surface area is increased.
FIG. 7 is SEM pictures of cerium zirconium solid solutions prepared from the precursor solutions at different reaction temperatures, wherein the cerium zirconium ion concentration ratios are 6/4, the cerium zirconium ion concentration sum is 0.06M, glycine is added according to the stoichiometric ratio, (a) the combustion temperature is 800 ℃; (b) the combustion temperature was 1000 ℃. When the combustion temperature reached 1000 ℃, a large amount of chips appeared, the sphericity was poor, and in addition some cake-like structures appeared.
Performance Studies of catalytic CO
Firstly, the Ce with good sphericity and uniform dispersion is measured0.6Zr0.4O2The catalytic performance, FIG. 8, is a plot of its CO oxidation conversion as a function of temperature.
The initial temperature is 100 ℃, the end temperature is 170 ℃, the single increase is 10 ℃, and the preliminary exploration is carried out on the catalysis of the cerium-zirconium solid solution. The catalytic rate is increased along with the temperature rise before 150 ℃, and then the catalytic temperature is increased and decreased, the maximum catalytic rate only reaches 25 percent, and the temperature T for catalyzing 20 percent of CO20％Is 130 ℃. The catalytic effect is not good.
The temperature range was 160 ℃ to 300 ℃ with a single 20 ℃ rise. The results are shown in fig. 9, the catalytic change of the sample is more obvious after the temperature span is increased and the single temperature change, the conversion rate of the sample with the cerium-zirconium ratio of 8/2 is increased along with the temperature rise before 240 ℃, and then fluctuates slowly, the same properties are shown as those of the sample with the cerium-zirconium ratio of 6/4, the maximum catalytic rate is 28%, and the T is 28%20％220 ℃ higher by 90 ℃ than 6/4. The conversion rate of the sample with the cerium-zirconium ratio of 9/1 gradually increases, and T20％The temperature was 300 ℃. The test method of the sample with the cerium-zirconium ratio of 7/3 is different, the conversion rate is 100% after the sample is heated to 360 ℃, the conversion rate is up to 64% after the sample is cooled to 180 ℃, the conversion rate reaches 85% after the sample is played at 220 ℃, and the conversion rate reaches 100% after the sample is played at 240 ℃.
To obtain a complete measurement curve, the temperature span and the single temperature change are again stretched. FIG. 10 is Ce0.5Zr0.5O2The change rate of the catalytic CO oxidation conversion rate along with the temperature is measured in the range from 150 ℃ to 500 ℃ and is increased by 50 ℃ in a single time. The catalytic rate reaches 14% at 250 ℃, and the catalytic activity of the catalyst is greatly increased compared with that at 200 ℃. The catalytic conversion rate after 250 ℃ rises quickly, and the sampleThe catalytic rate is 79% at 450 ℃, and the catalysis is complete at 500 ℃. T is20％The temperature was 300 ℃.
FIG. 11 shows Ce at concentrations of cerium and zirconium ions of 0.06M, 0.12M and 0.24M0.6Zr0.4O2The catalytic CO conversion rate was varied with temperature, and the sample preparation temperature was 800 ℃. The sample with a concentration of 0.24M had a conversion of 70% at 160 ℃ and was completely catalyzed at 180 ℃. The conversion rate of the sample with the concentration of 0.12M is only 20% at 420 ℃, and the catalytic rate is 55% after the sample is heated to 500 ℃. The catalytic rate of the sample with the concentration of 0.06M fluctuates before 260 ℃, and then the catalytic rate gradually rises, T20％340 ℃ which is 80 ℃ lower than the 0.12M sample.
FIG. 12 is Ce prepared at 600 ℃ and 800 ℃0.6Zr0.4O2The catalytic conversion rate was varied with temperature, and the sum of the cerium and zirconium ion concentrations was 0.06M. The conversion rate is not greatly different before 260 ℃, and then the difference begins to appear and becomes larger and larger. The sample prepared at 600 ℃ shows catalytic activity after 340 ℃, and the catalytic rate reaches 26 percent at 400 ℃, and T is20％The temperature was 370 ℃. The sample prepared at 1000 ℃ shows catalytic activity at 280 ℃, the conversion rate at 400 ℃ reaches 70%, the conversion rate at 420 ℃ reaches 87%, and T is20％300 ℃ lower than the corresponding sample by 70 ℃.
In general, the nano-structure cerium-zirconium solid solution hollow sphere is successfully synthesized, and the particle size and the sphericity of the product are adjusted by changing the concentration of cerium-zirconium ions in a precursor solution, the ratio of cerium-zirconium ions, the reaction temperature and the like. Under the reaction conditions that the concentration sum of cerium nitrate and zirconyl nitrate in the precursor solution is 0.05M, the concentration ratio is 6/4, glycine is the stoichiometric ratio and the temperature of the tubular furnace is 800 ℃, the cerium-zirconium oxide solid solution hollow spheres with uniform particle size and good sphericity can be prepared. Since the prepared hollow sphere is not of a porous structure, the specific surface area is not large as a whole. The cerium-zirconium solid solution is prepared by spray combustion, the temperature of a tubular furnace is increased, the concentrations of cerium nitrate and zirconyl nitrate in a precursor solution are increased, the crystallization performance of the product can be improved, but the morphology of the product can be influenced, and fragments in the product are increased. The surface area is increased, the concentration of cerium zirconium ions is increased, and the preparation temperature is increased, so that the catalytic oxidation performance of the catalyst on CO can be improved.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims (10)

1. A method for synthesizing cerium-zirconium oxide solid solution hollow spheres by spray combustion is characterized by comprising the following steps: a method for synthesizing cerium zirconium oxide solid solution hollow spheres by spray combustion is characterized in that an auxiliary agent ammonium nitrate or chloride is added into a precursor solution, an organic fuel is added into the precursor solution, and the precursor solution generates liquid drops under the action of an atomizer, so that the liquid drops generate violent low-temperature self-propagating combustion reaction in a reaction furnace to obtain a product.
2. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 1, wherein: weighing cerium carbonate, zirconyl nitrate and glycine according to a designed proportion, dissolving and quantifying with nitric acid to obtain a precursor solution I, ultrasonically atomizing the precursor solution I into small drops, loading the small drops into a reaction chamber of a vertical tube furnace by compressed air for reaction, collecting powder, washing with absolute ethyl alcohol and deionized water to remove impurity ions, performing suction filtration, and performing vacuum drying to obtain the final product cerium-zirconium oxide solid solution hollow sphere powder.
3. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the prepared cerium-zirconium solid solution is represented as CexZr1-xO2Wherein x is the molar ratio of Ce; the reaction equation of the experiment, which is related to the molar ratio x of cerium and the content of fuel glycine, is as follows,
xCe2(CO3)3·+2(1-x)ZrO(NO3)2·+2ψNH2CH2COOH+((9ψ+11x-10)/2)O2＝2CexZr1-xO2+(ψ+2(1-x))N2+(3x+4ψ)CO2+5ψH2O
here, (Gly: Ce2(CO3)3) 2 psi/x when O2When the index of (b) is "0", the reaction formula is a stoichiometric reaction formula, in which case ψ is (10-11x)/9, Gly is Ce2(CO3)3(20-22x)/9 x; when O is present2When the coefficient of (b) is larger than "0", the reaction is a rich reaction, in which case ψ>(10-11x)/9，Gly:Ce2(CO3)3>(20-22x)/9 x; when O is present2Is less than "0", the reaction is a lean combustion reaction, and in this case, #<(10-11x)/9，Gly:Ce2(CO3)3<(20-22x)/9x。
4. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the flow rate of carrier gas in the preparation process is 0.5L/min, and the atomization frequency is 2.4 MHz.
5. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the reaction temperature is 800-1000 ℃.
6. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the cerium-zirconium solid solution is Ce0.5Zr0.5O2When the reaction formula is a stoichiometric reaction formula, it is represented as: ce2(CO3)3+2ZrO(NO3)2+2NH2CH2COOH＝4Ce0.5Zr0.5O2+3N2+7CO2+5H2O。
7. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the cerium-zirconium solid solution is Ce0.6Zr0.4O2When the reaction formula is a stoichiometric reaction formula, the tableShown as follows: 27Ce2(CO3)3·+36ZrO(NO3)2·+34NH2CH2COOH＝90Ce0.6Zr0.4O2+53N2+149CO2+85H2O。
8. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the cerium-zirconium solid solution is Ce0.7Zr0.3O2When the reaction formula is a stoichiometric reaction formula, it is represented as: 63Ce2(CO3)3·+54ZrO(NO3)2·+46NH2CH2COOH＝180Ce0.7Zr0.3O2+77N2+281CO2+115H2O。
9. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the cerium-zirconium solid solution is Ce0.8Zr0.2O2When the reaction formula is a stoichiometric reaction formula, it is represented as: 12Ce2(CO3)3·+6ZrO(NO3)2·+4NH2CH2COOH＝30Ce0.8Zr0.2O2+8N2+44CO2+10H2O。
10. The method for synthesizing the cerium-zirconium oxide solid solution hollow sphere by spray combustion as claimed in claim 2, wherein: the cerium-zirconium solid solution is Ce0.9Zr0.1O2When the reaction formula is a stoichiometric reaction formula, it is represented as: 81Ce2(CO3)3·+18ZrO(NO3)2·+2NH2CH2COOH＝180Ce0.9Zr0.1O2+19N2+247CO2+5H2O。
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