A yttria-zirconia material with a worm-like structure and its preparation method and application

Abstract

The present invention belongs to the technical field of catalytic material preparation, and specifically relates to a yttria-zirconia material with a worm-like structure, and its preparation method and application; the material of the invention has a worm-like structure, and the worm-like structure is a multi-level nanostructure self-assembled from a chain-like structure; the pore size of the worm-like structure is no more than 20nm, and the pore size distribution is unimodal; the present invention prepares a yttria-zirconia material with a worm-like structure, which has a unique morphology and can withstand high temperature environments. It can be used as a carrier material for motor vehicle exhaust after-treatment catalysts. The material is loaded with precious metal palladium, and the worm-like structure is conducive to the dispersion of active components and the protection of active components at high temperatures. It has a low ignition temperature for CH4 catalytic oxidation. In addition, the preparation method is simple and the raw materials are easily available.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic material preparation, and in particular relates to an yttria-zirconia material with a worm-like structure, a preparation method and an application thereof. Background Art

[0002] With the further tightening of automobile exhaust emission regulations, the improvement of fuel economy performance and the tightening of CO2 emission control, the development of suitable alternative fuel engine clean cars has become an inevitable development trend for environmental protection and energy considerations.

[0003] Compressed natural gas (CNG) engines offer significant environmental advantages over traditional gasoline and diesel engines due to their higher combustion efficiency and lower pollutant emissions. However, CNG engines have relatively low exhaust temperatures (300-550°C), and their exhaust gas contains high levels of water (10-15%) and sulfur. Currently, the greatest challenges lie in preventing CH4 oxidation at low temperatures and improving the catalyst's hydrothermal stability and sulfur resistance.

[0004] The composition, structure, and morphology of a catalyst, as well as its dynamic changes during synthesis and service, play a decisive role in its catalytic activity. Palladium-supported catalysts, due to their low light-off temperature and ability to maintain high catalytic activity even under lean-burn conditions, have become a hot topic of research. Currently, γ-Al₂O₃ is a commonly used support, but it is unstable at high temperatures and susceptible to sulfur poisoning. To address these issues, other oxide supports have been extensively investigated.

[0005] ZrO2-based supports have excellent water resistance and sulfur poisoning resistance, making them suitable for natural gas vehicle exhaust purification. They offer the potential to overcome the vulnerability of current catalysts to water and sulfur poisoning. Therefore, ZrO2-based catalysts are a hot topic in the catalytic oxidation of methane in vehicle exhaust. However, ZrO2 has a low specific surface area and is prone to sintering and phase separation at high temperatures, resulting in a decrease in catalytic activity. Therefore, some researchers have attempted to improve ZrO2's specific surface area by improving its preparation methods to enhance its performance. Others have also attempted to enhance its stability and sulfur tolerance by doping it with rare earth and transition metal elements. Rare earth and transition metal doping of ZrO2 can modify the support's microstructure and surface chemical composition, optimizing the active species and catalytic performance of the catalyst. Y doping can significantly improve the thermal stability of ZrO2. Furthermore, different preparation methods can lead to different interactions between the support and the catalyst, resulting in variations in texture, structure, and catalytic activity. In recent years, researchers have prepared ZrO2 and its mixed oxides with diverse structures and morphologies, but the influence of morphology on the catalytic performance of the catalysts remains to be further investigated. Current methane combustion catalysts still face problems such as water and sulfur resistance, low-temperature oxidation performance, and hydrothermal stability that cannot meet actual needs. Future research focuses may be on the controllable synthesis of nanomaterials with special structures, morphologies, and exposed crystal surfaces, so as to achieve atomic-level regulation of the interactions between components and between components and reactants.

[0006] Currently published patents or papers use yttrium sources and zirconium salts as raw materials, and one or more of rare earth metals, alkaline earth metals, and transition metals as stabilizing agents. Yttrium zirconium oxides with different structures and morphologies are prepared by impregnation, coprecipitation, hydrothermal methods, and other methods. These are mainly used in thermal barrier coatings and ceramic materials (mainly used in aviation and engineering equipment such as aircraft heat-resistant components, missile radomes, and truck brake pads, CN 113845367B, CN 111574811 B). Gao Yanfeng et al. (CN102976405 A) used a hydrothermal method to prepare flower-shaped yttrium-doped zirconia powder. The prepared YSZ material has excellent thermal conductivity and a large thermal diffusivity coefficient. Shu Zhanxia et al. (Hydrothermal / solvothermal controlled synthesis and characterization of zirconium dioxide nanomaterials) prepared hollow tetragonal yttrium-stabilized zirconia (YSZ) spheres via a template-free solvothermal method in a butanol / acetylacetone or ethanol / acetylacetone homogeneous solution using ZrOCl2·8H2O and Y(NO3)3·6H2O as the reactants. Zhang Wangying (morphology-controlled synthesis of zirconia using organic templates) prepared dendritic nanostructured zirconia using the organic macromolecule PEG200 as a template. The interaction mechanism between PEG200 and ZrOCl2·8H2O was explored through conductivity and infrared analysis of the product. Existing technologies do not address worm-like yttria-zirconia materials.

[0007] Therefore, the present application proposes a yttria-zirconia material with a worm-like structure and a preparation method thereof. Summary of the Invention

[0008] The purpose of the present invention is to provide a yttria-zirconia material with a worm-like structure and its preparation method and application. The yttria-zirconia material with a worm-like structure prepared by the present invention has a unique morphology and can withstand high-temperature environments.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] A yttria-zirconia material with a worm-like structure. The material of the present invention has a worm-like structure, which is a multi-level nanostructure formed by self-assembly of chain-like structures. The maximum pore size of the worm-like structure does not exceed 20 nm, and the pore size distribution is unimodal.

[0011] The worm-like structured yttria-zirconia material of the present invention has good thermal stability. After calcination at 950°C, the specific surface area can reach 36m 2 / g or more; yttrium oxide is evenly distributed in zirconium oxide, has a relatively stable tetragonal phase, and the pore size is unimodal distribution, and the pore size is in the range of 0 to 16 nm.

[0012] The worm-like structured yttria-zirconia material of the present invention has the following components measured in terms of oxides: 90-98 wt% of zirconium oxide and 2-10 wt% of yttria.

[0013] The method for preparing the yttria-zirconia material having a worm-like structure of the present invention comprises the following steps:

[0014] (1) taking a zirconium compound and a yttrium compound, adding them to deionized water, dissolving them, and then adding a precipitant and a dispersant dropwise simultaneously, stirring to form a gel;

[0015] (2) Pour the gel into a hydrothermal reactor, seal it, and then heat the reactor. No additional pressure is added to the reactor, and only the pressure generated by water evaporation is used to pressurize it. Keep it warm for a certain period of time. After the insulation is completed, let the reactor cool naturally to room temperature;

[0016] (3) The product in step (2) was filtered and washed four times with deionized water, and the product was dried in an oven;

[0017] (4) grinding and calcining the product obtained in step (3) to obtain the yttria-zirconia material;

[0018] Furthermore, the zirconium compound is zirconium oxychloride, and the added concentration is 0.2740-0.2940 mol·L -1 , preferably 0.2930 mol·L -1 .

[0019] Furthermore, the yttrium compound is yttrium nitrate, and the added concentration is 0.0300-0.0360 mol·L -1 , preferably 0.0355 mol·L -1 .

[0020] Furthermore, the precipitant is sodium hydroxide, and the added concentration is 0.300-0.500 mol·L -1 , preferably 0.328 mol·L -1 .

[0021] Furthermore, the dispersant is ethylenediaminetetraacetic acid (EDTA), and the added concentration is 0.1400-0.1700 mol·L -1 , preferably 0.1642 mol·L -1 .

[0022] Furthermore, the hydrothermal reaction conditions in step (2) are 120° C. to 160° C., preferably 120° C., and the insulation time is 4 h to 6 h, preferably 4 h.

[0023] Furthermore, in step (3), an equal volume of deionized water is added each time the filtration is performed.

[0024] Furthermore, in step (4), the calcination temperature of the muffle furnace is 550° C., the calcination time is 4 h, and the heating rate is 5° C. / min.

[0025] Furthermore, the method for preparing the yttria-zirconia material with a worm-like structure of the present invention does not contain the use of organic solvents such as alcohol and ether.

[0026] Furthermore, the yttria-zirconia material is used as a carrier material for a motor vehicle exhaust after-treatment catalyst.

[0027] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0028] This invention produces a yttria-zirconia material with a unique worm-like structure. This material, with its unique morphology and high-temperature resistance, can be used as a support material for automotive exhaust after-treatment catalysts. The material is loaded with precious metal palladium, and its worm-like structure facilitates the dispersion and protection of the active component at high temperatures, resulting in a low light-off temperature for CH4 catalytic oxidation. Furthermore, the preparation method is simple and the raw materials are readily available.

[0029] The preparation method of the yttria-zirconia material with a worm-like structure of the present invention does not require the use of organic solvents such as alcohol and ether, and has little impact on the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an SEM image of fresh worm-like yttrium zirconium oxide in Example;

[0031] Figure 2 The pore size distribution diagram of fresh and aged yttrium-zirconium samples in Example;

[0032] Figure 3 This is the SEM image of fresh flower-shaped yttrium zirconium oxide in comparative example 1;

[0033] Figure 4 This is the SEM image of fresh spherical yttrium zirconium oxide in comparative example 2. DETAILED DESCRIPTION

[0034] like Figure 1-4 In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] Example 1

[0036] Weigh 14.87g zirconium oxychloride and 1.08g yttrium nitrate and add them to deionized water, stir and dissolve to prepare 0.2750mol·L -1 and 0.030 mol·L -1 Then, 5.0 g of EDTA dispersant solution (concentration 0.1400 mol·L) was added dropwise. -1 ), 2.05g sodium hydroxide solution (concentration 0.300mol·L -1 ), stirred for 2 h to form a gel.

[0037] The gel was poured into a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, sealed, and then heated to 120°C for 4 hours. After the end of the heat preservation, the reactor was allowed to cool naturally to room temperature.

[0038] The above product was filtered and washed four times with an equal volume of deionized water, and the product was dried in an oven at 120°C. Grind and calcine the resulting powder in a muffle furnace at 550°C for 4 hours to obtain fresh yttrium zirconium oxide. The fresh samples were placed in a muffle furnace at 950°C for high temperature aging to obtain aged samples. The SEM image of the fresh yttrium zirconium oxide is shown in FIG. Figure 1 .Depend on Figure 1 It can be seen that all fresh yttrium zirconium oxide samples exhibit a worm-like structure.

[0039] The specific surface area of the fresh and aged yttrium-zirconium samples is 72.9 m 2 ·g -1 , 36.8m 2 ·g -1 , has good thermal stability. The pore size distribution diagram of the fresh yttrium zirconium oxide sample and the 950℃ aged yttrium zirconium oxide sample is shown in Figure 2 .Depend on Figure 2 It can be seen that the pore size of the yttrium-doped zirconia material of the present invention is unimodal before and after aging, and the pore size is mainly distributed in the range of 0 to 16 nm.

[0040] 20 g of the prepared worm-shaped yttrium zirconium oxide powder was taken and loaded with 0.5 wt% of the precious metal Pd by the equal volume impregnation method. The obtained catalyst powder was calcined at 950°C and then tested for the catalytic oxidation activity of CH4 using a multifunctional catalyst evaluation device (this evaluation device is a non-standard equipment. The main principle is: the reaction mixture is configured through the gas distribution system, and the mass flow meter controls the flow rate of each gas to simulate the composition and content of the real engine exhaust atmosphere. The mixture passes through a heatable reactor equipped with a catalyst. During the heating process of the furnace, the mixture is oxidized or reduced by the catalyst. A gas analyzer is used to test the gas and concentration after passing through the catalyst. The conversion efficiency of the gas at different temperature points can be calculated based on the concentration of each gas before and after the reaction. All descriptions of the multifunctional catalyst evaluation device in the following content are the same). The ignition temperature of CH4 is shown in Table 1. The material with a worm-like structure has a lower CH4 ignition temperature.

[0041] Example 2

[0042] Weigh 15.10g zirconium oxychloride and 2.16g yttrium nitrate and add them to deionized water, stir and dissolve them to prepare 0.2860mol·L -1 and 0.032 mol·L -1 Then, 6.0 g of EDTA dispersant solution (concentration 0.1600 mol·L) was added dropwise. -1 ), 2.25g sodium hydroxide solution (concentration 0.400mol·L -1 ), stirred for 3 h to form a gel.

[0043] The gel was poured into a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, sealed, and then heated to 140°C for 5 hours. After the end of the heat preservation, the reactor was allowed to cool naturally to room temperature.

[0044] The above product was filtered and washed four times with an equal volume of deionized water, and the product was dried in an oven at 120°C. After drying, it was ground and the resulting powder was calcined in a muffle furnace at 550°C for 4 hours to obtain fresh yttrium zirconium oxide. The fresh samples were placed in a muffle furnace at 950°C for high-temperature aging to obtain aged samples. The fresh yttrium zirconium oxide samples all showed a worm-like structure. The specific surface area of the fresh and aged yttrium zirconium samples was 75.1m 2 ·g -1 , 38.2m 2 ·g -1 , with good thermal stability. The pore size is mainly distributed in the range of 0 to 16 nm.

[0045] 20 g of the prepared worm-like yttrium zirconium oxide powder was taken and loaded with 0.5 wt% of the precious metal Pd by the equal volume impregnation method. The obtained catalyst powder was calcined at 950°C and the catalytic oxidation activity of CH4 was tested using a multifunctional catalyst evaluation device. The ignition temperature of CH4 is shown in Table 1. The material with a worm-like structure has a lower CH4 ignition temperature.

[0046] Example 3

[0047] Weigh 15.24g zirconium oxychloride and 0.56g yttrium nitrate and add them to deionized water, stir and dissolve, and prepare 0.2930mol·L -1 and 0.035 mol·L -1 Then, 3.0 g of EDTA dispersant solution (concentration 0.1700 mol·L) was added dropwise. -1 ), 1.86g sodium hydroxide solution (concentration 0.500mol·L -1 ), stirred for 2 h to form a gel.

[0048] The gel was poured into a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, sealed, and then heated to 160°C for 6 hours. After the end of the heat preservation, the reactor was allowed to cool naturally to room temperature.

[0049] The above product was filtered and washed four times with an equal volume of deionized water, and the product was dried in an oven at 120°C. After drying, it was ground and the resulting powder was calcined in a muffle furnace at 550°C for 4 hours to obtain fresh yttrium zirconium oxide. The fresh samples were placed in a muffle furnace at 950°C for high-temperature aging to obtain aged samples. The fresh yttrium zirconium oxide samples all showed a worm-like structure. The specific surface area of the fresh and aged yttrium zirconium samples was 70.1m 2 ·g -1 , 36.0m 2 ·g -1 , with good thermal stability. The pore size is mainly distributed in the range of 0 to 16 nm.

[0050] 20 g of the prepared worm-like yttrium zirconium oxide powder was taken and loaded with 0.5 wt% of the precious metal Pd by the equal volume impregnation method. The obtained catalyst powder was calcined at 950°C and the catalytic oxidation activity of CH4 was tested using a multifunctional catalyst evaluation device. The ignition temperature of CH4 is shown in Table 1. The material with a worm-like structure has a lower CH4 ignition temperature.

[0051] Comparative Example 1

[0052] Weigh 8.89g zirconium sulfate and 0.85g yttrium nitrate and add them to deionized water, stir and dissolve, and prepare 0.3102mol·L -1 and 0.046 mol·L-1 The solution was mixed with zirconium sulfate and yttrium nitrate solution, and then 0.58g sodium hydroxide solution (concentration 0.300mol·L -1 ), stirred for 1 h to form a gel.

[0053] The gel was poured into a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, sealed, and then heated to 200°C for 4 hours. After the end of the heat preservation, the reactor was allowed to cool naturally to room temperature.

[0054] The above product was filtered and washed four times with an equal volume of deionized water, and the product was dried in an oven at 120°C. Grind and calcine the resulting powder in a muffle furnace at 800°C for 4 hours to obtain fresh yttrium zirconium oxide. The SEM image of the fresh yttrium zirconium oxide is shown in FIG. Figure 3 .Depend on Figure 3 It can be seen that the fresh yttrium zirconium oxide samples all exhibit a flower-like structure. The specific surface area of the fresh and aged yttrium zirconium samples is 22.1 m 2 ·g -1 , 15.0m 2 ·g -1 .

[0055] 20 g of the prepared flower-shaped yttrium zirconium oxide powder was loaded with 0.5 wt% of the precious metal Pd by the equal volume impregnation method. The obtained catalyst powder was calcined at 950°C and the catalytic oxidation activity of CH4 was tested using a multifunctional catalyst evaluation device. The ignition temperature of CH4 is shown in Table 1.

[0056] Comparative Example 2

[0057] Weigh 14.87 g of zirconium oxychloride and 2.04 g of yttrium nitrate and dissolve them in a mixed solvent of acetylacetone and n-butanol (the volume ratio of acetylacetone to n-butanol is 1:1), and stir until the solution becomes clear.

[0058] The above solution was poured into a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, sealed, and then the reactor was heated to 200°C and kept warm for 12 hours. After the end of the heat preservation, the reactor was allowed to cool naturally to room temperature.

[0059] The above product was filtered and washed twice with anhydrous ethanol, then filtered and washed twice with an equal volume of deionized water, and the product was dried in an oven at 75°C. Grind and calcine the resulting powder in a muffle furnace at 550°C for 4 hours to obtain fresh yttrium zirconium oxide. The SEM image of the fresh yttrium zirconium oxide is shown in FIG. Figure 4 .Depend on Figure 4 It can be seen that the fresh yttrium zirconium oxide samples all present a spherical structure. The specific surface area of the fresh and aged yttrium zirconium samples is 82.0 m 2 ·g -1 , 9.0m 2 ·g -1 .

[0060] 20 g of the prepared spherical yttrium zirconium oxide powder was taken and loaded with 0.5 wt% of precious metal Pd by the equal volume impregnation method. After the obtained catalyst powder was calcined at 950°C, the catalytic oxidation activity of CH4 was tested using a multifunctional catalyst evaluation device. The ignition temperature of CH4 is shown in Table 1. The material with a worm-like structure has a lower CH4 ignition temperature.

[0061] Experimental analysis:

[0062] The ignition temperatures of the catalysts prepared from yttrium zirconium oxide loaded with Pd in Examples 1, 2, 3 and Comparative Examples 1 and 2 for catalytic oxidation of CH4 are shown in Table 1:

[0063] serial number Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 <![CDATA[CH4 / T 50 ℃]]> 435 430 442 500 487

[0064] Each embodiment in this specification is described in a related manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiment is generally similar to the method embodiment, so the description is relatively simple. For related parts, refer to the description of the method embodiment.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A method for preparing a yttria-zirconia material with a worm-like structure, characterized in that: The following steps are involved: Weigh 14.87 g of zirconium oxychloride and 1.08 g of yttrium nitrate into deionized water and stir to dissolve to prepare 0.2750 mol·L-1 and 0.030 mol·L-1 solutions, respectively. Then, add 5.0 g of 0.1400 mol·L-1 EDTA dispersant solution and 2.05 g of 0.300 mol·L-1 sodium hydroxide precipitant solution dropwise simultaneously and stir for 2 h to form a gel. The gel was poured into a stainless steel hydrothermal reactor lined with polytetrafluoroethylene, sealed, and then heated to 120°C for 4 hours. After the end of the insulation, the reactor was allowed to cool naturally to room temperature. The product was filtered and washed four times with an equal volume of deionized water, and the product was dried in an oven at 120°C; the powder was ground and calcined in a muffle furnace at 550°C for 4 hours to obtain fresh yttrium zirconium oxide; the fresh yttrium zirconium oxide was placed in a muffle furnace at 950°C for high temperature aging to obtain aged yttrium zirconium oxide; the fresh yttrium zirconium oxide exhibited a worm-like structure; The specific surface areas of the fresh yttrium zirconium oxide and the aged yttrium zirconium oxide are 72.9 m 2 ·g -1 , 36.8m 2 ·g -1 , has good thermal stability; The pore sizes of the fresh yttrium zirconium oxide and the aged yttrium zirconium oxide obtained by aging at 950° C. are unimodal, and the pore sizes are mainly distributed in the range of 0 to 16 nm. The catalyst is prepared by loading 0.5 wt% of precious metal Pd on the obtained fresh yttrium zirconium oxide powder by an equal volume impregnation method; The ignition temperature of the obtained catalyst for CH4 catalytic oxidation is 435℃.

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