阅读说明：本技术 一种贵金属高分散的单层涂覆三效催化剂的制备方法 (Preparation method of single-layer coating three-way catalyst with high noble metal dispersion ) 是由 贾海建 杨进进 王颖 何静 蔡肇皓 于 2019-09-23 设计创作，主要内容包括：本发明涉及催化剂技术领域,具体公开了一种贵金属高分散的单层涂覆三效催化剂的制备方法,包括以下步骤：S1：准备硝酸Pd、硝酸Rh、粉体1、粉体2和惰性载体；S2：使用浸渍法,将硝酸Pd负载在粉体1上,烘干焙烧制备得到基层催化剂粉体；S3：使用浸渍法,将硝酸Rh负载在基层催化剂粉体和粉体2上,球磨后形成催化剂涂层浆料；S4：将催化剂涂层浆料涂覆于惰性载体上,烘干焙烧后,即得到三元催化剂。本发明能够提高贵金属在载体材料表面的吸附,减少制备体系中游离态贵金属,提高贵金属在材料表面的分散,避免贵金属形成合金,降低催化剂背压,简化催化剂制备工艺,降低催化剂成本。(The invention relates to the technical field of catalysts, and particularly discloses a preparation method of a single-layer coating three-way catalyst with high dispersion of precious metals, which comprises the following steps: s1: preparing Pd nitrate, Rh nitrate, powder 1, powder 2 and an inert carrier; s2: loading Pd nitrate on the powder 1 by using an impregnation method, and drying and roasting to prepare base catalyst powder; s3: loading nitric acid Rh on the base catalyst powder and the powder 2 by using an impregnation method, and forming catalyst coating slurry after ball milling; s4: and coating the catalyst coating slurry on an inert carrier, and drying and roasting to obtain the three-way catalyst. The method can improve the adsorption of the noble metal on the surface of the carrier material, reduce the free noble metal in a preparation system, improve the dispersion of the noble metal on the surface of the material, avoid the noble metal from forming alloy, reduce the back pressure of the catalyst, simplify the preparation process of the catalyst and reduce the cost of the catalyst.)

1. A preparation method of a single-layer coating three-way catalyst with high dispersion of noble metals is characterized by comprising the following steps:

s1: preparing Pd nitrate, Rh nitrate, powder 1, powder 2 and an inert carrier;

s2: loading Pd nitrate on the powder 1 by using an impregnation method, and drying and roasting to prepare base catalyst powder;

s3: loading nitric acid Rh on the base catalyst powder and the powder 2 by using an impregnation method, and forming catalyst coating slurry after ball milling;

s4: and coating the catalyst coating slurry on an inert carrier, and drying and roasting to obtain the three-way catalyst.

2. The method for preparing a single-layer coated three-way catalyst with high noble metal dispersion as claimed in claim 1, wherein the specific operations in step S2 are as follows: dispersing 70-130g/ft3 powder 1 in deionized water, controlling the solid content to be 28% -40%, then adding Pd nitrate, controlling the pH value, and after the Pd nitrate is fully loaded, drying and roasting to obtain the base catalyst powder.

3. The method of claim 2, wherein in the step S2, the Pd element content in the Pd nitrate is 3-200g/ft3, the Pd nitrate is added 1-50 times, and the pH is controlled to 0.5-4.

4. The method for preparing a single-layer coated three-way catalyst with high noble metal dispersion as claimed in claim 1, wherein the specific operations in step S3 are as follows: dispersing 50-110g/ft3 of powder 2 and base catalyst powder in deionized water, controlling the solid content to be 25% -40%, then adding nitric acid Rh, controlling the pH value of the system, adding a binder after the nitric acid Rh is fully loaded, and forming coating slurry after ball milling.

5. The method of claim 3, wherein in the step S3, the Rh content of the Rh nitrate is 1-50g/ft3, the Rh nitrate is added for 1-20 times, and the pH of the system is controlled to be 0.5-4.

6. The method for preparing a noble metal highly dispersed single-layer coated three-way catalyst according to claim 1, wherein in step S3, 5% to 30% of a binder is added, the binder is alumina gel, and a coating slurry is formed after ball milling, wherein the solid content of the coating slurry is 15% to 30%.

7. The method for preparing the noble metal highly dispersed single-layer coating three-way catalyst according to claim 1, wherein the powder 1 and the powder 2 are both rare earth oxide, alumina or a mixture of the rare earth oxide and the alumina; the inert carrier includes cordierite, a metal carrier, or a silicon carbide carrier.

8. The method for preparing a single-layer coated three-way catalyst with high noble metal dispersion as claimed in claim 1, wherein in step S2, the drying temperature is 80-200 ℃, and the roasting temperature is 300-600 ℃; in step S4, the drying temperature is 80-200 ℃, and the roasting temperature is 300-900 ℃.

9. The method of claim 1, wherein the pH is controlled by adding acid or alkali in steps S2 and S3.

10. The method for preparing a single-layer coated three-way catalyst with high dispersion of noble metal according to claim 1, wherein the catalyst coating slurry after ball milling has a D50 range of 1-5 μm and a D90 range of 6-20 μm in step S3.

Technical Field

The invention relates to the technical field of catalysts, in particular to a preparation method of a single-layer coating three-way catalyst with high dispersion of precious metals.

Background

The main pollutants of automobile exhaust are carbon monoxide (CO), Hydrocarbons (HC) and nitrogen oxides (NOx). With the annual increase in automobile inventory, automobile exhaust emissions have become a major source of air pollution. The three-way catalyst installed in the gasoline vehicle exhaust aftertreatment system can oxidize carbon monoxide and hydrocarbon into carbon dioxide (CO2) and water (H2O) and simultaneously reduce oxynitride into nitrogen (N2), thereby realizing synchronous purification of three main pollutants in the exhaust. The three-way catalyst is generally composed of two parts: a honeycomb ceramic or metal support, and a catalyst coating attached to the support. The catalyst coating layer is generally composed of an inorganic oxide material (such as γ -Al2O3 and cerium-zirconium composite oxide containing CeO 2) with a large specific surface area and a precious metal active component (usually one or more of Pt (platinum), Pd (palladium) and Rh (rhodium)) loaded on the surface of the oxide.

With the increase of the keeping quantity of motor vehicles, the exhaust emission of the motor vehicles becomes a large pollution source of the environment, and the life quality of people is seriously influenced. The catalytic conversion of gasoline car tail gas by using a three-way catalyst (purifier) is an important method for preventing and controlling the pollutants in the tail gas of a motor vehicle at present and is an effective method for a long time in the future. In the development process of the three-way catalyst, the catalyst preparation process technology is always an important reason for influencing the performance of the catalyst. At present, the three-way catalyst is mostly coated in a layered mode with more two layers, and a common mixed coating method in single-layer coating is less used because Pd and Rh are easy to form alloy and reduce the performance of the catalyst. The current three-way catalyst has large noble metal consumption, the noble metal not only increases the system acidity, but also has high requirement on the acid resistance of the material, increases the cost of raw materials, and the noble metal usually has a large amount of free noble metal due to insufficient adsorption sites of the supported material, and is easy to agglomerate, thereby affecting the performance of the catalyst.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a preparation method of a single-layer coating three-way catalyst with high dispersion of precious metals, aiming at improving the adsorption of the precious metals on the surface of a carrier material, reducing free precious metals in a preparation system, improving the dispersion of the precious metals on the surface of the material, avoiding the precious metals from forming alloys, reducing the backpressure of the catalyst, simplifying the preparation process of the catalyst and reducing the cost of the catalyst.

In order to solve the technical problems, the invention adopts the following technical scheme:

a preparation method of a single-layer coating three-way catalyst with high dispersion of noble metals comprises the following steps:

s1: preparing Pd nitrate, Rh nitrate, powder 1, powder 2 and an inert carrier;

s2: loading Pd nitrate on the powder 1 by using an impregnation method, and drying and roasting to prepare base catalyst powder;

s3: loading nitric acid Rh on the base catalyst powder and the powder 2 by using an impregnation method, and forming catalyst coating slurry after ball milling;

s4: and coating the catalyst coating slurry on an inert carrier, and drying and roasting to obtain the three-way catalyst.

Further, in step S2, the specific operations are as follows: 70-130g/ft³The powder 1 is dispersed in deionized water, the solid content is controlled to be 28% -40%, then Pd nitrate is added, the pH value is controlled, and after the Pd nitrate is fully loaded, the base catalyst powder is obtained after drying and roasting.

Further, in step S2, the Pd element content in the Pd nitrate is 3-200g/ft³The adding times of the Pd nitrate is 1 to 50 times, and the pH value is controlled to be 0.5 to 4.

Further, in step S3, the specific operations are as follows: 50-110g/ft³The powder 2 and the base catalyst powder are dispersed in deionized water, the solid content is controlled to be 25% -40%, then nitric acid Rh is added, the pH value of the system is controlled, after the nitric acid Rh is fully loaded, a binder is added, and coating slurry is formed after ball milling.

Further, in step S3, the Rh content of the nitric acid Rh is 1-50g/ft³The adding frequency of the nitric acid Rh is 1-20 times, and the pH value of the system is controlled to be 0.5-4.

Further, in step S3, 5% to 30% of a binder is added, the binder is alumina gel, and a coating slurry is formed after ball milling, wherein the solid content of the coating slurry is 15% to 30%.

Further, the powder 1 and the powder 2 are both rare earth oxide, alumina or a mixture of the rare earth oxide and the alumina; the inert carrier includes cordierite, a metal carrier, or a silicon carbide carrier.

Further, in step S2, the drying temperature is 80-200 ℃, and the roasting temperature is 300-600 ℃; in step S4, the drying temperature is 80-200 ℃, and the roasting temperature is 300-900 ℃.

Further, in step S2 and step S3, the pH is controlled by adding an acid or a base.

Further, in step S3, the catalyst coating slurry after ball milling has a D50 range of 1 to 5 μm and a D90 range of 6 to 20 μm.

In summary, the preparation method of the single-layer coating three-way catalyst with high noble metal dispersion has the following beneficial effects:

1. the invention provides a preparation method of a single-layer coating three-way catalyst with high dispersion of precious metals, which is a method of adding precious metals in batches and controlling the combination of pH values in the preparation process of the catalyst. The noble metal is added into the powder in batches for multiple times, so that the damage of the powder material structure caused by overhigh acidity due to the addition of the noble metal is avoided, the noble metal can be slowly adsorbed on the powder by adding the noble metal in batches, the uniform distribution of the noble metal is facilitated, and the catalytic performance of the catalyst is improved.

2. After the noble metal is added each time, the pH value is adjusted to a certain value by using acid or alkali, so that the damage of the material structure caused by overhigh acidity caused by the noble metal is relieved, the noble metal keeps good adsorption capacity by using a proper pH value, part of free noble metal can be fixed, the agglomeration of the free noble metal in the aging process of the catalyst is reduced, and the catalytic performance of the catalyst is enhanced.

3. According to the preparation method of the single-layer coating three-way catalyst with the high dispersion of the noble metal, Pd is firstly fixed on the powder, and then Rh is impregnated, so that the formation of direct alloy addition of Pd and Rh is avoided, or the formation of alloy caused by the transfer of the noble metal in the drying and roasting processes after the Pd and Rh are impregnated in batches is avoided, and the performance of the catalyst is influenced.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is a process flow diagram of a preparation method of a single-layer coated three-way catalyst with high noble metal dispersion according to an embodiment of the present invention.

Fig. 2 is an SEM image of a single layer coated three-way catalyst.

FIG. 3 is a plot comparing the performance of a three-way catalyst prepared according to the present invention with a catalyst prepared according to the conventional process when the Pd/Rh ratio is 40/4.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, 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 some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in the figures 1-2 of the drawings,