A kind of single precious metal layer three-way catalyst preparation method

Abstract

The invention discloses a single noble metal layer three-effect catalyst and a preparation method thereof. The catalyst is made of a substrate and a single-layer or two-layer catalyst coating coated on the substrate; wherein, the single-layer coating or the surface coating of the two-layer coating on the surface of the substrate contains noble metals. The invention provides a process route that does not require heat-fixing precious metals, has low manufacturing cost and a single noble metal coating catalyst with excellent catalytic performance. By adding alkaline earth metals, complexing agents, and precipitating agents to the precious metal solution, the prepared catalyst precious metals are dispersed High degree of high temperature, high utilization rate of precious metals, high temperature self-aggregation of precious metals can be inhibited, good durability, the catalyst still shows good catalytic activity even when the content of precious metals is low.

Description

technical field [0001] The invention belongs to the technical field of three-way catalysts and their preparation, and relates to a method for preparing a three-way catalyst with a single noble metal layer and the prepared catalyst. Background technique [0002] After July 1, 2019, the emissions of motorcycles produced and sold in China must meet China's Phase IV emission requirements, namely GB14622-2016 "Motorcycle Pollutant Emission Limits and Measurement Methods (Working Condition Method, China Phase IV) "Requirements, compared with the national III emission regulations for motorcycles, the three pollutant emission limits of CO, THC, and NOx in the fourth stage of motorcycle emission regulations are 50% of the limit values ​​of the national III regulations, and the endurance mileage of the fourth stage is about It is twice that of the National III regulations. In order to make the emission of pollutants from motorcycles meet the requirements of national regulations, the ...

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Problems solved by technology

The main challenge in the design of TWC is how to effectively utilize the active components and prevent the inactivation of the active components. The inactivation of the active components mainly includes: 1. The active components are wrapped or buried by the catalytic material, so that the pollutants cannot contact the active components. , so that the activity of the catalyst is reduced; 2. The active component and the catalytic material generate irreversible substances, which lead to the deactivation of the active component. For example, the deactivation mechanism of rhodium on the alumina material is mainly to form rhodium aluminate; 3. Between the active components The formation of alloys leads to a decrease in the activity of noble metals. For example, when palladium and rhodium coexist, when the ambient temperature reaches above 750°C and is used under oxidizing conditions, Pd-Rh alloys can be formed and Pd generates PdO to cover the surface of Pd-Rh alloys. Can greatly reduce NOx conversion efficiency, patent CN201680018866 provides a catalyst preparation method to reduce the formation of Pd-Rh alloy

4. The active components are deactivated due to high temperature. Under engine operating conditions, when the temperature of the exhaust gas reaches 1000°C, the high temperature will cause the self-aggregation of the active components, resulting in a decrease in the proportion of active components that can be in contact with the exhaust gas, thereby reflecting the catalyst Decreased activity; 5. The active components are poisoned and deactivated due to the combination of S and P in the fuel. The reason for using palladium is that Pd will form palladium sulfide with S, which will reduce the activity of palladium;

Specific method: mix cerium-zirconium powder and rhodium nitrate, and add ammonia water as a precipitating agent. Ammonia water can make rhodium nitrate produce rhodium hydroxide jelly, so that rhodium hydroxide jelly can be more evenly dispersed. The above patents have deficiencies : The dispersion of precious metals is small, the dispersion uniformity of precious metals is poor, the catalyst performance is unstable, the process route is uneconomical, and the cost of waste gas treatment in the later period is high, etc.

Deficiencies: noble metals are reduced before being added to the catalytic material, the reduced elemental substance is difficult to redisperse, the dispersion performance of noble metals is poor, and the catalyst activity decreases

Insufficient: the precious metal part enters the micropores of the material, during the durability process, the material collapses and wraps the precious metal, the utilization rate of the precious metal is low, and the durability of the catalyst is poor

At the same time, the synergy between noble metals and alkaline earth metals is weak, and the problem of high-temperature aggregation of noble metals still exists

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