Ternary catalyst

Abstract

The invention relates to a ternary catalyst. The ternary catalyst comprises a cellular carrier, and is characterized in that a lower layer coating is adhered on the cellular carrier, an intermediate Rh coating is adhered on the lower layer coating, an upper layer Rh coating is adhdred on the intermediate Rh coating, the mass ratio of the Rh loaded in the intermediate layer Rh coating to the Rh loaded in the upper layer Rh coating is (1-5): 1, the Pd or Pt is loaded on the lower layer coating. The Rh in the upper layer Rh coating is loaded on a cerium-zirconium solid solution, and the component of the cerium-zirconium solid solution is as follows: one or a plurality of 20wt%-70wt% of ZrO2, 20wt%-70wt% of CeO2 or 10wt%-15wt% of La2O3, Y2O3, Pr6O11, Nd2O3, the Rh in the intermediate Rh coating is loaded on zirconia composite oxide, the component of the zirconia composite oxide is one or a plurality of 80wt%-90wt% of ZrO2 or 10wt%-20wt% of La2O3, Y2O3, Pr6O11 and Nd2O3. The ternary catalyst provided by the invention is higher in carbon monoxide, hydrocarbon and oxynitride treatment ability, especially the activity of the Rh catalytically reduced oxynitride is improved.

Description

technical field [0001] The invention relates to a three-way catalyst, in particular to a three-way catalyst used for purifying automobile tail gas. Background technique [0002] The main pollutants of automobile exhaust are carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). The catalyst installed in the exhaust system can oxidize carbon monoxide and hydrocarbons into carbon dioxide (CO 2 ), water (H 2 O), and at the same time reduce nitrogen oxides to nitrogen (N 2 ), to achieve the purification of exhaust gas, this kind of catalyst is usually called three-way catalyst. The three-way catalyst consists of two parts: a honeycomb ceramic or metal support, and a catalyst coating attached to the support. The catalyst coating is usually composed of an oxide material with a large specific surface area (such as alumina), an oxygen storage material, and a noble metal active component (usually Pt (platinum), Pd (palladium) dispersed on the surface of the oxide or ox...

AI Technical Summary

Problems solved by technology

Although the loading of Rh on the oxygen storage material can greatly improve the oxygen storage capacity and inhibit the adverse interaction between Rh and alumina under high temperature conditions, the oxygen storage and release function of the oxygen storage material makes the loaded Rh easier to handle. In the oxidized state, Rh in the oxidized state has a very low activity in catalyzing the reduction of nitrogen oxides, even in the transient condition of engine exhaust from lean to rich

For this reason, in recent years, some researchers have proposed to load Rh on a CeO-free 2 Or contain a very small amount of CeO 2 ZrO 2 On the composite oxides, the activity of Rh to catalytically reduce nitrogen oxides after high-temperature aging is significantly improved, but due to insufficient oxygen storage capacity, the pollutant emissions in transient conditions are very high, especially those that are very sensitive to changes in the exhaust air-fuel ratio NOx emissions

Although the oxygen storage capacity can be improved by adding an oxygen storage material to the underlying Pd (or Pt) coating, the improvement of the oxygen storage capacity is very limited due to the great influence of the gas diffusion distance on the oxygen storage capacity.

In addition, too much Pd (or Pt) coated oxygen storage material will also cause more Rh to migrate to the lower layer and interact with Pd (or Pt) under high temperature and oxygen-enriched conditions, resulting in a decrease in catalyst activity.