Three-element catalyst for treating automobile exhaust

Abstract

The invention relates to a three-way catalyst for treating automobile exhaust. The three-way catalyst comprises a honeycomb-like carrier and is characterized in that a lower Pd coating is attached on the honeycomb-like carrier, a middle Pd coating is attached on the lower Pd coating, an upper Rh coating is attached on the middle Pd coating, wherein the lower Pd coating comprises a Pd-loaded cerium-zirconium solid solution and La2O3-doped aluminum oxide (La2O3-Al2O3), the middle Pd coating comprises Pd-loaded La2O3-Al2O3 and a binding agent, and the upper Rh coating comprises Rh-loaded cerium-zirconium solid solution and the La2O3-Al2O3. As for the three-way catalyst disclosed by the invention, as the middle Pd coating does not contain a CeO2 component and Pd is loaded on the La2O3-Al2O3, the catalytic ability of the catalyst is improved and the oxygen storage ability of the catalyst is improved; and compared with a traditional Pd / Rh double-coating three-element catalyst, the three-element catalyst disclosed by the invention has higher ability of processing hydrocarbons, carbon monoxide and nitrogen oxides, and especially has higher ability of transforming the nitrogen oxides.

Description

technical field [0001] The invention relates to a three-way catalyst used for treating automobile tail gas, and belongs to the technical field of car tail gas purification. 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 s...

AI Technical Summary

Problems solved by technology

However, under high temperature and oxygen-enriched conditions, the Rh in the upper coating tends to migrate to the lower coating and interact with Pd, which reduces the activity of the catalyst.

In addition, the loading of Rh on the oxygen storage material can greatly improve the oxygen storage capacity, but the oxygen storage and release function of the oxygen storage material makes the loaded Rh more likely to be in an oxidized state, and the oxidized Rh catalyzes the reduction of nitrogen oxides. Very low activity, even in transient conditions where the engine exhaust changes from lean to rich