Views: 0 Author: Cécile Favre, John May & Dirk Bosteels Publish Time: 2025-07-08 Origin: International Paper
Three-Way Catalysts are the main autocatalyst technology used to control emissions from gasoline engines. The catalyst uses a ceramic or metallic substrate with an active coating incorporating alumina, ceria and other oxides and combinations of the precious metals - platinum, palladium and rhodium. Three-way catalysts operate in a closed-loop system including a lambda or oxygen sensor to regulate the air:fuel ratio on gasoline engines. The catalyst can then simultaneously oxidize CO and HC to CO2 and water while reducing NOx to nitrogen.
Fast light-off catalysts allow the catalytic converter to work sooner by decreasing the exhaust temperature required for operation. Untreated exhaust emitted at the start of the legislated emissions test and on short journeys in the real world is curtailed. Changes to the thermal capacity of substrates and type and composition of the active precious metal catalyst have together resulted in big improvements (15).
More thermally durable catalysts with increased stability at high temperature allow the catalytic converter to be mounted closer to the engine and increase the life of the catalyst, particularly during demanding driving conditions (16). Precious metal catalysts with stabilized crystallites and washcoat materials that maintain high surface area at temperatures around 1000°C are needed for this. Improved oxygen storage components stabilize the surface area of the washcoat, maximize the air:fuel 'window' for three-way operation and help the oxygen sensors to indicate the 'health' of the catalyst for On Board Diagnostic (OBD) systems. “Close-coupled” catalysts mounted immediately after the engine exhaust manifold allow the catalyst to start working within seconds (17).
Electrically heated catalyst systems use a small catalyst ahead of the main catalyst. The substrate, onto which the catalyst is deposited, is made from metal so that, when an electric current is passed, it will heat up quickly. This brings the catalyst to its full operating temperature in a few seconds (18).
