Three-Way Catalyst Performance in Exhaust Emission Control

Three-way catalysts serve as the cornerstone of modern vehicular exhaust after-treatment by simultaneously oxidising carbon monoxide and hydrocarbons while reducing nitrogen oxides in a single converter chamber. These devices rely on noble metal particles (platinum, palladium and rhodium) dispersed over high-surface-area supports, frequently incorporating ceria-based oxygen storage materials to balance transient fluctuations in exhaust composition. Under stoichiometric conditions, the stored oxygen in the support enables rapid response to lean–rich oscillations, ensuring high conversion efficiency across a wide temperature range. Key challenges include degradation of active sites through thermal ageing, sensitivity to sulphur and lead contaminants, and reduced performance during cold starts. Advances in catalyst design have focused on optimising metal-support interactions, tailoring washcoat formulations and refining cell geometry to enhance mass transport, oxygen storage capacity and thermal stability. Practical applications encompass passenger cars, heavy-duty natural-gas engines and integration with selective catalytic reduction systems, all driven by increasingly stringent global emission standards.

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Three-Way Catalyst Performance in Exhaust Emission Control publication trend

The graph below shows the total number of articles in three-way catalyst performance in exhaust emission control across all publications each year (not limited to Nature Index journals).

Technical terms

Three-way catalyst (TWC): A catalytic system that simultaneously oxidises carbon monoxide and hydrocarbons while reducing nitrogen oxides under near-stoichiometric conditions.

Oxygen storage capacity (OSC): The ability of catalyst support materials, typically ceria-based, to reversibly store and release oxygen in response to exhaust composition changes.

Stoichiometric air–fuel ratio (λ): The precise mixture ratio at which all fuel and oxygen are consumed in combustion; λ = 1 indicates stoichiometry, λ < 1 fuel-rich and λ > 1 air-rich conditions.

Rich–lean operation: Alternating conditions of excess fuel (rich) and excess air (lean) that exploit oxygen storage for optimal pollutant conversion.

Thermal ageing: The degradation of catalyst activity and oxygen storage due to prolonged exposure to high temperatures, leading to metal sintering and loss of surface area.

References

1. Catalytic Converters for Vehicle Exhaust: Fundamental Aspects and Technology Overview for Newcomers to the Field. Chemistry (2021).
2. Assessing the effect of O2 dithering on CH4 oxidation on Pd/Al2O3. Chemical Engineering Journal (2023).
3. Emission of NH3 and N2O during NO reduction over commercial aged three-way catalyst (TWC): Role of individual reductants in simulated exhausts. Chemical Engineering Journal Advances (2022).
4. Experimental and numerical analysis of the effects of thermal degradation on carbon monoxide oxidation characteristics of a three-way catalyst. Heliyon (2024).