Catalytic Mechanisms in Automotive Emission Control Systems

Automotive emission control systems rely predominantly on three-way catalysts (TWCs) to simultaneously convert carbon monoxide, unburned hydrocarbons and nitrogen oxides into benign gases. Noble metals such as platinum, palladium and rhodium are dispersed on high-surface-area oxides (typically alumina, ceria–zirconia mixed oxides or perovskites), forming active sites that mediate adsorption, bond activation and redox cycles. During engine operation, fluctuating exhaust composition and temperature induce dynamic oxygen storage and release on ceria phases, enabling periodic regeneration of oxidised and reduced metal species. Key mechanistic steps include oxygen transfer between support and metal nanoparticles, activation of hydrocarbon C–H bonds, and associative or dissociative NOx reduction pathways. Thermal and hydrothermal ageing lead to metal sintering, support phase separation and loss of oxygen‐storage capacity, driving ongoing research into stabilisation strategies, alternative base‐metal formulations and advanced washcoat architectures. Such advances underpin compliance with stringent global emission standards and the transition to hybrid and lean-burn powertrains.

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Catalytic Mechanisms in Automotive Emission Control Systems publication trend

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Technical terms

Three-Way Catalyst (TWC): A catalytic system designed to oxidise CO and hydrocarbons and reduce NOx simultaneously under stoichiometric exhaust conditions.

Light-Off Temperature: The temperature at which a catalyst achieves 50 % conversion of a target pollutant, often used to assess low-temperature performance.

Oxygen Storage Capacity (OSC): The ability of an oxide support (typically ceria) to reversibly store and release oxygen, facilitating redox cycling of metal active sites.

Sintering: The thermally driven aggregation of metal nanoparticles or collapse of porous support structure, leading to loss of active surface area.

Washcoat: The porous layer, usually an oxide mixture, coated onto a monolithic substrate to disperse active metal phases and provide oxygen-storage functionality.

References

1. Automotive Emission Control Catalysts. Catalysts (2016).
2. High-Temperature Behavior of Pd/MgO Catalysts Prepared via Various Sol–Gel Approaches. Gels (2024).
3. High Catalytic Efficiency of a Nanosized Copper-Based Catalyst for Automotives: A Physicochemical Characterization. Molecules (2022).
4. Insights into the Reactivation Process of Thermal Aged Bimetallic Pt-Pd/CeO2-ZrO2-La2O3 Catalysts at Different Treating Temperatures and Their Structure–Activity Evolutions for Three-Way Catalytic Performance. Catalysts (2024).