Three-Way Catalysis in Automotive Emissions Control

Three-way catalysts constitute the cornerstone of gasoline engine exhaust treatment, achieving simultaneous oxidation of carbon monoxide and unburnt hydrocarbons alongside reduction of nitrogen oxides under stoichiometric conditions. Central to their function is the precise balancing of oxygen availability, typically mediated by ceria-zirconia supports that store and release oxygen to accommodate transient excursions in air–fuel ratio. Noble metals such as rhodium, platinum and palladium disperse on high-surface-area oxide carriers to furnish active sites for CO oxidation, HC oxidation and NOx reduction. Challenges in this field include ensuring high activity at low temperatures, maintaining thermal and hydrothermal stability against sintering and ageing, and reducing reliance on scarce precious metals. Advances in structured supports, alloy design and promoter chemistry seek to address these limitations, while stringent global emission standards drive the development of next-generation formulations with enhanced light-off performance, better durability and lower precious-metal content.

Research from Nature Portfolio

Recent studies have demonstrated that a Pd–Ru solid-solution alloy can mimic the electronic structure of rhodium, yielding superior NOx reduction activity while offering a cost-effective alternative to pure Rh. The alloy nanoparticles exhibit a pseudo-Rh character that enhances N₂ selectivity and lowers light-off temperatures for NO-CO reactions. In a complementary approach, a uniform nanometric rhodium overlayer deposited on stainless-steel foils via pulsed arc-plasma deposition achieves exceptionally high turnover frequencies despite minimal Rh loading. The two-dimensional Rh films on corrugated and flat honeycomb substrates reach practical light-off at typical space velocities, underscoring the promise of foil-supported designs for reducing precious-metal usage without sacrificing performance.

Three-Way Catalysis in Automotive Emissions Control publication trend

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

Technical terms

Three-way catalyst (TWC): A catalytic system that simultaneously oxidises CO and hydrocarbons while reducing NOₓ under stoichiometric conditions.

Oxygen storage capacity (OSC): The ability of a material to reversibly store and release oxygen to maintain catalyst redox balance during fluctuations in exhaust composition.

Turnover frequency (TOF): The number of reactant molecules converted per active site per second; a key metric of catalytic activity.

Hydrothermal ageing: Deactivation of catalyst performance due to prolonged exposure to high temperatures and water vapour, leading to sintering or phase changes.

Pseudo-Rh alloy: An engineered alloy whose electronic structure closely resembles that of rhodium, designed to replicate its catalytic properties at reduced cost.

References

1. A Synthetic Pseudo-Rh: NOx Reduction Activity and Electronic Structure of Pd–Ru Solid-solution Alloy Nanoparticles. Scientific Reports (2016).
2. A nanometric Rh overlayer on a metal foil surface as a highly efficient three-way catalyst. Scientific Reports (2016).
3. Recent progress of Rh‐based three‐way catalysts. Smart Molecules (2024).
4. Impact of Oxygen Storage Components in Prototype Pd-Based Three-Way Catalysts under Exhaust Conditions Relevant to Propane Engines †. Catalysts (2023).
5. Steam Treatment Promotion on the Performance of Pt/CeO2 Three-Way Catalysts for Emission Control of Natural Gas-Fueled Vehicles. Catalysts (2023).