NOx Storage and Reduction Catalysis in Automotive Emission Control

Oxides of nitrogen (NOx) emitted by internal combustion engines represent a major challenge for urban air quality and global climate targets. In lean‐burn and diesel engines, the excess oxygen in the exhaust prevents conventional three‐way catalysts from reducing NOx to benign nitrogen. NOx storage and reduction (NSR), also known as lean NOx trap (LNT) technology, addresses this by alternating lean periods, during which NOx is trapped on alkali or alkaline‐earth components (for example BaO) as nitrates and nitrites, with rich periods, in which stored NOx is released and reduced over platinum‐group metals (PGMs) to N₂. Selective catalytic reduction (SCR) with ammonia or hydrocarbon reductants is often combined downstream to capture slip and to improve conversion at higher temperatures. Recent advances target lower PGM loadings, enhanced thermal and hydrothermal stability, resistance to sulphur and water poisoning, and improved mass‐transfer characteristics. Novel supports such as layered double hydroxides, doped perovskites and graphene‐based hybrids have been developed to boost storage capacity, speed of NOx release and cycling robustness. Coupled experimental, operando spectroscopic and computational studies are refining mechanistic understanding of nitrate formation, NO oxidation and transient phenomena within catalyst beds. These innovations underpin next‐generation aftertreatment systems that meet ever‐tighter emissions regulations while minimising precious‐metal content and maximising durability in real driving conditions.

Research from Nature Portfolio

Recent studies have demonstrated that hybrid catalysts combining metal oxides with high‐surface‐area carbon supports can markedly improve NOx capture and release. In particular, Pt/K2CO3/MgAlOx–reduced graphene oxide composites exhibited enhanced dispersion of active phases, leading to almost double the NOx trapping capacity compared with conventional MgAlOx materials. Under lean–rich cycling, these hybrids sustained over 78 % NOx removal while retaining performance in the presence of water vapour. The intimate contact between Pt nanoparticles, carbonate storage sites and conductive graphene supports promotes rapid nitrate decomposition and efficient reduction during rich pulses, offering a pathway to reduced PGM loading without compromising cyclic stability.

NOx Storage and Reduction Catalysis in Automotive Emission Control publication trend

The graph below shows the total number of articles in nox storage and reduction catalysis in automotive emission control across all publications each year (not limited to Nature Index journals).

Technical terms

NOx: Collective term for nitric oxide (NO) and nitrogen dioxide (NO2), harmful air pollutants formed during combustion.

Lean‐burn: Operating condition in which excess oxygen remains in exhaust, improving fuel efficiency but hindering NOx reduction.

NOx storage and reduction (NSR): Catalytic process that traps NOx as nitrates/nitrites under oxidising conditions and reduces them during subsequent rich pulses.

Selective catalytic reduction (SCR): Process that selectively reduces NOx to N2 using ammonia or hydrocarbon reductants over a catalyst.

Perovskite: Class of mixed oxides with general formula ABO3, tunable for catalytic activity and thermal stability.

Platinum‐group metals (PGMs): Noble metals such as Pt and Pd, employed for their high activity in redox reactions.

References

1. Synthesis of Pt/K2CO3/MgAlOx–reduced graphene oxide hybrids as promising NOx storage–reduction catalysts with superior catalytic performance. Scientific Reports (2017).
2. Experimental and numerical investigation of NO oxidation on Pt/Al 2 O 3 - and NO x storage on Pt/BaO/Al 2 O 3 -catalysts. Catalysis Science & Technology (2022).
3. Boosting NO x Removal by Perovskite-Based Catalyst in NSR–SCR Diesel Aftertreatment Systems. Industrial & Engineering Chemistry Research (2021).
4. NOx Storage on BaTi0.8Cu0.2O3 Perovskite Catalysts: Addressing a Feasible Mechanism. Nanomaterials (2021).
5. Mechanistic insights into a NO x storage-reduction (NSR) catalyst by spatiotemporal operando X-ray absorption spectroscopy. Catalysis Science & Technology (2019).