The Three-Way Catalyst (TWC) is the cornerstone of gasoline emission control – a single device that simultaneously converts carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx) into harmless CO₂, H₂O, and N₂. Unlike diesel systems requiring multiple components (DOC, DPF, SCR), the TWC achieves >98% conversion efficiency under stoichiometric operation (lambda = 1.00). Our **TWC System** solutions cover port fuel injection (PFI), gasoline direct injection (GDI), hybrid electric vehicles (HEV/PHEV), and performance applications – with substrate options (ceramic or metallic), advanced washcoat formulations (Pd/Rh with high oxygen storage capacity), and integration with GPF for particulate control. Meet Euro 7, EPA Tier 3, and China 7 standards.
Application | Flow |
PFI (conventional) | Engine → Close-coupled TWC → Tailpipe |
GDI (with particulate control) | Engine → Close-coupled TWC → Underfloor GPF → Tailpipe |
GDI (compact, cGPF) | Engine → Close-coupled cGPF → Tailpipe |
HEV/PHEV (cold-start critical) | Engine → eHC → TWC → GPF → Tailpipe |
Ceramic honeycomb (cordierite): low cost, thermal shock resistant, 400-900 cpsi, 2-4 mil walls, open frontal area >80%, max 1,050°C continuous. Preferred for underfloor.
Metallic honeycomb (FeCrAlloy): fast light-off, 400-1,200 cpsi, 2-3 mil walls, light-off 15-25s, vibration-resistant, max 900-950°C. Preferred for close-coupled, motorcycles, hybrids, performance vehicles.
Substrate selection guide:
Performance → metallic or high-flow ceramic
Pd/Rh system: Pd 1-4 g/L (HC/CO oxidation), Rh 0.1-0.3 g/L (NOx reduction), Pd:Rh ratio 10:1–20:1, optional Pt for cold start, total PGM 1–5 g/L.
Oxygen Storage Capacity (OSC): Ceria-zirconia (20-50% of washcoat), 300–800 µmol O₂/g, buffers lambda fluctuations. Higher OSC (40–50%) for carbureted engines and hybrids.
Support & Layers:
Multi-layer coating: Bottom (poison trap), Middle (NOx reduction), Top (HC/CO oxidation)
Lambda = 1.00 ±0.01 via upstream wideband UEGO sensor, ECU PI control on injectors. Downstream sensor monitors OSC.
Carbureted engines: Higher OSC (40-50%) compensates, 75-85% conversion
Hybrid vehicles: eHC maintains 300°C+, predictive pre-heating
Gasoline direct injection challenge: PM/PN filtration required. Solutions: separate TWC + GPF or cGPF – single brick, TWC washcoat on wall-flow filter.
Filtration: >99% particles >23 nm
Gas conversion: >95%
Backpressure: 2–5 kPa
Passive regeneration: 500–700°C
Parameter | PFI + TWC | GDI + TWC + GPF | GDI + cGPF | HEV + eHC + TWC |
CO conversion | >98% | >98% | >95% | >98% |
HC conversion | >95% | >95% | >95% | >95% |
NOx conversion | >95% | >95% | >90% | >95% |
PN filtration | N/A | >99% | >99% | >99% |
Light-off time (cold start) | 30-45 s | 30-45 s | 35-50 s | 5-10 s |
Backpressure (kPa) | 2-4 | 3-6 | 3-5 | 3-5 |
Application | Substrate | Cell Density | Wall Thickness | PGM Loading | Special Features |
PFI (Euro 6) | Ceramic | 400-600 cpsi | 4 mil | 1-2 g/L | Standard OSC (20-30%) |
GDI (Euro 6d) | Ceramic | 600-900 cpsi | 2-3 mil | 2-3 g/L | + Underfloor GPF |
GDI (cGPF, Euro 7) | Wall-flow ceramic | 300 cpsi | 8-10 mil | 2-3 g/L | Single brick, vacuum coated |
Hybrid (HEV/PHEV) | Metallic | 400-600 cpsi | 2-3 mil | 2-4 g/L | eHC 1-4 kW, high OSC 40-50% |
Performance (sports car) | Metallic or high-flow ceramic | 400 cpsi | 2-3 mil | 1.5-2.5 g/L | Reduced volume 30-50%, backpressure optimized |
Motorcycle | Metallic | 200-400 cpsi | 2-3 mil | 1-2 g/L | Vibration-resistant, integrated with muffler |
High conversion efficiency: >98% CO, >95% HC, >95% NOx, maintains >90% after 150,000+ km
Fast light-off: Close-coupled mounting, thin-wall substrates, metallic for hybrids/performance, eHC for PHEV 5–10s
Durable and poison-resistant: La/Ba-stabilized alumina, ceria-zirconia OSC retention, cordierite withstands 1,050°C continuous, 1,200°C peak
Low backpressure: Open frontal area >80%, thin walls, cGPF reduces pressure vs. TWC+GPF separate
We engineer complete TWC systems for any gasoline application. Tailored for substrate geometry, washcoat formulation, PGM loading, and coating architecture for PFI, GDI, HEV/PHEV, performance vehicles, and motorcycles.
Partner with us to define your path to compliance – TWC efficiency, stoichiometric precision.