Key Factors Affecting Catalytic Converter Performance

The three-way catalytic converter (TWC) is the core device for purifying automotive exhaust gases, and its performance directly determines whether emissions meet standards. Many factors influence its final performance, but the most fundamental physical basis lies in the honeycomb ceramic carrier. It not only supports the catalyst but is also crucial in determining the efficiency, durability, and cost of the entire system.

Geometric Structure

Pore Density (unit: CPSI - pores per square inch): refers to the number of pores per unit area on the cross-section of the carrier. Common pore densities are 400 CPSI, 600 CPSI, 900 CPSI, and even higher, up to 1200 CPSI.

High pore density (e.g., 900 CPSI): means finer pores, providing a larger geometric surface area for the catalyst coating. This effectively increases the contact area for the chemical reaction, allowing harmful molecules in the exhaust gas (CO, HC, NOx) to come into more complete contact with the catalyst, thus significantly improving conversion efficiency, especially during cold starts. To meet stringent regulations such as China VI/Euro VI, high-porosity carriers have become the mainstream choice.

Low porosity (e.g., 400 CPSI): The pores are coarser, resulting in lower back pressure and less impact on engine power, but the surface area is smaller, leading to a lower theoretical upper limit for conversion efficiency. Increasing pore density slightly increases back pressure and raises manufacturing complexity and cost.

Wall thickness (unit: mil or millimeter): Refers to the thickness of the ceramic wall between the honeycomb channels.

Thin walls (e.g., 2-3 mil): At the same pore density, this further reduces back pressure and decreases the carrier's own heat capacity. Lower heat capacity means the carrier can be heated more quickly by the exhaust gas during cold starts, reaching the catalyst's ignition temperature faster, thus significantly reducing pollutant emissions during cold starts. Simultaneously, thin walls can create more space for the channels or increase pore density without increasing volume.

Thick-walled: Higher mechanical strength, better resistance to impact and vibration, relatively easier manufacturing process, and generally lower cost. Pursuing ultimate performance (low emissions, rapid ignition) requires a combination of "high pore density + thin-walled," but this places extremely high demands on material strength and manufacturing processes.

Material Nature

Coefficient of Thermal Expansion (CTE): A physical parameter measuring the degree of expansion of a material when heated. For catalytic converters that need to operate repeatedly between room temperature and 1000°C, CTE is crucial. A low and uniform coefficient of thermal expansion is the lifeline for the thermal shock resistance of the carrier. Under conditions such as rapid vehicle acceleration and DPF regeneration, a huge temperature gradient will be generated inside the carrier. If the CTE is too high or uneven, the inconsistent expansion and contraction of the material will generate huge thermal stress, leading to carrier cracking and shattering, causing permanent failure of the entire catalytic converter.

High-quality cordierite ceramic carriers can achieve a CTE close to zero or even negative, which is one of their core advantages for widespread application.

Coating

Catalyst Coating: A porous, high-surface-area material (typically γ-alumina) coated onto the walls of the honeycomb ceramic channels, internally loaded with trace amounts of precious metal active components (platinum, palladium, rhodium). The surface micro-roughness and pore structure of the ceramic support must perfectly match the coating to ensure strong and uniform adhesion, preventing peeling under high-temperature, high-speed airflow.

The support is not only a physical support; its material properties (such as acidity and alkalinity) affect the stability of the coated alumina and the dispersion of precious metals, ultimately influencing catalytic activity and lifespan.

Coating Process: The uniformity and penetration depth of the coating directly determine the actual utilization efficiency and durability of the catalyst. A high-quality support is the foundation of a perfect coating.

Summary

In the design and manufacture of catalytic converters, the first and most critical step is selecting a high-performance honeycomb ceramic support with precisely matched parameters. This selection defines the upper limit of the catalytic reactor's efficiency and lifespan potential at the physical level, and is a fundamental engineering decision for meeting the high efficiency and high durability requirements of modern emission regulations. We are a Chinese manufacturer of cellophane ceramics. For more information, please contact us via email at annayu@169chem.net or WhatsApp at +8618909016373.