Diesel particulate filters, oxidation and DeNOx catalysts

Diesel engine exhaust gases, especially particulates, are particularly critical for the environment and health because of their carcinogenicity. New exhaust emission limits limit the quantity and number of particles as well as nitrogen oxides, carbon monoxide and hydrocarbons, making appropriate exhaust gas after-treatment systems mandatory for almost all diesel engines.

Diesel particulate filters with pore sizes of 10-15 µm can achieve separation efficiencies of up to 99.9% and are cleaned periodically by burning off the separated soot particles. The high temperatures generated in this process are the reason why ceramics, primarily silicon carbide, aluminum titanate, mullite and cordierite, are used. The most common type is extruded honeycomb bodies with mutually closed channels. Special catalysts serve to lower the ignition temperature of the soot and thus facilitate regeneration. The reduction in service life due to ash deposits is counteracted by asymmetrical cell shapes.

DeNOx catalysts are designed for the so-called SCR technology (TiO₂-based or special zeolites) or as storage catalysts – both as fully extruded honeycomb bodies and as coatings on highly porous ceramic carriers. Combined systems of DPF with embedded DeNOx catalysts are also under development for future exhaust gas after-treatment.

The Fraunhofer IKTS develops both functionalized particulate filters and oxidation and DeNOx catalysts. For the investigation and optimization of catalysts or catalytically coated particle filters, the IKTS uses state-of-the-art synthesis gas test rigs. Light-off temperatures and conversion rates for oxidation and SCR catalysts can be determined in stationary or dynamic test cycles. The conversion behavior of three-way and NOx storage catalysts can also be determined as a function of temperature, exhaust gas composition and volume flow.

 

Products and services offered

 

• Design, development and modification of diesel particulate filters (RSiC, LPS-SiC, oxide-bonded SiC, cordierite) and exhaust gas catalysts (DOC, cDPF, TWC, SCR, LNT, sDPF)
• Characterization of diesel particulate filters and catalysts (new and post-mortem), especially composition, pore characteristics, permeability, specific surface area, strength, coefficient of expansion, thermal conductivity, ash analysis etc.
• Development and optimization of individual technological steps for the production of DPF (material selection, mass preparation, shaping, heat treatment, plugging)
• Sample production

 

Technical equipment

 

• Complete technological line for the development and production of honeycomb structures and diesel particulate filters on a pilot plant scale
• Catalytic and filtration test rigs for the characterization of diesel particulate filters and exhaust gas catalysts (overview)

 

Examples and references

 

• Development of off-road DPF from silicon carbide
• Diesel particulate filter with optimized pressure drop and filtration efficiency
• Catalytically coated particulate filter for small engines of less than 19 kW
• Open-cell foams of ceramic and metal as combined filter/catalyst carrier
• Open-cell particulate filters for large engines
• Basic characterization and post-mortem analysis of components for exhaust gas after-treatment (DPF, GPF, catalysts)
• Cross flow DPF with increased ash storage function
• Shaping of large-format SCR catalyst honeycombs