Rhodia Launches New Materials for NOx Reduction On Diesel Vehicles

15 April 2008

International chemical company Rhodia is launching two sets of materials for the formulation of deNO_x catalysts showing high performance and hydrothermal durability for NO_x trap technologies. Rhodia presented the emissions control materials, along with new light weight materials for weight reduction, at this week’s SAE 2008 World Congress in Detroit.

Both NO_x Storage Catalyst (NSC) and Selective Catalytic Reduction (SCR) technologies have shown limited efficiency at low temperature (<250°C) and poor durability due to the thermal deterioration at temperatures > 750°C with steam. Rhodia’s new materials address these limitations.

Materials for NO_x Storage Catalyst technologies (NSC). NSC are sensitive to sulfur poisoning and have to be periodically desulfated at 800°C. This desulfation step at high temperature damages the NO_x storage material, and the precious metal dispersion, and thus deteriorates the performances and the durability of the catalyst. With 20 years of R&D experience in synthesizing mixed oxides with high thermal resistance for gasoline catalysts, Rhodia has prepared a new generation of NSC materials based on ceria and alumina.

These recently developed ceria-based mixed oxides show an 80% NO_x storage capacity at temperatures as low as 200°C after hydrothermal aging at 750°C. They are completely desulfated at 500°C. These materials maintain precious metal finely dispersed even after hydrothermal aging at 850°C. At the same time, new functionalized alumina with improved durability shows a high NSC over a wide range of temperature from 200 up to 400°C.

NO_x trap AlBaCe materials are in the industrial upscaling phase. Rhodia can supply 100 kg batches, prepared in pilot tools on request. NO_x trap ceria-based mixed oxides are fully industrial and Rhodia already supplies significant volumes for growing NO_x trap applications.

Materials for Selective Catalytic Reduction technologies (SCR). SCR features continuous reduction of NO_x by ammonia. The industry has sought a substitute for the first generation of SCR catalysts based on vanadium – titania, due to a low thermal stability, and due to the potential health effect of vanadium. Base metal-exchanged zeolites are promising NH₃-SCR catalysts. However, they show poor conversion rates at low temperature (150°C – 200°C) and a limited thermal stability over 700°C. This is a major drawback for passenger car, and light-duty applications, when the exhaust line is fitted with a Diesel Particulate Filter (DPF).

Rhodia and MEL Chemicals, the world’s leading manufacturer of zirconium chemicals, are collaborating in the field of Zirconia-based acidic materials. The collaboration proposes mixed oxides with high thermal stability promoted by rare earths and base metals. These materials show pure phase, high surface area (more than 100 m²/g at 900°C in air) and a high stability after ageing at 750°C/16h in wet air. These oxides show a high NO_x conversion at 200°C, no N₂O formation and a very low NH₃ slip.

Acidic zirconias for SCR are in the industrial upscaling phase. Rhodia and MEL can supply 100 kg batches, prepared in pilot tools on request.