Development and Application of New Low Rhodium Three-Way Catalyst Technology 2007-01-0046
Rhodium is an important component of three-way catalysts for emissions control on gasoline engines1. It has unparalleled activity in NOx reduction under stoichiometric conditions, where very high conversion efficiencies are required to meet current and future legislative targets. Over 90% of world rhodium usage is in such catalysts, and in recent times the price of rhodium has increased enormously2. This has lead to significant focus on reducing the quantity of rhodium required whilst still retaining the ability to meet the most stringent emissions legislation. Experiments are described where three-way catalysts employing advanced washcoat formulations and coating techniques are evaluated with a range of rhodium levels right down to 1g/ft3 which nevertheless still meet Euro 4 emissions limits after 100,000 km-equivalent bench engine ageing. Extending the ageing to 160,000 km, equivalent to the proposed Euro 5 standards, shows that subsequent deterioration is minimal despite the ultra-low loadings involved. Further experiments involving a trade-off of Pd and Rh at approximately equivalent total PGM cost show that similarly low Rh levels appear to offer the best compromise between HC and NOx performance where these advanced formulations and coating techniques are used.