Durability Testing of Stabilized Ru-Containing Catalysts

Ruthenium-containing catalysts have good activity and selectivity for the reduction of the nitric oxides in automobile exhaust. Although designed to be operated under reducing conditions, these catalysts lose Ru by volatilization when subjected to lean transients. Attempts were made to stabilize these catalysts against volatilization by forming stable ruthenates. This paper deals with durability testing of stabilized ruthenate catalysts on a laboratory bench set-up, dynamometers, and vehicles. Post-mortem analysis of the durability-tested catalysts are presented showing the extent of stabilization. The results show that the Ru loss from ruthenate catalysts in present vehicle systems is in excess of acceptable limits. These losses can be minimized further, but at a cost of reduced selectivity in the NO reduction. Substantial further improvements are needed to achieve the required performance characteristics.

Another problem is the poisoning by S, Pb and P. The catalysts have been analyzed to determine the various poisons deposited by the engine exhaust. The retention of Pb, S, and P by catalysts from exhaust was determined in well-controlled dynamometer tests. The BET area and active metal area were measured before and after the tests to determine the extent of thermal sintering. Actual temperature traces of catalysts under customer-type driving have shown temperature excursions up to 1900°F.