Three-way catalysts which remove different kinds of pollutants, such as CO, THC(total hydro-carbon) and NOx, simultaneously from the automotive exhaust gas employ Rhodium(Rh) in combination with Platinum(Pt) and Palladium(Pd). Rh is the most effective for reducing NOx to N2, but Rh is the most expensive of these precious metals. The ratio of Rh to Pt applied for automobiles frequently exceeds the natural production. The gap between supply and demand of Rh sometimes causes the big price fluctuation.
Accordingly, many attempts to reduce the amount of Rh loaded or to develop non-Rh three-way catalysts have been made. Although Pd catalysts are considered to be promising candidates for non-Rh automotive three-way catalysts, some performance are still inferior to Pt-Rh catalysts.
We have found that an excellent three-way catalytic activity appears by compounding new Perovskite-structured oxides with Pd and auxiliary oxides. This paper reviews the performance of Perovskite-Pd catalysts by comparing with Pd/Al2O3 and Pt-Rh/Al2O3 catalysts both in an engine dynamometer testing and a vehicle emission testing. As the result, we have confirmed that the optimum designed Perovskite-Pd catalysts show the excellent catalytic activity and durability.