Development of high-performance automotive three-way palladium catalyst using nickel aluminate support

Although platinum and rhodium have usually been used for conventional three-way catalysts, development of a rhodium-free automotive catalyst is a recent target of investigation for reducing the cost of catalyst. In this regard, we attempted to develop an automotive three-way catalyst based on Pd only. The improvement an alumina-loaded Pd catalyst was tried with the addition (around 10 wt%) of transition metal oxides, and it was found that: several oxides, especially NiO, showed a remarkable promoter action. Encouraged with this fact, aluminates of various transition metals were synthesized to be loaded with Pd, Some of the Pd-loaded catalysts thus prepared, especially one supported on Ni-aluminate were found to exhibit higher performances in light-off activity as well as three-way catalytic activity than the conventional Pd catalyst supported on alumina. It was revealed that the Ni-aluminate was a spinel phase solid solution between NiO and gamma-Al2O3 and the Ni/2Al atomic ratio (x) as well as calcination temperature gave significant influences on its properties. The Ni-aluminate with x = 0.5, calcined at 800 degrees C, turned out to be the best support of Pd. This particular catalyst proved satisfactorily high performances as a three-way catalyst in engine dynamometer and chassis dynamometer tests.