SIMS Investigation of Fresh and Aged Automotive Exhaust Catalysts

Secondary ion mass spectrometry (SIMS) has been employed to examine the surface composition of fresh and aged three-way automotive exhaust catalysts. The washcoat components and poison species could be monitored due to the unsurpassed sensitivity of this technique. The outermost 1–2 nm was found to be covered with species containing the elements P, Ca, Zn, Pb and S. These species are known to originate from fuel and lubricating oil additives and the amounts on the surface of catalysts increased with increasing distance travelled. The presence of calcium phosphate and lead sulphate was confirmed, and these species are known surface fouling agents. Evidence of Ce sintering on each of the aged catalysts was also found using this technique. Depth profile experiments showed that the poison species penetrated the washcoat layer between 0.5 and 4 μm, depending on the distance travelled. Imaging SIMS displayed the lateral position of the washcoat components and poison species.