New Approaches to the Synthesis of Ultralow-Palladium Automotive Emission Control Catalysts

Laser electrodispersion has been used as an alternative to the chemical synthesis of palladium-containing catalysts. The thus produced catalysts supported on alumina and HZSM-5 zeolite have high catalytic activity and stability at ultralow palladium content (0.03 wt %) in a model reaction of CO oxidation under conditions of prompt thermal aging. According to X-ray photoelectron spectroscopy and transmission electron microscopy data, palladium in the catalyst samples predominantly occurs in the Pd⁰ state as fine particles about 2.0 nm in size, which almost completely cover the support surface. The textural characteristics of both supports are retained after the deposition of palladium. The modification of zeolite with palladium increases the adsorption capacity for hydrocarbons, which gives rise to a sorption effect in the temperature dependences of the CO conversion. The palladium-containing alumina-based catalyst demonstrated the best stability during heat treatment up to 1000°C.