Performance and characteristics of platinum, palladium/rhodium and palladium automotive catalysts when subjected to ethanol, acetaldehyde and a synthetic E85 exhaust gas mixture

Abstract

The performance optimization of automotive catalysts has been the focus of in-depth research for many years as the automotive industry has endeavoured to reduce the emission of toxic and pollutant gases generated from internal combustion engines. Just as the emissions from diesel and gasoline combustion vary, so do the emissions from the combustion of alternative fuels such as ethanol, with variation in both quantity and chemical composition. In particular, when ethanol is contained in the fuel, ethanol and acetaldehyde are present in the exhaust gas stream, and these are two compounds which the catalytic converter has not traditionally been designed to manage. The aim of the study outlined in this paper was to assess the performance of various catalyst formulations when subjected to a representative ethanol exhaust gas mixture. Three automotive catalytic converter formulations were tested, including a fully platinum sample, a palladium/rhodium three-way catalyst sample and a fully palladium sample. Initially the samples were tested using single component hydrocarbon light-off tests followed by a set of tests with carbon monoxide included as an inlet gas to observe its effect on each individual hydrocarbon oxidation. Finally, each formulation was tested using a full E85 exhaust gas mixture. The study was carried out using a synthetic gas reactor along with Fourier transform infrared spectroscopy and flame ionization detector exhaust gas analysers. All formulations showed selectivity toward acetaldehyde formation from ethanol dehydrogenation which resulted in negative acetaldehyde conversion across each of the samples during the mixture tests. The fully platinum sample was the most detrimentally affected by the introduction of carbon monoxide into the gas feed. The palladium and palladium/rhodium samples exhibited a tendency toward acetaldehyde decomposition resulting in methane and carbon monoxide formation. The platinum sample did not form methane but did form ethylene as a result of ethanol dehydration.