Adsorption and desorption analysis of NOx and SOx on a Pt/Ba thin film model catalyst

A NOx storage and reduction catalyst for automotive exhaust gas was investigated using a model catalyst consisting of a Pt/Ba thin film on a Si substrate. The NOx or SOx adsorption/desorption phenomena in the model catalyst were studied using EPMA, AES, XPS, and EELS by changing the treatment conditions, temperature, and atmosphere. Based on measuring the nitrogen and sulfur distributions, the following results were found: NOx was strongly adsorbed around an edge of platinum, and SOx was adsorbed on a barium oxide layer independent of the platinum distribution. The NOx adsorption around the platinum edge within a few micrometers was preferentially decreased; and the SOx adsorption around the platinum edge was decreased for a distance of a few nanometers. These visual results for NOx and SOx adsorption/desorption provided supporting evidence for the phenomenon occurring during practical use of NOx storage and reduction catalysts in the purification for automotive exhaust gases.