Design considerations for low-temperature hydrocarbon oxidation reactions on Pd based catalysts

Palladium-based catalysts are well known for their catalytic activity in hydrocarbon oxidation reactions in exhaust emission control. There is a need to develop catalysts that perform oxidation at low temperatures (< 300 degrees C), especially for future high efficiency combustion engines. In the present study, we investigate the role of Pd oxidation state in this temperature range for the oxidation of three different hydrocarbons (methane, propane and propylene). For each of these hydrocarbons, the reduced Pd catalyst was more active than the same catalyst after oxidation. Furthermore, when the reduced catalyst was tested under lean conditions, the activity for hydrocarbon oxidation declined due to formation of PdO. The addition of Pt helped to maintain Pd in a reduced state, even under lean conditions, and this is a major reason for improved performance of Pt-Pd catalysts compared to Pt or Pd alone. X-ray absorption near edge spectra (XANES) and temperature programmed reduction (TPR) experiments were used along with activity testing to understand the impact of the oxidation state of Pd on hydrocarbon oxidation performance. This study provides guidance in the development and operation of Pd catalysts for low temperature hydrocarbon oxidation.