Pd–Pt bimetallic catalysts for combustion of SOFC stack flue gas

Pd–Pt bimetallic as well as monometallic Pd and Pt catalysts were evaluated to study the catalyst activity and stability for combustion of SOFC stack flue gas. The simulated reactant gases consisting of H2, CO, CH4, air and water vapor were tested at two different GHSV for obtaining the behavior of catalyst activity versus temperature and catalyst stability versus on-stream operation hours. As H2 and CO were readily combusted under 200 °C and CH4 was combusted only above 300 °C, catalyst activity was evaluated by measuring CH4 conversion as a function of temperature for all five catalysts. Catalyst stability was evaluated by monitoring CH4 conversion for 1:1 Pd–Pt and 1:3 Pd–Pt catalysts exhibiting relatively better activity at 427 and 627 °C for 200 h. 1:1 Pd–Pt catalyst was the most active one based on the lowest CH4 light-off temperature and the lowest temperature for complete CH4 conversion, and this catalyst was deactivated less than 1:3 Pd–Pt catalyst in the 200 h-stability test. 1:1 Pd–Pt composition was attributed as the synergistic factor of active metal ingredients affecting the catalyst activity and stability. The presence of water vapor in the reactant gas inhibited catalyst activity and stability strongly by forming some less or inactive palladium species on catalyst surface via interaction between water molecules and catalyst active sites.