Understanding the reversible and irreversible deactivation of methane oxidation catalysts

Catalytic oxidation is a promising technology for controlling methane emissions from natural gas engines, but fast and severe deactivation prevents implementation. We investigated a commercial Pd on alumina oxidation catalyst under realistic conditions and identified two deactivation phenomena: fast, reversible inhibition and slow, irreversible loss of active sites. The loss of active sites occurs only during methane conversion, fortunately a brief oxygen cut-off is enough to regenerate the catalyst. Both types of deactivation increase the reduction temperature of PdO. From 36 kinetic experiments we propose a simple kinetic model encompassing both types of deactivation. The inhibition is confirmed to be due to water coverage of the active sites whereas dispersion of Pd on the surface is the cause of the irreversible loss of active sites. The new insight shows a pathway toward designing more durable catalysts for complete methane oxidation.