Pd Supported on Pr-Rich Cerium-Zirconium-Praseodymium Mixed Oxides for Propane and CO Oxidation

The activity of emission control catalysts must be improved in urban mode at low temperatures. One possible way is to tailor the metal-support interaction between platinum group metals (PGMs) and ceria to stabilize small clusters or single atoms, optimizing the utilization of costly PGMs. In this study, a small loading of Pd (<0.2 wt.%) was dispersed on Pr-rich cerium-zirconium-praseodymium mixed oxides (CZP45: Ce0.45Zr0.10Pr0.45O2-x). After the initial calcination at 800 degrees C, Pd was mainly in the form of dispersed isolated cations which were found to be efficient for low-temperature CO oxidation but inactive for propane combustion. Nevertheless, a pre-reduction step can trigger the formation of Pd nanoparticles and promote the propane oxidation. Pd nanoparticles, formed during the reduction step, coupled with the high oxygen mobility of CZP45, lead to outstanding catalytic activity for propane oxidation starting from 250 degrees C. However, the re-oxidation of Pd nanoparticles and their partial re-dispersion, promoted by the fast oxygen mobility of the mixed oxide, rapidly deactivate the catalysts in lean conditions.

Automated summary

Improving the activity of emission control catalysts in urban mode at low temperatures can be achieved by tailoring the metal-support interaction between platinum group metals (PGMs) and ceria. In this study, dispersing a small amount of Pd on Pr-rich cerium-zirconium-praseodymium mixed oxides led to efficient CO oxidation at low temperatures, but required a pre-reduction step to promote propane oxidation. However, the fast re-oxidation and re-dispersion of Pd nanoparticles by the high oxygen mobility of the mixed oxide rapidly deactivated the catalysts in lean conditions.