High-performance water gas shift induced by asymmetric oxygen vacancies: Gold clusters supported by ceria-praseodymia mixed oxides

Modifying and controlling sites at the metal/oxide interface is an effective way of tuning catalytic activity, beneficial for bifunctional catalysis by reducible oxide supported metal nanoparticles. We employed mixed ceriapraseodymia supported Au clusters for the water gas shift reaction (WGSR). Varying the Ce: Pr ratio (4:1, 2:1, 1:4) not only allows to control the number of oxygen vacancies but, even more important, their local coordination, with asymmetrically coordinated O# being most active for water activation. These effects have been examined by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), Xray photoelectron spectroscopy (XPS), Raman spectroscopy, temperature programmed desorption/reduction (TPD/TPR), and density functional theory (DFT). Using the WGSR performance of Au/CeOx as reference, Au/ Ce4Pr1Ox was identified to exhibit the highest activity, with a CO conversion of 75% at 300 degrees, which is about 5times that of Au/CeOx. Au/Ce4Pr1Ox also showed excellent stability, with the conversion still being 70% after 50 h time-on-stream at 300 degrees. Although a higher Pr content leads to more O vacancies, the catalytic activity showed a "volcano behavior". Based on DFT, this was rationalized via the formation energy of oxygen vacancies, the binding energy of water, and the asymmetry of the O# site. The presented route of creating active vacancy sites should also be relevant for other heterogeneous catalytic systems.