Effect of the interactions between Pt species and ceria on Pt/ceria catalysts for water gas shift: The XPS studies

The interactions between Pt species and ceria modified by using different preparation methods, ceria crystal planes such as {1 1 0}, {1 0 0}, {1 1 1} and NaCN leaching are studied by different techniques such as BET, TEM, SEM/EDS, XPS, H2-TRP and XRD. The researches manifest that the interactions of Pt species and different ceria crystal planes can be reflected by many factors such as Pt/Ce ratio, Ce4+/Ce3+ ratio, microstrain and Oxygen vacancy on the ceria surface, valence distribution of Pt species and OII concentration. The correlation studies between the interactions and the activities of water gas shift (WGS) manifest that the different crystal planes of ceria and preparation methods have great effect on the activity of Pt/ceria. The increase of lattice strain, Oxygen vacancies, OII and decrease of Ce4+/Ce3+ ratio are favorable for the CO conversion. The metallic Pt concentration increase on the surface of fresh catalyst will decrease its activity and the metallic Pt with high activity must be generated in situ through the WGS process. For impregnation and NH4OH deposition/precipitation (DP) method, the rod carrier catalysts have the highest activity. For (NH4)2CO3 DP method, the polyhedron carrier catalyst has the highest activity. The NaCN leaching not only removes metallic Pt from the surface of Pt/ceria but also alters the valence distribution of Pt and Ce species. After NaCN leaching, the CO conversion of Pt-rod-A increases from 30% to 70% at 300 °C, 82% to 96.2% at 350 °C and 94.4% to 96.3% at 400 °C.