Ce-Pr mixed oxides as active supports for Water-gas Shift reaction: experimental and density functional theory characterization

Abstract

Experimental measurements by several techniques and density functional theory (DFT) calculations are combined to characterize Ce-Pr mixed oxides and deeply understand the influence of Pr dopant in their geometric and electronic structure, reducibility and catalytic behavior concerning the Water-gas Shift reaction (WGSR). Samples with nominal Pr dopant content of 0, 5, 15 and 50 at% (atomic percentage) are synthesized via urea decomposition method and subsequent calcination in air at 450 °C. X-ray diffraction characterization shows an increase of ceria lattice parameter for Pr loadings lower than 15 at%, which is consistent with a solid solution formation. X-ray photoelectron spectra indicate a surface enrichment in Pr cations and a diminution of Ce3+ surface concentration as Pr content increases. DFT calculations confirm the preferential reduction of Pr cations due to a single oxygen vacancy formation in Ce-Pr mixed oxides, and also a significant decrease in the energy needed for this O removal compare to that in pure CeO2. Both experimental measurements and DFT calculations evidence that the addition of Pr dopant to ceria promotes oxygen vacancies formation, redox properties and oxygen storage capacity (OSC). Even more, the same promoting effect of Pr in the WGSR intrinsic catalytic activity of Ce-Pr mixed oxides is observed.