Origin of activation of Lattice Oxygen and Synergistic Interaction in Bimetal-Ionic Ce_0.89Fe_0.1Pd_0.01O_2−δ Catalyst

Abstract

Flourite-type nanocrystalline Ce0.9Fe0.1O2−δ and Ce0.89Fe0.1Pd0.01O2−δ solid solutions have been synthesized by solution combustion method, which show higher oxygen storage/release property (OSC) compared to CeO2 and Ce0.8Zr0.2O2. Temperature programmed reduction and XPS study reveal that the presence of Pd ion in Ce0.9Fe0.1O2−δ facilitates complete reduction of Fe3+ to Fe2+ state and partial reduction of Ce4+ to Ce3+ state at temperatures as low as 105 °C compared to 400 °C for monometal-ionic Ce0.9Fe0.1O2−δ. Fe3+ ion is reduced to Fe2+ and not to Fe0 due to favorable redox potential for Ce4+ + Fe2+ → Ce3+ + Fe3+ reaction. Using first-principles density functional theory calculation we determine M−O (M = Pd, Fe, Ce) bond lengths, and find that bond lengths vary from shorter (2.16 Å) to longer (2.9 Å) bond distances compared to mean Ce−O bond distance of 2.34 Å for CeO2. Using these results in bond valence analysis, we show that oxygen with bond valences as low as −1.55 are created, leading to activation of lattice oxygen in the bimetal ionic catalyst. Temperatures of CO oxidation and NO reduction by CO/H2 are lower with the bimetal-ionic Ce0.89Fe0.1Pd0.01O2−δ catalyst compared to monometal-ionic Ce0.9Fe0.1O2−δ and Ce0.99Pd0.01O2−δ catalysts. From XPS studies of Pd impregnated on CeO2 and Fe2O3 oxides, we show that the synergism leading to low temperature activation of lattice oxygen in bimetal-ionic catalyst Ce0.89Fe0.1Pd0.01O2−δ is due to low-temperature reduction of Pd2+ to Pd0, followed by Pd0 + 2Fe3+ → Pd2+ + 2Fe2+, Pd0 + 2Ce4+ → Pd2+ + 2Ce3+ redox reaction.

Giant piezoresponse and promising application of environmental friendly small-ion-doped ZnO

“…Fe 2p 1/2 and 2p 3/2 peaks in Zn 0.988 Fe 0.012 O films as deposited are located at 724.7 eV and 710.6 eV, respectively, which are similar to the values reported for Fe 2 O 3 :Fe 2p 1/2 at 724.9 eV and Fe 2p 3/2 at 710.7 eV [136]. The spectrum shows a shake-up contribution at about 718.6 eV, which indicates that Fe has a +3 oxidation state [137]. After H 2 annealing, Fe 2p 3/2 and 2p 1/2 signals of the films are centered at 709.6 eV and 722.7 eV, respectively, which are very close to those of Fe 2+ (709.30 eV for Fe 2p 3/2 and 722.3 eV for Fe 2p 1/2 ) [138].…”

NO Reduction Over Noble Metal Ionic Catalysts

“…In a similar way, [64][65][66][67][68]. Table 2 summarizes metal ion substituted oxides prepared by solution combustion method.…”

An experimental and DFT study of the adsorption and oxidation of NH3 on a CeO2 catalyst modified by Fe, Mn, La and Y

“…The results indicate that the decrease in the lattice distance results from doping with cations that have small radii (0.64Å for Fe 3+ , 0.66Å for Mn 3+ , 0.90Å for Y 3+ ) [26]. Their replacement of Ce 4+ (0.92Å) in the fluorite structure appears to be possible due to their similar structures and ionic radii [5][6][7]. We assume that dopant atoms could be well dispersed on the CeO 2 surface (solid solution) [5,27] and substitute surface cerium atoms to form point detects [8,13].…”

“…S3, the peaks of which can be attributed to the +3 oxidation state [5][6][7]. The spectra of Ce 3d and O 1s for the four catalysts are presented in Fig.…”

“…Gupta et al [5][6][7] systematically studied transition-metal, noble-metal and rare-earth cations doped onto CeO 2 and revealed that transition-metal and noble-metal, rather than rare-earth, greatly enhanced the OSC of CeO 2 and the weak, longer bonds that formed on the active surfaces were responsible for the higher reducibility of these solid solutions. Nolan [8,9] modeled the adsorptions of NO and CO molecules on the Ti, Zr, Hf doped CeO 2 surfaces by density functional theory (DFT) calculations and proposed that the dopants atoms significantly distort the surface structure compared to the undoped surface.…”