Surface studies of model supported catalysts: NO adsorption on Rh/CeO2(001)

Abstract

The adsorption and reaction of NO on a model catalyst composed of Rh supported on ceria has been studied. CeO2 films were grown epitaxially by laser ablation onto SrTiO3(001) substrates. X-ray diffraction and transmission electron microscopy indicate the films are single crystalline with (001) orientation. Comparison of experimental and computer simulated ion scattering distributions indicate that an annealed CeO2 surface is well ordered and is composed of both O and Ce terminated domains. Exposures to CO and H2 at various temperatures had little or no effect upon the ceria. Photoemission from the Ce 4d levels exhibits complex features that differ between a sputtered and a fully oxidized surface. NO does not adsorb on the Rh free, fully oxidized surface, but does adsorb upon a sputter reduced surface. The thermally induced conversion from molecular NO to atomic N was measured by both N 1s photoemission and x-ray absorption as a function of Rh coverage to determine substrate effects on Rh surface chemistry. Rh deposited on sputtered ceria is more active for NO decomposition and yields higher N2 desorption temperatures than does Rh on the fully oxidized support.

Variations in the surface chemistry of methanol with CeO2(100) at low and elevated pressures

“…After cleaning, the impurity level was below the experimental detection limit, the surface was fully oxidized, and there was no evidence of a breakthrough of Sr or Ti. Surface structural characterization was not conducted on these samples; however, low‐energy electron diffraction patterns and angle‐dependent low‐energy ion scattering from films grown in the same manner indicated that the surface was crystalline and reasonably well ordered …”

Defect interactions with stepped CeO2/SrTiO3 interfaces: Implications for radiation damage evolution and fast ion conduction

“…6,7,37 As the lattice parameters are a film = 0.5411 nm and a sub = 0.3905 nm, the lattice mismatch exhibited due to this orientation relationship is ∼2%. This lattice mismatch implies that the equilibrium misfit dislocation spacing to relieve long-range coherency stresses is 18.5 nm, which is calculated using d dis = |b|a sub /(a film − a sub ), where b is the Burgers vector component parallel to the interface, and in this case assumed to be a film 110 .…”

“…This is consistent with experimental results for the CeO 2 /STO interface, where O terminated planes are observed, 7, 54 although Ce and O terminated planes in equal ratio have also been observed. 6 More importantly, to eliminate the surface dipole that arises by terminating the ideal fluorite crystal in a (100) direction, half of the oxygen ions have been moved from one surface of CeO 2 to the other, similar to the lowest energy (100) surface found for UO 2 , resulting in sub-stoichiometric surfaces that are dipole-free. 55 The stepped interface model shown in Figure 1(c) was found to be structurally stable upon annealing at 2000 K for 10 ps.…”

“…In the field of reconfigurable microelectronics, perovskite-fluorite (BaTiO 3 -CeO 2 ) nanocomposites are pivotal as two structurally different immiscible phases, one a ferroelectric and the other a low-permittivity dielectric, are needed for such applications. 5 For use as an effective threeway catalyst in automotive applications 6,7 and high temperature superconductor applications, 8 CeO 2 is often grown on SrTiO 3 (STO) substrates. On the other hand, CeO 2 can also serve as a buffer layer for epitaxial deposition of STO to study ferroelectric properties of STO.…”

“…In addition, previous studies on CeO 2 /STO interfaces have mostly focused on coherent or misfit interfaces signifying that the present work on stepped interfaces can provide new insight. [6][7][8][9][10] Motivated by our recent experiments, here we use atomistic calculations with an empirical potential to investigate in detail the interaction of defects across the stepped CeO 2 /STO interface with a focus on implications for radiation damage evolution. In particular, we calculate the relative formation energy of point defects as a function of position within the stepped interface structure.…”