D. R. Huntley

Bio: D. R. Huntley is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Desorption & Chemisorption. The author has an hindex of 9, co-authored 11 publications receiving 1217 citations.

XANES studies of the reduction behavior of (Ce1-yZry)O2 and Rh/(Ce1-yZry)O2

Abstract: Using X-ray absorption near-edge spectroscopy (XANES) at the Ce LIII edge, we have measured the extent of reduction of Rh-loaded and Rh-free, mixed Ce-Zr oxides under hydrogen as a function of temperature. The high surface area, mixed oxides were synthesized by sol-gel techniques and hypercritical drying. Using a simple spectrum subtraction method, the degree of reduction has been measured and compared with previous results for CeO2 and (Ce0.5Zr0.5)O2. Addition of Zr lowers the temperature of reduction and increases the extent of Ce reduction. Rh catalyzes the reduction process at low temperatures but does not substantially affect the extent of reduction achieved at high temperature. A synergism between Rh and Zr is found which leads to very high reducibility in the range of 400–600 K.

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...

Toward the rational design of non-precious transition metal oxides for oxygen electrocatalysis

Abstract: In this Review, we discuss the state-of-the-art understanding of non-precious transition metal oxides that catalyze the oxygen reduction and evolution reactions. Understanding and mastering the kinetics of oxygen electrocatalysis is instrumental to making use of photosynthesis, advancing solar fuels, fuel cells, electrolyzers, and metal–air batteries. We first present key insights, assumptions and limitations of well-known activity descriptors and reaction mechanisms in the past four decades. The turnover frequency of crystalline oxides as promising catalysts is also put into perspective with amorphous oxides and photosystem II. Particular attention is paid to electronic structure parameters that can potentially govern the adsorbate binding strength and thus provide simple rationales and design principles to predict new catalyst chemistries with enhanced activity. We share new perspective synthesizing mechanism and electronic descriptors developed from both molecular orbital and solid state band structure principles. We conclude with an outlook on the opportunities in future research within this rapidly developing field.

Electron localization determines defect formation on ceria substrates.

Abstract: The high performance of ceria (CeO2) as an oxygen buffer and active support for noble metals in catalysis relies on an efficient supply of lattice oxygen at reaction sites governed by oxygen vacancy formation. We used high-resolution scanning tunneling microscopy and density functional calculations to unravel the local structure of surface and subsurface oxygen vacancies on the (111) surface. Electrons left behind by released oxygen localize on cerium ions. Clusters of more than two vacancies exclusively expose these reduced cerium ions, primarily by including subsurface vacancies, which therefore play a crucial role in the process of vacancy cluster formation. These results have implications for our understanding of oxidation processes on reducible rare-earth oxides.

Probing defect sites on CeO2 nanocrystals with well-defined surface planes by Raman spectroscopy and O2 adsorption.

Abstract: Defect sites play an essential role in ceria catalysis. In this study, ceria nanocrystals with well-defined surface planes have been synthesized and utilized for studying defect sites with both Raman spectroscopy and O2 adsorption. Ceria nanorods ({110} + {100}), nanocubes ({100}), and nano-octahedra ({111}) are employed to analyze the quantity and quality of defect sites on different ceria surfaces. On oxidized surfaces, nanorods have the most abundant intrinsic defect sites, followed by nanocubes and nano-octahedra. When reduced, the induced defect sites are more clustered on nanorods than on nanocubes, although similar amounts (based on surface area) of such defect sites are produced on the two surfaces. Very few defect sites can be generated on the nano-octahedra due to the least reducibility. These differences can be rationalized by the crystallographic surface terminations of the ceria nanocrystals. The different defect sites on these nanocrystals lead to the adsorption of different surface dioxygen...