Inert Oxide Research Articles

Fe2+ adsorption on iron oxide: the importance of the redox potential of the adsorption system

We have demonstrated that the redox potential of the solution containing an inert electrolyte, ferrous ions, and metal oxide allows a much better understanding of the process of Fe(II) adsorption on oxide with the increase of pH. We tested two oxides: γ-Fe2O3 (maghemite) and TiO2 (the mixture of anatase and rutile). For both of them, we determined proton surface charge, Fe(II) uptake curves, electrokinetic potential, and redox potential in solution. The all measured quantities except the last, behaved in an almost identical manner for ferric oxide and titanium dioxide. The redox potential strongly depends on the pH of the solution and stabilizes when the adsorption process is finished (pH above 6). We observed that for the solution consisting only of 0.2 mM Fe(II) and 0.1 KCl the redox potential in the pH range 3–6 can be expressed by the formula: Eh[mV]=1120 - 3 times 59 times {text{pH}} - 59 times log (a_{text{Fe}}({text{II}})).

A Single Layer of MoS2 Activates Gold for Room Temperature CO Oxidation on an Inert Silica Substrate

We demonstrate the facile deposition of catalytically active stable Au nanoparticles on single-layer MoS2, on an inert oxide substrate (SiO2). Unlike a gold surface, adsorption of CO on these gold particles proceeds even at room temperature. Subsequent exposure to oxygen leads to CO2 formation and desorption along a reaction pathway described, in detail, by density functional theory. The barrier to CO oxidation, along this pathway, is less than 300 meV, corroborating the facile nature of the CO oxidation reactions in this system. X-ray photoelectron spectroscopy directly reveals that the carbon monoxide, adsorbed on Au nanoparticles on single-layer MoS2, can be repeatedly titrated off the substrate by exposure to oxygen. Comparison of computational results assuming a defect-laden and pristine MoS2 substrate suggest that the pristine single-layer material may be superior in supporting this reaction.

Ultrathin oxide layers for nanoscale integration of molecular light absorbers, catalysts, and complete artificial photosystems.

Artificial photosynthesis is an attractive approach for the generation of renewable fuels because such systems will be suitable for deployment on highly abundant, non-arable land. Recently emerged methods of nanoscience to create conformal, ultrathin oxide layers enable the hierarchical integration of light absorbers, catalysts, and membranes into systems with far simpler synthetic approaches than available till now. This holds in particular for the coupling of molecular light absorbers and catalysts for sunlight to fuel conversion, providing photoelectrodes with greatly improved stability. Moreover, the use of ultrathin inert oxides as proton conducting, molecule impermeable membranes has opened up the integration of reduction and oxidation half reactions into complete photosynthetic systems on the shortest possible length scale-the nanometer scale. This capability affords minimization of energy-degrading resistance losses caused by ion transport over macroscale distances while separating the incompatible water oxidation and carbon dioxide reduction catalysis environments on the nanoscale. Understanding of charge transport between molecular components embedded in the oxide layers is critical for guiding synthetic design improvements of the light absorber-catalyst units to optimize performance and integrate them into complete artificial photosystems. Recent results and insights from transient optical, vibrational, and photoelectrochemical studies are presented, and future challenges and opportunities for engaging dynamic spectroscopies to accelerate the development of nanoscale integrated artificial photosystems are discussed.

Inert and Reactive Oxide Particles for High-Temperature Thermal Energy Capture and Storage for Concentrating Solar Power

Oxide particles have potential as robust heat transfer and thermal energy storage (TES) media for concentrating solar power (CSP). Particles of low-cost, inert oxides such as alumina and/or silica offer an effective, noncorrosive means of storing sensible energy at temperatures above 1000 °C. However, for TES subsystems coupled to high-efficiency, supercritical-CO2 cycles with low temperature differences for heat addition, the limited specific TES (in kJ kg−1) of inert oxides requires large mass flow rates for capture and total mass for storage. Alternatively, reactive oxides may provide higher specific energy storage (approaching 2 or more times the inert oxides) through adding endothermic reduction. Chemical energy storage through reduction can benefit from low oxygen partial pressures (PO2) sweep-gas flows that add complexity, cost, and balance of plant loads to the TES subsystem. This paper compares reactive oxides, with a focus on Sr-doped CaMnO3–δ perovskites, to low-cost alumina-silica particles for energy capture and storage media in CSP applications. For solar energy capture, an indirect particle receiver based on a narrow-channel, counterflow fluidized bed provides a framework for comparing the inert and reactive particles as a heat transfer media. Low-PO2 sweep gas flows for promoting reduction impact the techno-economic viability of TES subsystems based on reactive perovskites relative to those using inert oxide particles. This paper provides insights as to when reactive perovskites may be advantageous for TES subsystems in next-generation CSP plants.

Inert V2O3 oxide promotes the electrocatalytic activity of Ni metal for alkaline hydrogen evolution.

Here, we develop inert V2O3 oxide to enhance the HER activity of industrial Ni catalysts with the assistance of abundant metal/oxide interfaces. The as-synthesized Ni/V2O3 catalyst exhibits over 5 times the activity of a pure Ni sample due to the particle size control and metal/oxide interaction, and excellent durability as a result of oxide anchoring.

Impact of silicate substrate and cosintering on cathode performance in an inert substrate-supported solid oxide fuel cell

In this study, cathode performance of cost-effective inert substrate-supported solid oxide fuel cells fabricated by a single step cosintering process is investigated. The polarization resistance of cosintered inert substrate-supported cathode symmetrical cells (ISC) is compared with the polarization resistance of electrolyte-supported symmetrical cells (ESC) prepared by post- and cosintering. ESC prepared by cosintering have similar polarization resistance than ESC prepared by post-firing due to the addition of pore formers. However, the implementation of a porous inert substrate increases the polarization resistance. Analysis of electrochemical impedance spectra could exclude a gas-phase diffusion limitation due to the porous substrate. Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) reveals an accumulation of zinc, magnesium and silicon on the inner pore surface of the cathode layer. Thermodynamic calculations confirm desorption of these elements from the silicate substrate during the cosintering. In addition, a zinc manganite spinel is detected in the cathode layer via confocal Raman spectroscopy, which indicates a reaction between the cathode material and zinc. The larger cathode polarization resistance of the inert substrate-supported cell is attributed to microstructural changes and the coverage of the cathode surface.

Role of calcium looping conditions on the performance of natural and synthetic Ca-based materials for energy storage

In this work, the multicycle activity of natural CaO precursors (limestone and dolomite) and Ca-based composites (Ca3Al2O6/CaCO3 and ZrO2/CaCO3 mixtures) has been studied for Thermochemical Energy Storage (TCES) in Concentrated Solar Power (CSP) plants by means of the Calcium-Looping process (CaL), using two integration schemes proposed elsewhere that differ in the calcination stages. Under CSP-He conditions, calcination for CaO regeneration is performed under pure He at low temperatures (725 °C) while under CPS-CO2 conditions calcination is carried out under pure CO2 at high temperatures (950 °C). The latter avoids the use of selective membranes to separate He from CO2 even though it requires the use of more expensive materials for solar receptors. Carbonation/calcination conditions drastically affect the multicycle CO2 uptake of the materials tested. Effective multicycle conversion is higher in CSP-He tests due to the mild conditions employed for calcination, which mitigates CaO sintering. On the other hand, the harsh calcination conditions used in CSP-CO2 tests enhance sintering of CaO derived from limestone and the Ca3Al2O6/CaCO3 composite due to the low Tammann temperature of Ca3Al2O6. CaO sintering is hindered by the presence of inert oxides with high Tammann temperatures, such as ZrO2 in the ZrO2/CaCO3 composite and MgO in dolomite. Dolomite derived CaO shows high effective conversion values along the carbonation/calcination cycles when tested under both types of conditions, as compared to limestone and the composites, which suggests that the integration scheme based on CSP-CO2 conditions would be a feasible alternative to CSP-He if natural dolomite were used as CaO precursor.

Thermal stability of nanoscale oxides and carbides of W and Zr in Cu-Al-Fe alloy

Purpose: of this paper is to discover phases evolution of nanoscale tungsten, zirconium oxides and carbides during heating up to 1200°C in contact with the copper alloy CuAl8Fe3. Design/methodology/approach: The main investigation methods are X-ray phase analysis and thermal analysis. The X-ray phase analysis is done by automated X-ray diffractometer DRON-3.0 with cobalt anode, the thermal analysis is done with synchronous thermal analyser STA 449F1 Jupiter (NETZSCH). Findings: The initial interactions’ temperatures for the carbides and oxides with copper alloy CuAl8Fe3, also temperatures of isomorphic and polymorphic transitions are discovered. Comparative thermal analysis of the nanoscale powders reveals carbides are more stable in air and inert gas (argon) versus oxides ones. Research limitations/implications: Intermediate phase transitions during heating and cooling are predicted on the base of known thermodynamic data and scientific reports, X-ray phase analysis is performed only for initial and result material before and after heat treatment. Practical implications: Obtained data allows developing effective technological consolidation regimes of ESD nanoscale zirconium, tungsten carbides and oxides with cuprum-based alloys for wear and heat resistant composite materials production. Originality/value: The paper exposes new thermal data of isomorphic and polymorphic transformations for zirconium, tungsten carbides and oxides nanoscale powders obtained by ESD and their interactions with copper CuAl8Fe3 alloy in temperature range: 25-1200°C.

Fine‐Tuning Surface Properties of Perovskites via Nanocompositing with Inert Oxide toward Developing Superior Catalysts for Advanced Oxidation

AbstractCost‐effective, stable, and highly efficient heterogeneous catalyst is the key challenge for wastewater treatment based on Fenton‐like advanced oxidation processes. Perovskite oxides offer new opportunities because of their versatile compositions and flexible physiochemical properties. Herein, a new strategy is proposed that is different from the frequently used alien‐metal doping, to tune surface properties of perovskite oxides by nanocompositing perovskite with inert oxide, resulting in improved activity and stability for catalytic oxidation. By in situ modification of LaFeO3 with inert La2O3 oxide through one‐pot synthesis, several important surface properties such as surface defects, H2O2 adsorption capacity, Fe2+ concentration, and charge‐transfer rate were improved, as well as resistance against iron leaching. In performance evaluation, among the various materials, La1.15FeO3 (L1.15FO) composite shows the highest Fenton activity (0.0402 min−1) for activating H2O2 to oxidize methyl orange, 2.5 times that of the pristine LaFeO3. Notably, in situ electron paramagnetic resonance analysis and radical scavenging tests unveil a faster generation of singlet oxygen as the dominant reactive species over L1.15FO, consequently a novel non‐radical activation mechanism is proposed. Such improved performance is assigned to the strong coupling effect between the nanosized LaFeO3 and La2O3 in the hybrids, which fine‐tune the surface properties of LaFeO3 perovskite as superior Fenton catalysts.

Inert substrate-supported microtubular solid oxide fuel cells based on highly porous ceramic by low-temperature co-sintering

Inert substrate-supported microtubular solid oxide fuel cells (MT-SOFCs) are attractive due to their advantages, including high reduction–oxidation (redox) cycling stability and thermal cycling tolerance. A method involving sequential dip-coating, leaching, and co-sintering was developed and applied to fabricate inert substrate-supported MT-SOFCs through acid leaching nickel from the conventional Ni–yttria-stabilized zirconia (YSZ) anode. A thin current collector was deposited onto the support surface to minimize the current collection losses by collecting current from the entire surface area of the anode. A dense electrolyte could be obtained at a co-sintering temperature of 1250 °C. The produced MT-SOFC with the configuration of porous zirconia support/Ni–Scandia-stabilized zirconia (SSZ) anode current collector/Ni-SSZ anode/SSZ electrolyte/strontium-doped lanthanum manganite (LSM)-SSZ cathode/LSM cathode current collector was evaluated by electrochemical characterization tests. The inert substrate-supported MT-SOFC exhibited the maximum power densities of 616, 542, 440, and 300 mW cm−2 at 800, 750, 700, and 650 °C, respectively using dry hydrogen and air. In addition, the thermal cycling stability of the MT-SOFC was evaluated. The cell survived from thermal cycling tests and came out intact after 50 thermal cycles between 700 °C and 400 °C during an operation time of 50 h.

Analysis of Oxide Film on Aluminum Electrode in Aluminum-Air Battery

In this research, aluminum air battery system was revisited to investigate key issues which have challenged its full application as a rechargeable battery. The Al-air battery had received intense attention once due to the excellent benefits such as low cost and high energy density, but due to the challenging issues such as hydrogen evolution, and inactive oxide film formed on the Al surface, it could not be fully applied. Recently, ionic liquid which is a salt in liquid form at room temperature started to be applied in the battery system to overcome the issues in aqueous electrolyte [1,2], but the inactive oxide film on Al surface is still dominant in decreasing cell performance and detailed research to understand how to control the oxide film was not conducted. In this study, 1-Ethyl 3-Methyl Imidazolium Chloride ([EmIm]Cl) and Aluminum Chloride (AlCl3) was applied in the Al-air battery, and its effect on oxide film on the surface aluminum electrode was analyzed through cell-base test, and SEM image analysis. It was found that the inert oxide film on aluminum, which is one of the most challenging issues, could be controlled and removed by using of proper ratio of [EmIm]Cl and AlCl3, and the growth/breakdown mechanism of the oxide film was theoretically considered. This research results are expected to suggest a new direction to control the surface of aluminum electrode to make it the most promising system.

Electrodeposition of nanocrystalline nickel embedded with inert nanoparticles formed via inverse hydrolysis

Nanocrystalline electrodeposits embedded with inert hard nanoparticles are applied to coating on engineering materials for high hardness and thermal stability. They have mainly been synthesized from a solution containing a suspension of particles in electrodeposition. In this conventional synthesis, finer particles tend to agglomerate in the electrolyte and are embedded inhomogeneously in the electrodeposits. This work provides a different approach to synthesizing nanocrystalline metal electrodeposits embedded with inert metal oxide particles that are formed through inverse hydrolysis in an electrolyte before embedding in the electrodeposits. In principle, this approach would allow the embedding of particles ranging, in size, from the molecular to the micron scale through control of the pH and the duration of stand-by reaction prior to electrodeposition. Effect of this approach on the hardness and thermal stability of Ni electrodeposits was validated, and agree semi-quantitatively with theoretical values predicted by Orowan strengthening and Zener pinning, both of which assume that dispersed particles are smaller than the matrix grain size.

Dipyramidal-Au@SiO2 nanostructures: New efficient electromagnetic nanoresonators for Raman spectroscopy analysis of surfaces

Plasmonic structures act as electromagnetic nanoresonators leading to a local enhancement of the intensity of the electric field of the incident radiation, which leads to an increase in the efficiency of Raman scattering for molecules in close proximity to such nanoresonators. Because many biological molecules can change their structure during interaction with metal surfaces, plasmonic nanostructures are sometimes covered with very thin layers of chemically inert oxides, which prevent direct interaction between the sample being analysed and the metal surface. The Raman analysis of surfaces using surface-protected plasmonic nanoparticles is called shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In this contribution, the first example of using dipyramidal-Au@SiO2 nanoparticles as nanoresonators for SHINERS is presented. Since such nanostructures contain many sharp edges and apexes (on which the highest field enhancement is usually generated), the Raman enhancement factor induced by the dipyramidal nanoparticles is significantly (about one order of magnitude) larger than the enhancement factor generated by standard semi-spherical nanostructures. Synthesized dipyramidal-Au@SiO2 nanoparticles were tested as nanoresonators in SHINERS measurements of some thiolate monolayers formed on a platinum surface and for detecting the pesticide thiram deposited on a tomato skin. For example, the limit of detection of thiram in the last system was estimated as about 0.9 ng cm−2. The method of synthesis and purification of dipyramidal-Au nanoparticles applied in this work makes it possible to obtain samples of SHINERS nanostructures having very high homogeneity, significantly better than the homogeneity of anisotropic gold nanostructures previously used for SHINERS measurements.

Heat transfer in counterflow fluidized bed of oxide particles for thermal energy storage

The potential for inert oxide particles as a heat transfer and thermal energy storage (TES) media in concentrating solar power (CSP) depends in part on particle receiver designs that provide high wall-to-particle heat transfer rates. This paper presents a novel continuous-flow approach to achieve high heat transfer coefficients hw for particle receivers by fluidizing net-downward-flowing particles in a narrow vertical channel bounded by an external irradiated/heated wall and a parallel interior wall with a metal mesh opening that allows the upward-flowing fluidizing gas to exit at the top of the channel. To demonstrate the high hw of this flow configuration, a fluidized bed in a 10 cm × 10 cm × 0.64 cm deep channel was heated through an external aluminosilicate wall with mid-IR quartz lamps that provided external wall heat fluxes up to 20 W cm−2. Extensive heat transfer measurements with fluidized Carbo Accucast ID50 particles (diameters between 150 and 350 μm) in steady-state continuous downward flow and in transient batch mode assessed total hw as functions of particle bed temperatures Tb, bed solids volume fractions αb, and superficial gas velocities Ug. Results showed that the narrow-channel fluidized bed can achieve overall hw as high as 1000 W m−2 K−1. The highest hw were measured at upward Ug between 2 and 4 times the minimum bed fluidization velocities, Umf, which decreased to0.12 m s−1 for the mean particle diameter at Tb=600°C. Increasing Ug further above Umf decreased hw due to an associated decrease in αb. hw increased strongly with Tb in part, because gas-phase conductivity and the radiative heat transfer contribution increased with Tb. The extensive measurements were fit to a modified version of the Nusselt number correlation by Molerus (1992). For αb⩾0.1, the Molerus correlation with adjusted dependence on excess fluidization velocity (Ug-Umf) provided an excellent fit to the measured convective fraction of hw (with <10% error). Adding the radiation component with the Molerus correlation provides an effective tool for calculating hw for this counterflow fluidized bed configuration. A simple analysis explored the impact of such high hw for an indirect receiver design with angled external walls to spread solar aperture fluxes. Results from the analysis indicated that total hw=1000 W m−2 K−1 can enable solar collection efficiencies approaching 90% with external wall temperatures Tw,ext≈1020°C. This potential performance motivates further exploration of this fluidized bed configuration for particle receivers for CSP applications.

A DFT mechanistic study of the ODH of n-hexane over isolated H3VO4

Catalytic (H3VO4) oxidative dehydrogenation (ODH) mechanistic studies of the activation of n-hexane have been conducted by means of Density Functional Theory (DFT).Catalytic oxidative dehydrogenation is an important strategy for the conversion of alkanes to alkenes to provide useful chemical feedstocks from saturated hydrocarbons. Transition metal oxide catalysts based on vanadium provide an important class of catalysts for this reaction. The catalyst is usually prepared with vanadium in a high oxidation state prepared as an over layer supported on a relatively inert main group oxide (silica, alumina, etc.). Activation of the hydrocarbon is then energetically possible through the reduction of vanadium cations which can be subsequently re-oxidised using molecular O2 to complete the catalytic cycle.The aim of this study was to use density functional theory to explore the catalytic mechanism of this type of reaction using the conversion of n-hexane to 1- and 2-hexene as an illustrative example. Calculations are performed for the 1- and 2-hexene radical pathways and the results extrapolated to discuss the expected selectivity under laboratory experimental conditions (573, 673 and 773 K). Consideration of 3-hexene is excluded as in our earlier experimental studies and in the general literature this product is not reported. The stationary points on the potential energy surfaces were characterized and the associated geometries and relative energies (ΔE#, ΔE, ΔG# and ΔG) were determined. The relative energies of all intermediates and transition states identified are used to lend insight on the mechanistic pathways for the reaction.We have concentrated on the role of the transition metal in this chemistry and so the catalyst model chosen is an isolated, tetrahedral H3VO4 cluster containing one vanadyl bond, V(V)O. The calculated rate-limiting step is the CH bond activation (β-hydrogen abstraction) from the C6H14 chain by the vanadyl O, with a calculated ΔE# = +27.4 kcal/mol. This produces a C6H13HOH3VO3 complex as an intermediate with vanadium reduced to V(IV). There are then two possible routes for the propagation step that leads to 2-hexene. Firstly, the abstraction of the second γ-hydrogen on the radical intermediate fragment (C6H13) can take place on a different active V(V) = O site. Secondly this step may involve reaction with gas-phase molecular O2. These alternatives are compared computationally and results used to discuss some existing experimental data.

Quantitative measurements of various gases in high and ultrahigh vacuum

Two calibration methods for ionization gauges, a measurement method for the effective pumping speed of turbomolecular pumps, and a method for introducing low gas flow rates into vacuum chambers were examined. Twenty-four gases were used, including inert gases, hydrocarbons, oxygen, carbon oxide, chlorofluorocarbons, and liquid vapors. Direct comparison with a reference spinning rotor gauge and incorporation of the standard conductance element into the conductance modulation methods were tested as calibration methods in the range from 10−6 to 10−3 Pa. The effective pumping speed of a turbomolecular pump with a nominal pumping speed of 0.37 m3/s for N2 was measured using the modified conductance modulation method. A standard conductance element, which is a porous plug fabricated from sintered stainless steel, was tested in the range of 10−8 to 10−4 Pa m3/s to quantitatively introduce gas into a vacuum chamber. The obtained results were compared with previously reported values.

Synthesis and characterization of (1-x)Ba(NO3)2: x ZrO2 composite solid electrolyte

In the present work, a Frenkel cationic conductor Ba(NO3)2 was dispersed with chemically inert oxide ZrO2 (<100nm in size) using mechanical mixing for an hour in the presence of acetone and it is done for different m/o of ZrO2 (5,10,15,20 and 25m/o). The pellets were prepared at a pressure of 4 tones/cm2 and sintered at 400oc for 12 hr. The characterizations of these samples were done through XRD, TG- DTA, SEM, EDAX and FTIR. X-Ray Diffractograms, TG- DTA and FT-IR spectrum revealed that there was neither formation of solid solution between host and dispersoid nor a new phase. Scanning Electron Micrographs have shown uniform distribution of dispersoid in the host material and also agglomerations of dispersoid particles at higher m/o of ZrO2. FT-IR spectroscopy gave evidence for the existence of OH-1(hydroxyl group) ion in pure ZrO2 and dispersed samples. EDAX confirmed the presence of Ba, N,O,Zr atoms in all the dispersed solid electrolyte system (1-x) Ba(NO3)2: x ZrO2.

Heterolytic dissociative adsorption state of dihydrogen favored by interfacial defects

The atomic-scale insight into dihydrogen on MgO(001) surface deposited on molybdenum substrate with interfacial defects was investigated in detail by employing density functional methods Here we report novel dissociative adsorption behaviors of single hydrogen molecule on the usually inert oxide surfaces, with consideration of two types of dissociation schemes. The heterolytic dissociation state −Mg(H)-O(H)- of dihydrogen is impossible to obtain on neighboring O-Mg sites of perfect bulk MgO(001) terraces. Unusually, the hydrogen molecule can form heterolytic fragmentation states on metal supported MgO(001) films with very low activation barrier (0.398eV), and the heterolytic dissociation state is much more favorable than homolytic dissociation state both energetically and kinetically in all cases. Electronic properties and bonding attribution of adsorbates and the oxide-metal hybrid structure are revealed by analyzing density of states, differential charge densities, orbital interaction and electron localization function. The characteristic changes to the property and activity of magnesia (001) can have potential application in catalytic reactions.

Application of quantitative X‐ray photoelectron spectroscopy (XPS) imaging: investigation of Ni‐Cr‐Mo alloys exposed to crevice corrosion solution

This paper explores quantitative X‐ray photoelectron spectroscopy imaging on three different Ni‐Cr‐Mo Hastelloy® alloys (BC‐1, C‐22 and G‐30) with differing Cr and Mo contents. The alloys were subjected to a simulated critical crevice corrosion solution. Ni‐based alloys have been shown to exhibit excellent resistance to a range of corrosive media due to the formation of an inert oxide layer, primarily containing Cr and Mo. However, these alloys may rapidly corrode in the crevice environment produced by seams, gaskets or deposits of debris on the alloy surface. Understanding how the oxide film is influenced by the Cr and Mo content is crucial in determining an optimal alloy composition that reduces or suppresses the possibility of crevice corrosion. The protective oxide films are very thin in nature, generally several nanometers. XPS imaging was used to monitor changes in oxide film composition and to correlate the distribution of Cr and Mo to the grain structure of the alloys. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Rendering Photoreactivity to Ceria: The Role of Defects.

The photoreactivity of ceria, a photochemically inert oxide with a large band gap, can be increased to competitive values by introducing defects. This previously unexplained phenomenon has been investigated by monitoring the UV-induced decomposition of N2 O on well-defined single crystals of ceria by using infrared reflection-absorption spectroscopy (IRRAS). The IRRAS data, in conjunction with theory, provide direct evidence that reducing the ceria(110) surface yields high photoreactivity. No such effects are seen on the (111) surface. The low-temperature photodecomposition of N2 O occurs at surface O vacancies on the (110) surface, where the electron-rich cerium cations with a significantly lowered coordination number cause a local lowering of the huge band gap (ca. 6 eV). The quantum efficiency of strongly reduced ceria(110) surfaces in the photodecomposition of N2 O amounts to 0.03 %, and is thus comparable to that reported for the photooxidation of CO on rutile TiO2 (110).