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The effect of water vapor on NO reduction by iron was experimentally investigated at 300-1100 °C in an electrically heated ceramic tubular flow reactor in N2atmosphere. The component changes of iron samples after reaction were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Results showed that water vapor reacted as oxidizer and the metallic iron was oxidized by both NO and water vapor. Compared to the result without water, NO reduction efficiency decreased when water vapor was added. NO reduction efficiency reached 88.1%, 91.6%, 94.8% above 900 °C in the presence of 2.5%, 5%, 7% water vapor. NO reduction efficiency decreased as the water vapor increased at lower temperature, e.g., 700°C, while decreased slightly first then increased again at higher temperature, e.g., above 800°C. As water vapor increased, the iron was oxidized to Fe3O4/Fe2O3and the surface of iron became more porous, which benefited the diffusion of NO and/or vapor into the inner of the iron to continue the reaction and resulted in the increased NO reduction. The mechanism was preliminarily analyzed.

NO reduction by iron was conducted in a one-dimensional ceramic tubular reactor at 300 - 1100 °C in N2and simulated flue gas atmosphere with 0.4% methane and 0.01%~0.04% SO2. The evolution of metallic iron was investigated by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and energy dispersive spectrum (EDS) methods. The results showed that SO2did not place negative effect on NO reduction by iron. XRD patterns showed that FeS was formed when there was SO2in the flue gas. The iron oxides were FeO and Fe3O4when methane was not and was used as reducing agent respectively. Rough and raised surface making up of a series of round smooth juts was formed over the iron surface after reaction with NO in N2atmosphere when there was 0.04% SO2. Porous surface consisting serried particles was formed when methane was used as reductant. White attachments were found locally on the iron surface when SO2existed in the flue gas, which was proved by EDS analysis to be FeS.

Introduction Materials with high oxygen surface exchange coefficients at low temperature are needed for Solid Oxide Fuel Cell (SOFC) electrode applications. Perovskite (ABO3−x) type oxides have been extensively studied as candidates for SOFC cathode materials1. The objective of this research was to understand the role stress and crystal structure have on the oxygen surface exchange coefficient. To achieve this objective, the oxygen surface exchange coefficients of Lanthanum Strontium Ferrite (LSF) thin films of various compositions and crystal structures were experimentally measured with a new curvature relaxation technique. These measurements, and lattice constant measurements from the literature, were then compared to Density Functional Theory (DFT) calculations of these same LSF compositions. Experimental Methods As a proof of concept, rhombohedral La0.6Sr0.4FeO3-x (LSF64) thin films were sputtered onto one-side-polished, 1 inch diameter, 200 μm thick, (100)-oriented, (Y2O3)0.13(ZrO2)0.87 (YSZ) single crystal wafers. These bilayers were subjected to mechano-chemical strain under different partial pressures of oxygen. Specifically, the equation shown in Figure 1 was used to measure the oxygen surface exchange coefficient (ki) from the curvature of a bilayer responding to a step change in oxygen partial pressure2-5, where K denotes the instantaneous bilayer curvature at a certain partial pressure of oxygen, K0 denotes initial bilayer curvature, Kinf is the equilibrium bilayer curvature, ki is the oxygen surface exchange coefficient for the fraction of a film with surface area Ai, t is time, and hf is the film thickness. Computational Methods Different crystal structures of LSF were modeled with DFT calculation using the Vienna Ab initio Simulation Package (VASP). The crystal lattices for orthorhombic, rhombohedral and cubic LSF were calculated using an energy minimization technique, as shown in Figure 2. The lattice for each of these structures was converted to a super-cell and extended in z-direction to create active surface. One oxygen atom was then deleted from the active surface to create an oxygen vacancy. The effect of lattice strain due to oxygen vacancy formation was calculated from comparisons between the original and relaxed structures. Result & Discussion The DFT calculated lattice parameters (a=3.8905 A) for cubic, perovskite-structured LSF was in good agreement with experimental measurements from the literature (a=3.858 A).7 The calculated lattice lengths (a=5.662 A, b=7.945 A, c=5.601 A) for orthorhombic LSF also compared well with experimental measurements from the literature (a=5.556 A, b=7.885 A, c=5.653 A).8 Additional work is ongoing to study intermediate compositions, and the role of stress has on oxygen surface exchange. Acknowledgements This work was made possible through a Michigan State University faculty startup grant. References 1. M.S. Islam, J. Mater. Chem., 10, 1027 (2000). 2. Q. Yang , T.E. Burye, R.R. Lunt and J.D. Nicholas, Solid State Ionics, 249–250, 123 (2013). 3. J. Crank, The Mathematics of Diffusion, 2nd edition., p. 60, Oxford University Press, Oxford, UK (1995). 4. G. Kim, S. Wang, A.J. Jacobson and C.L. Chen, Solid State Ionics, 177, 1461 (2006). 5. K. Kerman, C.H. Ko and S. Ramanathan, Phys. Chem. Chem. Phys., 14, 11953 (2012). 6. A. Fossdal, M. Menon, I. Waernhus, K. Wiik, M.A. Einarsrud and T. Grande, J. Am. Ceram. Soc. , 87, 1952 (2004). 7. Y. Takeda, K. Kanno, T. Takada, O. Yamamoto, M. Takano, N. Nakayama and Y. Bando, J. Solid State Chem., 63, 237 (1986). 8. J. Luning, F. Nolting, A. Scholl, H. Ohldag, J.W. Seo, J. Fompeyrine et al., Phys. Rev. B, 67, 214433 (2003).