Schlereth T W, Hedhili M N, Yakshinskiy B V, Gouder T, Madey T E
Laboratory for Surface Modification, Department of Physics and Astronomy, Rutgers-The State University of New Jersey, Piscataway, NJ 08854, USA.
J Phys Chem B. 2005 Nov 10;109(44):20895-905. doi: 10.1021/jp0526344.
To characterize UO(2) for its possible use in desulfurization applications, the interactions of molecular sulfur dioxide (SO(2)) with a polycrystalline uranium dioxide film have been studied by means of X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and low-energy ion scattering (LEIS). The stoichiometric, oxygen-deficient, calcium-precovered and sodium-precovered UO(2) surfaces have been characterized. The changes in oxide reactivity upon creation of oxygen vacancies and coadsorption of sodium and calcium have been studied. After creation of a reduced UO(2-x) surface (x approximately 0.44) via Ar(+) sputtering, the U 4f XPS spectrum shows conspicuous differences that are good indicators of the surface stoichiometry. Molecular SO(x) formation (x = 2-4) is observed after SO(2) deposition onto stoichiometric UO(2) and onto UO(2) precovered with small amounts (<1 ML) of Na or Ca; complete dissociation of SO(2) is not observed. Heating leads to desorption of the SO(x) species and to transformation of SO(2) to SO(3) and SO(3) to SO(4). On oxygen-deficient UO(2) and on UO(2) precovered with large Na or Ca coverages (> or =4 ML), both the formation of SO(x)= species and complete dissociation of SO(2) are observed. A higher thermal stability of the sulfur components is observed on these surfaces. In all cases for which dissociation occurs, the XPS peak of atomic sulfur shows similar structure: three different binding states are observed. The reactivity of oxygen-deficient UO(2) and sodium- and calcium-precovered UO(2) (coverages > or = 4 ML) is attributed to charge transfer into the antibonding LUMO of the adsorbed molecule.
为了表征二氧化铀（UO₂）在脱硫应用中的潜在用途，通过X射线光电子能谱（XPS）、程序升温脱附（TPD）和低能离子散射（LEIS）研究了分子二氧化硫（SO₂）与多晶二氧化铀薄膜的相互作用。对化学计量比、缺氧、预覆盖钙和预覆盖钠的UO₂表面进行了表征。研究了氧空位形成以及钠和钙共吸附时氧化物反应性的变化。通过Ar⁺溅射产生还原的UO₂₋ₓ表面（x约为0.44）后，U 4f XPS光谱显示出明显差异，这些差异是表面化学计量比的良好指标。在SO₂沉积到化学计量比的UO₂以及预覆盖少量（<1 ML）Na或Ca的UO₂上后，观察到分子SOₓ（x = 2 - 4）的形成；未观察到SO₂的完全解离。加热导致SOₓ物种脱附，并使SO₂转化为SO₃以及SO₃转化为SO₄。在缺氧的UO₂以及预覆盖大量Na或Ca（≥4 ML）的UO₂上，既观察到SOₓ物种的形成，也观察到SO₂的完全解离。在这些表面上观察到硫成分具有更高的热稳定性。在所有发生解离的情况下，原子硫的XPS峰显示出相似的结构：观察到三种不同的结合态。缺氧的UO₂以及预覆盖钠和钙的UO₂（覆盖度≥4 ML）的反应性归因于电荷转移到吸附分子的反键最低未占分子轨道（LUMO）中。
