EXAFS和XANES跟踪了镍-铀氧化物催化剂的形成和处理过程中铀和镍的局部配位变化。尽管当活性催化剂被钝化或暴露于空气时,在镍K边缘EXAFS中观察到的变化很小,但当样品进行类似处理时,在铀L 3边缘EXAFS数据中观察到了更显着的变化。在制备和处理的各个阶段采用的氧化铀晶格类型,是通过对数据与氧化铀记录的数据进行定性比较而确定的。显然,尽管活性和钝化催化剂的铀配位与UO 2相似活性催化剂暴露在空气中会导致结构变化,其中铀配位环境类似于α- U 3 O 8。
Reactions of pulsed‐laser evaporated uranium atoms with molecular oxygen: Infrared spectra of UO, UO<sub>2</sub>, UO<sub>3</sub>, UO<sub>2</sub><sup>+</sup>, UO<sub>2</sub><sup>2+</sup>, and UO<sub>3</sub>–O<sub>2</sub> in solid argon
作者:Rodney D. Hunt、Lester Andrews
DOI:10.1063/1.464045
日期:1993.3
Uranium atoms from the Nd:YAG laser ablation of a uranium target were codeposited with molecular oxygen and excess argon at 12 K. Infrared spectra following the U+O2 reaction revealed a wide range of reaction products. The 776.0 cm−1 band due to UO2 was the strongest product absorption, strong UO3 bands were observed at 852.5 and 745.5 cm−1, and a weak UO absorption appeared at 819.8 cm−1. These product absorptions are in agreement with earlier work, which evaporated UO2 from a tungsten Knudsen cell at 2000 °C. The 16O2/18O2 reaction gave only U 16O2 and U 18O2, which verified an insertion mechanism. New product absorptions were observed at 952.3, 892.3, and 842.4 cm−1. The 842.4 cm−1 absorption due to the UO3–O2 complex and the 892.3 cm−1 band assigned to the charge-transfer complex (UO2+)(O2−) grew markedly at the expense of the other uranium oxides during annealing the matrix to allow diffusion and reaction of O2. With 25% 16O2, 50% 16O18O, and 25% 18O2 samples, the 952.3 cm−1 band became a sharp triplet at 952.3, 936.5, and 904.5 cm−1 and exhibited an isotopic ratio appropriate for a linear OUO species. Agreement of this band with uranyl ion spectra suggests assignment to a (UO22+) complex. Mechanisms of formation of charged species are discussed.