Calla Jason T, Davis Robert J
Department of Chemical Engineering, University of Virginia, Charlottesville, Virginia 22904-4741, USA.
J Phys Chem B. 2005 Feb 17;109(6):2307-14. doi: 10.1021/jp0488719.
Alumina-supported Au particles (1.16 wt %) were prepared by a deposition-precipitation method involving a HAuCl4 precursor. X-ray absorption spectroscopy at the Au L(III) edge was used to monitor the evolution of the Au oxidation state and atomic structure during pretreatment in He up to 623 K. Although the as-prepared material had Au present in a +3 oxidation state, thermal treatment at 623 K facilitated autoreduction of Au cations to metal particles. Analysis of the EXAFS revealed a coordination number (Au-Au) of 7.2, which is consistent with spherical particles of 1.2 nm in average diameter. Steady-state isotopic transient kinetic analysis was used to evaluate the intrinsic turnover frequency (TOF intr) and the surface coverage of carbon-containing species (theta COx) on the gold catalyst during CO oxidation at 1.2 atm total pressure and 296 K. The artifacts in the kinetic parameters caused by re-adsorption of product carbon dioxide were removed by varying the total flow rate. The values of TOF intr and theta COx determined from the intrinsic lifetime of surface intermediates at infinite flow rate were 1.6 s(-1) and 4.9%, respectively. The intrinsic turnover frequency was nearly independent of temperature, indicating a very low activation energy for the reaction. However, the rate was significantly accelerated by the presence of water.
采用涉及 HAuCl4 前驱体的沉积沉淀法制备了氧化铝负载的金颗粒（1.16 wt%）。利用金 L(III) 边的 X 射线吸收光谱监测在高达 623 K 的氦气中预处理期间金的氧化态和原子结构的演变。尽管制备的材料中存在 +3 氧化态的金，但在 623 K 下进行热处理促进了金阳离子自动还原为金属颗粒。EXAFS 分析显示配位数（Au-Au）为 7.2，这与平均直径为 1.2 nm 的球形颗粒一致。采用稳态同位素瞬变动力学分析来评估在 1.2 atm 总压和 296 K 下 CO 氧化过程中，金催化剂上的本征周转频率（TOFintr）和含碳物种的表面覆盖度（θCOx）。通过改变总流速消除了产物二氧化碳再吸附导致的动力学参数中的假象。由无限流速下表面中间体的本征寿命确定的 TOFintr 和 θCOx 值分别为 1.6 s(-1) 和 4.9%。本征周转频率几乎与温度无关，表明该反应的活化能非常低。然而，水的存在显著加速了反应速率。
