Au/TiO₂ 上 CO 氧化过程中表面物种演化的原位瞬态傅里叶变换红外光谱和 X 射线吸收近边结构研究

In situ transient FTIR and XANES studies of the evolution of surface species in CO oxidation on Au/TiO2.

作者信息

Henao Juan D, Caputo Tiziana, Yang Jeff H, Kung Mayfair C, Kung Harold H

机构信息

Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208-3120, USA.

出版信息

J Phys Chem B. 2006 May 4;110(17):8689-700. doi: 10.1021/jp0568733.

DOI:10.1021/jp0568733

PMID:16640425

Abstract

The adsorption of CO and its reaction with oxygen were investigated using a combination of in situ Fourier transform infrared spectroscopy, step response measurements in a microreactor, (18)O isotopic labeling, and X-ray absorption near edge structure spectroscopy. An as-prepared sample in which Au is present as a surface oxyhydroxy complex does not adsorb CO. On an activated sample in which only metallic Au is detected, 0.18 +/- 0.03 mol CO/(mol Au) are adsorbed on Au at -60 degrees C, which shows an IR band at 2090 cm(-1). When oxygen is present in the gas phase, this species reacts with a turnover rate of 1.4 +/- 0.2 mol CO(mol Au min)(-1), which is close to the steady-state turnover rate. In contrast, there is a very small quantity of adsorbed oxygen on Au. A small IR peak at 1242 cm(-1) appears when an activated sample is exposed to CO. It reacts rapidly with oxygen and is shifted to 1236 cm(-1) if (18)O is used. It is assigned to the possible intermediate hydroxycarbonyl.

摘要

采用原位傅里叶变换红外光谱、微反应器中的阶跃响应测量、¹⁸O同位素标记和X射线吸收近边结构光谱相结合的方法，研究了CO的吸附及其与氧气的反应。所制备的样品中Au以表面羟基氧化合物形式存在，该样品不吸附CO。在仅检测到金属Au的活化样品上，在-60℃时，0.18±0.03 mol CO/(mol Au)吸附在Au上，在2090 cm⁻¹处出现红外吸收带。当气相中有氧气存在时，该物种以1.4±0.2 mol CO(mol Au min)⁻¹的周转速率发生反应，这与稳态周转速率相近。相比之下，Au上吸附的氧气量非常少。活化样品暴露于CO时，在1242 cm⁻¹处出现一个小的红外峰。它与氧气迅速反应，如果使用¹⁸O，则会移至1236 cm⁻¹。它被认为是可能的中间羟基羰基。