钯在超活态下用于 CO 氧化的活性表面。

Active surfaces for CO oxidation on palladium in the hyperactive state.

机构信息

State Key Laboratory of Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, China.

出版信息

Langmuir. 2010 Dec 7;26(23):18113-8. doi: 10.1021/la103140w. Epub 2010 Nov 8.

DOI:10.1021/la103140w

PMID:21053982

Abstract

Hyperactivity was previously observed for CO oxidation over palladium, rhodium, and platinum surfaces under oxygen-rich conditions, characterized by reaction rates 2-3 orders higher than those observed under stoichiometric reaction conditions [Chen et al. Surf. Sci. 2007, 601, 5326]. In the present study, the formation of large amounts of CO(2) and the depletion of CO at the hyperactive state on both Pd(100) and polycrystalline Pd foil were evidenced by the infrared intensities of the gas phase CO(2) and CO, respectively. The active surfaces at the hyperactive state for palladium were characterized using infrared reflection absorption spectroscopy (IRAS, 450-4000 cm(-1)) under the realistic catalytic reaction condition. Palladium oxide on a Pd(100) surface was reduced eventually by CO at 450 K, and also under CO oxidation conditions at 450 K. In situ IRAS combined with isotopic (18)O(2) revealed that the active surfaces for CO oxidation on Pd(100) and Pd foil are not a palladium oxide at the hyperactive state and under oxygen-rich reaction conditions. The results demonstrate that a chemisorbed oxygen-rich surface of Pd is the active surface corresponding to the hyperactivity for CO oxidation on Pd. In the hyperactive region, the CO(2) formation rate is limited by the mass transfer of CO to the surface.

摘要

在富氧条件下，先前观察到钯、铑和铂表面上的 CO 氧化的高活性，其特征在于反应速率比化学计量反应条件下观察到的高 2-3 个数量级[Chen 等人，Surf. Sci. 2007, 601, 5326]。在本研究中，通过气相 CO2 和 CO 的红外强度分别证明了在富氧状态下在 Pd(100)和多晶 Pd 箔上大量形成 CO2 和 CO 的消耗。使用红外反射吸收光谱法（IRAS，450-4000 cm(-1)）在实际催化反应条件下对钯的高活性表面进行了表征。在 450 K 下，CO 最终还原了 Pd(100)表面上的氧化钯，并且在 450 K 下的 CO 氧化条件下也还原了氧化钯。原位 IRAS 结合同位素（18）O2 表明，Pd(100)和 Pd 箔上 CO 氧化的高活性表面在富氧反应条件下不是氧化钯。结果表明，Pd 的化学吸附富氧表面是对应于 Pd 上 CO 氧化高活性的活性表面。在高活性区域，CO2 的形成速率受到 CO 向表面的传质限制。