Spendelow J S, Goodpaster J D, Kenis P J A, Wieckowski A
Departments of Chemistry of Chemical & Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801, USA.
J Phys Chem B. 2006 May 18;110(19):9545-55. doi: 10.1021/jp060100c.
Electrochemical techniques, coupled with in situ scanning tunneling microscopy, have been used to examine the mechanism of CO oxidation and the role of surface structure in promoting CO oxidation on well-ordered and disordered Pt(111) in aqueous NaOH solutions. Oxidation of CO occurs in two distinct potential regions: the prepeak (0.25-0.70 V) and the main peak (0.70 V and higher). The mechanism of reaction is Langmuir-Hinshelwood in both regions, but the OH adsorption site is different. In the prepeak, CO oxidation occurs through reaction with OH that is strongly adsorbed at defect sites. Adsorption of OH on defects at low potentials has been verified using charge displacement measurements. Not all CO can be oxidized in the prepeak, since the Pt-CO bond strength increases as the CO coverage decreases. Below theta(CO) = 0.2 monolayer, CO is too strongly bound to react with defect-bound OH. Oxidation of CO at low coverage occurs in the main peak through reaction with OH adsorbed on (111) terraces, where the Pt-OH bond is weaker than on defects. The enhanced oxidation of CO in alkaline media is attributed to the higher affinity of the Pt(111) surface for adsorption of OH at low potentials in alkaline media as compared with acidic media.
电化学技术与原位扫描隧道显微镜相结合，已被用于研究在NaOH水溶液中有序和无序的Pt(111)上CO氧化的机理以及表面结构在促进CO氧化中的作用。CO的氧化发生在两个不同的电位区域：预峰（0.25 - 0.70 V）和主峰（0.70 V及更高）。两个区域的反应机理均为Langmuir - Hinshelwood机理，但OH的吸附位点不同。在预峰中，CO氧化通过与强烈吸附在缺陷位点的OH反应发生。利用电荷位移测量已证实低电位下OH在缺陷处的吸附。并非所有的CO都能在预峰中被氧化，因为随着CO覆盖度降低，Pt - CO键强度增加。在θ(CO) = 0.2单层以下，CO结合过于牢固，无法与缺陷结合的OH反应。低覆盖度下CO的氧化在主峰中通过与吸附在(111)平台上的OH反应发生，其中Pt - OH键比在缺陷处弱。碱性介质中CO氧化增强归因于与酸性介质相比，Pt(111)表面在碱性介质中低电位下对OH吸附具有更高的亲和力。
