High-Pressure (1 Torr) Scanning Tunneling Microscopy (STM) Study of the Coadsorption and Exchange of CO and NO on the Rh(111) Crystal Face

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• 作者：Keith B. Rider ; Kevin S. Hwang ; Miquel Salmeron ; and Gabor A. Somorjai
• 刊名：Journal of the American Chemical Society
• 出版年：2002
• 出版时间：May 15, 2002
• 年：2002
• 卷：124
• 期：19
• 页码：5588 - 5593
• 全文大小：420K
• 年卷期：v.124,no.19(May 15, 2002)
• ISSN：1520-5126

文摘

The coadsorption of CO and NO on Rh(111) at room temperature was studied with scanningtunneling microscopy (STM) in the catalytically relevant range of ~1 Torr. For gas mixtures where NO isnot in large excess, a mixed layer with (2×2) structure is formed. The difference in binding energy betweenCO and NO on top sites was determined from the measured surface (by direct counting in STM images)and gas mole fractions of each species. A model for the molecular structure is proposed based on theanalysis of exchange events between CO and NO molecules in the images. In this model as the partialpressure of NO increases, NO molecules occupy hollow sites first, by displacing CO, and top sites later,where they coexist with CO. As the surface fraction of NO increases, favorable NO-NO interactions causethe formation of segregated NO-rich regions. As with pure NO, a phase transition from the (2×2)-NO tothe (3×3)-NO structure takes place in the NO-rich regions at high NO concentration. These resultsdemonstrate the unique ability of STM to obtain molecular-level information under catalytic pressureconditions.