AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM3
Formation of Surface Cyanide through Carbon-Nitrogen Coupling Reactions on Pt(111)

Monday, November 3, 2003, 9:00 am, Room 327

Session: Catalysis I: Adsorption and Reactions of Small Molecules at Surfaces
Presenter: E. Herceg, University of Illinois at Chicago
Authors: E. Herceg, University of Illinois at Chicago
M. Trenary, University of Illinois at Chicago
Correspondent: Click to Email
The C-N coupling reaction to form CN on the Pt(111) surface has been studied with temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). This reaction underlies the industrially important synthesis of HCN from NH@sub 3@ and CH@sub 4@ over platinum catalysts. In the absence of oxygen, the catalytic reaction is endothermic and occurs at 1200 °C. In previous kinetic studies using model reactors, it has been inferred that the C-N coupling reaction occurs through surface C and N atoms.@footnote 1@ The surface CN formed is then hydrogenated to HCN. However, direct support for this mechanism has been lacking. Alternatively, surface CH@sub x@ and NH@sub y@ with x = 1, 2, or 3 and y = 1 or 2, may react to form a CNH@sub z@ species with z@>=@2, which is then dehydrogenated to HCN. Therefore characterization of the possible CH@sub x@ and NH@sub y@ surface species is important. Although NH@sub 3@ and CH@sub 4@ do not react on Pt(111) under ultrahigh vacuum conditions, the present study shows that the C-N coupling reaction is readily achieved in UHV in various ways, such as from coadsorbed CH@sub 3@, produced from thermal decomposition of CH@sub 3@I, and NH, produced from electron beam induced dissociation of adsorbed NH@sub 3@. The conversion of adsorbed NH@sub 3@ to NH@sub 2@, NH, and N was monitored with RAIRS and TPD. The surface N atoms readily react with hydrogen to reform surface NH, which is identified by its intense NH stretch peak at 3317 cm@super -1@. The presence of surface CN is detected through its reaction with hydrogen to form a surface CNH@sub 2@ (aminocarbyne) species, which has characteristic RAIRS peaks, as well as by HCN desorption. From the fact that C-N bond formation occurs at a temperature above where all CH@sub x@ and NH@sub y@ species have dehydrogenated indicates that the reacting species are in fact surface C and N atoms. @FootnoteText@@footnote 1@ D. Hassenberg and L. D. Schmidt, J. Catal. 97, 156 (1986).