Surface hydrogenation reactions at the single-molecule level.

Hydrogenation and dehydrogenation reactions on metal surfaces are among the most important in heterogeneous catalysis. Such reactions can be observed and characterized at the single-molecule level with low temperature scanning tunnelling microscopy (LT-STM). A brief review of such studies is presented. A specific example, the hydrogenation of methyl isocyanide to methyl aminocarbyne on the Pt(111) surface, is described in detail. This reaction was first identified in a study with reflection absorption infrared spectroscopy, a technique that averages over monolayer quantities of molecules. The example illustrates the importance of characterization of surface reactions with complementary techniques in order to properly interpret the single-molecule LT-STM images. A second example of the complementary nature of LT-STM and other surface characterization methods is the tip-induced dehydrogenation on Pt(111) of acetonitrile, the more stable isomer of methyl isocyanide.