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This chapter focuses on the oscillatory catalytic reactions at single-crystal surfaces. Among oscillating chemical systems, catalytic reactions at well-defined single-crystal surfaces under low-pressure conditions are conceptually particularly attractive for the following reasons: The reacting medium is strictly two-dimensional and uniform on the mezoscopic length scale, which is relevant for spatial pattern formation. In addition, the low partial pressures cause only minor heat production by the reaction, so that usually isothermal conditions can be kept to within a very good approximation. By combining kinetic measurements with surface-sensitive techniques, it became possible to explore the elementary steps underlying the complex temporal and spatial effects in fair detail, which information, in turn, then could be used for theoretical modeling. For the systems described in the chapter, the following mechanisms is found to determine the occurrence of isothermal kinetic oscillations: (1) adsorbate driven structural transformation, (2) formation and depletion of a subsurface oxygen species, and (3) autocatalytic surface reaction.
