The Surface Structure of and Catalysis by Platinum Single Crystal Surfaces

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Abstract
The importance of the atomic structure of solid surfaces and of adsorbed molecules in heterogeneous catalysis has been advocated by many scientists throughout the years. Early studies by Balandin [l], for example, have suggested the presence of close-packed structures of adsorbed molecules that are intermediates in catalytic reactions. In his view both the atomic structure of the substrate metal surface and the structure of the adsorbed molecules were of primary importance in carrying out certain types of catalytic reactions. In the past, however, the difficulties of determining the atomic structure of catalyst surfaces proved to be almost insurmountable, mostly because of the configuration of the catalyst systems. In the case of metal catalysts most commercial catalyst systems consist of finely dispersed metal particles that are deposited on a high surface area support, most frequently silica or alumina. Even at present the atomic structure of such polydispersed systems cannot be ascertained unambiguously, although the application of several techniques, for example x-ray diffraction, small angle x-ray scattering, electron microscopy, and the electron microprobe have helped to define many of its structural and chemical characteristics. The difficulties of unraveling the role of surface structures in surface reactions were compounded by the variable active surface area of catalyst systems that also markedly influences the rates of catalytic reactions. The effects of surface area, particle size distribution, and structure had to be separated before the role of atomic surface structure in heterogeneous catalysis could be explored by definitive studies.