The role of carbon species in heterogeneous catalytic processes: an in situ soft x-ray photoelectron spectroscopy study

High pressure x-ray photoelectron spectroscopy (XPS) is used to characterize heterogeneous catalytic processes. The success of the new technique is based on the possibility of correlating the catalytic activity and the electronic structure of an active surface. The dynamic character of a catalyst surface can be demonstrated impressively by this technique. In this contribution the basics of high pressure XPS will be discussed. Three examples of heterogeneous catalytic reactions are presented in this contribution: the selective hydrogenation of 1-pentyne and the oxidation of ethylene over Pd based catalysts and the dehydrogenation of n -butane over V based catalysts. It is shown that the formation of subsurface carbons plays an important role in all the examples. The carbon incorporated changes the electronic structure of the surface and so controls the selectivity of the reaction. A change of the educts in the reaction atmosphere induces modifications of the electronic surface structure of the operation catalysts.