In situ characterization of supported metal catalysts and model surfaces by time-resolved and three-dimensional XAFS techniques

摘要

This paper emphasizes novel issues in in situ characterization techniques for catalysts and model surfaces, namely, energy dispersive X-ray absorption fine structure (DXAFS) for time-resolved structure analysis and polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) for 3D structure analysis, which have been developed in the past 5-10 years. DXAFS is a powerful technique for elucidating dynamic structural changes at active metal sites on catalyst surfaces that involve a sequence of formation and breaking of metal-metal, metal-adsorbate, and metal-support bonds; it opens a new area of structure kinetics, revealing kinetic parameters during catalytic reactions, catalyst preparations, and catalyst deactivation and regeneration. PTRF-XAFS is another powerful technique for elucidating 3D structures of active metal sites at single crystal model surfaces, determining structural parameters in three different directions independently with high surface sensitivity, which opens up a new area of catalytic structural chemistry, presenting information on asymmetric and anisotropic bond arrangements and transformations. The issues addressed in this paper are relevant to important key issues in understanding new catalytic structures and reaction mechanisms and to developing new concepts and strategies for novel catalytic materials, which can hardly be addressed by other techniques. (C) 2003 Elsevier Science (USA). All rights reserved. [References: 70]