Nano-scale chemical imaging of working catalyst

Recent progress in synchrotron X-ray microscopy has opened up extremely attractive applications. A group led by Professor B. M. Weckhuysen (Utrecht University, The Netherlands) recently watched heterogeneous catalysts in action at high temperature. Solid catalysts have been widely used in the chemical industry, and accelerate the production of many important compounds. They are typically composed of nanometre-sized metal or metal oxide particles attached to a solid support with a high surface area. As complex structural and chemical changes take place during catalytic reactions, direct observation of the reacting catalyst is extremely important. The team employed X-ray microscopy at the Advanced Light Source, Berkeley, United States, to study the catalytic Fischer-Tropsch reaction where a solid catalyst of iron oxide particles mounted on silica is used to convert carbon monoxide and hydrogen into liquid hydrocarbons that can be used as fuels. By the use of Fe LII, III and C K absorption edges, scanning transmission X-ray imaging has revealed that during the reaction the iron oxide underwent several transformations; the initial iron oxide (Fe₂O₃) is converted into another oxide (Fe₃O₄), before iron silicates (Fe₂SiO₄) and metallic iron begin to form. Iron carbides (Fe_xC_y) appear in the final stage. For more information, see the paper, "Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy", E. de Smit et al., Nature 456, 222-225 (2008).