X-raying Catalysts In Action

Thanks to a specially designed reactor cell, researchers can now probe changes in the chemical composition, morphology, porosity, and other properties of individual 20-μm-sized catalyst particles as the particles mediate chemical reactions (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201204930). The study conducted by Joy C. Andrews of SLAC National Accelerator Laboratory; Bert M. Weckhuysen of Utrecht University, in the Netherlands; and coworkers demonstrates a procedure for exploiting high-energy X-ray microscopy to penetrate deeply into complex materials and resolve chemically distinct nanoscale regions within their bulk. Solid catalysts often undergo substantial changes—sometimes beneficial, sometimes detrimental—upon exposure to reactive chemicals at high temperature and pressure. Mapping those changes in three dimensions as they occur could lead to improved catalysts, but capturing the information remains challenging. To demonstrate the new method’s capabilities, the team probed a model Fischer-Tropsch C–C coupling catalyst as it was exposed to 10 atm of a mixture of H₂ and CO at 350 °C. The method pinpointed regions rich in Fe₂O₃, Fe₂TiO₅, Fe₃O₄, ZnO, and K₂O and monitored the evolution of those regions over the course of several hours.