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Adding an analytical technique to catalysis researchers' toolbox, scientists in Denmark have demonstrated an electron microscopy procedure capable of probing catalytic materials with atomic resolution under conditions approaching those of industrial reactions. The new method was used to elucidate the chemical function of low-concentration additives known as catalyst promoters and may be useful in enhancing catalyst performance. Decades of instrumentation and method development have provided investigators with an assortment of powerful laboratory tools useful for measuring and deducing structure, bonding, chemical state, and other properties of heterogeneous catalysts in exquisite detail. But many techniques work best under carefully controlled conditions--temperature and pressure, for example--that are very different from real-world catalytic reaction environments.
This nagging question about the scientific relevance of data recorded under unrealistic conditions has driven researchers to try to develop in situ techniques designed to catch catalysts in the act of facilitating chemical reactions.
The small number of available in situ probes has just been augmented by authors. The group has designed a transmission electron microscope (TEM) cell that can hold catalyst specimens at high temperature and in high pressures of reactive gases while probing the material's structure with angstrom-level resolution. Using the newly designed TEM facility and procedure, the authors uncovered new details concerning the location, chemical state, and function of barium used to promote a boron nitride-supported ruthenium catalyst. Used for ammonia synthesis, the catalyst's activity increases by some 2.5 orders of magnitude with the addition of just a small amount of barium. Under reaction conditions, two barium phases grow on ruthenium particles in the highly active form of the catalyst, the group reports. Combining the microscopy work with computational studies, the researchers identify the promoter phase as the one characterized by very thin patches of barium oxide that form near particle edges at certain types of crystal sites.
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