The structure of catalytically active edges of industrial molybdenum disulfide nanocrystal catalysts has been determined on the atomic scale by a team led by researchers at Danish catalyst manufacturer Haldor Topsøe (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201103745). Such catalysts mediate hydrodesulfurization (HDS), a refinery process used for stripping sulfur from fuel feedstocks. Earlier studies showed that HDS proceeds exclusively along certain crystal edges in which the edge structure differs from that of the bulk lattice. Until now, researchers have studied model catalysts to determine the structure of those active edge sites, knowledge of which could be useful for improving catalysts. In contrast to model samples, which were prepared in vacuum on single-crystal supports to simplify analysis, the new samples were prepared in an industrial style via wet chemistry on high-surface-area supports. By using atomic-resolution microscopy, the team found that the outermost edge of the “realistic” catalyst consists of a one-atom-thin row of sulfur atoms (shown, purple spots). Individual molybdenum atoms and a two-atom-thick row of sulfur atoms (white caps and adjacent shorter peaks, respectively) line up just behind the outermost edge, the team reports.