Selective Stereochemical Catalysis Controlled by Specific Atomic Arrangement of Ordered Alloys

Unprecedented surface stereochemistry governed by specific atomic arrangement of intermetallic compounds (ordered alloys) is shown. Hydrogen-mediated cis–trans alkene isomerization is selectively catalyzed without overhydrogenation to alkanes by Rh-based intermetallic compounds displaying an orthorhombic Pnma structure such as RhSb. Multiple characterization techniques combined with DFT calculations revealed that (2 1 1), (0 2 0), and (0 1 3) planes comprising one-dimensionally aligned Rh rows separated by Sb atoms (1D-planes) dominated RhSb surfaces. Systematic DFT calculations indicated that geometric constraints of these 1D-planes and steric hindrance from one alkyl group of cis-alkene limited hydrogen access to the alkenyl carbon to one direction, enabling one-atom hydrogenation for isomerization, but inhibiting two-atom hydrogenation for overhydrogenation.