(647b) Iridium and Rhodium Pair-Site Catalysts Supported on MgO

Supported pair-site catalysts are the simplest form of supported metal clusters, and fundamental investigations of these materials are beginning to provide valuable resolution of the roles of neighboring metal centers in catalysis. However, this field is only in its infancy, hindered by the challenge of synthesizing supported pair sites to be uniform and by the challenge of removing ligands from the supported species remaining from organometallic binuclear precursors. Here we present results characterizing stable iridium pair-sites and rhodium pair-sites on MgO synthesized from M₂(μ-OMe)₂(COD)₂ (M = Ir or Rh; OMe = methoxy; COD = cyclooctadiene), respectively. The surface species were characterized with infrared and X-ray absorption spectroscopies and HAADF-STEM. By removing the ligands while retaining the pair-site structures of the rhodium catalysts, for example, we made catalysts with two orders of magnitude higher activity for ethylene hydrogenation reaction than their single-site analogues. The neighboring metal centers evidently by accelerate hydrogen activation. The class of stable metal pair-site catalysts offers the prospects of selective catalysts for numerous reactions.