Synthesis and Catalytic Application of Ag44 Clusters Supported on Mesoporous Carbon

4-(Fluorophenyl)thiolate-protected Ag-44 clusters (Ph4P)(4)[Ag-44(SC6H4F)(30)] were calcined on mesoporous carbon (MPC) under vacuum at 300-500 degrees C for 2 h. X-ray absorption spectroscopy, transmission electron microscopy, and thermal-desorption mass spectrometry revealed that sulfur-free Ag-44 clusters were successfully produced by the calcination of [Ag-44(SC6H4F)(30)](4-) at 300 degrees C, in sharp contrast to the formation of silver sulfide nanoparticles by the calcination of dodecanethiolate-protected Ag nanoparticles (3.0 +/- 0.6 nm). Ag-44/MPC was applied in the catalytic dehydrogenation of ammonia-borane (NH3BH3) as a test reaction. It turned out that the Ag-44/MPC catalysts produced 1 equiv of H-2 from NH3BH3 but only in the presence of O-2 (turnover frequency 1.9 x 10(3) h(-1) Ag atom(-1)). Given that nanoparticles of other metals (Pt, Pd, Rh, Ni, or Ru) produced 3 equiv of H-2 under an inert atmosphere, this result indicates that the Ag-44/MPC-catalyzed dehydrogenation of NH3BH3 proceeds by a different mechanism from that on other nanoparticles.