848
J. Org. Chem. 1982,47, 848-851
YatesUand Figueras and co-workers1° observed the effects of different supports (Al,O,, SiO,, Ti02,MgO, and zeolite) for CO adsorption on supported Ni. In our comparative studies of SMAD vs. conventional Ni/support catalysts we have found that electronic support effects are minimal for the SMAD catalysts but are significant for the conventional systems. Thus, the Ni-support interactions are definitely different in the two systems. For an explanation of this difference, recall that during low-temperature clustering of nickel atoms in organic media a competition exists between Ni-Ni bond formation (cluster growth) and reaction of the forming clusters with the organic medium. This process leads to extensive C-C and C-H cleavage of alkanes at temperatures even as low as -130 0C,2and a great deal of carbonaceous material is incorporated into the final clusters. Scott and co-workersm and we2have demonstrated that the final Ni clusters are surrounded by a protective carbonaceous layer. Arenes react similarly to alkanes with the bare Ni clusters. However, at low temperatures (
