Molecular Chemistry of Bimetallic Clusters on the Basic γ-Al2O3 Surface: Synthesis, Reactivity, and Catalytic Activity of - and Related Structures

Article abstract of DOI:10.1021/ja00259a023

, , , and were synthesized and characterized spectroscopically, and their reactivities with the basic -OH groups on the surface of γ-Al2O3 were investigated, the surface species being characterized by infrared and UV-vis spectroscopy and extraction of anions.Surface-bound anions were formed by adsorption of the salts.Alternarively, the surface-bound ion pair ^- was formed from by deprotonation on the surface; the anion is bonded to the surface through a bridging carbonyl group interacting with a surface Lewis acid site (Al³⁺ ion).This surface anion is readily converted at 50-70 deg C into ^-, evidently by reacting with surface water.The latter anion is also formed by deprotonation of on the surface. ^- is the precursor of a catalyst for isomerization of but-1-ene to give cis- and trans-but-2-ene at 53-77 deg C.The catalytic activity and the Langmuir-Hinshelwood kinetics parameters were the same, whether the catalyst was prepared by adsorption of or from , converted into ^- and then into ^-.The catalyst was stable for >2000 turnovers.Infrared spectra showed that ^- was the predominant surface organometallic species on the working catalyst.When the catalyst was used instead for ethylene hydrogenation, the activity changed as the cluster was degraded; metal particles were formed, and these and/or mononuclear metal complexes are the likely catalytic species.