Functions of organoaluminum and proton donor compounds in the formation and functioning of nanosized Ziegler-type nickel-containing hydrogenation catalysts

Abstract

The turnover frequency (TOF) and turnover number (TON) in styrene hydrogenation have been determined for catalytic systems based on Ni(acac)2 · nH2O (n = 0, 0.5, and 3.0), Ni(COD)2 (COD = cycloocta-1,5-diene), and AlEt3 at different Al/Ni molar ratios. The amount of water of crystallization determines the TON and TOF of the nickel catalysts and their dependence on the Al/Ni ratio. The TON and TOF of the nickel catalysts are markedly increased by the introduction of an optimum amount of a proton donor. The model of the ligand shell stabilizing the nickel nanoparticles has been refined. The refined model provides an explanation for the activating action of proton donor compounds in the formation of the hydrogenation catalysts. The functions of the organoaluminum compounds are not limited to Ni(II) reduction to Ni(0); they are also involved in the stabilization of the nickel-containing nanoparticles.