The role of lithium tetrahydroaluminate in the formation of nanodimensional nickel hydrogenation catalysts

The principal stages of formation and the nature of nanoparticles of the reduced nickel formed in the system Ni(acac)(2)-LiAlH(4) and catalytically active in hydrogenation catalysis are established. The reduction of Ni(II) to Ni(0) under the action of LiAlH(4) is shown: the Ni(0) atoms form clusters whose growth results in the formation of nanoparticles of the average size of 2-3 nm. Being adsorbed on the surface, the tetrahydroaluminate anions act as stabilizers of the nickel nanoparticles. Besides, the tetrahydroaluminate anions and the products of catalytic decomposition of LiAlH(4) (Li(n)Al(n+2)H(2n+2)), by occupying free positions on the surface, can be active as catalytic poisons. Highly efficient hydrogenation catalysts with well reproduced properties are obtained by the reaction of the products formed in the system Ni(acac)(2)-LiAlH(4) with proton-donating compounds (water, alcohols, weak acids). Alcoholysis (hydrolysis) of the surface compounds results in their dissolution, release of the centers of the catalytically active nickel nanoparticles and their stabilization. (C) 2011 Elsevier B.V. All rights reserved.