Hydrogenation of fullerenes C 60 and C 70 in the presence of hydride-forming metals and intermetallic compounds

Abstract

Hydrogen-absorbing intermetallics generate very pure and chemically active hydrogen. In this communication we report on the use of this property for hydrogenation of fullerenes (C 6 0, C 70) in solvent-free solid-phase systems. Fullerene hydrides with high contents of hydrogen (24–26 H atoms per fullerene molecule) have been obtained by hydrogenation of solid-phase mixtures of fullerite with either intermetallic compounds LaNi 5, LaNi 4.65Mn 0.35, CeCo 3 or V and Pd metals in relatively mild conditions, a hydrogen gas pressure of 1.0–2.5 MPa and 573–673 K. The mechanochemical treatment of initial solid compositions and repeated `hydrogenation–dehydrogenation' cycling are both essential to ensure the highest performance of the systems studied, thus emphasizing the importance of a highly developed contact surface between two solid phases and indicating a probable formation of metal–carbon bonds. The fullerene hydrides thus obtained decompose in all cases at 800 K, liberating hydrogen gas. After further heating up to 1000 K vanadium reacts with fullerenes yielding a cubic phase of vanadium carbide. Intermetallics under the same conditions react with fullerenes by disintegrating their cage and producing a metallic phase of the corresponding 3d metal. In the case of palladium that reaction is not observed and the fullerene remains intact. The nature of the transformations in the mechanical mixtures of fullerite with metals or intermetallics is discussed.