Catalysis by amorphous metal alloys. Part 4.—Structural modification towards metastable states and catalytic activity of amorphous NI62B38 ribbon alloy

Abstract

Alloys in the three different states, i.e. precrystallisation, metastable and stable crystallised states have been prepared by the structural modification of amorphous Ni₆₂B₃₈ ribbon alloy by thermal treatment. The catalytic activities of the alloys in these states for the hydrogenation of ethene and hydrogenolysis of ethane and cyclopropane have been correlated to the surface states which were characterised by XRD, DTA, SEM, ESCA, electrical resistivity and hydrogen chemisorption measurements. The maximum catalytic activity observed in the precrystallisation state is caused by the structural relaxation (rearrangement in short range) involving the change in the strength of the chemical bonding among nickel, boron and oxygen atoms. The aggregation of nickel atoms and the increase in the surface content of boron oxides, which is observed in the metastable state, reduce the number of active sites change the electronic state of surface nickel and bring about a great decrease in the catalytic activity. Further aggregation eventually brings about the crystallisation of the bulk alloy, leading to very low catalytic ability.