Catalytic properties of intermetallic hydrides in liquid-phase hydrogenation processes

摘要

Studied is the effect of the composition of LaMi_(5-x)Cu_x (x = 0-5) intermetallics on physicochemical and catalytic properties of their hydrides in liquid-phase reduction of nitrobenzene. The reduction is shown to involve hydorgen dissolved in hydrides. By surface adsorption, a solvent influences the kinetics of hydrogen sorption-desorption and the reaction temperature barrier. A characteristic property of the process run in water is the pronounced rate increase in the process of reduction of successive nitrobenzene portions. Auger electron spectroscopy and XPS data, and measurement of magnetization of the samples point to the surface segregation of alloy components to occur under the impact of reaction medium. As a result of segregation, the surface of LaNi_5H_n is enriched with nickel, while that of LaNi_(5-x)Cu_xH_n is enriched with nickel and copper forming Ni-Cu centress-more active than nickel ones. On the developed catalysts, hydrogen sorption-desorption rates increase whereas the reaction temperature barrier decreses. The composition of catalytically active surface and the kinetics of hydrogen sorption-desorption processes are the main factors determining the catalytic activity of intermetallic hydrides.