The Effect of Redox Treatment on the Structural, Adsorptive, and Catalytic Properties of Raney Nickel

The effect on Raney nickel catalyst of annealing in hydrogen, and of mild oxidation and subsequent reduction have been studied. The properties investigated are the structure, hydrogen adsorption, and activity for nitrobenzene and potassium maleate liquid-phase hydrogenation. Characterization involved X-ray line broadening, adsorption, and capillary condensation of Ar, XPS, and thermoprogrammed reduction. Thermodesorption studies indicate two forms of adsorbed hydrogen, one of which is a weakly bound molecular form and does not depend on treatment, while the other is strongly bound atomic hydrogen whose amount decreases with increase in the annealing temperature. Annealing in hydrogen at T ≥ 200°C causes sintering of the catalysts and a decrease in their activity. Mild oxidation leads to formation of a protective film from nonstoichiometric nickel-oxygen compounds on the Raney Ni surface, preventing it from deep oxidation in the air. A passivated catalyst can be reactivated by heating at 100-300°C in hydrogen, after which the activity for hydrogenation is on par with that of newly prepared catalyst.