The surface cobalt concentration in the powder bimetallic Ni-Co catalysts (ratio Co/Ni ≈ 0.25) was shown by X ray photoelectron spectroscopy to be 2-4 times that of the volume content. Both Ni and Co exist in mixed valent states, viz., M 0 and M 2+ , even after catalyst reduction. After ethyl acetoacetate hydrogenation, the cobalt content on the surface increases 16 times compared to that in the bulk. In addition, the metals are partially oxidized, and the amount of Ni 0 and Со 0 in the surface layers of the catalyst decreases 2-3 times. It was assumed that the increase in the cobalt content indicates an increase in the amount of cobalt complexes that involve the modifier, substrate, and reaction product, and which shield the nickel active sites. As a result, the enantioface differentiating ability of the catalyst decreases.Key words: X ray photoelectron spectroscopy, enantioselective catalytic hydrogenation, bimetallic Ni-Co catalysts, ethyl acetoacetate, modification, optically active ethyl hydroxy butyrate.We have previously 1-4 found that the bimetallic powder Ni-Co catalysts and intermetallic LaNi-Co catalysts modified by RR (+) tartaric acid (HOOC-CH(OH)-CH(OH)-COOH) are active in the asymmetric hydrogenation of the С=О bond of ethyl ac etoacetate (EAA) in (-) ethyl β hydroxybutyrate (EHB) with an optical yield of (ее) 41-54% (Scheme 1).Therefore, it was of interest to use XPS and trace how the catalyst modification by RR (+) tartaric acid and EAA hydrogenation affects electronic states of nickel and co balt on the catalyst surface.
ExperimentalThe powder Ni-Co catalyst containing 20 wt.% Co and 80 wt.% Ni (atomic ratio Co/Ni ≈ 0.25) were prepared by evapo Scheme 1 EAA EHB
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