Adsorption and reaction of ethyl pyruvate (EtPy), a model reactant in chiral hydrogenation of α-ketoester on Pt/γ-Al 2 O 3 were studied by IR spectroscopy. In vacuum and Ar flow at room temperature, several side reactions of EtPy are detected by IR spectroscopy: decomposition on Pt, aldol condensation, and hydrolysis on γ-Al 2 O 3 . When the quantity of adsorbed EtPy is small, CO formed from EtPy decomposition on Pt can react with the hydroxyl groups of Al 2 O 3 to generate formate species. It is very interesting to find out that H 2 not only acts as a reactant for the hydrogenation reaction but also plays an important role in suppressing the side reactions of EtPy on Pt/γ-Al 2 O 3 catalysts. The suppressing effect of H 2 is not observed on γ-Al 2 O 3 alone. The function of spilt-over H atoms in suppressing these side reactions was confirmed and discussed. Adsorbed cinchonidine (CD) alone cannot suppress the condensation and hydrolysis of EtPy on γ-Al 2 O 3, but the decomposition of EtPy on Pt can be suppressed by absorbed CD. The coexistence of CD and H 2 thoroughly inhibits all of these side reactions of EtPy on Pt/γ-Al 2 O 3 . Adsorbed CD can help hydrogen to avoid site-blocking with side-reaction products then facilitate hydrogenation on Pt, which may be a reason for the rate acceleration effect of the adsorbed CD.
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Liu et al. (2006) studied this question.
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