Abstract
Controlling the reaction selectivity of a heterobifunctional molecule is a fundamental challenge in many catalytic processes. Recent efforts to design chemoselective catalysts have focused on modifying the surface of metal nanoparticle materials having tunable properties. However, precise control over the surface properties of base-metal oxide catalysts remains a challenge. Here, we show that green modification of the surface with carboxylates can be used to tune the ammoxidation selectivity toward the desired products during the reaction of hydroxyaldehyde on manganese oxide catalysts. These modifications improve the selectivity for hydroxynitrile from 0 to 92% under identical reaction conditions. The product distribution of dinitrile and hydroxynitrile can be continuously tuned by adjusting the amount of carboxylate modifier. This property was attributed to the selective decrease in the hydroxyl adsorption affinity of the manganese oxides by the adsorbed carboxylate groups. The selectivity enhancement is not affected by the tail structure of the carboxylic acid.
Highlights
Controlling the reaction selectivity of a heterobifunctional molecule is a fundamental challenge in many catalytic processes
The effect of carboxylic acid surface modification on the adsorption of benzyl alcohol on manganese oxide (MnOx) was investigated with Fourier transform infrared (FT-IR) spectroscopy by adding benzyl alcohol to MnOx followed by evaporation of the unadsorbed species (Supplementary Figs. 1 and 2)
In summary, we have shown that carboxylate-modified MnOx can be used as an efficient catalyst for the selective ammoxidation of hydroxyaldehyde under mild conditions
Summary
Controlling the reaction selectivity of a heterobifunctional molecule is a fundamental challenge in many catalytic processes. We show that green modification of the surface with carboxylates can be used to tune the ammoxidation selectivity toward the desired products during the reaction of hydroxyaldehyde on manganese oxide catalysts. Surface modification has been clearly recognized as an ideal technique for controlling the selectivity, enabling an enhanced reactant orientation or fine-tuning of the active sites on the catalyst surface[7,8,9,10,11,12]. Owing to their flexibility and versatility, organic modifiers represent an important set of compounds for the surface modification of noble metal nanoparticles[11]. MnOx modified with carboxylic acids exhibits chemoselectivity in hydroxynitrile synthesis via aerobic ammoxidation of hydroxyaldehyde
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