Abstract
Glycine is an important fine chemical used in many fields, and the traditional synthetic methods like Strecker synthesis and ammoniation of chloroacetic acid use highly toxic reagents or produce equal molar byproducts. Herein, selective aerobic oxidation of monoethanolamine (MEA) to glycine using Au catalysts supported on various supports, including Al2O3, SiO2, TiO2, ZnO, and ZrO2, was investigated and the correlation between acid-base properties of the catalysts and catalytic performance was established. Catalysts with higher base content exhibited higher initial activity and that with lower acid content gave higher glycine selectivity. The influence of preparation methods was revealed using Au/ZrO2 with the best catalytic performance and it was demonstrated that the presence of polyvinyl alcohol (PVA) has a significant promoting effect. In-situ FTIR and 1H NMR analysis revealed that the hydrogen bonds between PVA and MEA can enhance adsorption of MEA on catalysts, resulting in doubled turnover frequency (TOF) and improved MEA conversion; and the preferential hydrogen bonds between the amino group of MEA and the hydroxyl of PVA can prevent the coordination of amino group with Au nanoparticles, favoring reaction of the hydroxyl group of MEA on the active sites, accounting for the enhanced glycine selectivity. The reaction conditions were optimized and the optimal yield of glycine was 95%.
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