New copper-containing catalysts based on modified amorphous silica and their use in flow azide—alkyne cycloaddition
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Сopper-containing catalysts supported on amorphous silica modified by amines were prepared using the chemical reduction method. The morphology of copper particles and their chemi calstate depend on the type of the reducing agent used. The use of ascorbic acid results in the formation of monodisperse submicron Cu0 particles 200—300 nm in size, whereas Cu0 particles with a size ranging from 50 to 150 nm are formed when hydrazine hydrate was used. The morphology and chemical state of the copper particles reduced with sodium borohydride depend substantially on the amount of the reducing agent: Cu0 nanoparticles 10—15 nm in size are formed if the reducing agent is an excess, layered Cu2O plates are formed at the equimolar amount of sodium borohydride, and a decrease in the amount of sodium borohydride results in spherical Cu2O particles. All the catalysts synthesized in the flow regime showed higher activity in the catalytic cycloaddition of azides to alkynes than the commercially available copper catalysts.
Key wordsmodified silica azide—alkyne cycloaddition reaction heterogeneous catalysis copper nanoparticles flow chemistry
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