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A silica-supported copper (Cu/SiO2) catalyst containing highly dispersed Cu nanoparticles was prepared via a crown-ether-assisted impregnation method. A 12-crown-4-ether-assisted Cu/SiO2 catalyst outperformed several Cu/SiO2 catalysts prepared with various organic additives in the dehydrogenation of 2,3- and 1,4-butanediol. It was found that the catalytic activity, i.e., the formation rate of acetoin from 2,3-butanediol and that of γ-butyrolactone from 1,4-butanediol, was proportional to the copper surface area.

The vapor-phase hydrogenation of acetoin (AC) to 2,3-butanediol (2,3-BDO) was investigated over SiO2-supported Ni (Ni/SiO2) catalysts prepared by impregnation assisted with organic additives. Among 14 catalysts with different organic additives, the Ni/SiO2 prepared with citric acid (CA) was found to show the highest activity. The Ni/SiO2 catalyst prepared with CA has a much higher hydrogenation ability for AC and a higher selectivity to 2,3-BDO than typical noble metal catalysts. In addition, it was preferable that the hydrogenation of AC was conducted at a low temperature in the hydrogenation-dehydrogenation equilibrium between AC and 2,3-BDO to provide 2,3-BDO selectively.

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