N-Monoalkylation of Amines with Alcohols by Tandem Photocatalytic and Catalytic Reactions on TiO2 Loaded with Pd Nanoparticles

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• 作者：Yasuhiro Shiraishi ; Keisuke Fujiwara ; Yoshitsune Sugano ; Satoshi Ichikawa ; Takayuki Hirai
• 刊名：ACS Catalysis
• 出版年：2013
• 出版时间：March 1, 2013
• 年：2013
• 卷：3
• 期：3
• 页码：312-320
• 全文大小：592K
• 年卷期：v.3,no.3(March 1, 2013)
• ISSN：2155-5435

文摘

TiO₂ loaded with Pd particles (Pd/TiO₂), when photoirradiated at 位 > 300 nm in alcohol containing primary amine, efficiently promotes N-monoalkylation of amine with alcohol, producing the corresponding secondary amine with almost quantitative yields. This occurs via tandem photocatalytic and catalytic reactions: (i) Pd-assisted alcohol oxidation on the photoactivated TiO₂, (ii) condensation of the formed aldehyde with amine on the TiO₂ surface, and (iii) hydrogenation of the formed imine by the surface H atoms on the Pd particles. The rate-determining step is the imine hydrogenation, and the reaction depends strongly on the size of the Pd particles. The catalyst with 0.3 wt % Pd, containing 2鈥?.5 nm Pd particles, shows the highest activity for imine hydrogenation, and smaller or larger Pd particles are inefficient. Calculations of the number of surface Pd atoms based on the cuboctahedron particle model revealed that the Pd atoms on the triangle site of Pd particles are the active site for hydrogenation. Larger Pd particles contain a larger number of these Pd atoms and are effective for imine hydrogenation. Alcohols, however, are strongly adsorbed onto the larger triangle site and suppress imine hydrogenation. As a result of this, the catalyst with 2鈥?.5 nm Pd particles, which contains a relatively larger number of Pd atoms on the triangle site and does not promote strong alcohol adsorption, shows the highest activity for imine hydrogenation and promotes efficient N-monoalkylation of amine with alcohol under photoirradiation.

Keywords:

photocatalysis; titanium dioxide; nanoparticles; palladium; N-alkylation