Pd and Pd Based Alloy Nanoparticles as Visible Light Photocatalysts for Coupling Reactions under Ambient Conditions

Abstract

Photocatalysis is a rapidly emerging research field, with great potential for a wide range of applications, since it can utilize solar energy. Solar light has received much attention as it is the most abundant and cleanest renewable energy source, which produces no pollution. Therefore, synthesis of fine chemicals with solar light at ambient temperature is of the utmost interest. Nonetheless, it is still a challenge to devise new catalysts, which exhibit high activity under the full solar spectrum and moderate conditions. This project aimed to develop novel metal nanoparticle photocatalysts for several important organic reactions under visible light irradiation.The prospect of visible light irradiation driving chemical synthesis may extend the scope of organic synthesis via a more controlled, simplified, and greener process.Firstly, we focused on a systematic study of palladium nanoparticle-catalysed cross-coupling and homo-coupling reactions under visible light irradiation. These metal nanoparticles strongly absorb the light primarily through interband electronic transitions. The excited electrons interact with the reactant molecules adsorbed on the metal particle surface to accelerate coupling reactions. Therefore, the rate of the catalysed reaction depends on the concentration and energy of the excited electrons, which can be increased by increasing the light intensity. Nevertheless, mild reaction conditions, such as ambient temperatures and pressures in the reaction systems make it more environmentally benign.Secondly, we incorporated palladium metal component with silver nanoparticles to obtain silver-palladium alloy nanoparticles (Ag-Pd alloy NPs): which can catalyse the reductive coupling of nitroarenes reactions by light irradiation at ambient conditions. This provided a general indication for the possibility of the design of an alloy nanoparticle photocatalysts using silver with other transition metals, such as nickel, cobalt. This photocatalytic process is a more efficient and greener approach than thermal reactions for the reductive coupling of nitroarenes, and this improving the product yield by avoiding over-reduced products. The alloy nanoparticles strongly absorb light, energizing the conduction electrons of silver, which migrate to palladium sites at the alloy nanoparticle surface because of charge redistribution between the two metals. The alloying affects the charge redistribution iv between silver and palladium, which enhances interaction between reactant molecules and the nanoparticles. The reduction activity is sensitive to the intensity of the irradiation, the wavelength of the incident light, metal molar ratio and atmosphere of the reaction. When the molar ratio of silver and palladium in alloy nanoparticles is nearly equal, the catalysts exhibited the best performance.Finally, supported gold-palladium alloy nanoparticles (Au-Pd alloy NPs) on zirconium dioxide (ZrO 2 ) can act as efficient visible light photocatalysts for reductive N-alkylation of nitrobenzene with benzyl alcohol. ...