Research Of Pickering Emulsion For Static Aqueous-Organic Biphasic Reactions

Green and sustainable chemistry is the fundamental goal of chemical development. Aqueous-organic biphasic reaction is widely used as a green chemical synthesis. However, the reaction system is immiscible, existing a huge mass transfer resistance, and it usually needs vigorous stirring to obtain higher reaction efficiency. Prolonged vigorous stirring not only consumes enormous energy, but also frequent collision causes fragmentation of the catalyst, which can eventually lead to problems on many processes. Therefore, seeking a simple, efficient, universal static catalytic reaction system becomes a challenging and meaningful topic.The paper studies the Pickering emulsion for static aqueous-organic biphasic reactions based on its potential applications in catalysis. In this paper, nanoparticles were modified with hydrophilic triaminesilane and hydrophobic octylsilane, then noble metal Pd was loaded on the modified particles to obtain Pd/SM-1. Pd/SM-1 was characterized with TEM and elemental analysis, contact angle, N2 sorption. The catalytic activity was examined by the model reaction of nitro-toluene reduction.Our experimental results show that the reaction efficiency of the static Pickering emulsion system is greatly improved and is nearly 100 times of the conversion of the static biphasic system, which has a higher order of magnitude about "phase-boundary" catalysis system in recently reported literature. The inner relationship between catalytic efficiency and the size of droplets was investigated by two series of kinetic experiments. It demonstrates that short diffusion distances, arising from the compartmentalization of densely packed droplets, play an important role in boosting the catalytic efficiency. Compared with the stirred Pickering emulsion system and conventional aqueous-organic system by investigating many substrates, the static Pickering emulsion system exhibits the comparative even much higher efficiency. To further verify the application and efficiency of static emulsion catalytic reaction, the static model of Pickering emulsion had been expended to epoxidation of allylic alcohol. Hydrogen peroxide as a oxidant, POM as the catalyst on epoxidation of allylic alcohol, which is a typical aqueous-organic biphasic reaction. Experimental results show that POM/SM-3 exhibited highly catalytic activity under the static emulsion system and its conversion is comparative or slightly higher than the reaction under stirring with the POM/SM-4 as a catalyst. The result shows that the model of static Pickering emulsion system has a application in catalytic reactions.