Preparation Of PH-Responsive And Interface Active SiO₂ Material And Research Of Catalyst Activity

Green chemistry, as the core to eliminate pollutants, remove security risk and save resource at the source, has been caused widespread concern at home and abroad during the last 20 years. It is far-reaching significance to take water as the reaction medium, which is green solution and possess the highest natural abundance. However, organic matter and gas have poor water solubility, exist a huge mass transfer resistance thus severely reduce aqueous phase reaction efficiency. Adding extra additives such as cosolvent, surfactant and phase tansfer substance to increase water solubility of organic matter and gas, can simultaneously cause trouble for product separation and purification. In recent years, with the emergence of solid particles-stabilized Pickering emulsion system and Pickering foam system, the problem of low aqueous reaction efficiency was solved to some extent, while it is still a great difficulty in separating of solid catalysts.In order to settle the problems of poor water solubility of organic and gas reactants, product separation and catalyst recycling in heterogeneous catalysis system, in this paper, we take pH-responsive hydrophilic triaminesilane and hydrophobic octylsilane to modify SiO2 nanoparticles, then Pd nonaparticles were loaded on the modified particles to obtain pH-responsive solid catalyst. The obtained solid catalyst was characterized with TEM, elemental analysis, contact angle, N2 sorption and MAS NMR. The solid catalyst was used to stabilize emulsion and foam, these Pickering emulsion system and Pickering foam system have larger reaction interface area and can address emulsification/demulsification or foaming/defoaming by tuning system pH, then the products can be separated and catalyst be recycled.Our experimental results show that a hydrogenation Pickering emulsion system exhibits fivefold reaction rate enhancement effects in comparison to the conventional biphase reaction. Its demulsification on command not only enables facile separation of organic product but also allows the nanocatalysts to be recycled at least 15 times. Similarly, a hydrogenation in a Pickering foam system exhibits catalysis efficiency enhancement effects of up to 6 times higher than conventional three-phase reactions. At the end of reaction, the Pickering foam systems can be destroyed with acid. Such a cycle can be repeated without loss of catalysis efficiency. In view of the fact that both pH-responsive Pickering reaction systems are variable, our strategy may be more generally accessible to efficient and green multiphasic catalysis processes.