Abstract:

A phosphine-functionalized polystyrene microcapsule with hundreds of microns in size was prepared using a microfluidic platform. The size distribution was narrow and the average size could be adjusted in the range 300-400 μm. The morphology and composition of the microcapsules were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma atomic emission spectroscopy. The results verified the effectiveness of the strategy we proposed for preparing uniform microcapsules with stable Pd immobilization. A Suzuki coupling reaction between aryl halides and phenylboronic acid was used as the model to evaluate their catalytic activity after Pd(PPh₃)₄ immobilized onto the microcapsule. It was found that the catalytic activity of microcapsule-supported Pd was always higher than that of the corresponding homogeneous catalyst, and was similar with that of the literature reported microcapsule-supported catalyst with about 7-8 μm particle size. Microcapsule-supported Pd with microcapsules of hundreds of microns in size, being easy to recover, showed good reusability and undetected active species loss, its productivity effect and controllability of the microcapsule-supported Pd catalyst were also expected to benefit from continuous preparation using the microfluidic platform. Moreover, they could be potentially exploited in a fixed-bed reactor with high catalyst density and good mechanical stability.

Key words: Microcapsule, Palladium, Supported catalyst, Microfluidic technique, Particle size control, Suzuki coupling reaction, Catalytic activity