Flow fabrication of a highly efficient Pd/UiO-66-NH2 film capillary microreactor for 4-nitrophenol reduction

A novel Pd/UiO-66-NH2 film quartz capillary microreactor was fabricated by a flow method in which fine control of the film thickness and metal loading could be readily achieved by adjusting flow time. Firstly, UiO-66-NH2 film as the catalyst support layer was synthesized on the inner wall of the quartz capillary employing a twostep procedure including surface modification with 3-aminopropyltriethoxysilane (APTES) and the subsequent flow growth of UiO-66-NH2 film. Secondly, Pd nanoparticles (NPs) were uniformly and firmly immobilized in the UiO-66-NH2 film as active catalysts using the same flow method. Such Pd/UiO-66-NH2 film capillary microreactor was applied as catalyst for the reduction of 4-nitrophenol (4-NP) to produce 4-aminophenol (4-AP) under continuous flow conditions. Nearly 100% conversion was achieved under mild conditions in a short residence time. Importantly, no deactivation was observed for this microreactor during the continuous flow reaction of 100 h, indicating its excellent stability due to the firm immobilization of active Pd NPs in UiO-66-NH2 film.