Preparation Of Intelligent Hydrogel-supported Pd,Pd/Cu Catalysts And Their Application In Catalysis

It is common knowledge that palladium is a highly active and selective catalyst in many organic reactions. However, the Pd black is easily formed in homogenous reactions so that the selectivity and efficiency of the catalyst deceased. In order to address this problem, the heterogeous Pd catalyst is developed.The intelligent hydrogels are three-dimensional networks of cross-linked polymer, which exhibit reversible volume change in response to small changes in the external environment. Of all the hydrogels, the poly (N-isopropylacrylamide) (PNIPAM) hydrogel, a typical and widely studied polymer for its thermosensivity due to the presence of both hydrophilic amide groups and hydrophobic isopropyl groups in its side chains. Currently, the based-PNIPAM hydrogels are used in a wide range of applications such as drug delivery, enzyme immobilized, bioseparation and tissue engineering. The ligands or pendants can be introduced in the backbone of the hydrogel and can thus immobilize catalysts. As support, the hydrogel can not only disperse catalyst well for its matrix but also can as nanoreactor for its networks. The based-PNIPAM hydrogels supported catalysts deswell with increasing temperature in reactions and the reactant molecules can be encapsulated in the matrix of the hydrogel at the same time. Moreover, lots of water in the matrix of the porous networks of the hydrogel is squeezed out result in every pore is a concentrated nanoreactor, in which a homogeneous-like reaction system was formed with high-efficiency. After reaction finished, the products can be released by reswelling of the hydrogel and then the catalyst can be separated and recovered directly from the solution. It can be seen that the intelligent hydrogel-supported catalyst is efficiency, pure reaction system with "concentrated effect", green solvent, handy separation. Herein we designed and prepared intelligent hydrogel-supported Pd, Pd/Cu catalysts and evaluate their catalytic activities by catalyzing Heck and Suzuki reactions in water. The main contents are summarized as followed:1. The thermosensitive and pH-sensitive hydrogel has been prepared with NIP AM,4VP and KAA comonomers by simultaneous free radical cross-linking polymerization, characterized by FT-IR, SEM. The hydrogel with a porous structure and quick responsiveness is obtained by adjusting the content of crosslinking agent, relative content of 4VP to KAA and total content of 4VP and KAA.2. The intelligent hydrogel-supported Pd (â…¡) catalyst has been prepared, characterized by SEM, TEM, XRD and AAS. The catalytic activity is evaluated by catalyzing Heck and Suzuki reactions in water and the results show that it is efficiency and stability and can be recycled 6 times with satisfied yield.3. The intelligent hydrogel-supported Pd (â…¡)/Cu (â…¡) bimetallic catalyst has been prepared, characterized by SEM and XRD. The catalytic activity is evaluated by catalyzing Heck and Suzuki reactions in water. The results indicate that the bimetallic catalyst has a "cooperative effect" and is efficient for Suzuki reaction.