Zn Gallate Catalysts Activated in Nanoporous Silica Nanoparticles for the Depolymerization of Poly(propylene carbonate) to Cyclic Carbonate under Mild Conditions

While the depolymerization of poly(propylene carbonate) (PPC) to cyclic propylene carbonate (PC) is environmentally valuable, efficient and recyclable catalysts for this conversion have been little explored. This work shows that the Lewis acid catalytic activity of zinc gallate (ZnG) is dramatically enhanced within nanoporous silica nanoparticles (PSiNP). The formation of ZnG in the presence of PSiNP resulted in incorporating ZnG into PSiNP. While both ZnG and PSiNP were ineffective in the depolymerization of PPC to PC, the ZnG/PSiNP-1 nanocatalyst with an optimal ZnG loading exhibited excellent activity at 90 °C, achieving a TON of 50 and a TOF of 8.3 h –1, and demonstrated recyclability over five runs with PC yields retained of 96–99%. The activated Lewis acid performance of the ZnG/PSiNP-1 nanocatalyst is attributed to the enhanced defective surface Zn sites within the nanospace.