Supported Lewis acid catalysts for the selective depolymerization of polysiloxanes

Abstract

A series of supported Lewis acid catalysts (InCl₃@TiO₂, InCl₃@Al₂O₃ and ZnCl₂@TiO₂) were prepared via an impregnation method to overcome the low selectivity and poor recyclability of homogeneous Lewis acids during the depolymerization of waste polysiloxanes. The physicochemical properties of all as-prepared catalysts were comprehensively characterized by XRD, Raman spectroscopy, SEM-EDS, Py-FTIR and N₂ physisorption (BET) aiming to establish the correlation between acid site distribution and catalytic activity. Hexamethyldisiloxane (HMDSO) was chosen as a model compound to evaluate the catalytic performance toward the alcoholysis depolymerization of polysiloxane. Under the optimized reaction conditions (140 °C, 4 h), InCl₃@TiO₂ delivered an HMDSO conversion of 65.2% and an exceptionally high selectivity of 98.8% toward high-value ethoxytrimethylsilane. Six successive cyclic tests verified that InCl₃@TiO₂ possessed excellent structural stability and satisfactory recyclability with no obvious decline in catalytic performance. Furthermore, the developed catalytic system was applicable to a wide range of polysiloxane substrates and various alcohol nucleophiles. This work proposes a facile heterogeneous catalytic strategy for resource recovery from waste organosilicon materials, which provides fundamental guidance for the industrial upcycling of discarded silicone polymers.