Biochar as supporting material for heterogeneous Mn(II) catalysts: Efficient olefins epoxidation with H2O2

Abstract

A novel type of hybrid catalytic materials [MnII-L@BC] has been developed using biochar (BC) as support material for covalent grafting of a MnII Schiff-base catalyst (MnII-L). The hybrid [MnII-L@BC] materials have been evaluated for an important catalytic process, epoxidation of olefins using H2O2 as oxidant. A number of different substrates were used, with cyclohexene achieving the highest yields. When compared to the non-grafted, homogeneous MnII-L, the hybrid catalysts [MnII-L@BC] show a significant enhancement of the catalytic efficiency i.e. as documented by the increase of Turnover Numbers (TONs) (826 for [MnII-L-SS550ox] and 822 for [MnII-L-SW550ox]) and Turnover Frequencies (TOFs) (551 h−1 for [MnII-L-SS550ox] and 411 h−1 for [MnII-L-SW550ox]). The interfacial catalytic mechanism and the role of the BC support have been analyzed by Raman and Electron Paramagnetic Resonance spectroscopies. Based on these data we discuss a mechanism where the high efficiency of the hybrid materials involves the biochar carbon layers acting as promoters of the substrate and products kinetics. To a broader context, this work exemplifies that biochar-based hybrid materials are potent for oxidative catalysis technologies.