A green approach for preparation of surfactant embedded sulfonated carbon catalyst towards glycerol acetalization reaction
The green synthesis of heterogeneous catalysts often required solid state reaction pathway. In this work, the cationic surfactant (CTAB; Cetyl trimethyl ammonium bromide) embedded sulfonated carbon catalyst was prepared by a sustainable route aiming to have a controlled surface hydrophobicity and acidity for glycerol acetalization reaction. The main objective of this study was tuning of hydrophobicity and acid site density either by adding a cationic surfactant or by changing the carbon sulphur ratio. The as-synthesized catalysts were characterized by XRD, N2 adsorption/desorption, SAXS, FESEM, FTIR, Pyridine-IR, High temperature DRIFT IR, TGA, 13C NMR, Raman, and XPS techniques. The incorporation of cationic surfactant (CTAB) reduces surface area but induced acid site density to a greater extent. The bonding between surfactant (CTAB) and surface hydroxyl groups was elucidated by XPS analysis. The DRIFT IR implied that the -SO3H groups are strongly bonded to the carbon network while the less water mass loss in TGA showed the substantial improvement of surface hydrophobicity after modification with the surfactant. Moreover, the combination of acid density and hydrophobicity are playing a key role in attaining around 90 % glycerol conversion and 98% solketal selectivity under ambient conditions. Notably, the characterizations of the used catalysts revealed that the loss of activity is mainly related to the drop of hydrophobicity due to the loss of surfactant during washing with methanol.