Synthesis of Sulfonic Acid Functionalized Silica Honeycombs

A honeycomb-type silica monolith was functionalized with sulfonic acid groups to synthesize a solid acid catalyst for flow reaction systems. The sulfonic acid groups were introduced via anchoring of 3-mercaptopropyltrimethoxysilane (MPTS) on the silica surface and subsequent oxidation using a H2O2 solution. The honeycomb-type monolith used as the substrate was prepared using ice crystals as a template and was found to have a high open frontal area of ≈85% and flow-through macropores (≈27 μm in diameter) that are surrounded by silica walls (≈2 μm in thickness). The catalyst was tested by the liquid phase esterification of ethanol with acetic acid at 333 K in a batch reactor as well as a flow reactor. The catalyst was found to exhibit about 2-fold higher catalytic activity than Amberlyst-15 in a batch reactor. The catalyst also showed a stable catalytic activity for 24 h in a flow reactor.