TBD-grafted activated carbon as an efficient solid base catalyst for continuous Knoevenagel reaction

Abstract

The development of a highly efficient and stable metal-free solid base catalyst for the Knoevenagel reaction remains a significant challenge. In this study, activated carbon is selected as support material to develop a new base catalyst due to its excellent chemical stability. A novel surface chloromethylation method is applied to modify the activated carbon surface, followed by covalent grafting of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), resulting in a highly effective solid organic base catalyst. A continuous platform based on a micro-packed bed reactor has been optimized for the Knoevenagel reaction. The system achieves excellent space-time yields (19129.4 $g_{Pro}{kg}_{cat}^{-1}{h}^{-1}$) and demonstrates a broad substrate scope. The solid organic base catalyst exhibits a turnover frequency (TOF) exceeding 140 $h^{-1}$, surpassing the performance of similar nitrogen-based catalysts reported in literature (7.6–68.0 $h^{-1}$). Moreover, the catalyst shows no signs of deactivation after more than 23 h of continuous operation with a turnover number (TON) exceeding 115, indicating comparable performance reported in literature (29.7–297.2). Catalyst deactivation is primarily attributed to the adsorption of raw materials and products onto the base sites, leading to a gradual loss of catalytic activity.