Covalent triazine frameworks with MgO sites as a basic catalyst for aldol condensation and transesterification reactions

Abstract

Covalent triazine frameworks (CTFs) have emerged as robust materials with high thermal and chemical stability, tunable porosity, and significant potential for sustainable applications in catalysis, adsorption, and gas storage and separation. Recent advances have focused on enhancing their intrinsic basicity through the incorporation of alkali oxides, which, although effective, exhibit limited moisture stability. For many practical applications, developing strongly basic, water-tolerant CTFs remains a critical challenge. In this work, magnesium oxide-impregnated covalent triazine frameworks (MgO@CTFs) were successfully synthesized through a sequential process involving the wet impregnation of magnesium salts onto CTFs, followed by thermal decomposition. The synthesis procedure was optimized by investigating the best ratio of the metal salt precursor to support, as well as the type of metal precursor. Impregnation of MgO at 5 wt% provided the best compromise between enhanced basicity and retention of porosity. The materials were thoroughly characterized to confirm their structure, composition, and porosity. Their catalytic performance was evaluated in the production of 2-hexyl-2-decenal from octanal, achieving over 80 % conversion at 170 °C within 4 h, as well as in the propanolysis of 4-nitrophenylacetate (4-NPA) and paraoxon-ethyl. Remarkably, reaction rates improved by factors of 4.5 (4-NPA) and 300 (paraxon) compared to the respective spontaneous reaction. DTF studies indicate that the CTF framework interacts with propanol and paraoxon-ethyl, facilitating the interaction between the reactive species. This study presents an effective strategy to introduce stable basic sites into CTFs without compromising their porosity or stability, expanding their applicability in base-catalyzed reactions and other advanced applications.