Sustainable Knoevenagel Condensation of Lignin-Derived Aldehydes over Basic Mesoporous Silica

The sustainable valorisation of biomass-derived molecules requires efficient, robust, and recyclable catalytic systems. In this study, amine-functionalised mesoporous silica nanoparticles (APTES@MSNs) were developed and investigated as heterogeneous base catalysts for the Knoevenagel condensation of lignin-derived aromatic aldehydes. Mesoporous silica nanoparticles were selected as supports due to their high surface area, ordered mesoporous structure, and tunable surface chemistry, enabling the stable grafting of organic functionalities. Post-synthetic functionalisation with (3-aminopropyl)triethoxysilane introduced accessible primary amine groups that act as basic catalytic sites, yielding a hybrid organic–inorganic material with high structural stability. The catalytic performance of APTES@MSNs was evaluated using vanillin, syringaldehyde, and 4-hydroxybenzaldehyde as representative bio-based substrates. Key reaction parameters, including solvent, temperature, and catalyst loading, were systematically examined to identify mild and environmentally benign operating conditions. The potential of amine-functionalised mesoporous silicas as sustainable heterogeneous catalysts is highlighted for the upgrading lignin-derived platform molecules within a circular chemistry framework.