Find in Library

Organosulfonic acid-functionalized mesoporous silica is a class of heterogeneous acid catalysts used in esterification processes due to its high surface area, shape-selective properties, and strongly acidic sites. Since water is generated as a by-product of esterification, the surface of mesostructured silica is modified to enhance hydrophobicity and catalytic performance. In this study, a series of propylsulfonic acid-functionalized nanocomposites based on natural rubber and hexagonal mesoporous silica (NRHMS-SO₃H) with different acidities were prepared via an in situ sol-gel process using tetraethyl orthosilicate as the silica source, dodecylamine as the nonionic templating agent, and (3-mercaptopropyl)trimethoxysilane as the acid-functional group precursor. Compared with conventional propylsulfonic acid-functionalized hexagonal mesoporous silica (HMS-SO₃H), NRHMS-SO₃H provided higher hydrophobicity, while retaining mesoporosity and high surface area. The catalytic activity of synthesized solid acids was then evaluated via batch esterification of levulinic acid (LA) with alcohols (ethanol, <i>n</i>-propanol, and <i>n</i>-butanol) to produce alkyl levulinate esters. NRHMS-SO₃H exhibited higher catalytic activity than HMS-SO₃H and ultra-stable Y (HUSY) zeolite owing to the synergistic effect between the strongly acidic-functional group and surface hydrophobicity. The activation energy of the reaction over the NRHMS-SO₃H surface was lower than that of HUSY and HMS-SO₃H, suggesting that tuning the hydrophobicity and acidity on a nanocomposite surface is a compelling strategy for energy reduction to promote catalysis.