Simple One-Pot Synthesis of Sulfonic-Acid-Functionalized Silica for Effective Catalytic Esterification of Levulinic Acid

Desinta Dwi Ristiana (Department of Chemistry, Faculty Mathematics and Natural Sciences, Universitas Gadjah Mada, Sekip Utara, PO BOX BLS 21, Yogyakarta 55281, Indonesia)
Suyanta Suyanta (Department of Chemistry, Faculty Mathematics and Natural Sciences, Universitas Gadjah Mada, Sekip Utara, PO BOX BLS 21, Yogyakarta 55281, Indonesia)
Nuryono Nuryono (Department of Chemistry, Faculty Mathematics and Natural Sciences, Universitas Gadjah Mada, Sekip Utara, PO BOX BLS 21, Yogyakarta 55281, Indonesia)

Indonesian Journal of Chemistry
Vol 22, No 1 (2022)

Silica functionalized with sulfonic acid catalyst (SiO2−SO3H) was synthesized through a one-pot method and evaluated as the catalyst material for esterification of levulinic acid in an excess amount of ethanol. Sodium silicate solution was used as the silica source, and then a silane coupling agent, namely GPTMS, was used to incorporate the sulfonic group of 2-aminoethanesulfonic acid (AS) into the silica. Functionalization of AS using GPTMS in the slightly acidic condition has been successfully carried out based on the characterization with FTIR, SEM-EDX, and TGA measurements. Catalyst with the AS to SiO2 molar ratio of 5:6 (SiO2−SO3H(5)) showed the highest acid content (1.02 mmol g–1) and the highest conversion of levulinic acid (70%). The reaction followed pseudo-first-order with the rate constant of 0.00414 min–1. Catalyst material was regenerated by washing with alcohol and water, and the catalyst material can be reused at least for 3 cycles. From this study, the SiO2−SO3H produced from a green process is an effective catalyst to produce esters used in fuel additives.