Single-pot template-free synthesis of a glycerol-derived C–Si–Zr mesoporous composite catalyst for fuel additive production

Abstract

Synthesis of a highly ordered mesoporous acid- as well as metal-functionalized carbon (–SO₃H/C–Si–Zr) material is achieved for the first time from a simple single-pot template-free carbonization of low-value bio-derived glycerol. Addition of TEOS to glycerol right before the carbonization was observed to facilitate molecular-level interactions between them to establish C–Si bonding, which eventually leads to the formation of a high surface area mesoporous –SO₃H/C–Si composite material. Unlike this, the addition of ZrO(NO₃)₂·xH₂O to glycerol could not have such an effect, but when Zr is used in the presence of TEOS the mixture could successfully produce the –SO₃H/C–Si–Zr composite possessing mesoporosity and uniform acidity suitable for bulky tri-acetin production useful for fuel applications. Here TEOS is observed to play two roles, (1) as a surface area and porosity improver of graphitic carbon by its C–Si interaction and (2) as a mediator to involve Zr in the carbon composite structure through its Si–OH group. Thus, the combined inclusion of Zr and Si sources in the glycerol-derived carbon structure could successfully introduce the positive aspects of porosity improvement (by Si) and acidity improvement (by zirconia) in the mixed composite –SO₃H/C–Si–Zr to produce the highest ever selectivity of tri-acetin (∼94 wt%) from the same low-value bio-derived glycerol by an acetylation reaction. The sustainability of the process lies in the utilization of waste glycerol as a source of the carbon composite, which in turn catalyzes selective low-value glycerol conversion to industrially important fuel additives.