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