Silica-Based Catalysts for Biodiesel Production: A Brief Review

Biodiesel, an environmentally friendly fuel, has been developed as a renewable fuel. It is accomplished through either a transesterification reaction with a base catalyst or a two-step reaction with an acid catalyst followed by a transesterification reaction with a base catalyst. A two-step reaction is performed on oil involving high levels of free fatty acids (FFA), such as used cooking oil or others. Silica is a material that has the potential to be developed as a heterogeneous catalyst based on its acidic and basic properties in biodiesel production. This review discusses the use of silica material and its modification as a catalyst to increase its acidity and/or basicity, which can increase its catalytic activity to produce biodiesel. Modification of silica as an acid catalyst, for example, in the sulfation process using sulfuric acid solution, has led to an increase in silica's acidity and a half-reduction in the FFA content of used cooking oil. The silica catalyst in the esterification and/or transesterification reactions shows good conversion of biodiesel. Loading base catalyst materials such as CaO, MgO, and KF onto silica has resulted in close to 100% conversion of an oil such as used cooking oil, corn oil, or Jatropha oil.