Heterogeneous acid catalysts are active in a wide range of applications. In this paper, an overview is given of the current knowledge available about the fly ash supported solid acid catalysts and their catalytic activity in the production of phenyl salicylate. An efficient nano crystalline solid acid catalyst (AFAC) with crystallite size of 14 nm has been synthesized by mechanical and thermal activation of F-type fly ash (SiO₂ and Al₂O₃ >70%) followed by chemical activation using concentrated HNO₃ at 110 °C. The activation of fly ash resulted in increased silica content (61.9% to 84%) and surface area (5.8 m²/g) having sufficient silanol activity for esterification of phenol. The catalyst was characterized by XRD, FT-IR, and SEM techniques. Fly ash generated catalytic material has shown sufficient catalytic activity for esterification of salicylic acid and phenol to give phenyl salicylate (salol), which is used in suntan lotions as an antiseptic and pain-relieving agent. The catalyst was completely recyclable without significant loss in activity up to five reaction cycles, which confers its stability during reaction. The work reports an innovative use of solid waste fly ash as an effective solid acid catalyst.
Keywords: Fly Ash; Mechanical Activation; Chemical Activation; Acid Treatment and Ball Milling; Phenyl Salicylate (Salol);