Porous catalysts fabricated from coal fly ash as cost-effective alternatives for industrial applications: A review

Coal fly ash (CFA) -an industrial solid waste- has tremendous potential to be used as a starting material for development of valuable porous catalysts and adsorbents because of its silicon and aluminum content. Among various products fabricated from CFA by chemical synthesis process, CFA-based porous catalysts have recently gained remarkable interest among researchers. Each CFA-based catalyst has different properties, the most important of which is the ion exchange capability that depends on the chemical composition and structure of the synthesized product. Studies proved that CFA-based compounds can be used as catalysts/photocatalysts in different environmental processes such as degradation of pollutants. Chemical conversion reactions and synthesis of fine chemicals are among other applications, in which CFA is used as substrate for developing different catalysts. In this review paper, CFA-based catalysts have been classified based on their properties and applications. Methods of characterizations including kinetics and isotherm models are discussed. Furthermore, the effect of several parameters including reaction time, reaction temperature, and the ratio of active compounds to CFA substrate on chemical reactions catalyzed by CFA-based catalysts are discussed. This review paper reveals that CFA-based catalysts are highly efficient compounds not only for application in environmental pollution remediation processes, but also in achieving comparable results in chemical conversion reactions for synthesizing fine chemicals. It can be concluded that CFA as a solid waste should be considered as a low-cost source of alumino-silicate that is a promising candidate for developing inexpensive methods of manufacturing highly efficient and eco-friendly porous catalysts for a wide array of applications.