Unconventional heterogeneous catalysts synthesis from waste in biocrude hydrotreatment processes

ABSTRACT Heterogeneous catalysts for biocrude hydrotreatment are typically synthesized using commercial supports such as Al 2 O 3 , SiO 2 , ZrO 2 , TiO 2 , zeolites, and activated carbons. Synthesizing catalysts or supports from waste materials is a less conventional approach, yet it is increasingly recognized within the framework of the circular economy. This work summarizes the main methods developed to synthesize heterogeneous catalysts from industrial wastes such as red mud, coal fly ash, and carbonaceous materials. It also discusses the main characterization methods and applications of these catalysts in biocrude hydrotreatment processes. The work concludes by highlighting the advantages, limitations, and future perspectives of employing industrial waste in the synthesis of heterogeneous catalysts.