Direct synthesis of Fe-aluminosilicates from red mud for catalytic deoxygenation of waste cooking oil

Abstract

Conversion of red mud (RM) that contains a high level of silica, alumina and iron minerals into heterogenous catalysts, offers a route for the utilization of abundant toxic by-products of bauxite refining. In this study, the conversion of red mud into mesoporous Fe-aluminosilicate produced selective catalysts for the deoxygenation of waste cooking oil to green diesel hydrocarbons. Direct conversion of red mud in the presence cetyltrimethylammonium bromide into Fe-aluminosilicate (RM-CTA) produced a highly mesoporous structure with oligomeric Fe₂O₃ clusters within the pores. When red mud was treated with citric acid (RM-CA-CTA), a wide distribution of Fe₂O₃ particles was obtained on the aluminosilicate external surface. TEM analysis showed a well-defined hexagonal mesoporosity of Fe-aluminosilicate obtained from untreated red mud, while the treated red mud produced lower regularity mesopores. RM-CTA exhibits 60% WCO conversion and 83.72% selectivity towards liquid products with 80.44% diesel hydrocarbon (C₁₁–C₁₈) yield. The high selectivity was due to the high acidity of Fe-aluminosilicate to dissociate the C–O bond and the regularity of mesostructure for efficient hydrocarbon diffusion, preventing a cracking reaction.