Abstract:The use of catalytic ozonation processes (COPs) for the advanced treatment of recalcitrant petroleum refinery wastewater (RPRW) is rapidly expanding. In this study, magnesium (Mg), cerium (Ce), and Mg-Ce oxide-loaded alumina (Al 2 O 3 ) were developed as cost efficient catalysts for ozonation treatment of RPRW, having performance metrics that meet new discharge standards. Interactions between the metal oxides and the Al 2 O 3 support influence the catalytic properties, as well as the efficiency and mechanism. Mg-Ce/Al 2 O 3 (Mg-Ce/Al 2 O 3 -COP) reduced the chemical oxygen demand by 4.7%, 4.1%, 6.0%, and 17.5% relative to Mg/Al 2 O 3 -COP, Ce/Al 2 O 3 -COP, Al 2 O 3 -COP, and single ozonation, respectively. The loaded composite metal oxides significantly increased the hydroxyl radical-mediated oxidation. Surface hydroxyl groups (-OHs) are the dominant catalytic active sites on Al 2 O 3 . These active surface -OHs along with the deposited metal oxides (Mg 2+ and/or Ce 4+ ) increased the catalytic activity. The Mg-Ce/Al 2 O 3 catalyst can be economically produced, has high efficiency, and is stable under acidic and alkaline conditions.