Microwave-catalyzed pyrolysis of waste engine oil using steel slag catalyst: Structure design and insights into the intrinsic mechanism of active catalytic sites and microwave absorption functions

•The type and proportion of metal oxides were regulated by regulating the pH of pretreatment.•The modified steel slag catalyst promoted the formation of light hydrocarbon (C11-C20).•The modified steel slag catalyst has both catalytic and microwave absorption functions.•The electron density of oxygen vacancy and adsorption energy of tricosane were calculated by DFT.•The formation of oxygen vacancy can improve the catalytic and dielectric properties of the catalysts.