Depolymerization of polystyrene over Mgx-Aly-O catalysts derived from hydrotalcites: Effect of Mg/Al ratio on the basicity and catalytic performance

Abstract

• A series of hydrotalcite materials were prepared with a variation of Mg/Al ratio. • Hydrotalcites were calcined to obtain a set of Mg x -Al y -O catalysts with different Mg/Al ratio. • Depolymerization of polystyrene (PS) was conducted using Mg x -Al y -O catalysts. • Basicity was closely related to the catalytic performance of Mg x -Al y -O catalysts. • Catalytic performance increased with increasing basicity of Mg x -Al y -O catalysts. A series of hydrotalcites with various Mg/Al contents were prepared by a solid state reaction. They were then calcined at 450℃ to form a series of Mg x -Al y -O catalysts with different Mg/Al ratios for use in the depolymerization of polystyrene (PS) in a batch reactor. The prepared catalysts were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray analysis (EDX), induced coupled plasma-atomic emission spectroscopy (ICP-AES) measurements. The characterization results showed that the Mg x -Al y -O mixed metal oxide catalysts were successfully synthesized as attempted in this work. Basicity of Mg x -Al y -O catalysts was determined by CO 2 -TPD measurement to elucidate the catalytic performance in the depolymerization of PS. It was found that basicity and catalytic performance (PS conversion, oil yield, and styrene monomer (SM) yield) showed volcano-shaped trends with respect to the Mg/Al ratio of Mg x -Al y -O catalysts. Correlations between basicity and catalytic performance revealed that all of PS conversion, oil yield, and SM yield were improved with the increasing basicity. Among the catalysts tested, the Mg 1 -Al 2 -O (Mg/Al = 0.5) catalyst with the largest basicity showed the best catalytic performance. Thus, basicity of Mg x -Al y -O catalyst played an important role in the determining the catalytic performance in depolymerization of PS.