Catalytic compositions and processes for depolymerizing polyolefin-based feed into useful petrochemical products are described. The compositions are a composite of a zeolite catalyst component and a co-catalyst comprising an activated clay component and/or a solid base component. These catalyst systems, along with heat, are used to both increase the depolymerization reaction rate of the feed streams and suppress poisoning effects of impurities that may be present in the polyolefin-based feed. This results in a shorter residence time in the depolymerization unit and more efficient process.