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Tandem Methanolysis and Catalytic Transfer Hydrogenolysis of Polyethylene Terephthalate to p‐Xylene Over Cu/ZnZrO x Catalysts
Summary
Researchers demonstrated that methanol can serve a dual purpose in PET plastic recycling—first depolymerizing the plastic into dimethyl terephthalate at near-complete yields, then acting as an in-situ hydrogen source to catalytically convert that intermediate into p-xylene, a valuable aromatic chemical, using a copper-zinc-zirconium oxide catalyst with the metal-support interface playing a critical mechanistic role.
Abstract We demonstrate a novel approach of utilizing methanol (CH 3 OH) in a dual role for (1) the methanolysis of polyethylene terephthalate (PET) to form dimethyl terephthalate (DMT) at near‐quantitative yields (~97 %) and (2) serving as an in situ H 2 source for the catalytic transfer hydrogenolysis (CTH) of DMT to p‐xylene (PX, ~63 % at 240 °C and 16 h) on a reducible ZnZrO x supported Cu catalyst (i.e., Cu/ZnZrO x ). Pre‐ and post‐reaction surface and bulk characterization, along with density functional theory (DFT) computations, explicate the dual role of the metal‐support interface of Cu/ZnZrO x in activating both CH 3 OH and DMT and facilitating a lower free‐energy pathway for both CH 3 OH dehydrogenation and DMT hydrogenolysis, compared to Cu supported on a redox‐neutral SiO 2 support. Loading studies and thermodynamic calculations showed that, under reaction conditions, CH 3 OH in the gas phase, rather than in the liquid phase, is critical for CTH of DMT. Interestingly, the Cu/ZnZrO x catalyst was also effective for the methanolysis and hydrogenolysis of C−C bonds (compared to C−O bonds for PET) of waste polycarbonate (PC), largely forming xylenol (~38 %) and methyl isopropyl anisole (~42 %) demonstrating the versatility of this approach toward valorizing a wide range of condensation polymers.