Selective Upcycling of Polyethylene Terephthalate towards High‐valued Oxygenated Chemical Methyl p‐Methyl Benzoate using a Cu/ZrO₂ Catalyst

Abstract

Upgrading of polyethylene terephthalate (PET) waste into valuable oxygenated molecules is a fascinating process, yet it remains challenging. Herein, we developed a two-step strategy involving methanolysis of PET to dimethyl terephthalate (DMT), followed by hydrogenation of DMT to produce the high-valued chemical methyl p-methyl benzoate (MMB) using a fixed-bed reactor and a Cu/ZrO₂ catalyst. Interestingly, we discovered the phase structure of ZrO₂ significantly regulates the selectivity of products. Cu supported on monoclinic ZrO₂ (5 %Cu/m-ZrO₂ ) exhibits an exceptional selectivity of 86 % for conversion of DMT to MMB, while Cu supported on tetragonal ZrO₂ (5 %Cu/t-ZrO₂ ) predominantly produces p-xylene (PX) with selectivity of 75 %. The superior selectivity of MMB over Cu/m-ZrO₂ can be attributed to the weaker acid sites present on m-ZrO₂ compared to t-ZrO₂ . This weak acidity of m-ZrO₂ leads to a moderate adsorption capability of MMB, and facilitating its desorption. Furthermore, DFT calculations reveal Cu/m-ZrO₂ catalyst shows a higher effective energy barrier for cleavage of second C-O bond compared to Cu/t-ZrO₂ catalyst; this distinction ensures the high selectivity of MMB. This catalyst not only presents an approach for upgrading of PET waste into fine chemicals but also offers a strategy for controlling the primary product in a multistep hydrogenation reaction.