One-Pot Tandem Butanolysis and Hydrogenolysis of PET to Selectively Produce p-Xylene through Coordination of Basic Sites, Oxygen Vacancies, and Hydrogenation Sites of Cu–Mg–Al Catalyst

Upcycling polyethylene terephthalate (PET) plastic into high-value chemicals like p-xylene is challenging, due to the difficulty for achieving selective depolymerization of PET and deoxygenation of reaction intermediates. Herein, a tandem alcoholysis-hydrogenation/hydrogenolysis strategy for converting PET to p-xylene over Cu-based catalysts using n-butanol as both solvent and reactant at 205 °C was conducted using Mg-modulated Cu-based catalysts derived from layered double hydroxides. By precisely tuning the Mg/Al molar ratio, the multidimensional synergistic roles of Mg in enhancing the catalyst performance were unraveled, which serves as the core of heterogeneous PET depolymerization. Specifically, Mg reinforces metal–support interactions, confining Cu nanoparticles to an average size of 4.8 nm, which is far smaller than the 14.1 nm observed in Mg-free Cu1.0Al2.0, maximizing accessible active sites and accelerating the rate-determining step of PET butanolysis. Mg also induces pore coarsening to form a hierarchical mesoporous architecture, eliminating steric hindrance for the rapid diffusion of bulky PET oligomers. Moreover, Mg enriches surface basic sites (critical for ester bond cleavage, as confirmed by acid–base titration) and induces oxygen vacancies (promoting carbonyl adsorption and deoxygenation via in situ FT-IR). The optimized catalyst exhibits a low apparent activation energy (49.6 kJ/mol) and high p-xylene yield (99%), with exceptional recyclability by suppressing Cu sintering.