Oxidative Upcycling of Polybutylene Terephthalate to Dicarboxylic Acids over a Cubic Au/Ca(OH) ₂ Catalyst

Catalytic upcycling of poly(butylene terephthalate) (PBT) into high-value oxygenated chemicals offers an attractive pathway for plastic circularity. Here, we report a one-step tandem strategy that integrates depolymerization and oxidation of PBT to yield terephthalic acid (TPA) and succinic acid (SA) over Au/Ca(OH)2 catalysts. The catalytic performance is strongly governed by the morphology of the catalyst. Compared with conventional strip-type Au/Ca(OH)2, cubic Au/Ca(OH)2 exhibits a higher density of surface oxygen vacancies arising from the low coordination of Ca atoms, which induces electron transfer from Ca(OH)2 to Au. The resulting Auδ--Ov interfacial sites facilitate O2 activation and promote the subsequent oxidation of 1,4-butanediol intermediates. Benefiting from this surface structure, the cubic Au/Ca(OH)2 catalyst achieves near-quantitative conversion of PBT to 99.8% TPA and 85.1% SA based on the carbon balance. Moreover, this catalyst has been extended to the oxidative upcycling of other polyesters, including polyethylene terephthalate, polytrimethylene terephthalate, and poly(1,6-hexamethylene adipate), producing dicarboxylic acids in high yields.