Polyoxometalate-Based Zinc–Organic Network as a Dual-Site Acid Catalyst for the Conversion of Polyethylene Terephthalate Plastic to Terephthalic Acid
Qian Liu, Yanan Sun, Wei Yang, Yuan‐Yuan Ma, Jing Du, Zhangang Han
Abstract
Chemical depolymerization and recycling of poly(ethylene terephthalate) (PET) constitute a sustainable, resource-efficient, and environmentally beneficial approach, which requires the development of efficient heterogeneous catalysts. Herein, polyoxometalate(POM)-based zinc–organic networks were synthesized as dual-site acid catalysts for the alcoholysis of PET into the value-added terephthalic acid (TPA) product, with formulas of [Zn 2 (μ 2 -Cl)(H 2 O) 2 (DTAB) 3 ][PW 12 O 40 ]·4H 2 O ( 1 ), [Zn 2 (DTAB) 4 ][SiW 12 O 40 ]·4H 2 O ( 2 ), and [Zn 2 (H 2 O) 4 (DTAB) 2.5 ][HBW 12 O 40 ]·8H 2 O ( 3 ) (DTAB = 1,4-di(4 H -1,2,4-triazol-4-yl)benzene). Structural analysis showed that compounds 1 and 2 were composed of 2D Zn-ligand networks embedded POM clusters in an “egg-in-a-box” manner and that compound 3 consisted of a 3D POM-based host–guest framework constructed by {Zn 2 (H 2 O) 4 (N-N) 3 } units and [HBW 12 O 40 ] 4– clusters. Three compounds incorporate the Zn 2+ Lewis acid centers and heteropolytungstate clusters, having the acid strength order compound 3 > compound 1 > compound 2 . When employed as dual-site acid catalysts, the three compounds exhibited efficient catalytic performance for PET alcoholysis into TPA with >92% conversion rate and >94% selectivity of the TPA product, along with excellent recyclability and structural stability. This work offers a novel perspective for the development of POM-based heterogeneous catalysts in the upcycling of plastic waste.