Using a mechanism-based solvent-free tandem catalytic approach, commodity polyester plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) are rapidly and selectively deconstructed by combining the two air- and moisture-stable catalysts, Hf(OTf)4 and Pd/C, under 1 atm H2 , affording terephthalic acid (or naphthalene dicarboxylic acid for PEN) and ethane (or butane for PBT) in essentially quantitative yield. This process is effective for both laboratory grade and waste plastics, and comingled polypropylene remains unchanged. Combined experimental and DFT mechanistic analyses indicate that Hf(OTf)4 catalyzes a mildly exergonic retro-hydroalkoxylation reaction in which an alkoxy C-O bond is first cleaved, yielding a carboxylic acid and alkene, and this process is closely coupled to an exergonic olefin hydrogenation step, driving the overall reaction forward.
Keywords: PET; chemical recycling; hydrogenolysis; polyester plastics; tandem catalysis.
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