Tuning selectivity in the direct hydrogenolysis of PET plastic over Co catalysts through interfacial hydrogen
Baoyu Wang1,2, Ximing Yan2, Jinshu Huang1
1State Key Laboratory of Green Pesticides, State-Local Joint Laboratory for Comprehensive Utilization of Biomass, Center for R&D of Fine Chemicals, Guizhou University, Guiyang, China.
Abstract:
Polyethylene terephthalate (PET) plastic upcycling typically features two-step processes involving cascade depolymerization and functionalization to mixed products. Here, we realize the direct hydrogenolysis of PET over a Co@CoO heterogeneous catalyst, with high yield of either p-xylene (PX, >97 %) or 1,4-dimethylcyclohexane (1,4-DMC, >90 %). Pyrolysis of Co-MOF-71 yields carbon-supported Co nanoparticles partially encapsulated by CoO, whose metal/oxide interface facilitates hydrogen spillover. Experimental and computational investigations reveal Coδ+ atoms proximate to CoO particles selectively catalyze carboxylate C-O bond cleavage at 250 °C and 1 MPa H2 to yield PX. In contrast, hydrogen spillover from Co metal to CoO sites at 280 °C and 3 MPa H2 promotes selective ring hydrogenation to 1,4-DMC. Co/CoO-800 has excellent stability and efficacy for depolymerizing commercial PET plastics. Life cycle assessment indicates the PET-to-PX process offers negative CO2 emissions and outperforms fossil-fuel PX production. Direct hydrogenolysis over Earth-abundant catalysts offers a simple strategy for polyester waste upcycling.
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