Hydrogen spillover boosts PET upcycling to aviation fuel additives over Co–ReOx catalysts†

Abstract

Polyethylene terephthalate (PET) upcycling holds potential for producing aviation fuel additives such as benzene, toluene, and xylene (BTX), yet selectively activating C–O bonds over C–C bonds remains a formidable challenge. In this study, we have developed an innovative Co–ReO_x catalyst (Co/ReO_x-LDO (layered double oxides)) through a hydrothermal impregnation approach. This catalyst facilitates the direct and selective conversion of PET into p-xylene (PX) under mild conditions, achieving yields and productivities as high as 71.7% and 1.1 mmol g⁻¹ h⁻¹, representing a 3.0-fold improvement compared to the CoAl-LDO catalyst. The Co/ReO_x-LDO catalyst demonstrates remarkable recyclability and broad applicability across various esters. Characterization studies reveal that the robust Co–ReO_x interaction results in smaller Co particle sizes and higher charge densities, which effectively suppress ring hydrogenation and C–C bond cleavage. Meanwhile, the adjacent ReO_x sites promote hydrogen spillover, significantly enhancing the reactivity of Co–ReO_x. Spectroscopic analyses indicate that the rate-determining step involves C–O bond cleavage of the ester linkage to form acyl intermediates, and Co–ReO_x accelerates this process with a reduced energy barrier. This research offers valuable insights into catalyst design for efficient fuel additive production from waste polyesters.