Catalytic recycling of polylactic acid over zirconium phosphate supported WOx active sites

Chemical upcycling of end-of-life plastics is an economically and environmentally feasible way to tackle plastics crisis. Among them, methanol alcoholysis of polylactic acid (PLA) is a promising approach, which can produce methyl lactate (MLA) that can be further converted to lactide to achieve a sustainable development. In this work, a series of WO_x/ZrP catalysts with WO_x active sites in low coverage and high surface area were synthesized via anchoring WO_x species on the surface of zirconium phosphate (ZrP). Characterizations indicated that the strong interaction between WO_x and ZrP promoted the formation of WO_x active sites in low coverage. In particular, 10 %WO_x/ZrP catalyst was highly active and stable for the alcoholysis of PLA plastics under mild conditions due to the abundant WO_x active sites and strong acidity. The yield of MLA over 10 %WO_x/ZrP catalyst reached 94.5 % within 4 h at 160 °C, which was superior to the performance of traditional solid acids (α-ZrP, HZSM-5, Hβ and Amberlyst-45). In addition, 10 %WO_x/ZrP was versatile for the alcoholysis of discarded PLA-based products and could be recycled at least five times. The prominent performance of 10 %WO_x/ZrP catalyst and the possible reaction mechanism were discussed.