Comparison of In Situ Formed Metal (Mo, W) Phosphides and Oxides in the Hydroprocessing of Used PET Bottles

The development of an effective approach for plastic recycling using a highly active catalytic system represents a crucial step toward reducing the harmful impact of plastic waste on the environment. This work described the comparison of the catalytic performance of in situ formed molybdenum and tungsten phosphides and oxides in the hydroprocessing of such widely used plastics as polyethylene terephthalate and its intermediate conversion products (various carboxylic acids). MoP and MoO_x catalysts promoted conversion of PET toward p-xylene (69% over MoP and 86% over MoO_x at full PET conversion). In the presence of WP and WO_x catalysts, the formation of a mixture of toluene and p-xylene with selectivities of 55% and 77% at 100% PET conversion was observed. The possibility of reusing catalysts in PET processing during five test runs for MoO_x and WO_x and during three test runs for MoP and WP without significant loss of activity was shown. The obtained catalysts were characterized by XRD, XPS, HRTEM, EDX, and NH₃–TPD methods. In addition, a correspondence between the different nature of the active sites and the composition of the reaction products for various catalysts is presented.