Single pot catalyst strategy to branched products via adhesive isomerization and hydrocracking of polyethylene over platinum tungstated zirconia

[Display omitted] •Pt-WZr is a prototypical catalyst to probe LDPE hydrocracking at low temperatures.•The metal-acid balance (MAB) is a crucial descriptor in polyolefin hydrocracking.•The MAB tunes the product distribution and the branching degree in solid residues.•Cracking and isomerization pathways are decoupled in polymer hydrocracking.•A new macromolecular hydrocracking mechanism is proposed. Hydrocracking is an insufficiently explored route for chemical recycling of plastics waste. Platinum tungstated zirconia (Pt-WZr) was used in a batch reactor at low temperatures of 250 °C and 30 bar H2 pressure for 1−24 h reaction times using low-density polyethylene (LDPE, Mw∼76 kDa). We find Pt-WZr is a bifunctional catalyst for LDPE hydrocracking leading to higher value branched fuel- and lubricant-ranged alkanes. We demonstrate that the catalyst metal-to-acid site molar ratio (MAB) shifts the product distribution to larger cracked products and increases the isomerization degree in the residual polymer. We propose a new adhesive isomerization mechanism between the metal and Brønsted acid sites in parallel with slow polymer chain cracking, caused by competitive adsorption of the polymer over the liquid products and stereochemical hindrance of methines. This study provides a blueprint on how to engineer effective catalysts for hydrocracking polyolefin plastic wastes using the MAB as a catalyst descriptor.