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

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 degrees C and 30 bar H-2 pressure for 1-24 h reaction times using low-density polyethylene (LDPE, M-w similar to 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 Bronsted 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.

Automated summary

The study demonstrates that Pt-WZr is a bifunctional catalyst for LDPE hydrocracking, leading to higher value branched alkanes. The metal-to-acid site molar ratio (MAB) can shift the product distribution and increase the isomerization degree in the residual polymer. This research provides a blueprint for designing effective catalysts for hydrocracking polyolefin plastic wastes using MAB as a catalyst descriptor.