Polyolefin depolymerization over silica-alumina-based catalysts: mechanistic classifications and benchmarking

Abstract C-C bond cleavage mechanisms play a key role in the selective deconstruction of alkanes and polyolefins. The product distributions, i.e., formation of smaller hydrocarbons, unsaturated and isomerization products, serve as distinctive features that help to identify reaction pathways. Herein, Co, Ni or Ru nanoparticles immobilized on amorphous silica-alumina, Zeo-Y and ZSM-5, were evaluated as catalysts in the deconstruction of n-hexadecane (used as a model substrate for benchmarking purposes) with hydrogen to delineate the different mechanisms, i.e. monofunctional- (acid site dominated) or bifunctional-hydrocracking (acid site & metal site) versus hydrogenolysis (metal site dominated). The ZSM-5_H-based catalysts were further studied in the depolymerization of polyethylene. Based on these studies, the catalysts were plotted on an activity-mechanism map that functions as an expandable basis to benchmark catalytic activity and to identify the optimal depolymerization catalyst to afford specific products.