Identifying selective catalysts in polypropylene hydrogenolysis by decoupling scission pathways

Practical catalytic processing of polypropylene waste into high-value liquid alkanes via hydrogenolysis demands minimizing methane formation. Methane can mostly originate from either undesired demethylation of branched chains or inappropriate reaction conditions leading to excessively deep backbone scission. To date, identification of catalysts promoting backbone scission has been precluded by insufficient mechanistic tools. This work introduces scission preference, the metric providing the ratio between backbone scission and demethylation events when hydrogenolysis predominates obtainable from routine product analysis. Clear mechanistic differences on representative supported ruthenium catalysts could thus be quantified, with computed values ranging from 0.3 (Ru/CeO2) to 1.1 (Ru/Al2O3) under applied conditions. Ru/TiO2 displayed the best activity-selectivity trade-off. This tool also revealed the dynamic nature of the cleavage mechanism as demethylation is progressively favored over time. Metal content and metal oxide basicity could also be correlated with scission preference, underscoring its parallel value for catalyst design studies.