A comprehensive review of nanocatalysts for sustainable plastic waste valorization in circular economy

The rapidly growing amount of plastic waste has become one of the most difficult
environmental problems that humanity will have to face in the 21st century. Nano-engineered
catalysts have emerged as a technically promising approach. These offer systematic benefits over
bulk catalytic materials because of the higher surface-to-volume ratios, programmable acid–
base surface chemistry and morphology-dependent active site exposure. This review critically
evaluates the mechanistic basis, material-specific performance and practical limitations of four

major nanocatalyst types, namely metal oxide nanoparticles, magnetic nanocatalysts, nano-
zeolites and hybrid nanocomposites, in thermo-chemical plastic conversion, focusing on

catalytic pyrolysis. Under optimised laboratory settings and clean single polymer feeds, nano-
catalytic systems achieve plastic-to-liquid conversion efficiencies of 75-92 wt% with fuel

calorific values of 43-46 MJ/kg significant gains over uncatalyzed thermal pyrolysis. These

statistics, however, are for ideal situations and performance is often 15–25% lower with post-
consumer mixed plastic feeds. This review critically discusses deactivation mechanisms such as coking, sintering and chemical poisoning, multi-cycle stability constraints,nanotoxicological risk and economic feasibility at industrial scale features seldom covered in
the literature. Life cycle assessment evidence indicates net greenhouse gas savings of 1.2–2.8 kg CO2 equivalent per kilogram of plastic treated, but this range is quite sensitive to systemboundary assumptions, grid carbon intensity and catalyst recovery efficiency.