Valorization of Waste Tires via Catalytic Fast Pyrolysis Using Palladium Supported on Natural Halloysite

Abstract

We report for the first time Pd nanoparticles (NPs) supported on natural halloysite as catalysts for selective production of p-cymene from waste tire pyrolysis (WTP). The catalysts were prepared by dispersing Pd NPs on either the inner (PdHin, 3.4 nm) or outer surface (PdHout, 1.6 nm) of halloysite nanotubes to produce different acid–base properties. The performance of these catalysts for WTP was studied by micropyrolysis coupled to mass spectrometry (Py-GC/MS) between 400 and 500 °C and for discrete times (2, 12, 20, and 40 s). PdHin exhibited twice the selectivity (42%) of PdHout, which was attributed to its higher acidity (1.74 mequiv g–1) and its bifunctionality established between the support’s acidity and the Pd0 sites. From discrete time-dependent experiments, we estimated activation energies for waste tire conversion (72.8 kJ/mol) and p-cymene production on PdHin (101.0 kJ/mol) under a kinetically controlled regime (Biot ∼3.1, PyI ≫1, and PyII ≫1).