# Physicochemical Properties of Mechanochemical Activated HZSM‑5 Zeolite for Thermocatalytic Pyrolysis of Polypropylene

## TL;DR

This paper explores using ball milling to create HZSM-5 zeolites for converting polypropylene into useful hydrocarbons.

## Contribution

A mechanochemical method to synthesize HZSM-5 zeolites without hydrothermal processing is introduced.

## Key findings

- Five minutes of milling significantly altered the chemical structure and morphology of HZSM-5.
- The catalyst showed high selectivity for C7–C9 monoaromatic hydrocarbons during polypropylene pyrolysis.
- Enhanced porosity and retained acidity of the zeolite contributed to improved catalytic performance.

## Abstract

In this work, we
explore a mechanochemical approach using ball
milling to synthesize hierarchical HZSM-5 zeolites, eliminating the
need for hydrothermal processing. The synthesis was conducted using
dual organic templates, cetyltrimethylammonium bromide (CTMABr), and
tetrapropylammonium bromide (TPABr), under varying conditions of milling
time, rotational speed, and solvent presence. The aim was to investigate
the structural evolution of ZSM-5 under mechanical activation while
avoiding amorphization. Characterization techniques including X-ray
diffraction (XRD), Fourier transform infrared spectroscopy (FTIR),
scanning electron microscopy (SEM), and nitrogen physisorption revealed
that even five minute of milling induced significant modifications
in the chemical structure and morphology. These changes involved recrystallization
processes and the formation of new Si–O and – Al–O–
bonds, resulting in restructured pore environments that may influence
catalytic behavior. The best HZSM-5 sample mechanochemically activated
was evaluated in the thermocatalytic pyrolysis of polypropylene at
475 °C in a fixed-bed reactor, under nitrogen as a gas carrier.
After 30 min of reaction, the products were collected and analyzed
by coupled gas chromatography and mass spectrometry. The catalyst
demonstrated high selectivity toward monoaromatic hydrocarbons in
the C7–C9 range, particularly alkylbenzene,
toluene, xylene, and ethylbenzene. These results suggest a synergistic
effect between the enhanced porosity and retained acidity of the modified
zeolite, offering a promising route for the valorization of plastic
waste into valuable hydrocarbons.