Fabrication of mesopore-rich HZSM-5 to boost the degradation of plastic wastes

Abstract

Plastic waste is causing serious environment pollution and its efficient disposal is attracting more and more attention. The use of catalysts not only reduced the degradation temperature of plastic wastes but also facilitated the production of valuable chemicals. Herein, mesopores were introduced into HZSM-5 zeolites by alkali and acid treatment, which was expected to eliminate the diffusion resistance caused by bulky polymer molecules and improve the catalytic activity. It was found that HZSM-5 zeolites enhanced PE, PP and PS degradation, and an increase of mesopore volume further improved the catalytic activity and reduced the activation energy. For example, the use of HZSM-5 in PP degradation decreased the activation energy from 146.9 kJ mol⁻¹ to 93.1 kJ mol⁻¹, and mesopore-rich HZSM-5 further decreased the activation energy to 84.0 kJ mol⁻¹. The molecular diameter of the PP fragment was obtained by theoretical calculations, and it was close to 1.6 nm, which was significantly higher than the micropore diameter of HZSM-5 zeolites (0.5–0.6 nm) while lower than the mesopore diameter. It was concluded that the presence of mesopores provided the place and space for plastics degradation.