Pyrolysis-catalytic gasification of plastic waste for hydrogen-rich syngas production with hybrid-functional Ni-CaOCa2SiO4 catalyst

Abstract

The production of H₂-rich syngas from pyrolysis-catalytic gasification of plastic waste bottles has been investigated. The hybrid-functional materials consisting of Ni as catalyst, CaO as CO₂ sorbent and Ca₂SiO₄ as a polymorphic active spacer were synthesized. The different parameters (Ni loading, temperature, N₂ flow rate and feedstock-to-catalyst ratio) have been investigated to optimise the H₂ production. The catalysts were analysed by N₂ physisorption, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Temperature-programmed reduction (TPR) and in-situ Transmission Electron Microscopy (TEM). Temperature-programmed oxidation (TPO) was used to analyse the carbon formation on the used catalysts. The highest H₂ production of 59.15 mmol g^-1_{of plastic} was obtained in the presence of a catalyst with 20 wt.% Ni loading, which amounts to H₂ purity as high as 54.2 vol% in gas production. Furthermore, 90.63 mmol g^-1_{of plastic} of syngas was produced by increasing the feedstock-to-catalyst ratio to 4:1, yielding 84.4 vol.% of total gas product (53.1 vol.% of H₂ and 31.3 vol.% of CO, respectively). The Ni-CaOCa₂SiO₄ hybrid-functional material is a very promising catalyst in the pyrolysis-catalytic gasification process by capturing CO₂ as it is produced, therefore shifting the water gas shift (WGS) reaction to enhance H₂ production from plastic waste. Detailed elucidation of the roles of each component at the microscale during the catalytic process was also provided through in-situ TEM analysis. The finding could guide the industry for future large-scale application to convert abundant plastic waste into H₂-rich syngas, therefore contributing to the global ‘net zero’ ambition.