Pyrolysis-catalytic gasification of plastic waste for hydrogen-rich syngas production with hybrid-functional Ni-CaO-Ca2SiO4 catalyst

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-CaO-Ca2SiO4 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.