Upgrading of plastic waste-derived wax through air gasification using promoted Ni/Al₂O₃ catalysts for H₂ generation

Catalytic air gasification of plastic waste-derived wax (PW) was performed using Ni/X-Al₂O₃ (X = Ti, Sr, or La) catalysts to produce H₂-rich gas for the first time. For this purpose, X-Al₂O₃ supports were primarily synthesized by doping different promoters into the Al₂O₃ structure, followed by the loading of Ni. The catalytic performances of prepared catalysts were compared with that of 10Ni/Al, prepared by impregnation of Ni into commercial γ-Al₂O₃. Compared with using 10Ni/Al, the use of Ni/X-Al₂O₃ catalysts resulted in higher activity and selectivity, wherein the highest gas yield (74.78 wt%) and H₂ selectivity (25.30 vol%) were achieved using 10Ni/5Ti-Al. Also, the coke yield effectively decreased when using Ni/X-Al₂O₃ catalysts, particularly 10Ni/5Ti-Al, compared with using 10Ni/Al. These findings are ascribed to the versatile effects of well-dispersed metallic Ni active sites, increased density of Lewis acidic sites at the expense of Brønsted acid sites, and enhanced oxygen transfer capacity of the catalyst owing to Ti addition. Moreover, increasing the concentrations of Ni (up to 10 %) and Ti (up to 5 %) enhanced the catalytic activity and selectivity for H₂ production. Increasing the temperature (up to 750 °C) showed a positive effect on the production of H₂-rich gas. Furthermore, varying the catalyst-to-feedstock ratio affected the gas yield and H₂ selectivity.