Oxidative steam reforming of HDPE pyrolysis volatiles on Ni catalysts: Effect of the support (Al2O3, ZrO2, SiO2) and promoter (CeO2, La2O3) on the catalyst performance

Abstract

High density polyethylene (HDPE) pyrolysis and in-line oxidative steam reforming was carried out in a two-step reaction system consisting of a conical spouted bed reactor and a fluidized bed reactor. Continuous plastic pyrolysis was conducted at 550 °C and the volatiles formed were fed in-line to the oxidative steam reforming step (space-time 3.12 g_cat min g_HDPE⁻¹; ER = 0.2 and steam/plastic = 3) operating at 700 °C. The influence Ni based reforming catalyst support (Al₂O₃, ZrO₂, SiO₂) and promoter (CeO₂, La₂O₃) have on HDPE pyrolysis volatiles conversion and H₂ production was assessed. The catalysts were prepared by the wet impregnation and they were characterized by means of N₂ adsorption-desorption, X-ray fluorescence, temperature-programmed reduction and X-ray powder diffraction. A preliminary study on coke deposition and the deterioration of catalysts properties was carried out, by analyzing the tested catalysts through temperature programmed oxidation of coke, transmission electron microscopy, and N₂ adsorption-desorption. Among the supports tested, ZrO₂ showed the best performance, attaining conversion and H₂ production values of 92.2% and 12.8 wt%, respectively. Concerning promoted catalysts, they led to similar conversion values (around 90%), but significant differences were observed in H₂ production. Thus, higher H₂ productions were obtained on the Ni/La₂O₃-Al₂O₃ catalyst (12.1 wt%) than on CeO₂ promoted catalysts due to La₂O₃ capability for enhancing water adsorption on the catalyst surface.