Microwave catalytic co-pyrolysis of Chlorella vulgaris and wasted tires under NiO/CoO loaded on γ-Al2O3: Characteristics, production analysis and reaction mechanism

Catalysts effectively promote hydrodeoxygenation and denitrification, upgrading the pyrolysis liquid quality. This paper prepared X@γ-Al₂O₃ (X = NiO, CoO) catalysts by respectively loading NiO/CoO on γ-Al₂O₃. Different additions (10 wt%, 20 wt%, 30 wt% relative to feedstocks) effect of X@γ-Al₂O₃ on microwave co-pyrolysis of Chlorella vulgaris (CV) and waste tires (WT) were studied. The co-pyrolysis characteristics of CV and WT were improved by X@γ-Al₂O₃, while different metal active centers led to varying catalytic properties. Compared with CV: WT= 6:4 (noted as C6W4), 30 wt% NiO@γ-Al₂O₃ obtained the best catalytic effect on pyrolysis characteristics, with the maximum average weight loss rate (0.01952 wt%/s) and the maximum weight loss rate (0.05752 wt%/s). In contrast, when CoO@γ-Al₂O₃ addition exceeded 10 wt%, extensive carbon deposition deactivated numerous catalytic sites, leading to deteriorated catalytic performance. Compared with C6W4, the liquid yield under X@γ-Al₂O₃ was reduced by 4.40 %-10.37 %, while gas raised by 4.71 %-11.61 %. The aromatic hydrocarbons yield under 10 wt% CoO@γ-Al₂O₃ and 30 wt% NiO@γ-Al₂O₃ were respectively increased by 37.96 % and 41.12 % compared to C6W4, through promoting hydrogenation, deoxidation, cyclization, and aromatization. Furthermore, the pyrolysis liquid nitrogen and oxygen content were significantly reduced by catalysts. The highest denitrification (55.77 %) and deoxidation efficiency (43.53 %) were respectively obtained at 10 wt% CoO@γ-Al₂O₃ and 30 wt% NiO@γ-Al₂O₃. This study realizes the high-value reuse of solid waste, and provides theoretical guidance for new catalysts application under microwave co-pyrolysis.