Effect of eggshell- and homo-type Ni/Al₂O₃ catalysts on the pyrolysis of food waste under CO₂ atmosphere

This study highlights the potential of pyrolysis of food waste (FW) with Ni-based catalysts under CO₂ atmosphere as an environmentally benign disposal technique. FW was pyrolyzed with homo-type Ni/Al₂O₃ (Ni–HO) or eggshell-type Ni/Al₂O₃ (Ni-EG) catalysts under flowing CO₂ (50 mL/min) at temperatures from 500 to 700 °C for 1 h. A higher gas yield (42.05 wt%) and a lower condensable yield (36.28 wt%) were achieved for catalytic pyrolysis with Ni-EG than with Ni–HO (34.94 wt% and 40.06 wt%, respectively). In particular, the maximum volumetric content of H₂ (21.48%) and CO (28.43%) and the lowest content of C₂–C₄ (19.22%) were obtained using the Ni-EG. The formation of cyclic species (e.g., benzene derivatives) in bio-oil was also effectively suppressed (24.87%) when the Ni-EG catalyst and CO₂ medium were concurrently utilized for the FW pyrolysis. Accordingly, the simultaneous use of the Ni-EG catalyst and CO₂ contributed to altering the carbon distribution of the pyrolytic products from condensable species to value-added gaseous products by facilitating ring-opening reactions and free radical mechanisms. This study should suggest that CO₂-assisted catalytic pyrolysis over the Ni-EG catalyst would be an eco-friendly and sustainable strategy for disposal of FW which also provides a clean and high-quality source of energy.