Calcination temperature induced structural change of red mud and its enhanced catalytic performance for hydrocarbon-based biofuels production

Abstract

Red mud (RM) is a strongly solid waste from alumina production, and the disposal of RM leads to series of environmental problems such as alkalization of occupied land and pollution of nearby water systems. Using RM as catalyst or carrier is one of the important methods for the comprehensive utilization of RM. Herein, the application of Ni supported RM (Ni/RM) for the efficient hydrodeoxygenation (HDO) of waste oils to produce hydrocarbon-based biofuels is reported. The structural properties of Ni/RM catalysts were investigated. The catalytic performance for HDO of palmitic acid as the model compound was evaluated. The results showed that RM calcinated at low temperature (400–600 °C) has a larger specific surface area and well dispersion of Ni, while the high calcination temperature (700 °C ~ 900 °C) results in sintering of metal oxides and lower dispersion of Ni. Ni/RM-500 shows the largest specific surface area of 77 m2/g. The conversion of palmitic acid over Ni/RM-500 is 100% at 250 °C, and alkanes are the only products at 300 °C. The reaction path of HDO and DCO/DCO2 is related to reaction temperature. The Ni/RM-500 shows the feasibility to different feedstocks. Finally, the catalytic performance of Ni/RM-500 was tested for 135 h, and the main reason causing the deactivation of Ni/RM-500 was revealed.