Abstract
The study presented herein examines, for the first time in the literature, the role of CaO-MgO as a modifier of γ-Αl2O3 for Ni catalysts for the production of green diesel through the deoxygenation of palm oil. The characteristics of the catalytic samples were examined by N2 adsorption/desorption, XRD, NH3-TPD, CO2-TPD, H2-TPR, XPS and TEM analysis. The carbon deposited on the catalytic surfaces was characterized by TPO, Raman and TEM/HR-TEM. Experiments were conducted between 300 and 400 °C, at 30 bar. Maximum triglyceride conversion and the yield of the target n–C15–n–C18 paraffins increased with temperature up to 375 °C for both catalysts. Both samples promoted deCO2 and deCO deoxygenation reactions much more extensively than HDO. However, although both catalysts exhibited similar activity at the optimal temperature of 375 °C, the Ni/modAl was more active at lower reaction temperatures, which can be probably understood on the basis of the increased dispersion of Ni on its surface and its lower acidity, which suppressed hydrocracking reactions. Time-on-stream experiments carried out for 20 h showed that the Ni/modAl catalyst was considerably more stable than the Ni/Al, which was attributed to the lower amount and lower crystallinity of the carbon deposits and to the suppression of sintering due to the presence of the CaO-MgO modifiers.
•Ni on CaO-MgO-Al2O3 highly selective and stable for green diesel production.•Presence of CaO and MgO leads to significantly increased amount of Ni0 active phase.•Presence of CaO and MgO prevents Ni sintering during reaction.•Presence of CaO and MgO leads to the formation of less graphitic carbon structures.