Effect of Pore Structure of Ni–Mo/Al₂O₃ Catalysts in Hydrocracking of Coal Derived and Oil Sand Derived Asphaltenes

Effect of catalyst pore structure was studied by using four unimodal Ni–Mo/Al₂O₃ having different median pore diameters (MPD, 120–730 Å) for hydrocracking (425 °C, 1 h, 4.9 MPa H₂) of the asphaltenes derived from Akabira coal (Aka-Asp) and Athabasca oil sand bitumen (Aosb-Asp). The asphaltene conversions increased with increasing catalyst MPD up to 290 Å and then remained constant or decreased up to 730 Å. Aka-Asp has a much smaller molecular size but a higher aromaticity than Aosb-Asp, whereas conversion of the former appeared to be more sensitive to pore size. Higher oil yields were obtained with large-pore catalysts, while the highest oil yield from Aosb-Asp was still remarkably lower than that from Aka-Asp. Maximum hydrodeoxygenation activity appeared at an MPD of 150 Å for runs of both asphaltenes, while an MPD of 290 Å corresponded to the highest activity for hydrodesulfurization of the sulfur-rich Aosb-Asp. Characteristics of used catalysts are also discussed.