Hydrotreating of Heavy Gas Oil on Mesoporous Mixed Metal Oxides (M-Al2O3, M = TiO2, ZrO2, SnO2) Supported NiMo Catalysts: Influence of Surface Acidity

Mesoporous mixed metal oxides, TiO2Al2O3, ZrO2Al2O3, and SnO2Al2O3, were synthesized using a novel method and were used as a support material for the NiMo hydrotreating catalyst. The catalyst was prepared via the incipient wetness sequential impregnation method. All catalysts were characterized using N-2 adsorptiondesorption isotherms (BET), X-ray diffraction, FTIR, pyridine-FTIR, acridine-FTIR, CO-chemisorption, ICP-MS, TPD, and TPR. The HDS and HDN activities of the catalysts were determined using Athabasca bitumen derived heavy gas oil at industrial reaction conditions. The catalytic activity of synthesized NiMo/gamma-Al2O3 catalyst was also determined for comparative studies. Low angle XRD and BET analysis has confirmed that the method developed for synthesis is suitable for the preparation of a mesoporous mixed oxide based NiMo hydrotreating catalyst. H-2-TPR analysis has confirmed that the introduction of metal oxides such as ZrO2, TiO2, and SnO2 in alumina increases the active metal (Mo) and support (alumina) interactions. The highest reduction temperature is observed in the SnO2 containing catalyst. NH3-TPD has confirmed the increase in acidic strength of catalysts after introduction of metal oxides, and it follows the order NiMo/SnO2Al2O3 > NiMo/ZrO2Al2O3 > NiMo/TiO2Al2O3. It was observed from acridine-FTIR analysis that the catalysts having strong acidic strength hold acridine strongly at high temperatures. This implies that catalysts with higher acidity are prone to inhibition by nitrogen containing compounds present in feed, and it will affect the catalytic activity. The HDS and HDN activities follow the order NiMo/TiO2Al2O3 > NiMo/mesoAl(2)O(3)(mesoporous) > NiMo/ZrO2Al2O3 > NiMo/gamma-Al2O3 > NiMo/SnO2Al2O3. The higher activity of the NiMo/TiO2Al2O3 catalyst is due to higher metal dispersion as observed from CO-chemisorption and a moderate increase in acidic strength. Therefore, increasing the acidity of alumina support to much higher levels by incorporating metal oxides having strong Lewis acidity would not help in enhancing HDN and HDS activity for nitrogen rich feeds, such as Athabasca bitumen derived heavy gas oil due to inhibition effects.