MoO3/Al2O3 Catalyst: Comparison of Catalysts Prepared by New Slurry Impregnation with Molybdic Acid with Conventional Samples

Alumina-supported molybdena catalysts were prepared by conventional impregnation with (NH4)6Mo7O24 (CIM) and by a new slurry impregnation method (SIM). SIM is the reaction of alumina support with the slurry of MoO3 in water. Two commercial supports were used and the commercial MoO3/Al2O3 catalyst was included for comparison. Maximum amount of MoO3 deposited by SIM was about 19-20% MoO3 with the surface area of the support of 260-280m2 g-1 and this corresponded to saturation monolayer of similar density as described in literature for CIM catalysts. At the ratios of MoO3 to Al2O3 in the impregnation slurry below saturation monolayer, the pH of the slurry was 3.5-6 (depending on loading) and chemical erosion of alumina was negligible. However, using the large excess of MoO3 (35% MoO3), the pH was 2.4-3.4 and chemical erosion of alumina occurred. Silica contained in alumina supports was partly extracted as soluble silicomolybdic anions during SIM. The catalysts were characterized by BET, IR, DRS (UV-vis and NIR), TPR, and catalytic activity in hydrodesulfurization of thiophene. Calcination had no significant effect on the properties of SIM catalysts and this proved that calcination is not needed in that method. All catalysts exhibited features of high monolayer dispersion of molybdena and no significant difference in structure and catalytic properties was observed between SIM and CIM catalysts. This confirmed that SIM is a simple, clean and reliable method of preparation of monolayer typeMoO3/Al2O3 catalysts.