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Preparation Of Eggshell MoO3/Al2O3 Catalysts By Solvent Assisted Spreading Of MoO3 Over Al2O3 Extrudates: Effect Of MoO3 Particle Size And Temperature On Rate Of Spreading

Miroslav Zdrazil, Ludek Kaluza, Daniela Gulkov�?�?�?�?�?�?�?¡

MoO3/Al2O3 catalysts with sharp and deep eggshell profiles of Mo concentration were prepared by solvent assisted spreading, which is the reaction of Al2O3 extrudates with MoO3/H2O slurry. The profiles were visualized by two methods: electron probe microanalysis and sulfidation of samples. The concentration of Mo in the shell corresponded to the saturated monolayer loading. The dispersion of different sorts of MoO3 was characterised by XRD, N2 physisorption, the conductivity of their dispersion in water and solubility determined by AAS. MoO3 ground in planetary mill was of higher dispersity and reacted faster with Al2O3 extrudates than MoO3 ground in agate mortar mill. Using the extrudates of diameter 3.2 mm and SBET = 217 m2g-1 and the MoO3 ground in planetary mill, the shell of 0.8 mm thickness was formed after about 4 h, and the whole extrudate profile was saturated after about 24 h at 25 oC. The rate of the solvent assisted spreading increased exponentially with temperature in the range 25-100 oC; the shell thickness of 0.8 mm mentioned above was achieved after 1 h at 100 oC. It was shown with Al2O3 particles in the form of hollow cylinders, hollow stars and crosses that well developed sharp profiles copying the shape of particles can be achieved with any complex shape of the support. It was checked that activity in thiophene hydrodesulfurization of the active phase deposited by solvent assisted spreading was the same or slightly better than activity of the active phase deposited by conventional impregnation.