Spatially Resolved Raman and UV‐visible‐NIR Spectroscopy on the Preparation of Supported Catalyst Bodies: Controlling the Formation of H 2 PMo 11 CoO 40 5− Inside Al 2 O 3 Pellets During Impregnation

The physicochemical processes that occur during the preparation of CoMo–Al 2 O 3 hydrodesulfurization catalyst bodies have been investigated. To this end, the distribution of Mo and Co complexes, after impregnation of γ‐Al 2 O 3 pellets with different CoMoP solutions (i.e., solutions containing Co, Mo, and phosphate), was monitored by Raman and UV‐visible‐NIR microspectroscopy. From the speciation of the different complexes over the catalyst bodies, insight was obtained into the interaction of the different components in the impregnation solution with the Al 2 O 3 surface. It is shown that, after impregnation with a solution containing H 2 PMo 11 CoO 40 5− , the reaction of phosphate with the Al 2 O 3 leads to the disintegration of this complex. The consecutive independent transport of Co 2+ complexes (fast) and Mo 6+ complexes (slow) through the pores of the Al 2 O 3 is envisaged. By the addition of extra phosphate and citrate to the impregnation solution, the formation of the desired heteropolyanion can be achieved inside the pellets. Ultimately, the H 2 PMo 11 CoO 40 5− distribution could be controlled by varying the aging time applied after impregnation. The power of a combination of spatially resolved spectroscopic techniques to monitor the preparation of supported catalyst bodies is illustrated.