Raman microscopy has been applied to study the preparation of shaped Mo/Al2O3 catalysts. The speciation of different Mo complexes over γ-Al2O3 support bodies was followed in time after pore volume impregnation with aqueous solutions containing different Mo complexes. The addition of NO3 -to the impregnation solutions allows for a quantitative Raman analysis of the distribution of different complexes over the catalyst bodies as this ion can be used as an internal standard. After impregnation with an acidic ammonium heptamolybdate (AHM) solution, the strong interaction between Mo7O24 6-and Al2O3 results in slow transport of this complex through the support and extensive formation of Al(OH)6Mo6O18 3-near the outer surface of the support bodies. This may be prevented by decreasing the interaction between Mo and Al2O3. In this way, transport is facilitated and a homogeneous distribution of Mo is obtained on a reasonable time scale. A decrease in interaction between Mo and Al2O3 can be achieved by using alkaline impregnation solutions or by the addition of complexing agents, such as citrate and phosphate, to the impregnation solution. In general, time-resolved in situ Raman microscopy can be a valuable tool to study the physicochemical processes during the preparation of supported catalysts.

The physicochemical processes that occur during the preparation of CoMo–Al2O3 hydrodesulfurization catalyst bodies have been investigated. To this end, the distribution of Mo and Co complexes, after impregnation of γ‐Al2O3 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 Al2O3 surface. It is shown that, after impregnation with a solution containing H2PMo11CoO405−, the reaction of phosphate with the Al2O3 leads to the disintegration of this complex. The consecutive independent transport of Co2+ complexes (fast) and Mo6+ complexes (slow) through the pores of the Al2O3 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 H2PMo11CoO405− 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.

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Spatially resolved Raman and UV-vis-NIR microspectroscopy have been used as tools to study the preparation process of supported catalyst bodies. Detailed spectroscopic information on the local coordination geometry of two different metallic species along with their macro-distribution over the catalyst body has been obtained, enabling a good understanding of the physicochemical processes occurring during the drying process of impregnated γ-Al 2 O 3 bodies. The formation and decomposition of the Keggin-type complex H x PMo 11 CoO 40 (7-x)-, which is considered to be a potential precursor for CoMoS 2 /γ-Al 2 O 3 HDS catalysts, inside γ-Al 2 O 3 bodies is shown to be a function of the composition of the impregnation solutions, the aging time, and the drying conditions applied. This knowledge has been successfully applied to prepare samples with a well-defined distribution of the bimetallic complex, that is, either egg-shell, egg-yolk, or homogeneous distributions. The Raman results are presented in a semiquantitative way by subtraction of a reference spectrum of a sample containing a known amount of H x PMo 11 CoO 40 (7-x)from the spectra recorded along the cross-section of the catalyst bodies.