Insights into the preparation of supported catalysts:: A spatially resolved Raman and UV-vis spectroscopic study into the drying process of CoMo/γ-Al2O3 catalyst bodies

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 gamma-Al2O3 bodies. The formation and decomposition of the Keggin-type complex HxPMo11CoO40(7-x)-, which is considered to be a potential precursor for CoMoS2/gamma-Al2O3 HDS catalysts, inside gamma-Al2O3 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 HxPMo11CoO40(7-x)- from the spectra recorded along the cross-section of the catalyst bodies.