Chemical Speciation by Quick-XAS and Raman Spectroscopy: Validation of Two Cells for in situ Time-Resolved Monitoring of the Impregnation and Drying of CoMoP/Al2O3 Catalysts

This paper aims to describe and validate two cells designed to monitor, by in situ quick-EXAFS, the transformation of Mo based oxidic species occurring during maturation and drying preparation steps of a single hydrodesulfurization catalyst. These transformations occur firstly upon impregnation/maturation, due to the contact of the acidic impregnation solution with the basic alumina support, and furthermore upon drying. The Mo K edge in situ quick-EXAFS monitoring of these two elementary preparation steps is hereby reported for the first time, providing quantitative results of the Mo-speciation. Ex situ Raman spectroscopy is used effectively as a complement. It considers an impregnation solution with a Mo concentration of 0.75 M and molar ratios of P/Mo 0.56 and Co/Mo 0.4. A two-step drying mechanism is proposed to explain the evolution of the Mo-speciation during in situ drying where Strandberg's, Anderson's and Dawson's HPAs are transformed into lacunary Keggin's HPA, octa- and monomolybdates.