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. Hydrodesulfurization catalysts: This work presents the in situ EXAFS and ex situ Raman monitoring of the impregnation and drying of CoMoP hydrodesulfurization catalysts. Two cells were developed, which allow for the reproduction of the laboratory preparation conditions. The EXAFS spectra revealed that the pristine Strandberg's HPA (HxP2Mo5O23(6−x)−) partially decomposes upon maturation and then fully decomposes upon drying, a two‐step drying mechanism being proposed.