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The ability to gain access to the speciation of hydrodesulfurization (HDS) catalysts used for removing sulfur and nitrogen from transportation fuels is becoming a key feature in the understanding and improvement of their catalytic activity with the aim of reducing greenhouse gas emissions of fossil fuels. A novel coupling methodology between Raman spectroscopy and X‐ray absorption spectroscopy (XAS) was developed, which allows for precise qualitative and quantitative analysis of the oxide phase of Mo‐based catalysts. This enabled the detailed study of various impregnation parameters and the characterization of HDS catalysts before sulfidation. To illustrate this methodology, the effects of two additives (triethylene glycol and citric acid) were studied. The results demonstrated that organic additives exert a profound influence on the speciation of oxide precursors of molybdenum‐based catalysts. The presence of these additives enhances the dispersion of Keggin or Dawson heteropolyanions (HPAs) on the support by maintaining a high phosphorus‐to‐molybdenum ratio in solution. This is achieved by two strategies: triethylene glycol (TEG) exhibits a pronounced affinity for alumina hydroxyls, while citric acid compensates for phosphate adsorption through the formation of a stable Mo‐citrate complex. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To study the influence of ageing and drying steps onto the multiscale Mo active phase arrangement (i. e. MoS2 slabs and slab aggregates), a series of highly loaded CoMoP/γ‐Al2O3 catalysts aged, unaged, dried or freeze‐dried were prepared and tested in toluene hydrogenation. Electron Probe Micro Analyses (EPMA) and Anomalous Small Angle X‐Ray Scattering (ASAXS) permit to highlight the influence of each preparation steps. A growth of Mo entities occurs during ageing along with metal diffusion inside the support and leads to longer slabs. The same occurs during drying with metal redistribution due to solvent evaporation. Concomitantly, a fragmentation of slab aggregates takes place and leads to numerous small slabs aggregates. Slab length and aggregates amount were found to drive the catalytic activity, which translates the relationship between activity, number of active sites and their accessibility. Conversely, macroscopic metal distribution into the extrudates appears to have no impact on the catalytic performance. [ABSTRACT FROM AUTHOR]

Environmental regulations concerning fuel‐related sulfur emissions are currently experiencing worldwide expansion. This is motivating the research and development of improved hydrotreating (HDT) catalysts with carefully engineered synthesis methods that maximize activity as ultimate goal. In this contribution, the effect of phosphorus doping and triethylene glycol (TEG) incorporation on the genesis of the CoMoS phase of model HDT catalysts is assessed. Following a surface‐science approach, α‐Al2O3 single crystals with four orientations: C(0001), A(112‾ 0), M(101‾ 0), and R(11‾ 02) are used as model supports of the traditional γ‐Al2O3 support for the study of active phase‐support interactions at the molecular scale. The model catalysts are prepared by traditional impregnation of a solution containing metal and phosphorus precursors and TEG. The catalysts are characterized in the sulfide phase by XPS, XAS, TEM, and AFM, revealing that the calcination step is key in the emergence of distinctive metal‐support interactions, which are directly related to the nature of alumina surface sorption sites. In addition, TEG incorporation on dried catalysts increases metal sulfidation and enhances promotion with respect to non‐additivated systems, especially at mild sulfidation temperatures. The catalytic activity of the model catalysts is tested in a thiophene hydrodesulfurization reaction, revealing the following activity trend with respect to alumina surface orientations: A112‾0 ≫ M101‾0 >R11‾02 , C(0001). This trend is identical to the one observed for non‐phosphorus doped non‐TEG additivated model systems, confirming the predominance of surface effects on the catalytic activity over those exerted by P and TEG. By transposing these results to the industrial γ‐Al2O3 support, the (100) facet would provide surface sites that lead to better performing catalysts. This could result in the development of novel supports, engineered to expose surface sites that maximize hydrotreating activity. [ABSTRACT FROM AUTHOR]