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[Display omitted] • Co promotion do not alter metal-support interactions compared to non-promoted systems. • Co promotion is not surface-dependent but contingent to the formation of MoS 2. • Highest catalytic activity for metal-support interactions of intermediate strength. The current environmental and industrial contexts require constant revision and improvement of hydrotreating processes for obtaining cleaner (bio)fuels through the development of supported transition metal sulfide (TMS) catalysts. The present work proposes a surface-science approach to describe the surface-dependent genesis of the cobalt-promoted active phase (CoMoS) supported on α-Al 2 O 3 single crystals used as surrogates of the industrial γ-Al 2 O 3 support. Co-Mo precursor solutions are deposited by aqueous-phase impregnation onto four α-Al 2 O 3 single crystals of C(0001), A (11 2 ¯ 0) , M (10 1 ¯ 0) , and R (1 1 ¯ 02) orientations, which display specific OH sorption sites. The model catalysts are characterized in the oxide and sulfide states by XPS, AFM, and TEM revealing a surface dependent sulfidation and dispersion as a result of metal-support interactions of diverse nature. The surfaces can be ranked following metal-support interactions of increasing strength C(0001) < A (11 2 ¯ 0) , M (10 1 ¯ 0) < R (1 1 ¯ 02) in good agreement with model non-promoted catalysts. However, AFM and TEM imaging also reveal that cobalt incorporation leads to an increase in the stacking of CoMoS particles with respect to non-promoted catalysts. The activity of the model catalysts in thiophene hydrodesulfurization cannot be simply related to the common features of the active phase (sulfidation, dispersion, promotion extent) but a volcano-shape curve is obtained when plotting the activity as a function of metal-support interactions. These results suggest that high activity is obtained on surfaces with intermediate metal-support interactions that lead to an optimal metal-sulfur bond energy in agreement with the Sabatier principle. Transposing these results to the traditional γ-Al 2 O 3 support suggests an enhanced activity of the (1 0 0) facet, which can lead to the development of improved supports for hydrotreating catalysts. [ABSTRACT FROM AUTHOR]

The constant improvement of hydrotreating (HDT) catalysts, driven by industrial and environmental needs, requires a better understanding of the interactions between the oxide support (mostly alumina) and the MoS 2 active phase. Hence, this work addresses the support-dependent genesis of MoS 2 on four planar single-crystal α-Al 2 O 3 surfaces with different crystal orientations (C (0 0 0 1), R ( 1 1 ¯ 0 2 ) , M ( 1 0 1 ¯ 0 ) , and A ( 1 1 2 ¯ 0 ) ). In contrast to classical surface science techniques, which often rely on UHV-type deposition methods, Mo is introduced by impregnation from an aqueous solution in order to mimic standard incipient wetness impregnation. Comparison between different preparation routes, impregnation vs. equilibrium adsorption (selective adsorption), is also considered. Atomic force microscopy, X-ray absorption spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy show that the α-Al 2 O 3 orientation has a clear impact on the strength of metal–support interactions in the oxide state with consequences for the sulfidation, size, stacking, and orientation of MoS 2 slabs. Aggregation of molybdenum oxide particles is observed on the C (0 0 0 1) plane, suggesting weak metal–support interactions leading to a high sulfidation degree with large slabs. Conversely, the presence of well-dispersed individual oxide particles on the R ( 1 1 ¯ 0 2 ) plane implies stronger metal–support interactions, leading to a low sulfidation degree and shorter MoS 2 slabs. Both A ( 1 1 2 ¯ 0 ) and M ( 1 0 1 ¯ 0 ) facets, of similar crystallographic structure, display intermediate behavior in terms of sulfidation rate and MoS 2 size, in line with intermediate metal–support interactions. Polarization-dependent grazing-incidence-EXAFS experiments, as well as high-angle annular dark-field (HAADF) scanning transmission electron microscopy analysis, allow us to demonstrate a surface-dependent orientation of MoS 2 slabs. Predominant basal bonding is suggested on the C (0 0 0 1) plane, in agreement with the existence of weak metal–support interactions. Conversely, a random orientation (edge and basal bonding) is observed for the other planes. Generalization of these conclusions to industrial catalysts is proposed, based on comparison of the surface structure of the various model α-Al 2 O 3 orientations used in this work and the predominantly exposed γ-Al 2 O 3 surfaces ((1 1 0), (1 0 0), and (1 1 1)). [ABSTRACT FROM AUTHOR]