Influence of the preparation method on the hydrotreating activity of MoS2/Al2O3 extrudates: A Raman microspectroscopy study on the genesis of the active phase

Abstract

Raman microspectroscopy was used to study the preparation of industrial MoS 2 /Al 2 O 3 extrudates. Using this technique, the influence of the impregnation solution composition on the nature and macrodistribution of Mo complexes inside these catalyst bodies was evaluated during their preparation process (impregnation, drying, and calcination). It was found that poor dispersion of the MoO x phase in the calcined samples can be brought about by the formation of bulk (NH 4) 3 [Al(OH) 6 Mo 6 O 18 ] during impregnation or redistribution of Mo complexes during drying. The formation of crystalline MoO 3 and Al 2 (MoO 4) 3 in the oxidic precursors leads to a poorly dispersed MoS 2 phase in the final catalyst and significantly lower hydrodesulfurization activity. The spatially resolved information that can be obtained, and its inherent sensitivity for the detection of crystalline phases make Raman microspectroscopy a powerful characterization technique for studying the preparation of industrial supported metal oxide catalysts.

Tomographic Energy Dispersive Diffraction Imaging as a Tool To Profile in Three Dimensions the Distribution and Composition of Metal Oxide Species in Catalyst Bodies

“…As can be seen from the data, the dried Mo/Al 2 O 3 catalyst body contains no crystalline phases, aside from the support material, and has an inhomogeneous eggshell distribution of molybdenum. This result is consistent with earlier Raman microspectroscopy data, [9] which allowed us to assign the origin of this molybdenum signal to the presence of the [Al(OH) 6 Figure 2. In addition to the Mo fluorescence and g-Al 2 O 3 diffraction peaks, the MoO 3 crystalline phase has been monitored by measuring the diffractions at 25, 27, and 29 keV, corresponding to the (101), (400/201), and (210) reflections from MoO 3 , respectively.…”

“…Importantly, in hydrotreatment catalytic testing, this Mo/Al 2 O 3 sample displayed inferior performance because of the presence of large crystals of MoO 3 on the periphery of the extrudate and the subsequent difficulty in forming active MoS 2 nanoslabs from this material or from deeper inside the extrudate. [9] We propose that this "eggshell" effect might be caused by either an insufficient equilibration time during the impregnation step or by the high concentration of molybdenum exceeding the dispersion limit of the support.…”

Infrared and Raman imaging of heterogeneous catalysts

“…The Mo complexes formed within the extrudate pores due to local pH variation and the chemical interaction between the precursor and the support could be speciated. 36 After impregnation, the Mo/Al 2 O 3 catalysts are dried and calcined to obtain a MoO 3 which consequently undergoes sulfidation. When the pH of the impregnating solution was not adjusted, the drying resulted in an egg-shell distribution, that is, an enrichment of the outer layer of the pellet.…”

Monitoring Transport Phenomena of Paramagnetic Metal‐Ion Complexes Inside Catalyst Bodies with Magnetic Resonance Imaging

“…[12][13][14][15][16] The possibility to monitor the transport of different components inside catalyst bodies in a noninvasive manner was previously illustrated in a study in which the distribution of phosphate and Pt complexes was determined in a direct manner with a multinuclear (e.g., 31 P and 195 Pt) MRI technique. [17] Recently, we briefly reported how the distribution of paramagnetic [CoA C H T U N G T R E N N U N G (H 2 O) 6 ] 2 + complexes after impregnation of support bodies can be monitored quantitatively in a noninvasive manner via their destructive effect on the 1 H NMR signal of the water solvent in MRI measurements.…”