Spatially Resolved Raman and UV‐visible‐NIR Spectroscopy on the Preparation of Supported Catalyst Bodies: Controlling the Formation of H₂PMo₁₁CoO₄₀⁵⁻ Inside Al₂O₃ Pellets During Impregnation

Abstract

The physicochemical processes that occur during the preparation of CoMo–Al2O3 hydrodesulfurization catalyst bodies have been investigated. To this end, the distribution of Mo and Co complexes, after impregnation of γ‐Al2O3 pellets with different CoMoP solutions (i.e., solutions containing Co, Mo, and phosphate), was monitored by Raman and UV‐visible‐NIR microspectroscopy. From the speciation of the different complexes over the catalyst bodies, insight was obtained into the interaction of the different components in the impregnation solution with the Al2O3 surface. It is shown that, after impregnation with a solution containing H2PMo11CoO405−, the reaction of phosphate with the Al2O3 leads to the disintegration of this complex. The consecutive independent transport of Co2+ complexes (fast) and Mo6+ complexes (slow) through the pores of the Al2O3 is envisaged. By the addition of extra phosphate and citrate to the impregnation solution, the formation of the desired heteropolyanion can be achieved inside the pellets. Ultimately, the H2PMo11CoO405− distribution could be controlled by varying the aging time applied after impregnation. The power of a combination of spatially resolved spectroscopic techniques to monitor the preparation of supported catalyst bodies is illustrated.

Revealing Shape Selectivity and Catalytic Activity Trends Within the Pores of H‐ZSM‐5 Crystals by Time‐ and Space‐Resolved Optical and Fluorescence Microspectroscopy

“…To-date, a number of microscopic methods, such as IR, UV/Vis, Raman, and interference microscopy have been applied to study various steps in catalyst preparation and diffusion of organic compounds in the microporous materials. [7][8][9][10][11] Recently, two in-situ microspectroscopic techniques have been developed independently; these techniques allow us to study electrophilic substitution reactions in H-ZSM-5 crystals of micrometer dimensions in a space-and time-resolved manner. The first approach involves the use of an inverted confocal fluorescence microscope, as pioneered by Roef-A C H T U N G T R E N N U N G faers et al, [12,13] to investigate the alkylation of anisole and the self-condensation of furfuryl alcohol at room temperature.…”

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.…”

Monitoring the preparation of (Co)Mo/Al2O3 extrudates using spatially resolved spectroscopic techniques

“…3. and/or on cpordinatively unsaturated Al + -sites on the A1 2 O 3 surface at low pH [16]. A disintegration of the heteropolyanion and the formation of H x Mo 7 [8]. After impregnation with this solution, a slow transport of Mocomplexes is again observed as the O-Mo 6+ charge transfer band is absent in spectra recorded near the center of the pellet, 15 min after impregnation.…”

“…From an extensive spectroscopie study on the speciation of complexes in CoMoP-solutions, it was found that 90% of all Mo present in the CoMoP(O.l) solution is contained in a H 2 PMo,,CoO 40 " heteropolyanion [8]. This specific complex is stable in acidic CoMo-solutions at P:Mo ratios between 0.05 and 0.2.…”

“…Due to the high Raman cross-section of Mo-O vibrations, Raman microscopy is ideally suited to study the speciation of Mocomplexes inside catalyst bodies [6]. The d-d transitions of Co + -complexes that can be observed by UV-Vis micro spectroscopy yield detailed information on the nature and distribution of the Co-precursor in the extrudates [4,8,9]. The experimental procedure used for the spatially resolved Raman and UV-Vis spectroscopy measurements are depicted in Figure 1.…”