Vibrational Spectroscopy in the Study of Oxide (Excluding Zeolites) and Sulfide Catalysts

Abstract

The sections in this article are Introduction Infrared Spectroscopy IR Characterization of Surface Properties of Metal Oxides Information Deriving from the Activated Oxide Spectra Lattice Vibrations Surface Oxide Sites Identification of Main Impurities in Metal Oxides Electronic Transitions Hydroxyl Groups Information Deriving from Probe Adsorption Acidity Basicity Cationic and Redox Sites: Use of Methanol as Probe for Local Arrangement and Oxidation State Determination of Surface Cationic Sites IR Characterization of Oxide and Sulfide Supported Catalysts Information Deriving from the Spectrum of the Activated Catalyst Information Deriving from Probe Molecule Adsorption CUS Characterization of the Sulfided Phase B rønsted Acid Site Characterization of the Sulfided Phase Site Transformation in the Presence of H 2 Surface Characterization and Catalysis Conclusion R aman Spectroscopy General Considerations Bulk Oxide Catalysts Supports Supported Oxides Nature of the Supported Oxide Chemical Processes Involved During Catalyst Synthesis Adsorption of Probe Molecules Surface B rønsted and Lewis Acid Sites Adsorption of Molecules Acting as Reagents Active Phase: Genesis and Characterization Genesis of the Hydrodesulfurization Active Phase Sulfided Catalyst Catalyst Reactivity Conclusion Concluding Remarks and Outlook

New insight in the preparation of alumina supported hydrotreatment oxidic precursors: A molecular approach

“…Indeed, the XANES spectrum of the calcined solids exhibits an intense pre-edge characteristic of the tetrahedral environment [10]. Moreover, the Raman spectrum (Fig 3f) exhibits a main line at 1000 cm -1 that has been assigned to the stretching mode of the molybdenyl group (MoO t ) in distorded tetrahedral entities [11,12]. This suggests that upon calcination the AlMo 6 entities are decomposed and that the oxomolybdate surface phase consists of distorted tetrahedral entities with single molybdenyl groups that are linked to the support.…”

Lanthanum oxides for the selective synthesis of phytosterol esters: Correlation between catalytic and acid–base properties

“…It has been considered that the ν 3 splitting of this degenerated ν 3 vibration should selectively characterize each species structure [26]. According to the literature [17,27], the splitting of the ν 3 mode is far more pronounced for the carbonate structures I and Ia with respect to that commonly observed for mineral carbonates (type II). In our case, after the thermal treatment at 873 K under O 2 , only the most stable carbonate species were present on the surface of lanthanum oxides.…”

“…The possibility that the ν 3 splitting is specific to a given carbonate species structure has been considered; its value was about 100 cm −1 for unidentate species, 300 cm −1 for bidentate species, and 400 cm −1 for bridging species. Unidentate carbonates are currently less stable than bidentates [27]. If a carbonate species shows a strong resistance to thermal treatment and exhibits rather low ν 3 splitting, it likely corresponds to a polydentate structure [27].…”

“…Unidentate carbonates are currently less stable than bidentates [27]. If a carbonate species shows a strong resistance to thermal treatment and exhibits rather low ν 3 splitting, it likely corresponds to a polydentate structure [27]. On the basis of such principles and empirical observations, as well as a comparison of the thermal stability of the different species, we assigned the bands at 1455-1384 and 1515-1361 cm −1 to polydentate and bidentate carbonates, respectively ( Fig.…”

Pt/TiO2 brain biocompatible nanoparticles: GBM treatment using the C6 model in Wistar rats

“…Vibrational spectroscopy of adsorbed probe molecules is one of the most powerful tools to assess acidic properties of surfaces [16]. The adsorption of probe molecules is used in order to characterize the surface acid-base properties of our materials.…”