Photoinduced reactivity of titanium dioxide

Ordered mesoporous materials in catalysis

Supported Catalysts Weiting Yu,† Marc D. Porosoff,† and Jingguang G. Chen*,†,‡,§ †Catalysis Center for Energy Innovation, Department of Chemical and Bimolecular Engineering, University of Delaware, Newark, Delaware 19716, United States ‡Department of Chemical Engineering, Columbia University, New York, New York 10027, United States Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, United States

Review of Pt-based bimetallic catalysis: from model surfaces to supported catalysts.

Nanostructured oxides in chemistry: characterization and properties.

Oxidative dehydrogenation of ethane and propane : How far from commercial implementation?

https://www.lehigh.edu/operando/Publications/1999%20Titania-silica%20molec%20struc%20physico-chemical.pdf

Titania-silica as catalysts : molecular structural characteristics and physico-chemical properties

The molecularly dispersed V2O5/SiO2 supported oxides were prepared by the incipient wetness impregnation of 2-propanol solutions of V-isopropoxide. The experimental maximum dispersion of surface vanadium oxide species on SiO2 was achieved at ∼12 wt % V2O5 (∼2.6 V atoms/nm2). The surface structures of the molecularly dispersed V2O5/SiO2 samples under various conditions were extensively investigated by in situ Raman, UV−vis−NIR DRS and XANES spectroscopies. The combined characterization techniques revealed that in the dehydrated state only isolated VO4 species are present on the silica surface up to monolayer coverage. Interestingly, the three-member siloxane rings on the silica surface appear to be the most favorable sites for anchoring the isolated, three-legged (SiO)3VO species. Hydration dramatically changes the molecular structure of the surface vanadium oxide species. The specific structure of the hydrated surface vanadium oxide species is dependent on the degree of hydration. The molecular structure ...

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In Situ Spectroscopic Investigation of Molecular Structures of Highly Dispersed Vanadium Oxide on Silica under Various Conditions

UV−vis−NIR diffuse reflectance spectroscopy (DRS) was applied to study the local structures of V(V) cations on various oxide supports (Al2O3, ZrO2 TiO2, Nb2O5, CeO2, and SiO2) under hydrated and dehydrated conditions. The edge energy (Eg) of the LMCT transitions of V(V) cations was used to elucidate the local structures of V(V) cations, and a correlation between the edge energy and the number of the covalent V−O−V bonds (CVB) around the central V(V) cations was established based on some V(V) reference compounds/oxides. For TiO2, Nb2O5, and CeO2 supported vanadia catalysts, the strong support absorption in the same region as the V(V) cations prevents a reliable determination of the local structure of the surface vanadium oxide species by either the LMCT band position or the edge energy. For Al2O3, ZrO2, and SiO2 supported vanadia catalysts, the average CVB number derived from the edge energy allows the assignment of the possible structure of the surface vanadium oxide species, which is a strong function of...

https://www.lehigh.edu/operando/Publications/2000%20Supported%20VOx%20by%20UV-vis,%20Gao.pdf

Investigation of Surface Structures of Supported Vanadium Oxide Catalysts by UV−vis−NIR Diffuse Reflectance Spectroscopy

The molecularly dispersed TiO2/SiO2 supported oxides were prepared by the incipient wetness impregnation of 2-propanol solutions of titanium isopropoxide. Experimental monolayer dispersion of surfa...

/pdf/preparation-and-in-situ-spectroscopic-characterization-of-3qtjpp76dl.pdf

Preparation and in-Situ Spectroscopic Characterization of Molecularly Dispersed Titanium Oxide on Silica

The application of in situ Raman, IR, and UV-Vis DRS spectroscopies during steady-state methanol oxidation has demonstrated that the molecular structures of surface vanadium oxide species supported on metal oxides are very sensitive to the coordination and H-bonding effects of adsorbed methoxy surface species. Specifically, a decrease in the intensity of spectral bands associated with the fully oxidized surface (V5+) vanadia active phase occurred in all three studied spectroscopies during methanol oxidation. The terminal V = O (∼1030 cm−1) and bridging V–O–V (∼900–940 cm−1) vibrational bands also shifted toward lower frequency, while the in situ UV-Vis DRS spectra exhibited shifts in the surface V5+ LMCT band (>25,000 cm−1) to higher edge energies. The magnitude of these distortions correlates with the concentration of adsorbed methoxy intermediates and is most severe at lower temperatures and higher methanol partial pressures, where the surface methoxy concentrations are greatest. Conversely, spectral changes caused by actual reductions in surface vanadia (V5+) species to reduced phases (V3+/V4+) would have been more severe at higher temperatures. Moreover, the catalyst (vanadia/silica) exhibiting the greatest shift in UV-Vis DRS edge energy did not exhibit any bands from reduced V3+/V4+ phases in the d–d transition region (10,000–30,000 cm−1), even though d–d transitions were detected in vanadia/alumina and vanadia/zirconia catalysts. Therefore, V5+ spectral signals are generally not representative of the percent vanadia reduction during the methanol oxidation redox cycle, although estimates made from the high temperature, low methoxy surface coverage IR spectra suggest that the catalyst surfaces remain mostly oxidized during steady-state methanol oxidation (15–25% vanadia reduction). Finally, adsorbed surface methoxy intermediate species were easily detected with in situ IR spectroscopy during methanol oxidation in the C–H stretching region (2800–3000 cm−1) for all studied catalysts, the vibrations occurring at different frequencies depending on the specific metal oxide upon which they chemisorb. However, methoxy bands were only found in a few cases using in situ Raman spectroscopy due to the sensitivity of the Raman scattering cross-sections to the specific substrate onto which the surface methoxy species are adsorbed.

https://www.lehigh.edu/operando/Publications/2000%20in%20situ%20IR,%20Raman,%20UV-vis%20of%20VOx%20during%20MeOH.pdf

Xingtao Gao

Papers

Titania-silica as catalysts : molecular structural characteristics and physico-chemical properties

In Situ Spectroscopic Investigation of Molecular Structures of Highly Dispersed Vanadium Oxide on Silica under Various Conditions

Investigation of Surface Structures of Supported Vanadium Oxide Catalysts by UV−vis−NIR Diffuse Reflectance Spectroscopy

Preparation and in-Situ Spectroscopic Characterization of Molecularly Dispersed Titanium Oxide on Silica

In situ IR, Raman, and UV-Vis DRS spectroscopy of supported vanadium oxide catalysts during methanol oxidation