Interfacial Impregnation Chemistry in the Synthesis of Cobalt Catalysts Supported on Titania

Petsi, Theano; Panagiotou, Georgeâ D.; Garoufalis, Christos S.; Kordulis, Christos; Stathi, Panagiota; Deligiannakis, Yiannis; Lycourghiotis, Alexis; Bourikasâ, Kyriakos

doi:10.1002/chem.200900760

Cited by 24 publications

(42 citation statements)

References 61 publications

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“…Inspection of this figure shows the very high capability of γ-alumina to adsorb Co(II) species. In fact, the maximum surface density obtained (36 µmol m -2 ) is much higher than that obtained using titania under similar conditions (7 µmol m -2 ) at pH=7.5 [27]. Moreover, it is important to note that the maximum surface density of Co corresponds to a surface coverage equal to 11 monomolecular layers of the [Co(H 2 O) 6 ] 2+ ions.…”

Section: Co(ii)-species In Aqueous (Nitrate) Solutionsmentioning

confidence: 64%

“…Following this empirical method the charge of this complex (+2) is distributed equally in the water ligands (+0.33) assigning a zero charge above cobalt. We have recently improving this empirical charge distribution by performing ab-initio calculations in the frame of the density functional theory DFT [27]. The results are illustrated in Table 1.…”

Section: Co(ii)-species In Aqueous (Nitrate) Solutionsmentioning

confidence: 99%

“…Specifically, we follow the evolution of the various Co(II) species formed at the interface as the surface concentration of the Co(II) increases. The study is part of the entire efforts of our group to rationalize the method of preparation of supported catalysts and shift catalyst preparation from the art to the science [24][25][26][27][28][29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

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Structure of Co(II) Species Formed on the Surface of γ-Alumina Upon Interfacial Deposition

Vakros¹,

Bourikas²,

Kordulis³

et al. 2014

TOCATJ

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Abstract:The mode of retention of Co(H 2 O) 6 2+ species at the "γ-alumina/aquatic solution" interface is refined using simulations, adsorption isotherm, potentiometric mass titrations and mainly proton -ion titrations jointly with diffuse reflectance spectroscopy. It was found that the increase in the Co(II) surface concentration affects considerably the kind of the Co(II) species deposited. Mononuclear/mono-substituted inner sphere Co(II) complexes are formed at extremely low Co(II) surface concentration. A mixed surface state involving mononuclear/mono-substituted and binuclear/bi-substituted Co(II) complexes is formed at relatively low Co(II) surface concentration. Only binuclear/bi-substituted Co(II) complexes are formed at intermediate Co(II) surface concentration. Finally, oligo-nuclear inner sphere Co(II) species are formed at relatively high Co(II) surface concentration, in addition to the bi-nuclear ones. The above species concern a range of surface Co(II) concentration extending from zero to 2.7 theoretical surface layers of [Co(H 2 O) 6 ] 2+. The formation of Co(II) surface precipitate starts above these theoretical surface layers. The above indicates that one may control the surface Co(II) concentration, by adjusting the Co(II) concentration in the impregnating solution, and thus the Co(II) surface species formed. This control allows tailoring the preparation of cobalt catalysts supported on γ-alumina and thus the development of effective Co/γ-alumina catalysts.

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Section: Co(ii)-species In Aqueous (Nitrate) Solutionsmentioning

confidence: 64%

Section: Co(ii)-species In Aqueous (Nitrate) Solutionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structure of Co(II) Species Formed on the Surface of γ-Alumina Upon Interfacial Deposition

Vakros¹,

Bourikas²,

Kordulis³

et al. 2014

TOCATJ

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“…2 + species on g-alumina [38] and titania [39] surfaces, which was also attributed to the formation of inner-sphere complexes.…”

Section: à2mentioning

confidence: 94%

“…[47] Finally, it should be mentioned that the DE spectrum rules out the presence of deposited tetrahedral Ni II species (for details see the Supporting Information) in contrast to the similar Co II /TiO 2 system in which tetrahedral species coexist with octahedral ones, but to a much lesser extent. [39] A first approach to the interfacial structure of the deposited Ni II species by studying "proton-ion" curves: The deposition of the [NiA C H T U N G T R E N N U N G (H 2 O) 6 ] 2 + species and the H + ions released may be combined quantitatively in the context of the socalled "proton-ion" titration curves. [17] These are linear plots of the "amount of H + ions released versus the amount of deposited Ni II ".…”

Section: à2mentioning

confidence: 99%

Interfacial Impregnation Chemistry in the Synthesis of Nickel Catalysts Supported on Titania

Bourikas

Stavropoulos

Garoufalis

et al. 2010

Chemistry A European J

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The interfacial chemistry of the impregnation step involved in the preparation of nickel catalysts supported on titania is presented. Several methodologies based on deposition data, pH measurements, potentiometric mass titrations, and microelectrophoresis have been used in conjunction with diffuse reflectance UV/Vis/NIR spectroscopy, simulations, and semiempirical quantum chemical calculations. Three mononuclear inner-sphere complexes were formed at the compact layer of the "titania/electrolyte solution" interface: A monosubstituted, dihydrolyzed complex above a terminal oxo group, a disubstituted, dihydrolyzed complex above two terminal adjacent oxo groups, and a disubstituted, nonhydrolyzed complex above one terminal and one bridging adjacent oxo groups. The monosubstituted, dihydrolyzed complex predominates. The contribution of the disubstituted configurations is also important at very low Ni(II) surface concentration, but it decreases as the Ni(II) surface concentration increases. In addition, bi- and trinuclear inner-sphere complexes were formed. The receptor site involves one bridging and two terminal oxo groups in the first case and two bridging and three terminal oxo groups in the second case. The relative surface concentrations of these configurations increase initially with Ni(II) surface concentration and then remain practically constant. The understanding of these interfacial processes at a molecular level is very important to shift the catalytic synthesis from an art to a science as well as to obtain strict control of the impregnation step and, to some extent, of the whole preparative sequence. This study is very relevant to the synthesis of submonolayer/monolayer nickel catalysts supported on TiO(2) following equilibrium deposition filtration (otherwise called equilibrium adsorption).

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Interfacial Impregnation Chemistry in the Synthesis of Chromium Catalysts Supported on Titania

et al. 2011

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The interfacial impregnation chemistry involved in the synthesis of CrVI catalysts supported on titania is presented. The mode of interfacial deposition of the CrVI oxo‐species at the titania/electrolyte solution interface, the interfacial species, and the local structure of the deposited species were investigated. Several methodologies based on potentiometric titrations, microelectrophoresis, and adsorption experiments were used. Modeling of the interfacial deposition based on experimental results provided an integrated picture concerning the deposition features. The interfacial species were confirmed by using laser Raman spectroscopy. The deposited CrO42−, HCrO4−, and Cr2O72− ions are retained above the positively charged bridging hydroxyl groups (Ti2OH) of the titania surface as electrostatic forces cause the formation of ion‐pairs. Each CrO42− or HCrO4− ion is located above a bridging hydroxyl, and each Cr2O72− ion above two bridging hydroxyl groups. Only the CrO42− and HCrO4− ions are deposited, with a preference for the CrO42− ions, at low CrVI surface concentrations (up to 0.3 μmol CrVI m−2). Cr2O72− ions were deposited in addition to CrO42− and HCrO4− ions at higher CrVI concentrations. The direct probing of the interfacial species by using laser Raman spectroscopy confirmed the interfacial species determined by modeling the deposition data. The deposition model developed describes all of the experimental data (from adsorption, titration, and microelectrophoresis experiments) very well. Moreover, it accurately predicts the displacements of pzc and iep caused by the presence of these species in the solution.

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Interfacial Impregnation Chemistry in the Synthesis of Cobalt Catalysts Supported on Titania

Cited by 24 publications

References 61 publications

Structure of Co(II) Species Formed on the Surface of γ-Alumina Upon Interfacial Deposition

Structure of Co(II) Species Formed on the Surface of γ-Alumina Upon Interfacial Deposition

Interfacial Impregnation Chemistry in the Synthesis of Nickel Catalysts Supported on Titania

Interfacial Impregnation Chemistry in the Synthesis of Chromium Catalysts Supported on Titania

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