Brønsted acidity of amorphous silica–alumina: The molecular rules of proton transfer

Leydier, Fabien; Chizallet, Céline; Chaumonnot, Alexandra; Digne, Mathieu; Soyer, Emmanuel; Quoineaud, Anne-Agathe; Costa, Dominique; Raybaud, Pascal

doi:10.1016/j.jcat.2011.08.015

Cited by 104 publications

(171 citation statements)

References 106 publications

Supporting

Mentioning

163

Contrasting

Order By: Relevance

“…The characteristics of acid sites on amorphous silica-alumina have been debated for a long time in the literature. 17,[36][37][38] However, different reports using diffuse reflectance Fourier transformed infrared spectroscopy (DRIFTS), density functional theory (DFT) and their combination have clarified it. 17 It has been proposed that silica-alumina surface is formed by isolated silanols and/or hydrogen-bonded bridge silanols.…”

Section: Resultsmentioning

confidence: 99%

“…17,[36][37][38] However, different reports using diffuse reflectance Fourier transformed infrared spectroscopy (DRIFTS), density functional theory (DFT) and their combination have clarified it. 17 It has been proposed that silica-alumina surface is formed by isolated silanols and/or hydrogen-bonded bridge silanols. 17,39 The highest frequencies of OH vibrations are found for Si-OH groups (isolated silanols) and O−Si−OH-Al groups (called aluminic pseudo-bridging silanols).…”

Section: Resultsmentioning

confidence: 99%

“…17 It has been proposed that silica-alumina surface is formed by isolated silanols and/or hydrogen-bonded bridge silanols. 17,39 The highest frequencies of OH vibrations are found for Si-OH groups (isolated silanols) and O−Si−OH-Al groups (called aluminic pseudo-bridging silanols). 17 Thus, it may be suggested that the interaction of H 3 PW Keggin structure can take place preferentially at these sites, since most of the metal oxides interact to O−H surface sites of different supports.…”

Section: Resultsmentioning

confidence: 99%

“…17,39 The highest frequencies of OH vibrations are found for Si-OH groups (isolated silanols) and O−Si−OH-Al groups (called aluminic pseudo-bridging silanols). 17 Thus, it may be suggested that the interaction of H 3 PW Keggin structure can take place preferentially at these sites, since most of the metal oxides interact to O−H surface sites of different supports. 39,40 Nitrogen physisorption isotherm obtained for SiO 2 -Al 2 O 3 was analyzed by plotting the t-curve, i.e., 2017 amount of N 2 adsorbed versus thickness (t).…”

Section: Resultsmentioning

confidence: 99%

See 3 more Smart Citations

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Mattos¹,

Carvalho²,

Freitas³

et al. 2016

Journal of the Brazilian Chemical Society

View full text Add to dashboard Cite

This work deals with preparation and characterization of H 3 PW 12 O 40 (H 3 PW) supported on silica-alumina. Impregnation of H 3 PW (15, 20, 30 and 40 wt.%) on commercial silica-alumina support in acidic aqueous solution is effective for preparing this catalyst keeping its Keggin structure, according to different methods of characterization. The catalysts were tested in a model reaction of acetic acid with ethanol and 30 wt.% H 3 PW/SiO 2 -Al 2 O 3 had the highest activity under the conditions: catalyst calcination at 300 °C, temperature of 100 °C, acetic acid:ethanol molar ratio of 2:1 and catalyst:acetic acid mass ratio of 10 wt.%. The reaction yield was 79 and 100% selectivity for ethyl acetate over three reutilizations, for reaction time of 2 h. The calculated total acid site distribution was 0.299 mmol g -1 (97% of the theoretical probed by pyridine), and most of these (0.236 mmol g -1 ) were Brønsted weak-medium strength (pyridine desorption between 300 and 500 °C).

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Mattos¹,

Carvalho²,

Freitas³

et al. 2016

Journal of the Brazilian Chemical Society

View full text Add to dashboard Cite

show abstract

“…Structural hypotheses are not unanimous between research groups. [96][97][98][99][100][101] New insights have recently been acquired through DFT calculations, 87,[102][103][104] leading to a surface model for silicated alumina, which accounts for the presence of original surface sites at the origin of mild acidity. Note that, to the best of our knowledge, despite significant effort on the simulation of bulk aluminosilicate glasses for geology, 105,106 simulation studies of the surface of ASA have not been undertaken before, except for some earlier attempts to choose "local" models, as aluminosilsesquioxanes.…”

Section: 81mentioning

confidence: 99%

Density functional theory simulations of complex catalytic materials in reactive environments: beyond the ideal surface at low coverage

Chizallet

Raybaud

2014

Catal. Sci. Technol.

Self Cite

View full text Add to dashboard Cite

Most efficient heterogeneous catalysts used industrially are generally very complex systems. Far away from perfect crystallinity and well-defined oriented surfaces at low coverage, they involve structural disorder, heterogeneous site distribution with variable coordination and structural dependence upon the chemical environment. Unravelling their atomic-scale structures and understanding their roles in the catalytic reaction are not easy tasks, as the respective contributions of each type of site to the spectroscopic or catalytic responses are generally convoluted. Computational chemistry is of great help to address these issues. In the present perspective review, we highlight two relevant systems involved in numerous industrial applications: the amorphous silica alumina support; and subnanometric platinum clusters, possibly doped with tin and/or indium, supported on γ-Al 2 O 3 . The structural complexity is inherent to the amorphous nature of an oxide support on the one hand, and to the ultra-dispersed form of a mono-and multi-metallic catalyst on the other hand. In each case, Density Functional Theory (DFT) calculation was used to provide an original structure for active sites and to reveal how the corresponding multi-step reactions are influenced. Moreover, we highlight how theoretical studies including coverage effects on complex systems, induced by (T, P) reaction conditions, offer enriched perspectives with respect to studies on ideal surfaces at low coverage.

show abstract

Tuning the Metal–Support Interaction by Structural Recognition of Cobalt‐Based Catalyst Precursors

2015

Self Cite

View full text Add to dashboard Cite

Controlling the nature and size of cobalt(II) polynuclear precursors on g-alumina and silica-alumina supports represents achallenge for the synthesis of optimal cobaltbased heterogeneous catalysts.B yd ensity functional theory (DFT) calculations,w es how how after drying the interaction of cobalt(II) precursor on g-alumina is driven by as tructural recognition phenomenon, leading to the formation of an epitaxial Co(OH) 2 precipitate involving aCo-Al hydrotalcitelike interface.Onasilica-alumina surface,this phenomenon is prevented due to the passivation effect of silica domains.T his finding opens new routes to tune the metal-support interaction at the synthesis step of heterogeneous catalysts.Controlling the phenomena occurring at the interface between oxidic materials and metallic complexes has been achallenging topic during the last decades.[1] Indeed, they are involved in several environmentally and industrially important situations,s uch as corrosion, water treatments,a nd catalyst preparation. Cobalt in particular has drawn much attention:60 Co is ar adioactive isotope found in nuclear process wastewaters,w hereas cobalt-containing heterogeneous catalysts are widely used for hydrodesulfurization reactions, [2] Fischer-Tropsch synthesis [3] (both examples enabling the production of cleaner fuels), oxygen evolution reactions, [4] and alarge set of C 1 chemistry reactions (CO oxidation, [5] dry reforming of methane, [6] inter alia). g-alumina [7] or amorphous silica-alumina [8] are used industrially as efficient Co sorbent or supports for such applications.[9] Cobalt (as well as nickel) is known to exhibit strong chemical interactions with the galumina surface at the various preparation steps of catalysts (impregnation, drying, and/or calcination) which may lead to the formation of hardly reducible hydroxides or even mixed aluminium-cobalt (nickel) oxide phases being detrimental to the final catalytic activity. [1d, 9, 10] This feature might be explained by the adsorption mode and strength of cobalt precursors on the g-alumina surface.A lthough UV-visible spectroscopy [10d, 11] and EXAFS [1e, 12] analyses brought insights on the local environment of adsorbed Co species,t he chemical nature and local structure of the interface between cobalt species and the surface remain to be unraveled, which is mandatory for the control of the final catalyst. DFT calculations have shown their ability to provide predictive molecular insight in the structure of complex catalytic systems,including supported transition metals. [13] Herein, we propose aDFT study of the interaction of the most widely used cobalt precursor,c obalt(II) hexahydrate (Co(H 2 O) 6 2+ ), with the g-alumina surface as predominant after the drying step of the preparation process.W er eveal as pecific interaction between the cobalt precursor and the surface,d ifferent from the simple OH exchange usually invoked [14] and consistent with the concept of structural recognition, developed in the field of biochemistry by E. Fischer, [15] extended to c...

show abstract

Brønsted acidity of amorphous silica–alumina: The molecular rules of proton transfer

Cited by 104 publications

References 106 publications

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

Density functional theory simulations of complex catalytic materials in reactive environments: beyond the ideal surface at low coverage

Tuning the Metal–Support Interaction by Structural Recognition of Cobalt‐Based Catalyst Precursors

Contact Info

Product

Resources

About