IR and NMR studies of mesoporous alumina and related aluminosilicates

Góra‐Marek, Kinga; Derewinski, Miroslaw A.; Sarv, P.; Dátka, Jerzy

doi:10.1016/j.cattod.2005.01.010

Cited by 134 publications

(108 citation statements)

References 15 publications

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“…However, the number of Brønsted acidic sites is still low and it is comparable to the acidity of zeolites with an Si/Al ratio equal to 500. The number of Lewis acid sites is also low and is clearly lower than the related values for aluminosilicate mesoporous materials with an Si/Al ratio from 1 to 10, calculated in a similar way [21]. On the other hand, the strength of both Brønsted and Lewis acid sites of vanadium modified MCF material is low and is comparable to that recorded for mesoporous aluminosilicates with an Si/Al equal to 10 ( Table 2).…”

supporting

confidence: 56%

MCF Material as an Attractive Support for Vanadium Oxide Applied as a Catalyst for Propene Epoxidation with N2O

et al. 2018

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Vanadium modified mesocellular silica foams (MCF) materials (V content ca. 3 and 5 wt%) prepared by the impregnation method show mainly isolated or low-polymeric VO x species, which was confirmed by means of Raman spectroscopy and DR UV-Vis. Textural measurements, and also XRD and TEM results indicate that the characteristic mesocellular structural features of MCFs are preserved after vanadium incorporation. The MCF-supported vanadia catalysts exhibit much higher propene conversion and propene oxide productivity when compared to vanadium modified mesoporous silicas of 2D structure, demonstrating that apart from the presence of highly dispersed isolated vanadium species, internal molecular transport within three-dimensional ultra large pores of MCF materials also plays an important role in gas-phase propene epoxidation. Graphical Abstract

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supporting

confidence: 56%

MCF Material as an Attractive Support for Vanadium Oxide Applied as a Catalyst for Propene Epoxidation with N2O

et al. 2018

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“…Its presence indicates that a non negligible fraction of Al atoms are not inserted as isolated species in the silica walls, but rather belong to Al-rich zones [27]. The peak located at d = 50-55 ppm can be assigned to tetracoordinated Al and is usually linked to the presence of Brønsted acid sites (Si-O(H)-Al) [28]. In addition to these two main peaks, a third signal is observed near d = 30 ppm.…”

Section: Structural Characterizationmentioning

confidence: 97%

Comparing Al-SBA-15 Support and Pt/Al-SBA-15 Catalyst: Changes in Al Speciation and Acidic Properties Induced by the Introduction of Pt via Aqueous Medium

et al. 2009

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Differences between the acidic properties of silicoaluminic Pt-containing catalysts and those assessed on their parent supports have been reported in the literature and attributed to the presence of the metal nanoparticles and to their influence on the acid sites. It is shown here that for mesoporous materials containing various types of Al species, an alternative explanation can be proposed. 27 Al NMR spectroscopy, FTIR of adsorbed CO and probe catalytic tests suggest the redistribution of aluminium atoms upon contact of the parent support with the aqueous solution containing the Pt precursor. Upon contact with water and thermal treatment, strong and mild Brønsted sites (Si-O(H)-Al) transform into strong Lewis sites (isolated tetracoordinated Al atoms). As a consequence, it may not be straightforward to deduce the acidic properties of metalcontaining catalysts supported on Al-containing mesoporous materials from those of the bare support, because the surface species may differ significantly.

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“…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.

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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.

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IR and NMR studies of mesoporous alumina and related aluminosilicates

Cited by 134 publications

References 15 publications

MCF Material as an Attractive Support for Vanadium Oxide Applied as a Catalyst for Propene Epoxidation with N2O

MCF Material as an Attractive Support for Vanadium Oxide Applied as a Catalyst for Propene Epoxidation with N2O

Comparing Al-SBA-15 Support and Pt/Al-SBA-15 Catalyst: Changes in Al Speciation and Acidic Properties Induced by the Introduction of Pt via Aqueous Medium

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

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