Isophorone Isomerization as Model Reaction for the Characterization of Solid Bases: Application to the Determination of the Number of Sites

Figuéras, F.; López, Joaquín; Sánchez-Valente, J.; Vu, T.T.H.; Clacens, Jean‐Marc; Palomeque, Jorge

doi:10.1006/jcat.2002.3743

Cited by 15 publications

(14 citation statements)

References 23 publications

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“…The as-synthesized hydrotalcites displayed specific surface areas in the range of 90-100 m 2 g À1 . A similar observation was also reported by Figueras et al; [10,[23][24][25] the surface area of the mixed oxide (95 m 2 g À1 ) decreased to 20 m 2 g À1 after rehydration of the sample in the vapour phase, which led to a restoration of the layered structure. According to these authors, this accounted for a limitation of the rehydration process by the diffusion of water within the particles, and the surface corresponds to the external area of the crystals.…”

supporting

confidence: 81%

Aldol Condensations Over Reconstructed Mg–Al Hydrotalcites: Structure–Activity Relationships Related to the Rehydration Method

Abelló

Medina

Tichit

et al. 2004

Chemistry A European J

227

188

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Two different rehydration procedures in the liquid or gas phase have been applied to reconstruct mixed oxides derived from calcined hydrotalcite-like materials to be used as catalysts for aldol condensation reactions. The as-synthesized hydrotalcite, its decomposition product, as well as the reconstructed solids upon rehydration were characterized by XRD, N(2) adsorption, He pycnometry, FTIR, SEM, TEM, (27)Al MAS-NMR and CO(2)-TPD (TPD=temperature-programmed desorption). Compared to the Mg-Al mixed oxide rehydrated in the gas phase (HT-rg), that rehydrated in the liquid phase (HT-rl) exhibits a superior catalytic performance with respect to the aldol condensation of citral with ketones to yield pseudoionones and in the self-aldolization of acetone. The textural properties of HT-rl and HT-rg differ strongly and determine the catalytic behavior. A memory effect led to a higher degree of reconstruction of the lamellar structure when the mixed oxide was rehydrated in the gas phase rather than in the liquid phase, although liquid-phase rehydration under fast stirring produced a surface area that was 26 times greater. This contrasts to typical statements in the literature claiming a higher degree of reconstruction in the presence of large amounts of water in the medium. CO(2)-TPD shows that the number of OH(-) groups and their nature are very similar in HT-rg and HT-rl, and cannot explain the markedly different catalytic behavior. Accordingly, only a small fraction of the available basic sites in the rehydrated samples is active in liquid-phase aldol condensations. Our results support the model in which only basic sites near the edges of the hydrotalcite platelets are partaking in aldol reactions. Based on this, reconstructed materials with small crystallites (produced by exfoliation during mechanical stirring), that is, possessing a high external surface area, are beneficial in the reactions compared to larger crystals with a high degree of intraplatelet porosity.

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supporting

confidence: 81%

Aldol Condensations Over Reconstructed Mg–Al Hydrotalcites: Structure–Activity Relationships Related to the Rehydration Method

Abelló

Medina

Tichit

et al. 2004

Chemistry A European J

227

188

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“…Test reactions : Isomerisation of β‐isophorone to α‐isophorone (Scheme ) can be used as a test reaction to probe the basicity of the catalysts 16. 99, 114 The rate constant for isophorone isomerisation is proportional to the number of basic sites.…”

Section: Probing the Basicity Of Hydrotalcitesmentioning

confidence: 99%

Exploring, Tuning, and Exploiting the Basicity of Hydrotalcites for Applications in Heterogeneous Catalysis

Debecker

Gaigneaux

Busca

2009

Chemistry A European J

470

265

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Basic catalysis! The basic properties of hydrotalcites (see picture) make them attractive for numerous catalytic applications. Probing the basicity of the catalysts is crucial to understand the base-catalysed processes and to optimise the catalyst preparation. Various parameters can be employed to tune the basic properties of hydrotalcite-based catalysts towards the basicity demanded by each target chemical reaction.Hydrotalcites offer unique basic properties that make them very attractive for catalytic applications. It is of primary interest to make use of accurate tools for probing the basicity of hydrotalcite-based catalysts for the purpose of 1) fundamental understanding of base-catalysed processes with hydrotalcites and 2) optimisation of the catalytic performance achieved in reactions of industrial interest. Techniques based on probe molecules, titration techniques and test reactions along with physicochemical characterisation are overviewed in the first part of this review. The aim is to provide the tools for understanding how series of parameters involved in the preparation of hydrotalcite-based catalytic materials can be employed to control and adapt the basic properties of the catalyst towards the basicity demanded by each target chemical reaction. An overview of recent and significant achievements in that perspective is presented in the second part of the paper.

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“…Furthermore, mixed oxides formed by the calcination of LDHs can function as solid-base catalysts for many organic reactions. Thermally decomposed LDHs containing transition metal ions such as nickel, iron and copper have been particularly investigated as catalyst precursors [110][111][112][113].…”

Section: Catalytic Activity Of Ldhsmentioning

confidence: 99%

Geomaterials: their application to environmental remediation

Yamada

Tamura

Watanabe

et al. 2011

Science and Technology of Advanced Materials

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Geomaterials are materials inspired by geological systems originating from the billion years long history of the Earth. This article reviews three important classes of geomaterials. The first one is smectites-layered silicates with a cation-exchange capacity. Smectites are useful for removing pollutants and as intercalation compounds, catalysts and polymer nanocomposites. The second class is layered double hydroxides (LDHs). They have an anion-exchange capacity and are used as catalysts, catalyst precursors, sorbents and scavengers for halogens. The third class of geomaterials is zeolites-microporous materials with a cation-exchange capacity which are used for removing harmful cations. Zeolite composites with LDHs can absorb ammonium and phosphate ions in rivers and lakes, whereas zeolite/apatite composites can immobilize the radioactive iodine. These geomaterials are essential for environmental remediation.

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Isophorone Isomerization as Model Reaction for the Characterization of Solid Bases: Application to the Determination of the Number of Sites

Cited by 15 publications

References 23 publications

Aldol Condensations Over Reconstructed Mg–Al Hydrotalcites: Structure–Activity Relationships Related to the Rehydration Method

Aldol Condensations Over Reconstructed Mg–Al Hydrotalcites: Structure–Activity Relationships Related to the Rehydration Method

Exploring, Tuning, and Exploiting the Basicity of Hydrotalcites for Applications in Heterogeneous Catalysis

Geomaterials: their application to environmental remediation

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