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Modified Hydrotalcites

Hydrotalcite is a natural mineral that was discovered in 1842 in Norway (47). Hydrotalcites are also known as a member of a large mineral group of naturally occurring layered double hydroxides. [Pg.210]

There are a number of techniques that have been successfully applied to synthesize modified hydrotalcites (48). The most commonly method used is the co-precipitation of two metal salts in alkaline solution at a constant pH value of about 10. Another method uses the classical ion exchange process in which the guest anions are exchanged with the anions in the interlayer spaces of preformed layered double hydroxides to produce specific anion intercalated modified hydrotalcites. StiU another method is a lattice reconstruction after heating, i.e., calcination, which is based on the structural memory effect of these materials, due to which the original structure is reproduced after rehydration. [Pg.210]

Modified hydrotalcites are technologically promising materials for their addition to concrete in order to improve its durability in aggressive environments, owing to their low cost, relative simplicity of preparation, and plenty of unique composition variables that may be adopted (48). [Pg.210]

Only a few studies have been focused on cementitious materials concerning their potential applications in corrosion protection of reinforced concrete structures. The mechanism of corrosion in reinforced concrete and concrete properties that affect corrosion of reinforcement have been briefly detailed. The existing knowledge concerning the synthesis and characterization methods of modified hydrotalcites, ion exchange within the modified hydrotalcite structure as well as the application of modified hydrotalcites in the cementitious materials have been reviewed. It is expected that modified hydrotalcites can improve the durability of reinforced concrete materials (48). [Pg.210]


Roelofs, J. C. A. A., van Dillen, A. J. and de Jong, K. P. Base-catalyzed condensation of citral and acetone at low temperature using modified hydrotalcite catalysts, Catal. Today, 2000, 60, 297-303. [Pg.200]

The selectivity of modified hydrotalcite material for carbon dioxide with respect to water vapor (an important prerequisite for the water-gas shift reaction) was good, but it adsorbed large quantities of HCN, even though carbon dioxide is the more acidic component, making it wholly unsuitable for the direct HCN synthesis, especially as it subsequently proved impossible to recover the adsorbed HCN as such [21],... [Pg.215]

Use of a heterogeneous catalyst simplifies workup. A copper-modified hydrotalcite was used to catalyze the oxidation of phenylacetylene by oxygen (4.41), giving yields comparable with those obtained in homogenous oxidations.198... [Pg.84]

Buchheit, R.G., Mamidipally, S.B., Schmutz, P., and Guan, H. (2002) Active corrosion protection in Ce-modified hydrotalcite conversion coatings. Corrosion, 58, 3. [Pg.488]

To date a wide range of material have been developed and tested as part of the STEPCAP project. The key materials under development are microporous polymers, surface modified hydrotalcites, and co-doped sorbents. The performance of these materials has been assessed under a range of conditions and will be presented. Current key developments are summarized as follows ... [Pg.31]

Buchheit R. G., Mamidipally S. B., Schmutz P. and Guan H. (2002), Active Corrosion Protection in Ce-Modified Hydrotalcite Conversion Coatings , Corrosion, 58, 3-14. [Pg.254]

The objective of this work is to study the potential of modified ZSM5 zeolite, MCM41 mesoporous silica, hydrotalcites (HD) and HD originated mixed oxides as catalysts for degradation of PE, PP PS and PVC using thermal analytical measurements and laboratory reactor experiments. [Pg.268]

The catalyst samples were prepared in our laboratory. The synthesized Na-ZSM-5 zeolite was modified by conventional or solid state ion-exchange [11] to form H-, Fe-, Cu-, Ni- and Ti-ZSM5 samples, while the mesoporous catalysts (Fe- and Ti-MCM-41) were synthesized by isomorphous substitution [12], as well as the hydrotalcites containing Fe-, Cu-, Cr- or Ca-oxide in the Mg,Al-LDH structure [13]. [Pg.268]

We are studying the glycerol transformation in the presence of different catalysts of porous structure such as layered double hydroxides (hydrotalcites, HT and mixed oxides, MO), modified zeolites (ZSM5) and new type of Raney-Ni (RNi) to find optimal conditions for producing valuable components. [Pg.437]

As part of a search for environmentally friendly solid acid-base catalysts, a modified Mg-Al hydrotalcite has been used as a base catalyst for aldol and Knoevenagel condensations. Yields are often quantitative, reaction times are about Ih, the catalyst can be recovered by filtration, and only moderate temperatures are required (60 °C for the aldol, ambient for the Knoevenagel). [Pg.14]

Lakshmi Kantam, M., Choudary, B. M., Reddy, C. V., Koteswara Rao, K. and Figueras, F. Aldol and Knoevenagel condensations catalyzed by modified Mg-Al hydrotalcite a solid base as catalyst useful in synthetic organic chemistry, Chem. Commun., 1998, 1033-1034. [Pg.200]

It has also been reported that the interlayer spacing in hydrotalcite particles can be increased by intercalation with organic molecules, such as citric acid.88 Results were given for linear burning rates from a UL-94 horizontal bum test comparing nano- and micro-hydrotalcite modified epoxy resin. At 5 wt % addition level the microcomposite gave a reduction in bum rate of unmodified epoxy resin from around 22 to 18mm/min. With the apparent nanocomposite variant, also at 5 wt %, the burn rate was less than 5mm/min. [Pg.180]

Kumbhar, P. S., Sanchez-Valente, J. and Figueras, F. (1998). Modified Mg-Al hydrotalcite a highly active heterogeneous base catalyst for cyanoethylation of alcohols../ Chem. Soc., Chem. Commun., 1091. [Pg.323]

Modified from Ref. T35. "Other components mainly P2O5 (0.2%) other phases mainly alkalis (adsorbed or in solution), insoluble residue and PjO (form of combination unknown). Fe HP = hydrogarnet-type product from ferrite phase. Mg HP = hydrotalcite-type phase. AFm and Mg HP include poorly crystalline materials intimately mixed with C-S-H. Discrepancies in totals arise from rounding. [Pg.219]

Scavetta, E., Berrettoni, M., Nobili, F., and Tonelli, D. 2005. Electrochemical characterisation of electrodes modified with a Co/Al hydrotalcite-like compound. Electrochimica Acta 50, 3305-3311. [Pg.298]


See other pages where Modified Hydrotalcites is mentioned: [Pg.214]    [Pg.307]    [Pg.65]    [Pg.420]    [Pg.31]    [Pg.32]    [Pg.210]    [Pg.136]    [Pg.59]    [Pg.43]    [Pg.214]    [Pg.307]    [Pg.65]    [Pg.420]    [Pg.31]    [Pg.32]    [Pg.210]    [Pg.136]    [Pg.59]    [Pg.43]    [Pg.31]    [Pg.77]    [Pg.267]    [Pg.2]    [Pg.46]    [Pg.55]    [Pg.100]    [Pg.173]    [Pg.200]    [Pg.180]    [Pg.196]    [Pg.100]    [Pg.217]    [Pg.289]    [Pg.136]    [Pg.254]    [Pg.69]    [Pg.125]   


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