Calcined layered double hydroxide

Raja. T Jyothi, TM Sreekumar, K Talawar, MB Santhanalakshmi, J Rao, BS. Calcined layered double hydroxides as basic heterogeneous catalysts for the Oppenauer oxidation of alcohols. Bulletin of the Chemical Society of Japan, 1999 72. 2117-2119. 

Shumaker, J. L., Crofcheck, C., Tackett, S. A., Santillan-Jimenez, E., Morgan, T., Ji, Y, Crocker, M., and Toops, T. J. Biodiesel synthesis using calcined layered double hydroxide catalysts. Applied Catal B Environ 82,120-130 (2008). 

Keywords Layered double hydroxides Application Intercalation Calcination... 

Yang, L., Shahrivari, Z., Liu, P.K.T. et al. (2005) Removal of trace levels of arsenic and selenium from aqueous solutions by calcined and uncalcined layered double hydroxides (LDH). Industrial and Engineering Chemistry Research, 44(17), 6804-15. 

Cr3+ can also be integrated into the structures of layered double hydroxides. A mixed oxide, prepared by calcination of ZnCr-LDH-CCh, was used in combination with t-BuOOH for the ketonization of alkyl and of benzyl pyridines and for the oxidation of benzyl amines to give Schiff bases (67,68). In contrast to MgAl-LDHs, for example, these materials display hardly any basicity so that base-catalyzed side reactions such as aldol condensations are avoided. 

A final example of a stereoselective heterogeneous catalytic system is the work of Laycock, Collacott, Skelton and Tchir.17 Layered double hydroxide (LDH) synthetic hydrotalcite materials were used to stereospecifically polymerize propylene oxide [PO] to crystalline isotactic and liquid atactic poly(propyleneoxide) [PPO]. These authors suggest that the LDH surface acts as other inorganic or organometallic coordination initiators or catalysts by providing specific surface orientations for propylene oxide monomer. X-ray powder diffraction showed some loss of crystallinity after calcination and X-ray photoelectron spectroscopy showed an enhancement of Mg/Al content due to restructuring of the Mg and A1 surface atoms. The surface was also rich in Cl ... 

Chibwe, K. and Jones, W. (1989). Synthesis of polyoxometalate-pillared layered double hydroxides via calcined precursors. Chem. Mater. 1, 489. 

Rocha, J., del Arco, M., Rives, V. and Ulibarri, M. A. (1999). Reconstruction of layered double hydroxides from calcined precursors a powder XRD and Al-27 MAS NMR study. J. Mater. Chem. 9, 2499. 

Carlino, S., Hudson, M. J., Husain, S. W. and Knowles, J. A. (1996). The reaction of molten phenylphosphonic acid with a layered double hydroxide and its calcined oxide. Solid State Ionics 84, 117. 

Kagunya, W., Baddour Hadjean, R., Kooli, F. and Jones, W. (1998). Vibrational modes in layered double hydroxides and their calcined derivatives. Chem. Phys. 236, 225. 

Layered double hydroxides with the hydrotalcite stmcture were synthesized with varying Mg A1 atomic ratios and with different contents of exchangeable CT and CO3 anions. The CO2 adsorption isotherms showed an increase of the uptake and consequently of the basicity with initial CO content and calcination temperature up to 800 K. Increasing the Mg A1 ratio of the hydrotalcites from 2.33 to 3 resulted in an increase of the total number of basic sites [94]. 

The decarbonation of carbonated layered double hydroxides containing Mg with either Al, Fe or Cr bivalent cations or A1 with Mg, Ni, Cu or Zn divalent cations has been studied by thermal analysis. The enthalpy of adsorption of CO2 on the resulting calcined mixed oxides was measured by calorimetry, with initial heats of adsorption close to those reported for MgO (about lOOkJmol ) and a relatively homogeneous strength distribution [100],... 

Layered double hydroxide carbonates of magnesium and aluminum are called hydrotalcites (e.g., Mg6Al2(OH)i6 CO3-H2O). They can be used as solid bases before or after calcination to produce mixed magnesium-aluminum oxides.74 They have been used to catalyze the addition of alcohols to acrylonitrile 75 the reduction of ketones with iso-... 

Fe-Co layered double hydroxides with Co/Fe ratios of 2 and 3 were prepared with or without the presence of Beta zeolite and their catalytic potential was tested in toluene total oxidation. These calcined solids synthesised with p-zeolite were less active and selective than those prepared without zeolite. However, a mechanical mixture of 1/3 Fe,Co-LDH (Co/Fe = 3) + 2/3 NaP-zeolite presented higher catalytic performance which could be explain by a synergetic effect of the both Fe,Co-double oxide and p-zeolite. The mechanism could undergo through a spillover of the adsorbed toluene from zeolite, which has a high toluene storage/release capacity, to the Fe,Co double oxide, which is highly performant for this oxidation. 

The COj species in the HT interlayer could be exchanged with OH ions by calcination at 723 K and hydration at room temperature. A spinel phase of Mg-Al mixed oxide obtained after the calcination transforms into the original layered structure during the hydration. This reconstruction is known as the memory effect of HT materials. The reconstructed HT catalyzed the Knoevenagel condensation of various aldehydes with nitriles in the presence of water [119]. The reconstracted HT also showed an aqueous Michael reaction of nitriles with a,p-unsaturated compounds. The layered double-hydroxide-supported diisopropylamine catalyzed the Knoevenagel condensation of aromatic carbonyl compounds with malononitrile or ethyl cyanoacetate [120]. This solid base could be recycled at least four times, and exhibited activity for aldol, Henry, Michael, transesterification, and epoxidation of alkenes. 

Narita, E., Kaviratna, P., and Pinnavaia, T. J. 1991. Synthesis of Heteropolyoxometalate Pillared Layered Double Hydroxides via Calcined Zinc-Aluminium Oxide Precursors. Chem. Lett. 805-08. 

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. 

D llario L., Fiancohni L, Martinelli A., Piozzi A. (2009), Insight into the Heparin-Toluidine Blue (C.I. Basic Blue l)late[3ctioif Dyes and Pigments, 80, 3, 343-8. Auxilio A.R., Andrews PC., Junk PC., Spiccia L. (2009), The Adsorption Behavior of Cl Acid Blue 9 onto Calcined Mg-Al Layered Double Hydroxides Dyes and Pigments, 81,2,103-12. 

Fig. 10.2 Schematic illustrations and HRTEM images of the different stages in the fabrication of carbon nanorings (CNRs) in the cobalt(II)-aluminum (III) layered double hydroxide (LDH) containing co-intercalated dodecyl sulfonate (DSO) anions and methyl methacrylate (MMA) CoAl-DSO-MMA-LDH matrix (a) the (CoAl-DSO-MMA-LDHCoAl-DSO-MMA-LDH precursor, (b) CoAl-DSO-MMA-LDH after calcination in an Ar atmosphere at 800 °C and (c) isolated CNRs obtained after dissolution of the matrix. Reproduced with permission from [117], Copyright 2013 Wiley...

The reaction of benzaldehyde with ethanol in the presence of MgO, CaO, and mixed oxides obtained by calcination of double layered hydroxides was investigated by Aramendia et a/.1851 in liquid phase. CaO was found to be the most active catalyst for the process. 

Isomerization of jS-isophorone to a-isophorone has been represented as a model reaction for the characterization of solid bases 106,107). The reaction involves the loss of a hydrogen atom from the position a to the carbonyl group, giving an allylic carbanion stabilized by conjugation, which can isomerize to a species corresponding to the carbanion of a-isophorone (Scheme 9). In this reaction, zero-order kinetics has been observed at 308 K for many bases, and consequently the initial rate of the reaction is equal to the rate constant. The rate of isomerization has been used to measure the total number of active sites on a series of solid bases. Figueras et al. (106,107) showed that the number of basic sites determined by CO2 adsorption on various calcined double-layered hydroxides was proportional to the rate constants for S-isophorone isomerization (Fig. 3), confirming that the reaction can be used as a useful tool for the determination of acid-base characteristics of oxide catalysts. 

Hydrotalcite Hydrotalcite (Mg6Al2(C03)(0H)i6 4H20) and other double-layered hydroxide compounds may effectively sorb As(V) from water. Hydrotalcites remove As(V) through sorption and/or exchanges with interlayer anions. The minerals may also be heated (calcinated) until most carbonate anions leave the interlayers. The calcinated hydrotalcites are then placed in water, where the vacant interlayers can sorb anions, including As(V) oxyanions (Yang et al., 2005, 6805). 

The layered hydroxides by themselves are catalytically inactive, probably due to a lack of accessible sites. Upon calcination up to 450°C, materials intercalated with COj or NO3-anions have been found active for aldol condensation ( ), olefin isomerization and 8-propiolactone polymerization (9). Although many elimination reactions have been studied over decomposed double metal hydroxides, the nature of the sites involved is still unclear. 

Ikeda and coworkers synthesized a novel silicate zeolite CDS-1 (CDO) with a cylindrically double saw-edged framework in 2004 [114]. CDS-1 was converted by dehydration-condensation between the layers of pentagonal cylinder-layered silicate (PLS-1). Then in 2008, Okubo and coworkers synthesized novel silicate sodalite (SOD) by topotactic conversion [119]. Another example is shown by Gies and coworkers with the preparation of silicate zeolite RUB-41 (RRO) [109]. By studying the synthesis of hydrous-layered silicates carefully, they used dimethyldipropylammonium hydroxide as the organic SDA to synthesize the layered silicate precursor (RUB-39), and RUB-41 was synthesized after the calcination of RUB-39. 

---