Hydrotalcite-like LDHs, synthesis

The PXRD patterns for both the LDH and MH are shown in Figure 1. The LDH showed a PXRD pattern with very intense and sharp peaks, characteristic of a very well ordered hydrotalcite-like compound. The basal spacing obtained was 7.68 A, very close to the reported data [17,20,21] for carbonate containing LDH. From the chemical analysis we obtain the following molecular formula Zn2 9Cr(OH)7 8(C03)o5-2,3H20 (normalized to Cr = 1). The Zn Cr ratio obtained, 2.9, was slightly lower than the one expected, 3, indicating a preferential solubilisation of Zn(II) cations, a feature widely reported in the synthesis of LDHs [11]. 

Layered double hydroxides (LDHs) known as hydrotalcite-like layered metal hydroxosalts, are extensively explored as precursors of various catalysts. Interest in LDHs is provided by the fact that two, three or more metal cations may be introduced in the bracite-like layers, besides various anions (e.g. decavanadate, paramolybdate, etc) may be incorporated into the interlayer space [1]. However information on the application of such materials as multi-component catalysts for oxidative dehydrogenation (ODH) of ethylbenzene (EB), light alkanes and alcohols is still scanty. We have performed an extensive investigation of the synthesis of the complex hydrotalcite-like hydroxosalts and then-application as precursors of the catalysts. The performance of the latters was studied in ODH of ethylbenzene, light alkanes and alcohols. 

The method of synthesis of multi-component hydrotalcite-like layered metal hydroxosalts (LDHs) was elaborated. The products obtained have been used as precursors of V-Mo-W-Nb-0 catalysts for ODH of EB, ethane, propane and alcohols. Considerable increasing of EB, alkane and acohols conversion simultaneously with the selectivity to alkene, styrene and carbonyl compounds has been successively achieved using the purposeful progressive complication of the composition of the LDHs precursors. Investigations made it possible to formulate scientifically substantiated preparation and application of the V-Mo-W-Nb-0 catalysts to obtain high activity and selectivity in the ODH processes. 

Co-precipitation methodology is the most cotmnon synthesis techniqne to obtain LDHs, however nucleation and the kinetics growth can not be controlled easily. An alternative method for the synthesis of nanomaterials is reverse microemnlsion (water-in-oil) in which an aqueous phase is dispersed into an oil phase stabihzed by a surfactant film. Microemulsions can be used as nanoreactors leading to homogeneous nanomaterials with a narrow particle size and better textural properties [3]. In this work, Mn and binary Mn-Cu, Mn-Co hydrotalcite-like precursors synthesized in reverse microemulsion and the effects of preparation methods on the performance of catalysts for deep oxidation of VOCs have been studied. 

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