The decrease of the surface area may be due to the

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Unformatted text preview: ue to the formation of divalent metal oxide and spinel phases and their improving crystallinity with increasing temperature.  >1L ,, 0J ,, $O ,,, &2@  DWRPLF UDWLR  >1L ,, $O ,,, &2@ 1L$O2   VXUIDFH DUHD >P J@  DWRPLF UDWLR          FDOFLQDWLRQ WHPSHUDWXUH >ƒ&@ Fig. 2 Change of surface area during calcination of Ni containing HTs [25]   1. Introduction 19 1.2.3. Applications of HTs and HT derived materials Because of their interesting properties discussed above HTs and HT derived materials are used for many applications such as waste water treatment, ion exchanger, molecular sieves, halogen free flame retardant, antiacids, stabilisers for polymers, pharmaceuticals and agricultural goods, additive to rubbers, halogen scavenger and heterogeneous catalysts [1, 2, 64]. 1.2.3.1. HTs as catalyst precursors in heterogeneous catalysis In the field of heterogeneous catalysis HTs themselves are not used, but mixed metal oxides derived from HT precursors are used for various applications (Tab. 4). They have various inherent advantages [1, 2, 7, 25, 53]. HTs can contain basic metal ions like Mg2+, giving the final catalysts basic properties, hence their wide spread industrial use as solid bases for example. Furthermore HTs have the same structure regardless the composition allowing the substitution of suitable metal ions without changing the morphology and hence structure related properties, like the high surface area found for HT derived catalysts. Another important advantage of HT precursors is the uniform distribution of the metal ions in the brucite-type sheets as this means that the metal ions are evenly mixed in the precursor. By the perfect mixing of the elements synergetic effects between the elements are favoured not only in the HT, but also in the final catalysts. The uniform distribution of the metal ions is also responsible for the formation of well dispersed and stable metal particles as a result of an appropriate calcination...
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This document was uploaded on 10/07/2013.

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