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Synthesis of LDH-Based Catalysts

Anions that are incorporated in the interlayer of LDH during the synthesis must have high affinity towards LDHs and must be present in excess amount. For the LDH synthesis with anions that are not carbonates, the synthesis should be carried out using ion exchange method or the reconstruction method (memory effect) due to the higher affinity of CO from the atmosphere towards the LDH structure. [Pg.488]

Coprecipitation synthesis method enables the use of a wide range of cations and anions for their incorporation in the layers and interlayers of LDHs. Large quantities of synthesized materials can be obtained using this synthesis method. As previously mentioned, the pH value of coprecipitation is of great importance and may affect the nature and properties of the synthesized material. In general, the pH ranges from 8 to 10 and is considered to be the optimal for the preparation of LDHs [2]. [Pg.488]

In this synthesis method the mixed aqueous solutions of M and M ions are used as precursors. With the variations of the M VM ratio the LDH composition changes, where only narrow interval ratio can enable the formation of the particular phase. [Pg.488]

This method allows the incorporation of a wide range of anions in the interlayer. Considering that it is important to provide simultaneous coprecipitation of precursors, this synthesis method must be carried out in oversaturated conditions, while controlling and regulating the pH value of the solution that must be higher or equal to the pH value for the precipitation the most soluble hydroxide [20]. Two coprecipitation synthesis methods are most commonly used for LDH synthesis coprecipitation at low supersaturation (LS) and coprecipitation at high supersaturation (HS) methods. The LS synthesis method is performed by slow addition of mixed aqueous solutions of M and M ions in the selected ratio with simultaneous addition of alkaline solution at such a rate to maintain constant pH. On the contrary, the HS synthesis method is carried out by the instant addition of the mixed M VM solution to the alkaline solution containing the desired interlayer anion [20]. [Pg.489]

LDHs synthesized by sol-gel synthesis methods have smaller crystallites and high BET surface area in comparison with materials synthesized by the coprecipitation method. It is based on dissolution of the alkoxide precursor of M cations by acid hydrolysis (HCl or HNO3), and gradual addition of a solution of acetyl-acetonate precursors at a constant pH value controlled by NH OH. After the gel is obtained, it is washed with ethanol and then dried [2, 20]. [Pg.489]


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