Catalysis of Organic..

56Hydrotalcite-like Catalysts[A n- ] x/n • m H 2 O, where M 2+ = Mg 2+ , Ni 2+ , Zn 2+ , etc; M 3+ = Al 3+ , Fe 3+ , Ga 3+ , etc; A n- =(CO 3 ) 2- , Cl - , (NO 3 ) - , etc.The physicochemical properties of HTs and the solid solutions produced aftertheir calcination can be easily tuned by changing the nature and amount of metalcations and anions (10). Therefore, to elucidate the role of the chemical compositionon the gas phase acetone self-condensation reaction, a series of bimetallic andtrimetallic HTs were prepared, characterized and tested.Results and DiscussionTable 1 summarizes the different chemical composition of the fresh HTs,where the molar ratios M 2+ /M 3+ varied from 2 to 3. Even if from synthesis it wasestablished a nominal molar ratio M 2+ /M 3+ =3, the real values varied from 3.0 forZnAl to 2.0 for MgZnAl-12, these differences can be attributed to an incompleteincorporation of the cations inside the layers. The increasing of Zn loading can bestated from the formulae, it ranges from 7.56 wt.% for MgZnAl-7 up to 43.62 wt.%for ZnAl3.Table 1. Chemical composition of the fresh hydrotalcite-like compounds.Sample Chemical Formulae M 2+ /M 3+MgAl3 [Mg 0.744 Al 0.256 (OH) 2 ] (CO 3 ) 0.128·0.850 H 2 0 2.9MgZnAl-7 [Mg 0.614 Zn 0.093 Al 0.293 (OH) 2 ] (CO 3 ) 0.146·0.731H 2 0 2.4MgZnAl-12 [Mg 0.493 Zn 0.165 Al 0.342 (OH) 2 ] (CO 3 ) 0.171·0.978 H 2 0 2.0ZnAl3 [Zn 0.75 Al 0.25 (OH) 2 ] (CO 3 ) 0.125·0.840 H 2 0 3.0Figure 1 exhibits the XRD powder patterns of fresh HT´s; they present thecharacteristic reflections corresponding to a hydrotalcite-like structure.003Relative Intensity (a.u.)006009015018MgZnAl-12110113MgZnAl-7ZnAl3MgAl310 20 30 40 50 60 702-ThetaFigure 1. XRD powder patterns of fresh HT´s.