Oxidative catalysis of Keggin anion [XW11O39Z(H2O)]n− pillared clays in the reaction of acetaldehyde with H2O2

Abstract In aqueous solution, the layered double hydroxides (LDHs) pillared by heteropolyanions, Co 2 Al–XW 11 Z and Ni 2 Al–XW 11 Z (X=B 3+ , Si 4+ , Ge 4+ and As 5+ ; Z=Cu 2+ , Co 2+ and Ni 2+ ), have been synthesized by the direct ion exchange reaction of the monosubstituted Keggin-type heteropolyanion containing transitional element with the Co 2 Al–NO 3 and Ni 2 Al–CO 3 precursors. The results of XRD and FTIR measurements indicate that they are the pillared layered compounds with gallery height of 0.99±0.01 nm and that Keggin-type framework of the heteropolyanion still remain inside the layers. The composition and properties of these compounds have been evidenced by TG and ICP analyses. The catalytic feature of these pillared layered clays for the oxidative reaction of acetaldehyde with H 2 O 2 has been studied. The formation rate of the product acetic acid was between 20–53 mmol (g-cat.) −1 h −1 and the selectivity for acetic acid was nearly 100%, showing that they were excellent oxidative catalysts in liquid–solid system. In addition, if the catalytic activities are expressed as per mmole of heteropolyanion instead of per gram of the catalyst, the catalytic activities of Co 2 Al–XW 11 Z and Ni 2 Al–XW 11 Z were between three times and nine times that of XW 11 Z as potassium salts in homogeneous system. This may be because the clay layer has a significant effect on the heteropolyanions against decomposition resulting from H 2 O 2 . Furthermore, the composition of the layer and heteropolyanion also influences on the catalytic activity. The experimental results of catalytic activity for the two kinds of clay catalysts of Co 2 Al–SiW 11 Cu and Co 2 Al–NO 3 calcined at different temperatures show that not only the pillared layered structure makes a contribution to the catalytic activity but also the thermo-decomposition product of them, a complex oxide with spinel structure, is a fine catalyst for the oxidation of acetaldehyde into acetic acid.