Rare-earth elements modified hydrotalcites and corresponding mesoporous mixed oxides as basic solid catalysts

摘要

The inspection of a series of hydrotalcites (HTs) samples prepared under different supersaturation conditions, has allowed the selection of the low supersaturation method conducting to a more disordered HT structure as appropriate to accommodate rare-earth elements (REE) species in HTs structures. The goal is to prepare mesoporous mixed oxides to be used as catalysts for basic catalyzed organic reactions. A series of REE (Y3+, Dy3+, Gd3+, Sm3+, La3+) modified HTs samples are prepared under low supersaturation conditions. Their derived mixed oxides were obtained by the thermal decomposition of HTs at 460 degrees C for 18 h under argon flow. The properties of HTs modified REE and of their corresponding mixed oxides are analyzed from XRD structural data, textural measurements and basicity data. The HTs modified REE in an amount of approximately 10% (w/w), from 6.78% (w/w) for Mg0.75Al0.23Y0.02 to 11.74% (w/w) for Mg0.75Al0.23Dy0.02 proved to be effective precursors for the manufacturing of mixed oxides catalysts very active and selective in the reaction of cyanoethylation of ethanol with acrylonitrile. A relation between their conversions and their properties, in particular, the number of weak and medium-strength basic sites could be proposed. (c) 2005 Elsevier B.V. All rights reserved.