Epoxidation catalysts derived from aluminium and gallium dawsonites

As-synthesised and reconstructed NH4-Al-dawsonite and NH4-Ga-dawsonite, and the materials obtained by thermal treatment in the range 373-873 K, were studied as heterogeneous catalysts for the epoxidation of cyclooctene with hydrogen peroxide at 353 K and ambient pressure by means of High-Throughput Experimentation. The structural, morphological, and textural properties of the materials were investigated by elemental analysis, ICP-OES, XRD, FTIR, TEM, N-2 adsorption, and TGA. The temperature at which the dawsonite precursors were treated proved to be crucial in determining the activity of the catalysts. The best catalyst identified in this work was obtained by calcination at 573 K of reconstructed Ga-dawsonite. This material provides an epoxide yield of 51% and 99% selectivity after 4 h at 353 K. Remarkably, many of the catalysts derived from Al-dawsonite displayed an enhanced epoxidation activity upon recycling, reaching up to 30% epoxide yield with 98% selectivity over Al-dawsonite treated at 473 K. (C) 2009 Elsevier B.V. All rights reserved.