Binary Cu-Al mesophases precursors to uniformly sized copper particles highly dispersed on mesoporous alumina

A series of binary Cu-Al mesoporous precursors have been prepared by direct synthesis using "catanionic" (mixed cationic and anionic) surfactants. The as-synthesized materials, involving a mesotructured framework composed of minor Cu hydroxynitrate domains overdispersed within the major alumina base d mesophase, yielded through controlled calcination and reduction, Cu-0 par ticles of variable size, well dispersed and quite strongly attached on the alumina support. In each calcined sampler combined transmission electron mi croscopy and energy dispersive X-ray analyses revealed the presence of both very small, nanometer sized, CuO particles and of larger CuO domains, the size of which depends on the initial copper amount. The fact that each Cu h ydroxynitrate domain in the as-synthesized sample yields, upon calcination and subsequent reduction, respectively the corresponding CuO domains and Cu -0 particles of about the same size and similar dispersion, reflects the re gular pre-dispersion of the Cu islands during the very first synthesis stag es. The (Cu,AI) mesoporous samples have been tested as catalysts for select ive hydrogenation of cinnamaldehyde (CNA) and compared to classical Cu-impr egnated alumina catalysts. The remarkable selectivity of the (Cu,Al) mesopo rous samples towards the formation of unsaturated alcohol (hydrogenation of the carbonyl group of CNA) was attributed to the particular strong interac tion of the nanometer sized Cu-0 "islets" with the Al mesoporous walls, whi le the conjugated C=C bond is more readily hydrogenated on larger Cu-0 clus ters in weaker interaction with the support. (C) 2001 Elsevier Science B.V. All rights reserved.