Synthesis, characterization and study of lanthanum phosphates as light alcohols dehydration catalysts
Résumé
Four preparation methods have been developed for the synthesis of lanthanum orthophosphate catalysts, which are shown to be active and selective catalysts for the dehydration of light alcohols (C-2 to C-4). Their crystallinity, surface area, surface composition and acid-base properties appear to differ according to the preparation method used. The most important parameter influencing their catalytic properties appears to be their surface composition since this has a direct influence on their surface acidity. All of the solids presented weak and moderately strong Bronsted and Lewis acid sites, and only weak basic sites in low quantities. These acid-base properties resulted in the prevalence of an E-1-type mechanism for 1-butanol dehydration. Bronsted acid sites, which appear as the most efficient sites, are associated with the presence of an excess of phosphorus at their surface and from spectroscopic data this is attributed to (H2PO4)(-3+n) (n=1 or 2) species from spectroscopic data. The prevalence of these species and their optimum surface distribution make them extraordinarily efficient and ultra-selective for the dehydration of several alcohols. Published by Elsevier B.V.