Reactions of Aqueous Salts with High Area Aluminas

Abstract

The coupled or equivalent exchange of the cations and anions of 11 salts, chiefly alkali metal and alkaline earth chlorides, with surface Hf and OH-of a commercial a-basic aluminum oxide was studied. Adsorption equilibrium constants and reaction site densities are reported. These site densities and those for two salts with other aluminas are low, so that the area per site is of the order of 1-10 X lo2suggesting the reaction is very specific.In three other systems which are a t least partially irreversible (where the salts are LiC1, XiC12, or Cu(N03)*) the total amount of reaction with the surface is much greater. Here, there are probably both exchange reactions, which are partially irreversible, and equivalent exchange reactions.Site density depends upon both anion and cation.

Deposition of Active Component

“…However, recent works [26,27,36,[42][43][44]711 devoted to the anchoring/grafting in vapor phase (CVD) (see Sections 4.1.2.3 and 4.1.2.4). Some studies suggest that they are less reliable for obtaining species as well-defined as with ally1 precursors.…”

“…Lateral interactions between adsorbed ions (ion coadsorption) have been reported [27,281 and make questionable the use of mass action equations at interfaces. In particular, lateral interactions between adsorbed ions, site heterogeneity as well as phenomena involving the oxide dissolution or rehydration are not taken into account systematically.…”

Ion Exchange and Impregnation

“…Lateral interactions between adsorbed ions (ion coadsorption) have been reported [27,28] and make questionable the use of mass action equations at interfaces. In particular, lateral interactions between adsorbed ions, site heterogeneity as well as phenomena involving oxide dissolution or rehydration are not systematically taken into account.…”

“…As a consequence, complexation of dissolved Al(III) by molybdenum resulted in extensive dissolution of the alumina support, even at pH-values close to neutrality. Surface-selective 27 Al CP-MAS solid-state NMR showed that these species are not only formed in solution but also deposited on the support, and are thus the real precursors of the molybdic species present in the finished catalyst. Surface-selective 27 Al CP-MAS solid-state NMR showed that these species are not only formed in solution but also deposited on the support, and are thus the real precursors of the molybdic species present in the finished catalyst.…”

Determination of chloride in platinum-rhenium alumina-based reforming catalyst by ion chromatography

“…The ion-exchange properties of the hydrous alumina have been extensively studied (16)(17)(18)(19) and depend upon the pH of the ion-exchange medium. At pH values greater than the isoelectric point (iep) Le., 6.8 for y-alumina, the oxide behaves as a cation exchanger, while below the iep it possesses anion exchange properties.…”