Alumina interactions

Catalysts with Sn-alumina interaction were prepared by the reaction of the lithiated alumina surface and SnCl4 (Scheme 7.14).243... 

All these results are easily explained on the basis of structural properties of samples provided by X ray and EPR studies. It was actually pointed out that for low contents of chromium in the catalysts, alumina interacts with the amorphous active phase and favours the stabilization of low coordinate chromium ions... 

In conclusion, the TPD spectra can be characterized by two broad peaks, one at 100° and the other at 450°. However, these could be made up of a combination of several different peaks. Assignments of these individual peaks to specific Pt states are hardly possible, but the broad TPD profile arises out of two possible causes either to structural changes in the Pt crystallite forms or to variation of Pt-alumina interactions due to the heterogeneity of the alumina surface. 

Based on the above data, one may suggest that, CoPc molecules seem to lie flat on the surface of alumina and alumina-rich supports. This may arise most likely from the interaction of Co + with A13+ centers (with possibility of N(of CoPc)- weaker acid sites (of alumina) interaction [31,32]) resulting in a stoichiometry value-1. In this case, Co ion in molecular dispersed CoPc is accessible for O2 from one side. However, the higher stoichiometries obtained in the case of samples on silica and silica-rich support may reflect that CoPc molecules are oriented on the support surface. This implies that CoPc molecule is accessible for O2 from different sides (both sides ofcentral Co ion and exposed peripheral N s). Such increased accessibility is favored by inclined edge interactions mainly between nitrogens of the macro-cycle of Pc and the hydroxyl groups of the support surface (Br[Pg.413]

Ringenbach, E., Chauveteau, G., and Pefferkom, E.. Effect of soluble aluminum ions on polyelectrolyte-alumina interaction. Kinetics of polymer adsorption and colloid stabilization. Colloids Surf. A, 99, 161, 1995. 

Bouhamed, H., Boufi, S., and Magnin, A., Alumina interaction with AMPS-MPEG random copolymers. 1. Adsorption and electrokinetic behavior, J. Colloid Interf. Sci., 261, 264, 2003. 

The rhodium dispersion becomes progressively worse on the higher temperature and, therefore, lower surface area alumina phases, NO uptake also falls sharply as the ageing temperature of each Rh/A1 0 phase is increased. The lower NO uptake can be explained partially by rhodium sintering (as the oxide) and also by a metal support interaction (Ref. 36). The interaction is less for the high temperature, less reactive alumina phases but even here NO absorption is not measurable after ageing at 850 C. The rhodium/alumina interaction is also observed when temperature programmed reduction (TPR) is performed (Fig. 14(A) and (B). 

This is why a new approach for controlling precursors-alumina interactions through surface functionalization has been developed in this work. Support functionalization is known to modify support acidity [9] and has thus successfully been used by Kera ef 0/ [10, 11] to prepare catalysts with improved selectivity for methanol oxidation. 

X-ray studies of two systems prepared with the same alumina samples by the same procedure and calcined at the same conditions allow us to conclude that alumina stabilization by Ce is weaker than by La [49]. The formation of the solid solution based on the y-alumina structure by substitution of AP+ on La + ions imposes limitations on the transitions to 5, 0, a-alumina. Alumina modified by Ce does not show essential stabilization of the structure of alumina. This is caused by the limitations on alumina interaction with Ce ions. 

Pielaszek JJ, Kepinski L, Kazachkin DV, Kovalchuk VI, d Itri JL. Characterization and catalytic activity of differently pretreated Pd/Al203 catalysts the role of acid sites and of palladium-alumina interactions. J Catal. 2004 227 11. 

NiA15M catalysts specially, the Ni°-MgO interactions are weakened. This phenomenon could favour Ae formation of nickel-alumina interactions which could be promote by lower dispersion of MgAl203. The formation of nickel-alumina interactions could provide a similar activity for the NiA3M catalyst and lower activity for the NiA15M catalyst than the NiA eatalyst. 

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