Y-AljO

Radiochemical studies indicate that the pore base is the actual site of formation of aluminium oxide, presumably by transport of aluminium ions across the barrier-layer, although transport of oxygen ions in the opposite direction has been postulated by some authorities. The downward extension of the pore takes place by chemical solution, which may be enhanced by the heating effect of the current and the greater solution rate of the freshly formed oxide, but will also be limited by diffusion. It has been shown that the freshly formed oxide, y -AljOj, is amorphous and becomes slowly converted into a more nearly crystalline modifipation of y-AljO . 

The effect of hot water sealing is to convert anhydrous y-AljO, into the crystalline monohydrate, AljOj.HjO, which occupies a greater volume and blocks up the pores, thus preventing further absorption of dyes or contaminants. The monohydrate is also less reactive. 

The characteristics of the supported Pt catalysts used in this study are compiled in Table 1. The activity of the catalysts during a typical time-on-stream experiment are shown in Fig 1. While Pt/ZrOj catalyst showed high stability (less than 5% loss in conversion during 180 hours time on stream), Pt/y-AljO, lost all catalytic activity after 3 hours and Pt/Ti02 deactivated gradually during 40 hours. The supports alone were catalytically inactive. 

Coke formation on these catalysts occurs mainly via methane decomposition. Deactivation as a function of coke content (see Fig. 3 for Pt/ y-AljO,) seems to involve two processes, i e, a slow initial one caused by coke formed from methane on Pt that is non reactive towards CO2 (see Table 3) In parallel, carbon also accumulates on the support and given the ratio between the support surface and metal surface area at a certain level begins to physically block Pt deactivating the catalyst rapidly. The coke deposited on the support very close to the Pt- support interface could be playing an important role in this process. 

Fig. I NO conversion in NO reduction over Au/y-AljO, and Cu-ZSM-5 catalysts. Reaction conditions as in Table I...

MoOj. After this reduction the Pt atoms may form a surface complex with the partially reduced Mo ions. For the Pt-Mo/y-AljO catalysts which are used at temperatures < 600°C, the active complex may be the dispersed PtM.oOx (where X = 2-3), under the reducing conditions. For temperatures > 600°C, the catalyst can have the surface complex of PtMoOj where x ranges from 0 to 2 depending upon the temperature of reduction. 

Pt-Mo/y-AljO catalyst (1) lowers the activity but increases the selectivity of the Pt catalyst for the NO reduction by H2, and (2) increases the activity for the NO reduction by CO and the activity and selectivity for the NO reduction by CO + H2> Based on the TPR and IR data, we attribute these results to a strong interaction between Pt and Mo oxides on the y-A170, support. Such interaction facilitates the removal of the surface... 

RhCo catalysts, supported on y-AljO, curvefitting results, 38 346-347 Rh CojCCO),, 38 346... 

Two different supports were used a commercial (y-AljO, (CK-300 from Cyanamid Ketjen, 835. = 180 m ) and a ZnAlj04 (833. = 34 m g" ) prepared in the laboratory. The ZnAlj04 spinel was obtained by solid phase reaction between (y-AljOj and pure ZnO at 1173 K for 72 h. The solid was then cooled to room temperature and submitted for XRD analysis, which showed the characteristic lines of Z11AI2O4 and weak lines of ZnO. To eliminate the unreacted ZnO (which could produce PtZn alloys with a very low dehydrogenation capacity), the solid was repeatedly washed with portions of (NH4)jC03 solution (1 M). After washing, the solid was dried and a new XRD analysis showed the total absence of the ZnO phase. 

Cheah, S.E.. Brown, G.E., and Parks, G.A., XAFS spectroscopy study of Cufll) sorption on amorphous SiOj and y-AljO, Effect of substrate and time on sorption complexes, J. Colloid Interf. Sci., 208, 110, 1998. 

The catalysts Pt/NaY, Pt/mordenite and Pt/erionite yield the highest enantiomeric excesses (75 to 80% ee), whereas Pt/NaX (64% ee) and Pt/y-AljO, (54% ee) give comparatively poor optical yields. On the other hand, the high value of Pt/y-AljO, is remarkable. Therefore a correlation between enantioselectivity and the mass-related k values is not discernible. 

On the contrary, the mass-related catalytic activity of Pt/y-AljO, is much reduced when acetic acid is used as solvent. This disproportionate diminution of the ko value might be induced by... 

The percentage of y-AljO, was calculated based on the total amount of the PVDF solution. 

Figure 4-8. Synthesis of iridium carbonyl clusters in neutral solutions and on the nearly neutral surface of amorphous y-AljOs. The chemistry is very similar to that occurring in the cages of NaY zeolite (Fig. 4-7). [3, 5] Whereas the clusters can be readily extracted from the surface of y-AljOj, under the same conditions they cannot be extracted from the zeolite because they are too large to fit through the cage windows and are thus trapped in the supercages.

Besides a-A Os (corundtun) there are at least eight oxides mostly classed under the term of y-AljO, (cf. Ginsberg et al. 1957). Some of these forms may be non-stoechiometric oxide-hydroxides. 

TiOj ZfOj, y-AlOOH, y-AljO, BaTiO, Cao jStojTiijFejOj, ZnO, CoFc204,... 

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