No abstract

The rdf for the 21.4 wt % sample differs from the ones for the samples with lower loading, especially with respect to the relatively high intensity of the peak at 0.3 nm. This points to a high degree of polymerization, which is in accordance with the expected formation of precipitates. This rdf also differs from that of the AHM reference compound. This suggests that the precipitate has a different structure. No attempt was made to unravel this structure. The amount of Mo(IV) present in this sample is still consistent with the adsorption model, however.During the preparation of catalysts by impregnation, the time allowed to reach equilibrium is often about 1 h or even less. In the case of the AHM/y-Al203 system, the EXAFS results indicate that 1 h is too short for equilibrium to be attained, since it was found that in the impregnated sample less Mo(IV) is present than in the material obtained in an adsorption experiment. ConclusionsThe present EXAFS study has resulted in a modification of the model describing the adsorption of AHM onto 7-Al203. It appears that two adsorption sites are necessary: (1) basic OH groups, leading to adsorption of Mo(IV); (2) coordinatively unsaturated Al3+ sites, leading to adsorption of Mo(VI).Of the site-blocking reactions employed here, the F exchange of basic OH groups gives results in line with the above adsorption model, but the reaction of Al3+ sites with acacH leads to more ambiguous results.A normal catalyst impregnation time of about 1 h is too short for the reaction of AHM with the basic OH groups to proceed to completion.

No abstract

No abstract

No abstract