Yttrium distribution ratio

Figure 6. Distribution of titanium and the yttrium/lanthanum ratios.

Rare earth stabilization, as it relates to zeolite performance, has already been discussed. However, catalyst performance also varies depending on how the rare earths are deposited within the zeolite and the matrix, and also on how the ratio of individual species (such as lanthanum, cerium, and the other rare earths) are distributed. Yttrium can also be used to enhance zeolite catalyst performance and stability. These also seem to help mitigate the detrimental effect of vanadium, the most common and controversial contaminant. 

The rapid exchange between the in situ-formed yttrium alkoxide and the alcohol allows the average number of the initiated chains to be controlled by the excess of alcohol with respect to Y. At a molar excess of 50, all the alcohol molecules participate to the exchange and thus to the initiation of s-CL polymerization at 20°C. In addition to Mn, which can be predicted from the monomer/alcohol molar ratio, the molecular weight distribution is narrow even at high monomer conversion. The same strategy has been extended to the preparation of neodynium alkoxides from tris(bis(trimethylsilyl)amido) neodynium (Nd[N(SiMe3)2l3) (62). 

The polymerization of PDL, initiated by yttrium isopropoxide, has been carried both in bulk and in solution over the temperature range of 60-100 °C [39]. All isopropoxide groups of the initiator participated in the initiation, and the polymerization proceeded by acyl-oxygen cleavage of the monomer. The molecular mass of the polymer could be controlled effectively by varying the initial monomer-to-initiator molar ratio. An induction period which was observed for the bulk polymerization at 60 °C was attributed to structural rearrangement processes of the initiator to form the actual active sites. The molecular weight distribution (PDl) was approximately 1.6. 

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