| Popis: |
Porous aluminophosphates, which are useful as catalyst supports for polymerization, isomerization, or other hydrocarbon conversions, can be made by coprecipitation when an acidic solution of A13+ and PO43− ions is neutralized. When the P Al ratio in solution is equal to or greater than one, A1PO4 is obtained often as a crystalline material, leaving the excess phosphate in solution. However, when excess Al3+ is present in solution ( P Al ) then it also precipitates and the resulting support retains a similar P Al ratio to that in solution. In this study the structure of such aluminophosphates has been examined by means of X-ray diffraction and high resolution solid state NMR spectroscopy using both 27Al and 31P nuclei. These materials are not simple coprecipitated mixtures of A12O3 and A1PO4. In fact, no evidence for the presence of either species was detected. Instead they appear to be amorphous structures in which the phosphate is randomly dispersed, and the aluminum exists in one octahedral and several different tetrahedral environments. Results from ethylene polymerization over these catalysts also support this view. |
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