Abstract
The objective of this presentation is to give a characterization of aluminosilicate MCM-41, in particular with respect to acidity and the nature of the acid sites. 29Si MAS NMR spectra of MCM-41 closely resemble those of amorphous silica, suggesting that the pore walls are amorphous. This fact could also imply that the types of acid sites in these materials are different from those generally found in zeolitic materials. The obtained results from 1H MAS NMR and combined FTIR and temperature-programmed ammonia desorption (TPAD) investigations indicate that the washed, template-free MCM-41 and its protonic form behave as a solid-state acid with a broad acid strength distribution. With regard to the presence of bridging hydroxyl groups in the investigated MCM-41 materials, the findings of these two methods are not consistent. Therefore, it is assumed that the broad absorption between 3650–3400 cm−1 in the FTIR spectra is connected with hydrogen-bonded vicinal silanol pairs. The results of the catalytic testing suggest that the weak Brönsted acid sites interact with neighbouring coordinatively unsaturated aluminium species and that synergistically stronger acid sites are formed.
Published Version
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