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Transition metal containing spherical MCM-41 silicates were prepared and characterized by transmission electron microscopy (TEM), XRD, BET, TPR and IR spectroscopy. Incorporation of aluminum, iron, cobalt, copper ions into the wall of the pores has been established. These ions were almost completely built in into the silicate framework from the synthesis gel. With increasing iron content the ordering of pores decreased, the hydrogen uptake increased, the acidity gained. Only one electron transfer took place (Fe3+ → Fe2+) during the reduction of Fe-MCM-41 samples up to 923 K, which means that iron is stabilized in the mesoporous structure and probably linked with framework via oxygen ions. For cobalt ion containing samples practically no reduction was observed, however, significant Lewis acidity was detected. The copper containing samples behaved different. Two electron transfers took place upon hydrogen treatment proving the reduction of Cu2+ ions to metallic copper, however, a part of the metallic species can be reversible reoxidized to cationic form. The Cu-MCM-41 samples showed also Lewis acidic character. Both Bronsted and Lewis acidic sites could only be observed by IR spectroscopy when aluminum or iron was incorporated into MCM-41. The Fe-MCM-41 samples showed significant catalytic activity in the acid catalyzed alkylation of toluene with benzyl chloride at 333 K. |
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