Catalytic Properties Of Ti Modified Mcm-41 For Benzene Hydroxylation

The work described in this Thesis involves the introduction of aluminum ions and basic centers into the MCM-41 framework in order to modify its structural and surface properties in a controllable fashion. It has been previously shown that MCM-41 materials are active as catalysts for aromatic hydroxylation reactions. In this work, the way in which the catalytic properties of the materials are affected by variations in surface properties is subjected to a detailed systematic study.This Thesis reports an investigation of the effect of titanium substitution in the framework of MCM-41 on the stability of the catalyst. It was found that the used catalyst was much less active than the fresh catalyst. The reasons for this loss in activity were explored. It was found that although both the used catalyst and the calcined used catalyst retained the long range structural order, relatively large pore sizes and high surface areas of the fresh catalyst, a fraction of the titanium catalytic centers had migrated from the framework into non-framework sites. Titanium ions in non-framework sites are catalytically inactive in aromatic hydroxylation reactions, accounting for the observed loss in activity.In order to prevent this deactivation of the catalyst, the titanium centers were grafted onto the surface of the MCM-41. It was found that the grafting process did not affect the long-range structural order of the material and furthermore the grafted titanium centers not only retained the catalytic activity of the framework sites but were also present in much larger amounts. The activity of the uncalcined grafted titanium catalyst was found to be higher than that of the material after calcination. The stability of the uncalcined grafted titanium catalyst was further investigated in detail. It was found that the uncalcined grafted titanium catalyst displayed both excellent activity and stability in aromatic hydroxylation reactions.