ACID SOFTNESS AND HARDNESS IN LARGE-PORE ZEOLITES AS A DETERMINANT PARAMETER TO CONTROL SELECTIVITY IN ORBITAL-CONTROLLED REACTIONS

It has been found by means of quantum chemical calculations that by mo difying the framework composition, i.e., changing the Si/Al ratio, and substitution of Al by other trivalent atoms such as Ga and B, in a gi ven zeolite, the energy of the frontier orbitals of the zeolite change s and therefore the softness of the acid site changes. The acidity sof tness increases when increasing the Si/Al ratio and also when going fr om B to Ga and to Al in the framework. Since the acid softness can pla y a determinant role specially in orbital-controlled reactions, the ca talytic implications of the changes in the acidity softness-hardness o f zeolites have been shown by carrying out the alkylation of toluene b y methanol and looking into the para-ortho selectivity changes obtaine d when using HY zeolites with different framework Si/Al ratios and H-b eta zeolites with Al, Al + Ga, Ga, and B as trivalent framework elemen ts.