Preparation of heteroatom Y zeolite by secondary synthesis and its performance in adsorptive desulfurization

A heteroatom Y zeolite (AlY) was prepared by introducing gallium atoms into the framework of Y zeolite through a secondary synthesis method (isomorphous substitution), i.e. treating Y zeolite with an aqueous solution of ammonium hexafluoro gallate. The performance of AlY in adsorptive desulfurization was investigated with various model fuels containing about 500?10^-6 sulfur. The results indicated that the sulfur adsorption capacities of AlY towards thiophene, tetrahydrothiophene (THT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), dibenzophiophene (DBT), benzothiophene (BT) and 4-methyldibenzothiophene (4-MDBT) are 7.0, 17.4, 14.5, 16.9, 6.9 and 5.8 mg-S/g-adsorbent, respectively. A density functional theory (DFT) calculation shows that the charges on S atom in thiophene, THT, 4,6-DMDBT, DBT, BT and 4-MDBT molecules are -0.159, -0.298, -0.214, -0.211, -0.193 and -0.188, respectively, implying that the S-M bond between the adsorption sites and thiophene molecules is much weaker than that between the adsorption sites and the molecules of THT, 4,6-DMDBT or DBT. Moreover, the sulfur removal rate of FCC gasoline on AlY is 68%.