Density functional study of SO2 adsorption in HY zeolites

The interaction of SO2 molecules with active sites of HY zeolite was studie d by means of density functional model cluster calculations employing a gen eralized gradient approximation (GGA) of the exchange-correlation functiona l. A fragment of the zeolite framework which contains an acid bridging hydr oxyl group and an adjacent basic oxygen center was modeled by the cluster H 3SiO(H)AlSiH3. The equilibrium geometry structures were determined for vari ous donor-acceptor and hydrogen-bonded conformers of SO2/HY adsorption comp lexes, These two adsorption interactions are similarly weak with the hydrog en-bonded form being more stable by about 2 kcal/mol. In this most stable c onformer, the interaction of the sulfur atom with the adjacent oxygen cente r leads to additional stabilization. The assignment of the SO2/HY complexes to hydrogen bonded species is confirmed by a comparison of experimental an d calculated adsorption induced shifts of SO2 and OH vibrational frequencie s. (C) 1999 Elsevier Science B.V. All rights reserved.