Adsorption of carbon monoxide in H-ZSM-5 and Li-ZSM-5 zeolites: an embedded ab initio cluster study

The absorption of carbon monoxide with H-ZSM-5 and metal-substituted Li-ZSM-5 zeolites has been investigated by Ž . using both cluster and embedded cluster approaches at the HFr6–31G d,p level of theory. For the H-ZSM-5 zeolite, the binding energy of CO on a 3T quantum cluster is predicted to be 2.25 kcalrmol for the C-bound complex. The O-bound complex was found to be less stable by about 0.84 kcalrmol. Inclusion of the Madelung potential was found to increase the acidity of the Brønsted acidic site and the CO-binding energy to 4.95 kcalrmol, consequently, it leads better agreement with experimental observation. Similar results were also obtained for the Li-ZSM-5rCO complex. The Madelung potential field from the zeolite framework was found to reverse the order of relative stability of C-bound and O-bound adducts in comparison to the Li–CO system. q 2000 Elsevier Science B.V. All rights reserved.