Local structure of highly dispersed lead containing zeolite. An ab initio and density functional theory study

Ab initio quantum chemical studies at the HF/Lan12dz, B3PW91/Lan12dz and B3LYP/Lan12dz levels were carried out to investigate the local structures of the Pb²⁺ active site of lead containing zeolites. It was shown that the coordination number which equals three is found to be the most favorable one for the Pb²⁺ site within the zeolite lattice. The latter arises from the ground electronic state for the Pb²⁺ within the zeolite lattice that involves lone pair of electrons at the 6s-AO. Thus, the Pb²⁺ site would be in a strongly distorted tetrahedral environment. Due to the presence of the above lone pair of electrons, the adsorbate molecules would experience the repulsion from these electrons. The latter may explain some differences observed for the decomposition of pollutant molecules over the Cu⁺ as well as Ag⁺ ion-exchanged zeolites and the Pb²⁺ ion-exchanged ones.