SUMMARY:The electronic structure and geometry of polymethylaluminoxane (MAO) [ 1Al(CH 3 )O1 ] n with different size (n = 4 -12) have been studied using quantum-chemical DFT (density functional theory) calculations. It has been found: 1) Starting from n = 6, the three-dimensional oxo-bridged (cage) structure of MAO is more stable than the cyclic structure. 2) Both for cage structure and for cyclic structure the Lewis acidity

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A cluster model quantum chemical approach is used to study the electronic structure of Co in bimetallic sulfide catalysts Co/MoS 2 . The oxidative addition of hydrogen to the Co-Mo component is considered. Ab initio HF/MP2 and DFT calculations show that hydrogen occluded in the catalyst bulk is sorbed on the cobalt ion and stabilizes the Co(III) d 6 electronic state of cobalt ions in the sulfide catalysts. This electronic state is rather active, when surface sites interact with the S-containing reagents participating in the HDS catalysis. A model of active sites on the Co/MoS 2 catalyst is used to discuss the suggested molecular mechanism of the HDS catalysis.

The various quantum chemical models of catalytic active site in Cu-ZSM-5 zeolites are analyzed. The density functional theory (DFT) is used to calculate the electronic structure of molecular cluster (HO) 3 Al-O-Cu-O-Cu modeling the catalytic active site in Cu-ZSM-5 zeolites and study the interaction and decomposition of NO. It is assumed that the rate-determining stage of the low-temperature selective catalytic reduction of NO is the formation of the π-radical (N 2 O 2 ) -on electron donor sites of Cu-ZSM-5 catalysts. This is in good agreement with the high electron affinity of the molecular dimer ONNO (E a ) -1.5 eV) and is confirmed by the experimental data on the formation of surface anion π-radical (N 2 O 2 ) -on electron donor sites of supported organo-zirconium surface complex. The DFT calculated electronic structure and excitation energy spectra for the model system (HO) 3 Al-O-Cu-O-Cu show that it is a satisfactory model for description of experimental UV-vis spectra of Cu-ZSM-5, containing (-O-Cu-O-Cu-) chain structures in the zeolite channels. The calculated reaction energy profile of ONNO adsorption and decomposition on the model catalytic active site shows the possibility of the low-temperature decomposition of dimer (NO) 2 with low activation energy and the important role of copper oxide chains (-O-Cu-O-Cu-) in the channels of Cu-ZSM-5 zeolite during selective reduction of NO.