Molecular Models of the Stabilization of Bivalent Metal Cations in Zeolite Catalysts
||Practical Aspects of Computational Chemistry I
Springer Dordrecht Heidelberg London New York. 2012.
680 c. ISBN 9789400709188.
Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Pr. Akad. Lavrentieva 5, Novosibirsk 630090, Russia
Chemistry Department, Lomonosov Moscow State University, Leninskiye Gory 1-3, Moscow, GSP-2, 119992, Russia
A review of quantum chemical modeling of bivalent metal ion stabilization in zeolites is presented. Location of single metal ions in zeolite cationic positions and formation of polynuclear metal-oxo clusters are considered. Special attention is paid to the stabilization of single bivalent metal ions in the cationic positions with distant separation of the two lattice Al ions forming these exchange positions. It is shown that such a type of cation trapping generates increased number of the Lewis acid sites. Comparative stability and catalytic reactivity of different forms of cation species in zeolites are discussed on the example of Zn/HMFI. Dehydrogenation catalytic reaction of ethane molecule on the single Zn(II) and polynuclear zinc-oxo ions is considered. It is found that binuclear metal-oxo ions can be the effective traps of molecular oxygen and so they can direct the way of oxidation catalysis. This is demonstrated by the theoretical treatment of CO oxidation on alkaline earth zeolites. The CO2 molecule can be activated by the binuclear metal-oxo ions with possibility of further reaction functionalization. The last part of this review is devoted to discussion of the structure of single Fe(II) active sites in Fe/HZSM-5 zeolites. This system has attracted great attention as selective oxidation of hydrocarbons with N2 O but up to now the understanding of the active structures remains challenging.