Framework transition metal cations

Reduction of Extra-framework Transition Metal Cations... 

The porous character of the cyanometallates structure is linked to the coordination taken up by the metal (M) in the hexacyanometallate anion, M(CN)f, ", that shapes the salt of the cyanomet-allate anion [238], For example, hexacyanometallates can be considered as a three-dimensional framework of a molecular block, the hexacyanometallate anion, [M(CN)6]", through a transition metal cation Tm+, which connects the N ends of the adjacent blocks [239],... 

In sustained efforts to localize transition metal cations within the zeolite framework, EPR, UV, IR and X-ray diffraction studies were undertaken by several authors (1-5). This localization was thought to help clarify and possibly account for variations of catalytic properties upon various parameters including the exchange level. The overwhelming conclusions of these investigations was the high mobility of the exchanged transition metal... 

Cation exchanged zeolites are successfully applied as catalysts or selective sorbents in separation technologies. " For both catalytic and sorption processes a concerted action of polarizing cations and basic oxygen atoms is important. In addition, transition metal cation embedded in zeolites exhibit peculiar redox properties because of the lower coordination in zeolite cavities compared to other supports." " Therefore, it is important to establish the strength and properties of active centers and their positions in the zeolite structure. Various experimental methods and simulation techniques have been applied to study the positions of cations in the zeolite framework and the interaction of the cations with guest molecules.Here, some of the most recent theoretical studies of cation exchanged zeolites are summarized. 

Cobalt(II) has a special place in the open framework family because it is one of the few transition metal cations that easily exhibits tetrahedral coordination, in addition to five and sixfold ones. Moreover, magnetic couplings can give rise to interesting magnetic properties, similar to those described above for iron. Furthermore, it is well known that Co doping enhances the catalytic performance of certain zeolites and related compounds. For instance, CoAPO-5 and CoAPO-11 have been used for the autoxidation of cyclohexane [77] and p-cresol [78]. 

K. Wang, J. Yu, Y. Song, and R. Xu, Assembly of one-dimensional A1P2083 Chains to Three-dimensional Framework MA1P208 C2N2H9 through Transition Metal Cations (M=Ni2+, Co2+ and Fe2+). Dalton Trans., 2003, 99-103. 

Since the incorporation of transition metals into the frameworks of zeolites or micro-porous ahiminophosphates to form heteroatom-containing molecular sieves with important application values, the synthesis, structure, and characterization of microporous transition metal phosphates have been extensively studied in the last decade. In particular, because transition metal cations possess redox and coordination features, they are a kind of catalytic material with useful applications, and promise potential... 

For analysis of the state of iron were employed EPR, FTTR, and Mossbauer spectroscopies. For structural interpretation of these results the concept of divalent transition metal cation siting was used as recently established for pentasil ring zeolites in a wide range of metal concentrations and Si/Al compositions. With help of UV-Vis and FTIR this approach evidenced three zeolite coordination of divalent cations in similar six-membered rings of framework local structures. Three cationic fiiamework sites were thus suggested, denoted as a, p and y. (For details see [7-11]). 

Zeolite catalysts incorporated or encapsulated with transition metal cations such as Mo, or Ti into the frameworks or cavities of various microporous and mesoporous molecular sieves were synthesized by a hydrothermal synthesis method. A combination of various spectroscopic techniques and analyses of the photocatalytic reaction products has revealed that these transition metal cations constitute highly dispersed tetrahedrally coordinated oxide species which enable the zeolite catalysts to act as efficient and effective photocatalysts for the various reactions such as the decomposition of NO into N2 and O2 and the reduction of CO2 with H2O into CH3OH and CH4. Investigations on the photochemical reactivities of these oxide species with reactant molecules such as NOx, hydrocarbonds, CO2 and H2O showed that the charge transfer excited triplet state of the oxides, i.e., (Mo - O ), - O ), and (Ti - O ), plays a significant role in the photocatalytic reactions. Thus, the present results have clearly demonstrated the unique and high photocatalytic reactivities of various microporous and mesoporous zeolitic materials incorporated with Mo, V, or Ti oxide species as well as the close relationship between the local structures of these transition metal oxide species and their photocatalytic reactivities. 

P-23 - Modelling transition metal cations in zeolites how do they interact with the framework ... 

It is possible to oxidise and reduce atoms in the framework and also those within the pores of microporous (and mesoporous) solids of appropriate chemical compositions. Although pure aluminosilicate, silicate and aluminophosphate frameworks cannot be oxidised or reduced, transition metal and some lanthanide cations within the framework can exist in different oxidation states. Also, although typical alkali, alkali metal and most lanthanide cations in extraframework positions possess no redox chemistry, transition metal cations such as nickel, copper and platinum do. In the case of the transition metals, this enables them to become important catalysts. The included sulfide species in ultramarine-related pigments described above are also prepared through the reduction of sulfate species. 

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