Transition metals active space selection

We prepared a new carrier material, suitable as a host for ship in a bottle . Zeolites X and Y have been highly dealuminated by a succession of different dealumination methods. This generated mesopores completely surrounded by microporous space. The catalytic behavior of bulky transition metal complexes entrapped in these new was investigated in stereoselective epoxidation. The organometallic complex is entrapped without considerable loss of activity and selectivity... 

In the case of alumina (or other simple oxides), the reaction occurs at high temperatures and under low space velocity conditions. The activity was found to be improved by the addition of platinum group metals [13, 14] and of transition metal oxides [15], especially copper [16, 17, 18]. For alumina-supported copper oxide catalysts a maximum effect has been found by the addition of 0.3 wt % Cu and it has been considered that, for higher copper contents, the formation of cupric oxide would give a solid selective for the oxidation of the hydrocarbon by oxygen [16]. In the case of alumina-supported Cu-Cs oxide catalysts the formation of an isocyanate species has been evidenced by exposition to mixtures "nitric oxide/oxygen/propene (or acetylene)" but not with propane [18, 19], In fact the mechanism of the reaction and the nature of the active sites are still unknown. 

In Tables XVI and XVII we have collected the natural orbital occupation numbers from different CASSCF calculations on a selection of octahedral and tetrahedral molecules of first-row transition metals. In all cases a CASSCF calculation was performed using a basic active space of 10 orbitals. For some of the molecules additional calculations with larger active spaces (up to 14 orbitals) are also presented. Only ground-state results are presented, except for the molecules CrFg , Cr(CN)g , CoFg, and Co(CN)g , for which we have included a selected number of excited states. 

This review is intended to highlight any new reaction types that have been discovered, novel structural features that have been encountered, and chemical patterns and principles that have been observed for this class of compounds. Due to space limitations, only very selective examples of reactions are presented. Heterobimetallic species have been prepared and characterized for most combinations of iron and other transition metals. Their potential in the cooperative activation of small molecules, such as CO and unsaturated hydrocarbons, is an important research focus for this class of compounds. For mixed-metal clusters, enormous efforts have been made to develop rational cluster build-up methods and their potential applications in catalysis. Some important reviews that are pertinent to this type of species have appeared in the literature. 

Non-metallic homogeneous catalyst systems were also reported for methanol synthesis. Recently, Ashley et al. [49] demonstrated the selective hydrogenation of COj to methanol using a FLP-based nomnetal mediated procedure at low pressures (1-2 atm). N-Heterocyclic carbine (NHC) was found to be an elFective organic catalyst for methanol synthesis from CO2 reduction with silane. Compared to transition metal catalyst, NHC is more efficient at ambient reaction conditions [50,51]. Table 5.1 lists catalytic activities of different heterogeneous catalysts employed for methanol synthesis from CO. It shows that maximum CO conversion of 25.9%, methanol selectivity of 99.5% and methanol yield of378 mg/g-cat h could be achieved. The space velocities were tried between 1800 and 18,000 h and the temperature from 170 to 270 C. 

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