Surface of MgO

Fig. 4 Oxygen Is XPS spectra including curve-fitted components for (a) Catalyst I, (b) Catalyst I after reduction In Fig. 2, a marble-like pattern was observed, which is attributable to solid solution phase of CoO and MgO, because XRD measurement on Catalyst II showed the existence of CoO-MgO solid solution phase [7, 8]. On the other hand, for Catalyst I, no solid solution phase of CoO-MgO was observed. In addition, XRD pattern of Catalyst I indicated the existence of CoO or C03O4. These results suggest that in the case of Catalyst I, Co is loaded on the surface of MgO as CoO or C03O4 phase. Magnified TEM image of Catalyst I after reduction is shown in Fig. 3. In this figure, crystalline lattice image was observed. It is likely that the observed lattice corresponds to the metal phase of Co, because XRD measurement on Catalyst I after reduction showed the existence of Co metal phase [7, 8].

Figure 5.9 shows the different bulk terminations of MgO in the cubic rock salt structure. The (100) surface is by far the most stable, and MgO particles usually show only (100) facets. Note that there are two different (111) surfaces, namely those terminated by magnesium or by oxygen. Such surfaces possess a net dipole moment and are called polar. The (100) and (110) surfaces of MgO contain equal amounts of Mg and O these are neutral or nonpolar. 

Fig.1 Surface-mediated synthesis of osmium carbonyl clusters on the surface of MgO...

Et4N]2[Fe2lr2(CO)i2] cluster precursor, which exhibit a high activity in the synthesis of methanol from CO and H2, were studied by Ir and Fe Mossbauer spectroscopy. The study extends from the precursors via the fresh to the aged catalysts. The presence of iridium in the metallic state as well as the presence of trivalent, divalent and alloyed iron is detected. Representative Ir and Fe Mossbauer spectra are shown in Fig. 7.69. Information about the adsorption on the surface of MgO... 

Stable rhenium tricarbonyls bonded to the surface of MgO have been prepared and characterized by EXAFS. Heating under He, O2 or vacuum of a sample obtained by impregnation of Re2(CO)io produced the oxidative fragmentation of the initial surface organometallic species [39-41]. These types of supported well-characterized species can be used as models in the study of reaction mechanisms [42]. 

Ir4(CO)i2 reacts with the surface of MgO to generate surface species in which the tetrahedral metal framework is preserved. The structures obtained after decar-bonylation under H2 at 573 K depend on the degree of hydroxylation of the support The iridium cluster nuclearity of 4 was maintained for a low degree of MgO hydroxylation (MgO pretreated at 973 K), but it increased to 6 when the MgO was highly hydroxylated (MgO pretreated at 573 K) [206, 207]. The activity in propane hydrogenolysis of the tailored catalyst is two orders of magnitude less than that of the conventional catalyst at atmospheric pressure and 200 °C. 

The behavior of a ZnO surface toward [Fe3(CO)i2] [9] is very similar to that of the surface of MgO or AI2O3. The surface OH groups behave as nucleophiles toward coordinated CO, generating the anion [HFe3(CO)n]T which can be extracted from the surface with [(Ph3P)2N]Cl dissolved in CH2CI2. Yields of the isolated products were not reported. 

Various ruthenium carbonyl compounds can be prepared on the surface of Si02 (Scheme 16.2) or on the surface of MgO, AI2O3, ZnO or La203 (Scheme 16.3), as described below. 

Scheme 16.3 Convenient syntheses of ruthenium carbonyl compounds on the surface of MgO AI2O3, ZnO, or La203, (the subscript x refers to the pretreatment temperature, in °C).

RusCfCOjis] " on the Surface of MgO Treatment of RuCl3-nH20 adsorbed on MgO withCO -r H2 (molar ratio 1 1,10atm) at 225 °Cfor 24h, affords [Ru6C(CO)ns] (Scheme 16.3) [16]. 

Both anionic clusters can be extracted with [(Ph3P)2N]Cl dissolved in acetone but in 65% yield only because they are partially retained by the surface of MgO [3, 15-17]. 

The chemistry of Ir carbonyl clusters on the surface of MgO clearly mimics that occurring in basic solution [58] or on the silica surface added with alkali carbonates... 

Hlr4(CO),]" on the Surface of MgO When a slurry of [Ir4(CO)i2] in hexane is brought in contact with Mg04oo, [HIr4(CO)n] is formed [112]. This cluster is also generated by reductive carbonylation (latm CO, 25°C) of [Ir(CO)2(acac)] adsorbed on Mg04oo (Scheme 16.12). Yields are not reported. 

Notably, when surface-mediated syntheses are carried out in the absence of solvent, reactions must occur on the surface of the inorganic oxide. However, when surface-mediated syntheses are carried out in the presence of a solvent the reactions leading to the product can really occur in solution, influenced by the surface. For example, in the synthesis of [Pti5(CO)3o] ", by using MgO and methanol as reaction medium, the surface of MgO behaves only as a solid base, working as a slurry. 

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