Metal oxide homogeneity ranges

The heavier metal tantalum is distinctly less inclined than niobium to form oxides in lower oxidation states. The rutile phase TaOz is known but has not been studied, and a cubic rock-salt-type phase TaO with a narrow homogeneity range has also been reported but not yet fully characterized. TazOs has two well-established polymorphs which have a reversible transition temperature at 1355°C but the detailed structure of these phases is too complex to be discussed here. 

The initial interaction of Ru3(CO)i2 with the surface of several oxides has been extensively studied by EXAFS and IR spectroscopy [70,100]. Representative studies of materials prepared from Ru3(CO)i2 and zeolites ]101, 102] or MCM-41 related supports [97] have also been reported. Ru/Si02 has also been prepared by the sol-gel method, using Ru3(CO)i2 and tetramethoxysilane as precursors [98] spheroidal metal particles homogeneously dispersed into the sihca matrix with a size range from 1 to 4nm were obtained after decarbonylation at 573 K under He, followed by H 2-treatment. 

The interconversion of the various oxidation states of Mn in natural waters is influenced by UVR through its effects on reactions involving ROS [Chapter 8] and natural phenols, photoinduced charge transfer reactions, and microbial processes. The oxidation of Mn + is slow at pH < 8.5 in the absence of a catalyst. The oxidation of Mn(ii) is faster on metal oxide surfaces than in homogeneous solution in the pH range of 8 to 9 [217], and its oxidation also can be biologically mediated in the environment [153]. In comparison to bacteria-free waters, the oxidation rate of Mn(ii) in seawater is increased dramatically by catalysis on bacterial surfaces. However, even with such catalysis, its half-life still is of the order of weeks to months in open ocean waters [153]. 

Metal oxides have specific structural features that control their oxidation properties. They are far from rmifbrm homogeneous solids and have a stoichiometric composition only at limited ranges of temperature and pressure. The oxides usually have either a deficit or an... 

---