Simple metallic oxides

When the Diels-Alder reaction between butadiene and itself is carried out in the presence of alkah metal hydroxide or carbonate (such as KOH, Na2C02, and K CO on alumina or magnesia supports) dehydrogenation of the product, vinylcyclohexene, to ethylben2ene can occur at the same time (134). The same reaction can take place on simple metal oxides like Zr02, MgO, CaO, SrO, and BaO (135). 

For this purpose, all elements have been considered either as metals or non-metals and of the latter, halogens, hydrogen, nitrogen, oxygen, and sulfur were selected as specially important. Group names have then been coined from suitable combinations of these, such as the simple METAL OXIDES, NON-METAL SULFIDES,... 

Hafifad, D. Chambellan, A. Lavalley, J.C. Propan-2-ol transformation on simple metal oxides Ti02, Zr02 and Ce02. J. Mol. Catal. A Chem. 2001,168,153-164. 

The use of simple metal oxides and functionalized derivatives to solve the problems found in industrial chemical operations may be an important one. Any catalyst or reagent that is inexpensive, recyclable, separable, and allows reactions to occur more selectively and under milder reaction conditions would certainly be of... 

Another example of the interaction of water with a relatively simple metal oxide surface is provided by the water vapor/a-Al203(0001) system (Figure 7.9(a)). Oxygen Is synchrotron radiation photoemission results indicate that significant dissociative chemisorption of water molecules does not occur below 1 torr p(H20) [149]. However, following exposure of the alumina (0001) surface to water vapor above this threshold p(H20) , a low kinetic energy feature in the Is spectrum grows quickly,... 

Heats of NH3 absorption further confirm that the heteropolyacids are stronger acids than zeolites or simple metal oxides 150kJmol 1 for HZSM-5 and 140 kJ mol" for y-Al203 (133). 

This equation works for most simple metal oxides dispersed in HCl or KOH or KCl. Table 9.7 gives the values of pK, pK2, and PZC for various oxides. 

Supported VO, catalysts show good catalytic performance in both oxidation and reduction reactions for example, they are among the most active and selective simple metal oxides for dehydrogenation and oxidative dehydrogenation of alkanes. The possibiUty of using oxide systems other than chromia is being... 

Another area that has been of interest since the development of this field is that of metal oxides. Simple metal oxides such as MgO provide a test bed for new methods. More complex oxides have attracted much interest for their commercially important properties—solid electrolytes, ferroelectrics, catalysts, semiconductors, superconductors, multiferroics. Relatively simple calculations can, for example, track the path of ions through ionic conductors and suggest alternative solids for fuel cells or batteries. Solids with interesting electrical and magnetic properties such as high Tc superconductors and solids showing colossal magnetoresistance (CMR) have been... 

Simple metal oxides were the subject of much early work and provide test systems for new methods. There is still work to be done though as evidenced by recent papers on simple solids such as and MgO remains popular as... 

Crystal structures of many simple metallic oxides, including strong alkalis, are considered to consist of hexagonal or cubic close-packing structures of two types 1.) Voids surrounded by... 

The X-ray crystal structures of many of the simple metal oxides used in catalysis have been determined. The structures of the surfaces are more pertinent, however, since that is where catalysis takes place. Inferences about surface structure can occasionally be drawn from bulk structure, but in general structures of metal oxide surfaces are complicated and highly nonuniform. With oxide and other surfaces the catalytically active sites constitute only a small fraction of the surface. It is, therefore, generally difficult to determine the structures of catalytic sites. 

High-valent metal ions tend to promote deprotonation to form oxo-metal complexes and further desolvation to eventually yield simple metal oxides. Thus pure aqua complexes are found mainly with metals in oxidation states III and below. 

Figure 2 Unlike many simple metal oxides, such as those possessing the corundum structure, there is very little reconstruction at the outer layers of zeolite L...

Haffad, D Chambcllan, A Laval Icy, JC. Propan-2-ol transformation on simple metal oxides TiO>, nd C efJ-. Journal of Molecular Catalysis A Chemical, 2001 168, 153-164. 

H2 and H adsorption on simple metal oxides has been studied even less than that on transition metal oxides. H2 adsorption onto various defects on the MgO(lOO) surface has been treated theoretically using defect lattice techniques, including the relaxation of the lattice around the defects. Surface defects (F- and V-centers and self-trapped holes) were all found to activate dissociative chemisorption, resulting in the formation of OH radicals [127, 128]. This is in general agreement with the observed catalytic activity of MgO after the creation of F-centers by X-rays... 

Finally, Satterfield (p. 185) states that highly mobile" oxygen should result in a highly active, nonselective catalyst. Germain in fact says that for simple metal oxides there is a direct, but limited, correlation between activity and oxygen mobility. Satterfield also points out, however, that oxygen mobility as a sole criterion for catalyst activity and selectivity is somewhat limited. For instance, this concept does not account for the effect of partially oxidized intermediate adsorption on selectivity in series-type reactions nor for the effects of mixed oxide composition and catalyst surface defects on catalytic reactivity, especially in partial oxidation reactions. 

Aside from simple metal oxides, more intricate oxide compounds may also be prepared by the radiation method, as was illustrated by powder yttrium aluminum garnet (YAG, Y3AI5O12) synthesis (Cuba and Niki 2011, Cuba et al. 2011). YAG powders were prepared from aqueous solutions containing potassium formate, yttrium nitrate, and aluminum chloride or nitrate via irradiation by accelerated electrons or UV light and consequent calcination of formed amorphous solid phase. 

A Frenkel defect forms when an atom (ion) goes into an interstitial site leaving behind a vacancy and therefore consists of a defect pair of an interstitial atom and its vacancy. For a simple metal oxide compound MO with full ionization, its formation equation is expressed as... 

The mass spectra do not give any conclusive evidence in the gas phase probably due to the breakdown of the heterometallic alkoxides into simple metal alkoxides, and finally decomposes into simple metal oxides under the high vacuum pressure used in mass speedometer. 

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