Semiconductor catalysts room temperature oxidations

Room Temperature Oxidations, Isotopic Exchanges, and Dehydrogenations over Illuminated Neat or Metal-Supporting Semiconductor Catalysts... 

It has been demonstrated in earlier sections that the catalytic activity of nickel oxide in the room-temperature oxidation of carbon monoxide is related to the number and the nature of the lattice defects on the surface of the catalyst and that any modification of the surface structure influences the activity of the solid. Changes of catalytic activity resulting from the incorporation of altervalent ions in the lattice of nickel oxide may, therefore, be associated not only with the electronic structure of the semiconductor (principle of controlled valency ) (78) but perhaps also with the presence of impurities in the oxide surface or a modification of the surface structure because of this incorporation. In order to determine the influence of dopants on the lattice defects in the surface of the solid and on its catalytic activity, doped nickel oxides were prepared under vacuum at a low temperature (250°). Bulk doping is not achieved and, thence, one of the basic assumptions of the electronic theory of catalysis (79) is not fulfilled. 

J. D. F. Marsh North Thames Gas Board, England) We have measured the thermoelectric potential of chromia reduced at 500° in H2 and found that it is an n-type semiconductor even if this H2 is saturated with water at room temperature, that is, under conditions where bulk chromous oxide is not stable. Thus, addition of water to dry reduced catalyst does not cause a shift to beyond the maximum resistivity, as postulated in the last paragraph of the paper (Lecture 22), and the increase in resistivity follows naturally from the observed decrease in the amount of chemisorbed hydrogen. 

Anosovite (type II) [12065-65-5] P-TijO, M = 223.0070 64.1 wt.% Ti 35.9 wt.% 0 (Oxides and hydroxides) Orthorhombic Distorded pseudobrookite TiO 191-210 pm mC32(Z=4) S.G. C2/m Biaxial ( ) n.a. 4900 Habit acicular cry als. Color bhie-daik. Diaphaneity opaque. Luster metallic. Streak black. Type II can be prepared by the hydrogen r uction of solid TiO, at temperature around 1500 Cwith magnesia as a catalyst. Anosovite type 11 is similar to that found in artiftcial titania dags and it is stabilized at room ten erature with small amount of iron. This oxide is dimorphic with a rapid phase transition from semiconductor to metal occuring at roughly 120 C. 

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