Light catalytic properties

Beyond the catalytic ignition point there is a rapid increase in catalytic performance with small increases in temperature. A measure of catalyst performance has been the temperature at which 50% conversion of reactant is achieved. For carbon monoxide this is often referred to as CO. The catalyst light-off property is important for exhaust emission control because the catalyst light-off must occur rehably every time the engine is started, even after extreme in-use engine operating conditions. 

N-doped titania demonstrated promising activity under visible light for the degradation of Rhodamine B in aqueous solutions [85], In thin-films of N-doped Ti02, the formation of nitride phases enhanced the catalytic properties of the film [86]. 

The bisbarium complex of azobis(berizo-18-crown-6) ether 28 exhibits catalytic properties that can be reversibly activated-deactivated by light-induced changes in molecular geometry [32]. The azobenzene unit is a well-known photochromic [33], often used in the construction of molecular switches [34]. 

After this paper was accepted for publication in November, 1992, a number of reports have appeared that deal with the subject of oxidative dehydrogenation of light alkanes. The effect of the structure of vanadia on a support has been investigated for the oxidation of butane [87J and propane [88-90], The evidence supports the concepts that the bridging oxygen in V — O — V plays an important role in the oxidation reaction [87, 90], The data also show that vanadia species of different structures on these supports have different catalytic properties, and that isolated V04 units are the most selective [91]. 

On account of their physical, photo-physical, or catalytic properties, metallodendrimers have become a widespread class of compounds. Combination of the characteristics of dendrimers with those of transition metals can, for example, produce light-harvesting effects (see Section 5.2) and energy-transfer gradients. 

These results can be explained under the light of the experiment shown in the previous section the inertness and catalytic properties [47] of the initially formed aggregates (seeds), which allow the J species to retain the memory of chirality transferred from A- or A-[Ru(phen)3]2+ [51]. The increase of the pH value to around... 

The light orange hydrido complex melts with decomposition at 280°C. Since the hydrido ligand is coordinated to rhodium (rRh H 1902cm-1, rRh D 1465cm-1), the complex is coordinatively saturated and exhibits poor catalytic properties. 

The lack of reactivity of the semiquinone per se with either thioredoxin or NADPH shows that it cannot be involved in catalysis. The rapid production of semiquinone by irradiation of partially reduced enzyme is a light-activated disproportionation since it is totally dependent upon the presence of some oxidized enzyme. Enzyme fully reduced by dithionite forms no semiquinone, while enzyme partially reduced by dithionite rapidly forms semiquinone upon irradiation. Furthermore, the light-activated disproportionation of enzyme first reduced with NADPH results in the reduction of NADP. Thus, FAD catalyzes the disproportionation in keeping with the known photosensitizing nature of free flavins. This reaction is reversed slowly (half-time ca. 150 min 25°) in the dark. The semiquinone is rapidly reoxidized by oxygen to yield an enzyme with unaltered spectral and catalytic properties (58). Similar reactions have been very briefly reported for lipoamide dehydrogenase the dark reverse reaction is comparatively rapid, being complete in 30 min (16S). 

---