Hydrogen-deficient conditions

On the other hand, Sarkany (55) observed that on a Pd catalyst, chain lengthening of small alkanes was commensurable to their isomerization. Therefore, participation of adcarbenes in the isomerization (as well as in homologation) is feasible under hydrogen-deficient conditions. However,... 

Two hydrogen-deficient conditions are possible one is partial hydrogen coverage that damages the air electrode and the other is fnel starvation that damages the fuel electrode. These two conditions can be distingnished by the relationship between fuel flow and current. Specifically, if... 

Loss of alkyl chains always accompanies thermal cracking, and dehydrogenation/ condensation reactions are a consequence of hydrogen-deficient conditions. 

Aside from the above reforming reactions, a small amount of feed components are converted to polymeric hydrogen deficient products which deposit on the catalyst as "coke." A coke buildup results in activity and selectivity loss which ultimately requires catalyst regeneration. In semi-regenerative operation, the coking rate is maintained at a low level to provide cycles of at least three to six months. In cyclic units, coking conditions are inherently much more severe so that frequent regenerations are required. 

Risers are normally designed for an outlet vapor velocity of 50 ft/sec to 75 ft/sec (15.2 to 22.8 m/sec). The average hydrocarbon residence time is about two seconds (based on outlet conditions). As a consequence of the cracking reactions, a hydrogen-deficient material called coke is deposited on the catalyst, reducing catalyst activity. 

Nitrogen-fixing, heterocystous cyanobacteria such as Anabaena cylindrica can also liberate hydrogen and oxygen simultaneously under anaerobic, nitrogen-deficient conditions (Benemann and Weare, 1974). A. cylindrica does... 

This catalyst deactivation results from the oxidation of the Rh complex by formal addition of iodine (eqs. (18)-(20)). This form of deactivation in particular occurs at high temperatures under CO-deficient conditions [58]. The state of activity of the rhodium complex system can be observed by IR spectroscopy (Figure 2). Inactive Rh species are transformed to the Rh complex by reduction with hydrogen. 

The synthesis of light alkenes by modification of the Fischer-Tropsch process is recognised as an important route to high value fuel components (refs. 1,2). The essential requirement of the F-T catalyst is high selectivity towards alkenes, suppression of methane and resistance to coking under conditions which favour the formation of hydrogen deficient products. 

Hagenmaier et al. (1987) studied the catalytic effect of fly ash on the formation and decomposition of dioxins and dibenzofurans under oxygen-deficient and oxygen-surplus conditions. While under oxygen-deficient conditions, fly ash catalyzed dechlorination or hydrogenation reaction, in the presence of surplus oxygen an increase in polychlorinated dibenzo-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) was observed. 

Polycyclic aromatic hydrocarbons are present as aerosols in the atmosphere because of their extremely low vapor pressures. These compounds are the most stable form of hydrocarbons having low hydrogen-to-carbon ratios and are formed by the combustion of hydrocarbons under o g gen-deficient conditions. The partial combustion of coal, which has a hydrogen-to-carbon ratio less than 1, is a major source of PAH compounds. 

Lignin (LiP) and manganese dependent (MnP) peroxidases of R chrysosporium are secreted in conjunction with a number of other enzymes and chemicals under nutrient deficient conditions (3, 33, 44-47, 86, 92, 93). The peroxidases are known to catalyze a number of free radical reactions. Research on these enzymes has been extensively reviewed recently (5, 49, 85). The resting enzyme (ferric-heme protein) is initially oxidized by two electrons in a reaction with hydrogen peroxide (Fig. 6). The resulting intermediate, com-... 

The reliability of this work has also been questioned by Brown and Nelson339, who could not get any reaction at all with benzene under the conditions quoted by Szmant and Dudek382. If the benzene value is in error it could account for the low selectivities that were observed. By using the competition technique with a deficiency of paraformaldehyde (but an excess of hydrogen chloride) they obtained a toluene benzene reactivity ratio of 112 and partial rate factors of / Me = 117, /mMc = 4.37, /pM = 430. 

The hydroaminations of electron-deficient alkenes with aniline or small primary alkylamines proceed at high conversions (85-95%, nnder mild conditions, 5 mol%, rt), giving exclnsively the anh-Markovnikov addition product. Secondary dialkyl or bnlky primary amines require longer reaction times. With amines containing P-hydrogens, no imine side-products were observed. 

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