Atmosphere hydrogen-rich

Such a thought-provoking model was naturally subject to criticism Catling (Department of Earth Science, University of Bristol) considered the calculations to be unrealistic, since (for example) the authors had underestimated the temperatures of the upper layers of the atmosphere. The prompt answer of the authors to these criticisms was quite clear Hence, the ancient atmosphere was hydrogen rich (Catling, 2006 Tian et al., 2006). J. F. Kasting and M. Tazewell (2006) have given a detailed account of the climate of the primeval Earth and the composition of its atmosphere. 

Direct ( hydrogenative ) Cj cyclization of alkanes to give saturated C5 cyclic products. This is a typical metal-catalyzed reaction occurring in a hydrogen-rich atmosphere over a narrow group of metals (25). 

Zhu et al. [95] demonstrated the use of Pd/amorphous Ba g Sro jjTij 0 03/Pt as a sensor. The /-V characteristic of this device showed a very large shift when exposed to hydrogen. This was about 5V for a switch between an oxygen-rich and a hydrogen-rich atmosphere. 

The composition of the synthesis gas, particularly the concentrations of hydrogen, carbon monoxide, and carbon dioxide, affects the atmosphere throughout the reactor directly, and also indirectly by its effect on the composition of the recycle gas. Synthesis gas, prepared by partial combustion of methane or some less hydrogen-rich carbonaceous material, lacks sufficient hydrogen for the conversion of all the carbon monoxide to hydrocarbons, and in this sense the synthesis gas is deficient in hydrogen. Stoichiometrically methane has sufficient hydrogen to convert all its carbon to olefins by the two-step process ... 

The chief examples are smelting for the recovery of metals from ores, cement manufacture, and lime burning. The converters, roasters, and kilns for these purposes are huge special devices, not usually adaptable to other chemical applications. Shale oil is recovered from crushed rock in a vertical kiln on a batch or continuous basis—moving bed in the latter case—sometimes in a hydrogen-rich atmosphere for simultaneous denitrification and desulfurization. The capacity of ore roasters is of the order of 300-700 tons/(day)(m3 of reactor volume). Rotary kilns for cement have capacities of 0.4-1.ltons/(day)(m3) for other purposes the range is 0.1-2. 

Tian F, Toon OB, Pavlov AA, De Sterck H. A hydrogen-rich early earth atmosphere. Science 2005 308 1014-1017. 

Astronomers now believe that helium, with a density nearly twice that of hydrogen, tends to fall inward from the planet s outer atmosphere toward its core. If one were able to travel through the hydrogen-rich soup of the lower atmosphere, it might he possible to detect a "rainfall of helium droplets, which are immiscible in hydrogen, falling from the "sky," the planet s outer atmosphere. 

These problems are proving to be more tractable in the context of a related thermal loss mechanism, hydrodynamic escape (Zahnle and Kasting 1986 Hunten et al. 1987, 1988, 1989) Sasaki and Nakazawa 1988, 1990 Zahnle et al. 1990a Pepin 1991, 1994, 1997, 2000). Here atmospheric loss is assumed to occur from much larger bodies, partially or fully accreted planets. Their hydrogen-rich primordial atmospheres are heated... 

With suitable choices of parameter values, hydrodynamic escape of hydrogen-rich primary atmospheres and outgassed volatiles from the terrestrial planets (plus sputtering... 

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