Hydrogenation temperatures, carbon species

By increasing the electrical energy in a fixed amount of gas, the temperature is raised and may reach 5000°C or higher.P i Such high temperatures produce an almost complete dissociation of the hydrogen molecules, the CH radicals, and other active carbon species. From this standpoint, arc-plasma deposition has an advantage over microwave-plasma or thermal CVD since these produce much less atomic hydrogen. 

These different types of carbon tend to have different reactivities toward gases such as hydrogen, oxygen, or steam. Hence, a relatively simple technique such as temperature-programmed hydrogenation or oxidation can be used to classify them. Table 4.2 summarizes different reactivities of carbon species toward hydrogen. 

Examples of Various Carbon Species on Cobalt FTS Catalysts along with Their Hydrogenation Temperatures... 

The use of Ru(acac)3 under very high temperature (268 °C) and pressure (1300 bar of H2/CO) in THF provides a catalyst for the hydrogenation of carbon monoxide to methanol and methyl formate [73]. The active species is derived from Ru(CO)5. 

The measured 8 C- and 8 0-values of carbonates can be used to estimate the carbon and oxygen isotope composition of the fluid in the same way as has been discussed before for oxygen and hydrogen. The isotopic composition of carbon and oxygen in any carbonate precipitated in isotopic equilibrium with a fluid depends on the isotopic composition of carbon and oxygen in the fluid, the temperature of formation, and the relative proportions of dissolved carbon species (CO2, H2CO2, HCO2, and/or ). To determine carbonate speciation, pH and temperature must... 

At temperatures of about 4000°K., the free energy of formation of acetylene from its elements approaches zero, and the equilibrium yield of acetylene is appreciable. The system is complicated, however, by other reactions and phase changes which occur at these high temperatures. Carbon sublimes at about 4000°K., various species of carbon Ci, C2, and Ca are formed, and dissociation of molecular hydrogen occurs. 

On flat surfaces the residual carbon forms graphitic layers at high temperatures. C2 species without hydrogen derived from ethene adsorption have instead been observed on corrugated Pt surfaces, in the vicinity of 600 K, presumably bonded within the grooves. The same species clearly occurs from ethyne adsorbed on the nonflat Ni[5 (111) X (110)] surface after adsorption at the very low temperature of 150 K 195). 

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