Temperature programmed sulfuration

Figure 4.21. Temperature programmed sulfidation (TPS) of M0O3/AI2O3 catalysts in a mixture of H2S and H2, showing the consumption of these gases and the production of H2O as a function of temperature. Note that H2S evolves from the catalyst around 500 K, which is attributed to the hydrogenation of elementary sulfur. [Adapted from P. Arnoldy, J.A.M. van den Heijkant, G.D. de Bok and J.A. Moulijn, J.Coto/. 92 (1985) 35.]...

Interference from anions, originating from acid digestion procedures, is a significant factor in temperature-programmed GFAA analysis. To reduce this interference, nitric acid is preferred over any other acids for the digestion or solubilization steps. If the addition of another acid is necessary, a minimum amount is always used. This particularly applies to hydrochloric and, to a lesser extent, to sulfuric and phosphoric acids used in some digestion procedures. 

Table II. Peak temperature of sulfur containing model compounds during programmed temperature heating (25 C/min from 250 to 875 C)...

The sulfidation mechanism was investigated by temperature-programmed sulfidation, as the oxidic catalyst was heated in a flow of H2S and ff2, and the consumption of IH S and ff2 and the evolution of H20 were measured continuously (13). ft was found that IH S is taken up and H20 given off, even at room temperature, indicating a sulfur-oxygen exchange reaction. This conclusion was confirmed by quick extended X-ray absorption fine structure (QEXAFS) studies (Fig. f, phase 2), which also demonstrated... 

Resolution. The evolutions of H2S from aliphatic sulfides and from iron pyrite coincide to the extent that it was almost impossible to resolve the two peaks. However, since only a small fraction of the pyrite is reduced, it was possible to estimate the relative contribution of pyritic sulfur and sulfidic sulfur to the unresolved peaks. Somewhat better resolution was obtainable at slow rates of heating however, in these cases the overall recovery and the signal-to-noise ratio were reduced. The dependence of the resolution between two peaks on the rate of temperature programming a is given by Equation (38) ... 

Among the works of supercritical fluid separations of PCBs, UV has been the most popular detector. A Microbore Cig column was used to separate individual PCB congeners in Aroclor mixtures. Density and temperature programming was also utilized for separation of PCBs. Both packed (with phenyl and Cig) and capillary (Sphery-5 cyanopropyl) columns were used in this work. Carbon dioxide, nitrous oxide, and sulfur hexafluoride were tested as mobile phases for the separation of PCBs. 

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