Temperature-programmed surface carbon deposits

The amount of carbon deposited was measured and the temperature programmed surface... 

The apparent activation energy of both reactions was found to decrease when they were carried out over the doped Rh catalysts. The decrease was found to be about 20 kJ moP for the CO/H2 reaction and 25-30 kJ moP for the CO2/H2 reaction, almost independent of the dopant content in the Ti02 support. Doped Rh catalysts also exhibited superior stability with time on stream in both reactions. While the activity of the undoped Rh catalyst declined by about 30-50% in the first 3 h on stream, the activity of the doped catalysts remained practically constant even after 4—5h on stream. This implies that carbon deposition is retarted on doped catalysts, a phenomenon also investigated by temperature programmed surface reaction techniques [107]. 

The nature of the carbon deposits formed on an alumina-supported nickel catalyst have been characterized by their reactivity with H2 and H 0 during temperature-programmed surface reaction (TPSR). 

In order to compare the nature of the carbon deposits on Pc and Pt-Sn catalysts, carbon deposition on three catalysts with different Sn/Pt ratio was carried out in the in situ reaction and TPO system for n-butane dehydrogenation and successive temperature programmed oxidation. The areas of Peaks 1 and 2 of the TPO profiles of the three catalysts after carbon deposition were resolved and detemnined by an integraph. The ratios of areas of Peak 1 to Peak 2 of the TPO profiles were calculated and ploued against the Sn/Pt ratio in Fig. 4. Becanse the addition of Sn can inhibit the cart)on deposition on metallic surfaces, the proportion of Peak 1 to Peak 2 decreases with the increasing of Sn/Pt ratio These results imply that the ratio of carbon deposits on metal surfaces to total carbon deposits decreases with the incorporation of tin. 

FIGURE 4.12 Thermograms of the deposition of organic substances at a heating of carbosils synthesized from phenylethanol. (Adapted from Carbon, yi, Pokrovskiy, V.A., Leboda, R., Turov, V.V., Charmas, B., and Ryczkowski, J., Temperature programmed desorption mass spectrometry of carbonized silica surface, 1039-1047, 1999, Copyright 1999, with permission from Elsevier.)... 

A new preparation method is described to synthesize porous silicon carbide. It comprises the catalytic conversion of preformed activated carbon (extrudates or granulates) by reacting it with hydrogen and silicon tetrachloride. The influence of crucial convoaion parameters on support properties is discussed for the SiC synthesis in a ftxed bed and fluidized bed chemical vapour deposition reactor. The surface area of the obtained SiC ranges ftiom 30 to 80 m /g. The metal support interaction (MSI) and metal support stability (MSS) of Ni/SiC catalysts are compared with that of conventional catalyst supports by temperature programmed reduction. It is shown that a Ni/SiC catalyst shows a considnable Iowa- MSI than Ni/Si(>2- and Ni/Al203-catalysts. A substantially improved MSS is observed an easily reducible nickel species is retained on the SiC surface after calcination at 1273 K. 

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