Carbon deposition on nickel

Fig. 10. Carbon deposition on nickel-containing catalysts at 973 K as determined by TGA. Before reaction, the catalysts were reduced at 1073 K for 3 h. Reaction conditions temperature, 973 K feed gas molar ratio, C02/CH4 = 1/1 GHSV, 144,000 mL (g catalyst)-1 h-1 (214).

Higher Hydrocarbons. - A number of papers describing the steam reforming of higher hydrocarbons are particularly concerned with the subject of carbon deposition on the catalysts. The subject of carbon deposition on nickel catalysts is considered to be somewhat outside the subject of this review, especially as the subject is covered by two excellent recent discussions of papers on carbon deposition and coking during steam reforming, methanation, and other reactions.202 203... 

The results reported here agree with results reported by Lobo co-workers for carbon deposition on nickel (10,11). 

The amount of carbon deposited on nickel foils following reaction in ethane at atmospheric pressure and temperatures from 870 to 1070 K is presented in Table 1. Examination of these data shows that titanium oxide provides an effective barrier towards carbon deposition at 870 K with or without hydrogen pretreatment however, at higher temperatures only titanium oxide reduced in hydrogen exhibits an inhibiting effect. 

Amount of carbon deposited on nickel specimens which have been reacted at various temperatures in 1 atm ethane for 1 h... 

Carbon Deposited on Nickel via 02 Exposure TPSR with 1-atm H2 Carbon deposited on alumina-supported nickel (17 wt%) following ethylene exposure at various temperatures has a wide range of activity for reaction with H2 (Figure 2). Different states of carbon are identified by maxima in the rate of CH production. The temperature of the rate maximum (T ) for a particular carbon state was generally found to he independent of both the amount of carbon in that state and the temperature of deposition. Thus T will be taken as characteristic of the reactive state of... 

TPSR CHARACTERIZATION OF CARBON DEPOSITED ON NICKEL CATALYSTS FOLLOWING ETHYLENE EXPOSURE... 

Carbon Deposited on Nickel Catalysts by Exposure to Carbon Monoxide. In a previous TPSR study (9) carbon was deposited on at 25-wt% Ni/A Oj catalyst (G-65) by exposure to CO at temperatures between 550 and 610 K. TPSR (t ) of carbon produced by the dissociation/Qisproportionation of chemisorbed CO showed the presence of large a and p states (Figure 7). Although some chemisorbed CO may have contributed to the a states, it was, conclusively shown that most of the a carbon state was more reactive than a monolayer of chemisorbed CO. In this study, we extended the deposition of carbon by CO exposure to higher temperatures to deter-mine if the 6 and 6 filament carbon states in addition to the a and p states can be populated by a hydrogen-free source. The TPSR (H2) results (Figure 8) clearly show the presence of the filament carbon (6T carbon) state at 773 K. Comparison of the peak temperatures for carbon deposited by C2H and CO exposure (Table IV) shows little difference in the reactivity of the carbon states. 

The kinetics of carbon deposition on nickel have been studied in detail previously (17,18,19), and a mechanism which explains most observations has been advanced. Coke precursors proceed through a series of dehydrogenation steps on the nickel surface, resulting eventually in carbonaceous species. These species dissolve in, and precipitate from, the metal phase detaching nickel crystallites from the surface of the bulk nickel or the silica-alumina surface. Further coke deposition incorporates additional nickel into the growing carbon layer, as shown by electron microscopic examination of the deposits (18). 

Mermelstein J, MiUan M, Brandon NP (2011) The interaction of biomass gasification syngas components with tar in a solid oxide fuel cell and operational conditions to mitigate carbon deposition on nickel-gadolinium doped ceria anodes. J Power Sources 196 5027-5034... 

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