Carbon deposit characterization

The products of decomposition of metal carboxylates vary to some extent with the constituent cation and the final residue is usually either the metal or an oxide, occasionally the carbide and sometimes some elemental carbon deposit. Dollimore et al. [94] have described the use of Ellingham diagrams for the prediction of the composition of the solid products of oxalate decompositions. The complete characterization of residual material can be difficult, however, since the solids may be finely divided, pyrophoric [1010], metallic and amorphous to X-rays. 

Like NiO, CoO and FeO are characterized by the same crystal structure as MgO and have comparable lattice parameters, and, hence, can form CoO/MgO and FeO/MgO solid solutions. Therefore, it was expected that CoO/MgO and FeO/MgO would inhibit carbon deposition and metal sintering, just as Ni/MgO does, resulting in high stability (171). 

In contrast to MgO, the other alkaline-earth oxides, such as CaO, SrO, and BaO, were found to be poor supports for NiO, as they provided catalysts with low activities, selectivities, or stabilities (Fig. 14) (239). Although the reduced Ni0/Al203 catalyst provided high initial conversions (CH4, 91% C02, 98%) and selectivities (>95% for both CO and H2), it was characterized by the fastest carbon deposition, which led to the complete plugging of the reactor after only 6 h of reaction (197). The reduced Ni/Ti02 catalyst gave relatively low initial... 

There are a number of informative reviews on anodes for SOFCs [1-5], providing details on processing, fabrication, characterization, and electrochemical behavior of anode materials, especially the nickel-yttria stabilized zirconia (Ni-YSZ) cermet anodes. There are also several reviews dedicated to specific topics such as oxide anode materials [6], carbon-tolerant anode materials [7-9], sulfur-tolerant anode materials [10], and the redox cycling behavior of Ni-YSZ cermet anodes [11], In this chapter, we do not attempt to offer a comprehensive survey of the literature on SOFC anode research instead, we focus primarily on some critical issues in the preparation and testing of SOFC anodes, including the processing-property relationships that are well accepted in the SOFC community as well as some apparently contradictory observations reported in the literature. We will also briefly review some recent advancement in the development of alternative anode materials for improved tolerance to sulfur poisoning and carbon deposition. 

Bartholomew and coworkers32 described deactivation of cobalt catalysts supported on fumed silica and on silica gel. Rapid deactivation was linked with high conversions, and the activity was not recovered by oxidation and re-reduction of the catalysts, indicating that carbon deposition was not responsible for the loss of activity. Based on characterization of catalysts used in the FTS and steam-treated catalysts and supports the authors propose that the deactivation is due to support sintering in steam (loss of surface area and increased pore diameter) as well as loss of cobalt metal surface area. The mechanism of the latter is suggested to be due to the formation of cobalt silicates or encapsulation of the cobalt metal by the collapsing support. 

Pegmatites represent a residual phase of igneous depositions, characterized by extremely coarse crystalline material, that results Ironi the presence of associated volatiles, e.g.. water vapor, carbon dioxide, sulfur dioxide, and others, which decrease tile viscosity and facilitate crystallization. Quartz, feldspar, and mica are the more common minerals found in this environment. but Mich bodies are also hosts for many rare minerals and several types of gem stones, e.g.. beryl, tourmaline, and topaz. 

The purpose of this paper is to describe the nature of carbon deposition on hydrotreating catalysts. A further goal is to characterize the deactivating role of the deposits using model compound reactions. 

Ni0.03Mgo.97O solid solution catalyst has high resistance to carbon deposition in COj reforming of methane. From the characterization results, this catalyst was found to have highly dispersive nickel metal particles with the interaction with support surface. The inhibition mechanism is suggested to be the activation of adsorbed COj at the interface between metal and support surface and rapid supply of oxygen species to nickel surface. 

Characterization of carbon deposits on commercial catalysis from the dehydrogenation of long chain n-parafilns... 

This study focused on carbon deposits on alununa- and zeolite-supported cobalt catalysts and their effects on CO hydrogenadon. A thermogravimetiic flow system and Auger electron spectrometer were employed to characterize the carbon deposits. 

The fresh and used Ni/YSZ and l%wt Sn/Ni/YSZ catalysts were characterized with scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). The SEM and STEM measurements show that carbon filaments completely cover the Ni/YSZ catalyst see Eig. 13.8a [16]. On the other hand, the SEM and STEM images of the used Sn/Ni/YSZ catalysts, shown in Fig. 13.8b, demonstrate that no observable carbon deposits are formed on Sn/Ni/YSZ. 

Chilingar, G.V., 1964. Relationship between porosity, permeability, and grainsize distribution of sands and sandstones. In Van Straaten, L.M.J.U. (ed.) Deltaic and shallow marine deposits I. Elsevier, Amsterdam, pp. 71-75 Chilingarian, G.V., Mazzullo, S.J. and H.H. Rieke, 1992. Carbonate reservoir characterization a geologic - engineering analysis, part I, Developments in Petroleum Science 30, Elsevier, Amsterdam, 639 pp. 

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