CO2 Dry Reforming of Methane

7 Carbon Dioxide Conversion in High Temperanu e Reactions 

The C0 H2 ratio is affected by simultaneous occurrence of RWGS reactions (7.58) and produces more CO. The steam produced enables the steam/carbon gasification reaction to take place (7.59). 

The main issue of catalyst deactivation is carbon deposition originated from methane decomposition (7.60) and the Boudouard reaction (7.61). 

The catalysts used for the DRM process generally consist of noble metals (Rh, Pt, Rh) and some transitimi metal catalysts such as Ru and Ni. Noble metals are used for their resistance to corrosiOTi and oxidation, high activity, and good carbon resistance [148], 

Several studies have been carried out aimed at synthesizing nickel-based catalysts in the most suitable form for providing high activity and better carbon resistance. Some of the nickel-based catalysts synthesized include bimetallic catalysts, oxide-supported Ni catalysts, Ni-based perovskites, and Ni core-shell structure catalysts, which are discussed in this section. 

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In fact, the presence of methane induced the CO2 (dry) reforming of methane to take place, hence retarding the CO2 reforming of ethane. More ethane can, thus, be selectively converted into ethene through the CO2-ODHE process (7.30) instead of undergoing dry reforming. It was also found that the type of carbon deposited on the catalyst bed was more reactive (i.e., filamentous type) compared to the case in which no methane was co-fed. Hence, Peng et al. correlated the improvement in the ethene selectivity to the easier removal of filamentous carbon with CO2 [95]. 

As one possible method of processing large amounts of CO2, the dry reforming of methane process has been proposed (CO2 + CH4 —> 2CO + 2H2). Many investigations are continuously appearing in the literature for this... 

The experiments were performed in the Tapered Element Oscillating Microbalance (TEOM) reactor (7,8), in which carbon formation and deactivation could be measured simultaneously by coupling with on-line GC analysis. The dry reforming of methane was studied on an industrial Ni (11 wt%)/(Ca0)a-Al203 catalyst at temperatures of 500 °C and 650 °C, total pressures of 0.1 MPa and 0.5 MPa and a CO2/CH4 ratio of 1. The BET surface area of the catalyst was 5.5 m /g, and the Ni surface area 0.33 m /g. The detailed experimental procedures were similar to that reported previously (7). 

Combination of the SR and dry reforming of methane in the reaction zone of the MR (Abashar, 2004). This is an interesting way to reuse CO2 and decrease the anthropogenic... 

An alternate reforming process is dry reforming of methane (DRM), that is, methane reforming in which steam is replaced by CO2 as oxidant. Dry reforming is thus a CO2 utiUzation process in which methane and CO2 are processed at elevated temperatures (>700°C) over a catalyst (typically nickel or a noble metal) to produce syngas with an H2 CO ratio of 1 [81-86] according to ... 

Dry reforming of methane is gaining great interest owing to the fact that this process efficiently converts two greenhouse gases (CH4 and CO2) into synthesis gas (CO -I- H2), which can be further processed into liquid fuels and chemicals by Fischer-Tropsch and similar processes. 

The mechanism for the dry reforming of methane depends on the nature of the catalyst. It is well admitted that methane is adsorbed on the metal particle and is dissociated to form adsorbed hydrogen and a CH hydrocarbon species [3]. The activation of carbon dioxide proceeds also at the surface of the metal active site as soon as an acidic support is used. In this case, an acidic support such as Si02 plays httle role in the mechanism. A different pathway was proposed over a basic support such as Ti02, MgO, or La203 [4]. The activation of CO2 takes place on the surface of the basic support to form a carbonate species, which is then reduced by CH to form carbon monoxide. 

Kinetic measurements performed by Pichas et al. [32] confirmed the positive role of strontium in the dry reforming of methane reaction the activation energy of carbon dioxide is low compared to methane in the presence of strontium (Table 22.2), which was attributed to the reaction of CO2 with La20s and SrO to... 

Chapter introduces the high-temperature processes of CO2 conversion Dry Reforming of Methane (DRM) and the relevant general use of CO2 as oxidant or dehydrogenating (DH) agent. The conversion of CO2 into methanol is discussed here as it has similarities to the other processes. Such applications deal with the conversion of large volumes of CO2 into fuels or energy-rich molecules. 

Can support influence the kinetic rates and reaction mechanism that means, is it a bifunctional site system O Coimor [19] demonstrated the involvement of the oxygen of the zirconia network in the dry reforming of methane on Pt/Zr02 catalysts. DRIFTS results showed that the presence of carbonate during the reaction, due to the oxygen in the network of zirconia, was replaced by CO2 [20]. 

Carbon deposition is a particular problem with dry reforming, especially with nickel-based catalysts [44—46]. Platinum and rhodium based catalysts show greater tolerance to carbon deposition [47,48]. Therefore, in addition to steam, CO2 can also reform the methane, though it also represents a possible source of carbon deposition. Like steam reforming, dry reforming is also a strongly endothermic reaction. In the case of the dry reforming of methane (Eq. (9)). the heat of reaction AH is -t-248 kj mol . ... 

Figure 5. Relation between carbon deposition and deactivation rate in the reaction tests of steam (H2O), dry (CO2) and the oxidative steam (O2+H3O) reforming of methane over 0.1% P Nio.2Mgo,sO (a), Nio2Mgo.aO (o) and 0.1%> Pd/MgO ( ). Reaction conditions are described in Figures 1 and 5.

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