CO2 reforming of methane

In 1989, Gadalla and Sommer (252) reported that a solid-solution NiO/MgO (1 1.35) catalyst prepared by precipitation can inhibit the carbon deposition in the CO2 reforming of methane however, they obtained a low CO2 conversion (66%), a low H2 selectivity (79%), and a low CO selectivity (77%), even at the very low WHSV of 3714 cm3 (g catalyst)-1 h-1 with a CH4/CO2 (1/1, molar) feed gas and the high temperature of 1200 K. Their relatively high CH4 conversion was partly a consequence of homogeneous gas-phase reactions that occurred under their conditions. Indeed, the authors found extensive carbon deposits plugging the reactor upstream and downstream of the reaction zone. 

Reforming reactions have been studied in membrane reactors as well. Most well-known is the steam-reforming of various hydrocarbons [10-13], especially methane steam-reforming which is the major source of hydrogen in the world [14], Some research has been performed on CO2 reforming of methane [15] and also a considerable amount of effort has been put in performing the water-gas shift reaction in a membrane reactor [16,18],... 

The forty-eighth volume of Advances in Catalysis includes a description of a new and increasingly well understood class of catalysts (titanosilicates), a review of transmission electron microscopy and related methods applied to catalyst characterization, and summaries of the chemistry and processes of isobutane-alkene alkylation and partial oxidation and CO2 reforming of methane to synthesis gas. 

The purpose of this chapter is to provide a critical assessment of the literature regarding the partial oxidation of methane and the CO2 reforming of methane, with emphasis on the following challenging areas hot spots, O2 separation cost, and the issues of reaction pathways and catalyst selection we also address the issue of carbon deposition in the CO2 reforming of methane. The reason why we review these two reactions together is that they have many common characteristics, including the catalysts, the products, and CH4 as reactant. 

Deactivation of supported metal catalysts by carbon or coke formation, which has its origin in the CH4 dissociation and/or CO disproportionation, is the most serious problem hindering the application of the CO2 reforming of methane. Attempts to overcome this limitation have focused on the development of improved catalysts. 

In the CO2 reforming of methane, carbon formation can occur via two possible pathways CH4 decomposition and CO disproportionation (the Boudouard reaction). Carbon formation by CH4 decomposition is a structure-sensitive reaction (158,159). Specifically, the Ni(lOO) and Ni(llO) surfaces are more active in the decomposition of CH4 to carbon than the Ni(lll) surface (158). The CO disproportionation. 

To develop effective catalysts for the CO2 reforming of methane, other supports were also used for nickel catalysts, including perovskite (244), Y zeolite (245,246), 5A zeolite (247), high-silica ZSM-5 zeolite (248), and AIPO4 (tridymite) (249). 

Recently, Ruckenstein and Wang (264-266) also successfully developed excellent CoO/MgO solid-solution catalysts for CO2 reforming of methane. They reported that Co/MgO exhibited a good catalytic performance with a CO yield of 93% and a H2 yield of 90% at the high space velocity of... 

Fig. 25. TAP pump-probe experiments investigating the CO2 reforming of methane at 600°C. A pulse of CH4 is followed 0.5 s later by a pulse of C02 (after 173). (a) Responses over Ni/Si02 (b) responses over Ni/LajOj.

The Rh catalysts on the supports mentioned previously have been further characterized and their performance in the CO2 reforming of methane has been measured 178,179). The best catalysts in terms of both activity and stability (50 h) are those supported on YSZ, Si02, and AI2O3. FTIR spectra obtained during the first 30 min on stream for the Rh/A Os catalyst at 500°C are shown in Fig. 26. The formate at 1590 cm accumulates but is... 

Liu BS and Au CT. A La2Ni04-zeolite membrane reactors for the CO2 reforming of methane to syngas. Catal Lett 2001 77(l-3) 67-74. 

CO2 reforming of methane (equation 1) has been proposed as one of the most promising technologies for utilization of these two greenhouse gases, and this synthesis gas is suitable for Fischer-Tropsch synthesis and oxygenated chemicals. A serious problem is carbon deposition via Boudouard reaction (equation 2) and/or methane decomposition (equation 3). 

In the previous study, KNiCa/ZSI catalyst exhibited high activity and high resistance to coke in the CO2 reforming of methane at 700 C [2]. Its high activity showed near equilibrium conversions of CO2 and CH4 as well as near equilibrium yields on CO and H2, which were unchanged during over 140 h. On the other hand, Ni/ZSl catalyst was also highly active, but this showed severe coke deposition within several hours. 

In this study it was found that dissociation of CO2 and CH4 is an elementary step in the CO2 reforming of methane and that an active site for the dissociation of CO2 and CH4 (eqns. (1) and (2)) is metallic Ni on the KNiCa catalyst. Ni surface of KNiCa/ZSI catalyst was mostly occupied by adsorbed C and O species as intermediates during the reaction. Surface reaction of these species produced carbon monoxide and simultaneously rejuvenated nickel species (eqn. (5)), which was considered to be rate-determining step under the following reaction scheme. 

The addition of MgO to activated carbon-supported ruthenium catalysts in an optimal Ru Mg ratio results in efficient catalyts for the CO2 reforming of methane, with stable selectivities towards CO and H2 production. 

Rostrup-Nielsen, J.R. Bak Hansen, J.-H. CO2 reforming of methane over transition metals. J. Catal. 1993, 144, 38. 

The Effect of Pressure on CO2 Reforming of Methane and the Carbon Deposition Route Using Noble Metal Catalysts... 

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