Catalytic methane decomposition

Summary of literature data on methane decomposition catalysts and preferred temperature range. Catalysts 1 = nickel, 2 = iron, 3 = carbon, and 4 = other transition metals (Co, Pd, Pt, Cr, Ru, Mo, W). The dotted line arbitrarily separates heterogeneous (catalytic) and homogeneous (noncatalytic, gas phase) temperature regimes of the methane decomposition reaction. 

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The use of carbon-based catalysts offers certain advantages over metal catalysts due to their availability, durability, and low cost. In contrast to the metal-based catalysts, carbon catalysts are sulfur resistant and can withstand much higher temperatures. Muradov [98,99] screened a variety of carbon materials and demonstrated that the efficient catalytic methane decomposition can be accomplished over high surface area carbons at temperatures... 

Production of Carbon Filaments by Catalytic Methane Decomposition 176... 

At the outset, this section will address studies related to the catalytic methane decomposition step and then subsequently describe the work undertaken on the combined step-wise reforming (two step) process. 

Catalytic methane decomposition has received considerable attention in recent years. The reaction has been investigated for two main applications (a) production of hydrogen and (b) synthesis of carbon filaments. The important conditions necessary for clean hydrogen production are as follows ... 

Of particular interest are catalytic methane decomposition reactions producing special (e.g. filamentous) forms of carbon. For example, researchers have reported catalytic decomposition of methane over Ni catalyst at 500°C with the production of hydrogen and whisker carbon26 and concentrated solar radiation was used to thermally decompose methane into hydrogen and filamentous carbon.27 The advantages of this system included efficient heat transfer due to direct irradiation of the catalyst, and C02-free operation. 

Choudhary, V., Banerjee, S., Rajput, A. (2002). Hydrogen from step-wise steam reforming of methane over Ni/ZrOj factors affecting catalytic methane decomposition and gasification by steam of carbon formed on the catalyst. Appl. Catalysis A General 234,259-270. 

Let us now use the sequence of elementary steps to explain the activity loss for some of the catalysts The combination of hydrogen chemisorption and catalytic measurements indicate that blocking of Pt by coke rather than sintering causes the severe deactivation observed in the case of Pt/y-AljOj The loss in hydrogen chemisorption capacity of the catalysts after use (Table 2) is attributed mainly to carbon formed by methane decomposition on Pt and impeding further access. Since this coke on Pt is a reactive intermediate, Pt/Zr02 continues to maintain its stable activity with time on stream. 

NASA conducted studies on the development of the catalysts for methane decomposition process for space life-support systems [94], A special catalytic reactor with a rotating magnetic field to support Co catalyst at 850°C was designed. In the 1970s, a U.S. Army researcher M. Callahan [95] developed a fuel processor to catalytically convert different hydrocarbon fuels to hydrogen, which was used to feed a 1.5 kW FC. He screened a number of metals for the catalytic activity in the methane decomposition reaction including Ni, Co, Fe, Pt, and Cr. Alumina-supported Ni catalyst was selected as the most suitable for the process. The following rate equation for methane decomposition was reported ... 

Kim et al. [123] conducted the kinetic study of methane catalytic decomposition over ACs. Several domestic (South Korea) ACs made out of coconut shell and coal were tested as catalysts for methane decomposition at the range of temperatures 750-900°C using a fixed-bed reactor. The authors reported that no significant difference in kinetic behavior of different AC samples was observed despite the differences in their surface area and method of activation. The reaction order was 0.5 for all the AC samples tested and their activation energies were also very close (about 200 kj/mol) regardless of the origin. The ashes derived from AC and coal did not show appreciable catalytic effect on methane decomposition. 

Muradov, N., Catalytic activity of carbon for methane decomposition reaction, Catal. Today, 102-103,225,2005. 

There have been attempts to use catalysts in order to reduce the maximum temperature of thermal decomposition of methane. In the 1960s, Universal Oil Products Co. developed the HYPROd process for continuous production of hydrogen by catalytic decomposition of a gaseous hydrocarbon streams.15 Methane decomposition was carried out in a fluidized bed catalytic reactor from 815 to 1093°C. Supported Ni, Fe and Co catalysts (preferably Ni/Al203) were used in the process. The coked catalyst was continuously removed from the reactor to the regeneration section where carbon was burned off by air, and the regenerated catalyst returned to the reactor. Unfortunately, the system with two fluidized beds and the solids-circulation system was too complex and expensive and could not compete with the SR process. 

It was found that almost all transition metals (d-metals) exhibit catalytic activity toward methane decomposition reaction to some extent, and some demonstrate remarkably high activity. It should be noted, however, that there is no universal agreement among different groups of researchers regarding the choice of the most efficient metal catalyst for methane decomposition. For example, it was demonstrated that the rate of methane activation in the presence of transition metals followed the order Co, Ru, Ni, Rh > Pt, Re, Ir > Pd, Cu, W, Fe, Mo.20 Other researchers have found Pd to be the most active catalyst for methane decomposition,18-21 whereas still others found Ni was the catalyst of choice,22 or Fe and Ni.23-24 Finally, Co catalyst demonstrated highest activity in methane decomposition reaction.25... 

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