(461b) Methanation of Carbon Dioxide with a Novel Nickel/Magnesium Oxide Catalyst

Georg Baldauf-Sommerbauer, Susanne Lux, Matthaeus Siebenhofer

Institute of Chemical Engineering and Environmental Technology, Graz University of Technology The heterogeneous nickel-catalyzed conversion of carbon monoxide (Eq. 1) and dioxide (Eq.3) into methane has first been reported more than 110 years ago by Sabatier and Senderens [1]. In the last years, reports on the performance and kinetics of different nickel-based catalysts have increased due to rising interest in carbon dioxide valorization [2, 3]. One of the reasons for this growing interest in CO₂ methanation can be found in the quest for alternative hydrogen storage systems. In this broadly discussed concept [4], renewably produced hydrogen is stored as methane, benefitting from readily available natural gas storage and distribution infrastructure.

CO + 3 H₂ = CH₄ + H₂O (1)

CO₂ + 4 H₂ = CH₄ + 2 H₂O (2)

CO₂ + H₂ = CO + H₂O (3)

Most reports in this area focus on alumina Al₂O₃ as an inert catalyst support. Alumina based nickel catalysts are well characterized but often show deactivation. Furthermore, Al₂O₃ does not intervene in the catalytic process itself. Methanation of carbon dioxide possibly proceeds via the intermediate carbon monoxide. Thus, the reaction sequence would be CO₂ (Eq.3) --> CO (Eq.1) --> CH₄. Magnesium oxide [5] shows high activity for the reverse water-gas-shift reaction at moderate temperatures below 450 °C. Therefore, our approach is to combine the catalytic properties of MgO and nickel to facilitate the overall carbon dioxide conversion. Moreover, magnesium oxide is a cheap and abundant material that can be easily produced from mineral magnesium carbonate through calcination. Seemingly doping of catalysts with MgO increases the stability and resistance to carbon deposition of Ni/Al₂O₃ catalysts, as applied in CO methanation [6, 7].

Different types of Ni/MgO catalysts (8-20 %wt. nickel loading) were synthesized by a reactive impregnation of MgO with aqueous nickel nitrate solutions. After drying and calcination in air, nickel oxide was reduced to elemental nickel in hydrogen atmosphere. The catalytic activity was determined in screening experiments by applying a constant heating rate of 2 °C from 25 to 500 °C in a tubular reactor at process-like gas feed of H₂:CO₂:N₂ = 4:1:5 (15 - 60 L_STP h^-1) and at atmospheric pressure. Additional experiments were conducted at isothermal operation conditions. CO₂ conversion increases with increasing nickel loading at isothermal conditions. At high space velocity, carbon monoxide and methane is formed. Decreasing the space velocity at constant operation conditions increases the methane selectivity to above 90 %. This finding supports the suggested mechanism of intermediate carbon monoxide formation. Conversion of CO₂ of more than 80 % below operation temperature of 380 °C was achieved at 1 atm total pressure. The catalysts did not show loss of activity after more than 20 hours operation time.

[1] Sabatier P., Senderens J.-B.: Compt. Rendus Hebd. Chimie 1902 (134), 514-516

[2] Rönsch, S. et al.: Fuel 2016 (166), 276-296

[3] Wang, W.; Wang., S.; Ma, X.; Gong, J.: Chemical Society Reviews 2011 (40), 7, 3703-3027.

[4] Sterner, M.: PhD Thesis, University of Kassel 2009.

[5] Baldauf-Sommerbauer, G.; Lux, S.; Siebenhofer M.: Oral presentation, AIChE Annual Meeting 2015, Salt Lake City, Utah, USA.

[6] Hu, D. et al.: Industrial & Engineering Chemistry Research 2012 (51), 4875-4886.

[7] Fan, M. et al.: Applied Surface Science 2014 (307), 682-688