(544ex) CO2 Hydrogenation with Ni/MgO Catalysts

CO₂ hydrogenation makes use of CO₂ to produce either hydrocarbons or CO. The product selectivity depends on the catalyst and the process parameters. The hydrogenation activity of bifunctual Ni/MgO catalysts was investigated. Nickel provides the adsorbent capacity for H₂, and it is highly selective to CH₄. MgO provides CO₂-adsorption, and it contributes to suppression of catalyst deactivation. The Ni/MgO catalyst is a cheap, highly active, easy to synthesize, easy to recycle and robust catalyst, offering access to CO₂ hydrogenation of high CO₂-load off-gas in metallurgy and in the refractory industry.

The influence of the nickel load on the performance of Ni/MgO catalysts in terms of rate controlling steps and the reaction kinetics were investigated. The MgO backbone was compared to Ni/MgO catalysts with different Ni load between 11-27%wt.

The MgO backbone without Ni-load is selective to CO formation, admixture of nickel shifts the selectivity to methane with high nickel load leading to higher methane selectivity and higher CO₂ conversion. The reaction kinetics of the CO₂ methanation can be modelled with a Langmuir-Hinshelwood based approach, as proposed by Koschany et. al. [1]. Different rate models can be applied, depending on what is assumed to be the rate determining step. Temperature dependency was modelled with an Arrhenius approach. The activation energy depends on the Ni-load, suggesting that with increasing Ni-load mass transfer becomes a key step in conversion.

[1] F. Koschany, D. Schlereth, and O. Hinrichsen, “On the kinetics of the methanation of carbon dioxide on coprecipitated NiAl(O)x,” Appl. Catal. B Environ., vol. 181, pp. 504–516, 2016.