Direct methanation of CO 2 over ceria-and alumina-supported nickel catalysts in the feed stream containing methane and traces of H 2 S is reported. Stability tests for 20 h at 350 and 600°C with a packed-bed reactor showed high resistance of the catalysts to sintering processes. Higher conversion at 350°C was observed for ceria supported nickel catalyst. Thermodynamic analysis indicated that CO 2 contained in biogas can be converted to methane without carbon formation under specific reaction conditions. An introduction of CH 4 to CO 2 À H 2 feed stream led to the decrease in CO 2 conversion and CH 4 selectivity. An introduction of the trace amounts of H 2 S into the feed stream led to the fast drop of CO 2 conversion and CH 4 selectivity; higher durability (20 %) was observed for Al 2 O 3 than CeO 2 supported catalysts. An improved performance of catalysts coated onto high-pressure microchannel microreactors for the direct CO 2 methanation reaction applying model biogas mixture was demonstrated.
The sulfur tolerance of mono‐ and bimetallic ruthenium catalysts for CO2 hydrogenation was investigated in microchannel reactors. H2S was selected as a model compound. It was found that a Ru/CeO2 catalyst deactivates rapidly. Ni was a much better additive to improve the catalyst stability compared to Rh and serves as a sulfur trap. The influence of the support was evaluated showing that a SiO2‐supported catalyst has a higher stability and better selectivity compared to CeO2 and TiO2. A plant concept was developed comprising two‐step methanation with a first adiabatic reactor stage followed by a plate heat‐exchanger reactor with integrated cooling which allows more than 97 % CO2 conversion. A pilot plant will be put into operation in connection with a biogas plant and an electrolyser of 50 kW power consumption.
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