Direct Conversion of Carbon Dioxide to Methane over Ceria‐ and Alumina‐Supported Nickel Catalysts for Biogas Valorization

Abstract

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.

Recent Advances in Catalysis for Methanation of CO2 from Biogas

“…Both catalysts showed higher CO 2 conversion and higher CH 4 selectivity at 350 • C than at 600 • C. Compared to the reference experiment, the catalysts achieved a lower CO 2 conversion, which decreased to about the same value (81-82%) with CH 4 in the inlet gas [99]. The CO 2 conversion decreased by about 6% for Ni20/Al 2 O 3 and by about 10% for Ni40/Al 2 O 3 at 350 • C (Table 4).…”

“…At 350 • C and no CH 4 present, both catalysts achieved 100% CH 4 selectivity. Over 20 h, conversion rate and selectivity remained constant in both cases [99].…”

“…In a second series of experiments with the same catalysts, the effect of CH 4 was tested for about 70 h in microchannel reactors (Table 8) [99]. The resulting CO 2 conversions in the microchannel reactor (12.5 bar) were higher than in the experiments with the fixed-bed reactor, which were performed at 2 bar (Table 4).…”

“…A third study investigated the influence of CH 4 in the inlet gas on two unpromoted Ni catalysts prepared by impregnation [99]. The reaction conditions for the first series of experiments in a fixed-bed reactor are given in Table 7.…”

“…The reaction conditions for the first series of experiments in a fixed-bed reactor are given in Table 7. The experiments with CH 4 in the inlet gas were performed at 300 • C and 600 • C for 20 h respectively, while the reference experiment with no CH 4 in the inlet gas was performed at 350 • C for 20 h and then set to 600 • C for another 20 h [99]. The addition of CH 4 was compensated by the reduction of Ar concentration in the inlet gas (Table 4) to leave the inlet content of H 2 and CO 2 unaffected.…”