Methanation of Syngas in a Three‐Stage Serial Reactor System Using a Set of Nickel‐Based Catalysts

A set of nickel‐based catalysts was designed for testing its performance of methanation of synthesis gas (syngas) in a three‐stage, fixed‐bed reactors‐in‐series system. Process input feed stream ratios were simulated by reflecting the requirements for the ratio of H 2 /CO and steam/CO and an approximation of the extent of methanation that needs to be accomplished in each reactor stage. The content of active nickel species in the catalyst increased with the reactor stage sequence, and consequently, syngas conversion and methane yield increased progressively as well, due to the reaction kinetics and thermodynamics of syngas methanation. In parallel, the catalyst preparation method was varied in accordance with the reaction conditions and requirements of each reactor stage. For the catalysts in the first and second reactor stages contacting with the feeds of high and medium reactant concentrations, nickel and cerium precursors were deposited onto commercial alumina pellets by impregnation, followed by drying and calcination to form NiO‐CeO 2 /Al 2 O 3 . Nickel content increased from 5 wt% for the first stage catalyst to 10 wt% for the second stage catalyst, while cerium content was unchanged at 5 wt%. For the third stage catalyst contacting with a feed consisting of lower reactant concentration and having a higher nickel content, the nickel precursor was deposited onto titania (anatase) powder by impregnation, forming NiTiO 3 after calcination, followed by deposition of the cerium precursor onto the mixed oxide by impregnation. Cerium‐deposited NiTiO 3 powder was then physically mixed with alumina powder before being pelletized to a desired size. The recipes of these nickel‐based catalysts were effective in avoiding the formation of inactive NiAl 2 O 4 species during catalyst preparation and suppressing thermal sintering and coking of catalyst during methanation. Each catalyst prepared in this study was active for syngas methanation by exhibiting excellent CO conversion and methane yield in the temperature range of 623–723 K, while catalyst activity slightly decreased at 773 K. Stability of each catalyst was maintained at 623 K for 100 h under the reaction conditions simulated in each reactor stage. Syngas methanation was also run for alternate operation scenarios with different sequences of catalysts and higher space velocities, resulting in different syngas conversions from each reactor stage. The catalyst sequence for these additional works used the nickel‐based catalyst of 5 wt% nickel content in both the first and the last reactor stages, with the same catalyst of 10 wt% nickel content placed in the middle reactor stage.