Sorption-enhanced steam methane reforming (SE-SMR) is the most potential technology for producing hydrogen from methane reforming. This innovative technology converts methane into high-purity hydrogen simultaneously with the CO₂ removal in a single reactor. The key challenge in establishing this technology is the availability of a stable sorbent that could effectively work with the reforming catalyst for an extended number of sorption-desorption multi cycles. This study investigates the catalytic performance of monometallic Ni/Mayenite (Ca₁₂Al₁₄O₃₃) and bimetallic catalytic sorbents (Ni-Co/CaO-Ca₁₂Al₁₄O₃₃, with Ni:Co molar ratio of 1:1, 1:3, and 3:1) for SE-SMR reaction. The catalytic sorbents were synthesized using a wet impregnation method and characterized through XRD, BET, SEM and TGA to assess their structural, textural and CO₂ sorption properties. The SE-SMR performance of the catalysts was tested in a quartz fixed-bed reactor (I.D. 9mm). Before the SE-SMR runs, the catalyst was reduced at 1073K in 50% H2/N₂ flow (60 mL min^-1) for 1 h. Next, the CH₄, steam and N₂ were introduced to the reactor to start the reaction. The product compositions were analyzed by gas chromatography (GC-2014, Shimadzu) equipped with TCD and FID detectors.
The results revealed that Ni-Co/Ca₁₂Al₁₄O₃₃ exhibited the highest BET surface area of 32.26 m² g^-1, with a total pore volume of 0.064 cm³ g^-1 and an average pore diameter of 8.03 nm. The Ni/Ca₁₂Al₁₄O₃₃ catalyst showed initial significant H₂ production up to 30 mins. Once the sorbent is saturated at 30 min, CO₂ reappears in the product stream, and methane conversion decreases. A similar observation was noted for the Ni-Co/Ca₁₂Al₁₄O₃₃ catalyst, which shows a breakthrough time for CO₂ equal to 90 mins. The entire CO produced during SMR is oxidized into CO₂, which is completely absorbed. The activation of the three reactions of the process (reforming reaction, water gas shift and carbonation) occurs. CO₂ sorption enhances methane and CO conversion; H₂ increases, which agrees with the hypothesis based on the shift in the equilibrium of steam reforming and water gas reactions. The enhanced activity of the Ni-Co catalyst may be due to the synergistic effect of Ni and Co, which have been shown to improve deactivation resistance. Additionally, the CO₂ molar fraction showed a delayed increase, suggesting that the CO₂ sorption capacity of this catalyst was sustained for a longer period.

Ahmad Salam Farooqi

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