Dual-Bed catalyst architecture for steam reforming of ethanol with seawater: Sacrificial salt capture and coke nanostructure control

Seawater is abundant in coastal area and it might be alternative to deionized water for steam reforming. However, high salt content in seawater poses challenge on reforming by generating salt deposit on top of catalyst bed. Use of dual-bed system with upper-bed catalyst as guard or sacrifice catalyst might solve this issue. In this study, ethanol reforming with seawater was investigated over single-bed Ni/MgAl catalyst, or dual-bed catalysts with MgAl or Ni/MgAl as upper-bed and Ni/MgAl as lower-bed. The results demonstrated effectiveness of dual-bed catalysts for enhancing hydrogen production. The upper-bed catalyst acted as a barrier to refrain the salts from seawater from deposition onto the lower-bed Ni/MgAl, which was essential to maintain catalytic stability (decrease of H2 yield: 4.2% over Ni/MgAl-Ni/MgAl versus 24.3% over single-bed Ni/MgAl catalyst in 5 h of time-on-stream). The coke formed over single-bed Ni/MgAl (19.4%) was also higher than that over MgAl-Ni/MgAl (8.9%) or Ni/MgAl-Ni/MgAl (15.5%). The presence of salts in the single-bed Ni/MgAl system predominantly led to the formation of amorphous coke. Additionally, in MgAl-Ni/MgAl, MgAl as an upper-bed catalyst promoted condensation of carbonyl intermediates to form abundant olefinic C=C containing species, which resulted in formation of amorphous coke with mainly aliphatic components and lower C/H ratios. In comparison, in Ni/MgAl-Ni/MgAl, Ni/MgAl as an upper-bed catalyst promoted deoxygenation of reaction intermediates, forming aromatic coke with lower ID/IG ratio in mainly carbon nanotube form in lower-bed Ni/MgAl.