Tri-reforming of methane: A novel concept for catalytic production of industrially useful synthesis gas with desired H₂/CO ratios

A novel process concept called tri-reforming of methane has been proposed in our laboratory using CO₂ in the flue gases from fossil fuel-based power plants without CO₂ separation [C. Song, Chemical Innovation 31 (2001) 21-26]. The proposed tri-reforming process is a synergetic combination of CO₂ reforming, steam reforming, and partial oxidation of methane in a single reactor for effective production of industrially useful synthesis gas (syngas). Both experimental testing and computational analysis show that tri-reforming can not only produce synthesis gas (CO + H₂) with desired H₂/CO ratios (1.5-2.0), but also could eliminate carbon formation which is usually a serious problem in the CO₂ reforming of methane. These two advantages have been demonstrated by tri-reforming of CH ₄ in a fixed-bed flow reactor at 850°C with supported nickel catalysts. Over 95% CH₄ conversion and about 80% CO₂ conversion can be achieved in tri-reforming over Ni catalysts supported on an oxide substrate. The type and nature of catalysts have a significant impact on CO₂ conversion in the presence of H₂O and O₂ in tri-reforming in the temperature range of 700-850°C. Among all the catalysts tested for tri-reforming, their ability to enhance the conversion of CO₂ follows the order of Ni/MgO > Ni/MgO/CeZrO > Ni/CeO ₂ ≈ Ni/ZrO₂ ≈ Ni/Al₂O₃ > Ni/CeZrO. The higher CO₂ conversion over Ni/MgO and Ni/MgO/CeZrO in tri-reforming may be related to the interaction of CO₂ with MgO and more interface between Ni and MgO resulting from the formation of NiO/MgO solid solution. Results of catalytic performance tests over Ni/MgO/CeZrO catalysts at 850°C and 1 atm with different feed compositions confirm the predicted equilibrium conversions based on the thermodynamic analysis for tri-reforming of methane. Kinetics of tri-reforming were also examined. The reaction orders with respect to partial pressures of CO₂ and H₂O are different over Ni/MgO, Ni/MgO/CeZrO, and Ni/Al₂O₃ catalysts for tri-reforming.