Hydrogen production from a combination of the water-gas shift and redox cycle process of methane partial oxidation via lattice oxygen over LaFeO3 perovskite catalyst
ABSTRACT A redox cycle process, in which CH4 and air are periodically brought into contact with a solid oxide packed in a fixed-bed reactor, combined with the water-gas shift (WGS) reaction, is proposed for hydrogen production. The sole oxidant for partial oxidation of methane (POM) is found to be lattice oxygen instead of gaseous oxygen. A perovskite-type LaFeO3 oxide was prepared by a sol-gel method and employed as an oxygen storage material in this process. The results indicate that, under appropriate reaction conditions, methane can be oxidized to CO and H2 by the lattice oxygen of LaFeO3 perovskite oxide with a selectivity higher than 95% and the consumed lattice oxygen can be replenished in a reoxidation procedure by a redox operation. It is suggested that the POM to H2/CO by using the lattice oxygen of the oxygen storage materials instead of gaseous oxygen should be possibly applicable. The LaFeO3 perovskite oxide maintained relatively high catalytic activity and structural stability, while the carbonaceous deposits, which come from the dissociation of CH4 in the pulse reaction, occurred due to the low migration rate of lattice oxygen from the bulk toward the surface. A new dissociation-oxidation mechanism for this POM without gaseous oxygen is proposed based on the transient responses of the products checked at different surface states via both pulse reaction and switch reaction over the LaFeO3 catalyst. In the absence of gaseous-phase oxygen, the rate-determining step of methane conversion is the migration rate of lattice oxygen, but the process can be carried out in optimized cycles. The product distribution for POM over LaFeO3 catalyst in the absence of gaseous oxygen was determined by the concentration of surface oxygen, which is relevant with the migration rate of lattice oxygen from the bulk toward the surface. This process of hydrogen production via selective oxidation of methane by lattice oxygen is better in avoiding the deep oxidation (to CO2) and enhancing the selectivity. Therefore, this new route is superior to general POM in stability (resistance to carbonaceous deposition), safety (effectively avoiding accidental explosion), ease of operation and optimization, and low cost (making use of air not oxygen).
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ABSTRACT: During the past fifteen years, significant progresses have been achieved in material science, allowing the design of nanoscaled ABO3 perovskites. Such size-limited materials were evidenced to develop exceptional textural properties, making the redox – oxygen transfer properties – surface properties of the materials significantly improved. Such progresses obviously induced radical changes in intrinsic catalytic activity of the solids over nanostructures. Advances in the field of perovskite synthesis and development in the use of these materials in heterogeneous catalysis are presented and an emphasize is made on: - Oxidation reactions (CO and CH4, but also VOCs and Soot for gas phase reactions; water treatment by catalytic wet oxidation), - Reduction reactions (NOx decomposition, NOx reduction (as for SCR and TWC continuous process and for NOx storage reduction transient process), - Selective oxidation reactions (POM and OCM), - Reforming reactions (dry and steam reforming reactions), - Synthesis of carbon nanotubes; an emerging use of perovskite. Although ABXn perovskites with various heteroatoms have been described in the literature, only oxygen-based perovskites will be considered in this review.Chemical Reviews 09/2014; DOI:10.1021/cr500032a · 45.66 Impact Factor
AIChE Journal 11/2014; DOI:10.1002/aic.14695 · 2.58 Impact Factor
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ABSTRACT: CoWO4 (CW) promoted with 10% Ni (CW–Ni) and 10% La2O3 (CW–La) were used as oxygen carriers in redox cycles of CH4/Ar and H2O/Ar to evaluate their global kinetics (reaction rate, order, constant and activation energy) with methane for the production of hydrogen. CoWO4 was synthesized by co-precipitation from equimolar solutions of Na2WO4 and Co(NO3)2 and calcined at 950 °C. Ni and La nitrate solutions were incorporated to CoWO4 by impregnation. Kinetic data was collected by thermogravimetric analysis (TGA) at 2, 5 and 8% CH4/Ar and at 850, 900 and 950 °C for two consecutive redox cycles. Oxidation was performed using 5% H2O/Ar at 900 °C. Results indicate a global first order reaction for the three materials. Activation energies during the first cycle for CW, CW–Ni and CW–La were 52.8, 32 and 33.4 kcal/mol, respectively, thus reflecting the influence of Ni and La2O3 in a greater reaction rate with respect to CW.International Journal of Hydrogen Energy 09/2013; 38(28):12519-12526. DOI:10.1016/j.ijhydene.2012.11.109 · 2.93 Impact Factor