Orthogonal Preparation of SrFeO3-delta Nanocomposites as Effective Oxygen Transfer Agents for Chemical-Looping Steam Methane Reforming

Development of high-performance SrFeO3-delta-containing nanocomposites, which can be prepared by the Pechini method, for chemical-looping methane reforming is key to industrializing the chemical-looping reforming technique. To identify the importance of preparation parameters and screen the optimal ones with a relatively small number of experimental runs, an orthogonal experiment design was used in this work. The four parameters were the mole ratio of citrate to cations (CA/Me, factor A = 1, 2, and 3), the gelation temperature (factor B = 60, 80, and 100 degrees C), the cation concentration (factor C = 0.98, 0.49, and 0.33 mol/L), and the calcination temperature (factor D = 800, 1000, and 1200 degrees C). Regarding the specific surface area (SSA), the order of importance of the four factors is calcination temperature > CA/Me > gelation temperature > cation concentration. The sample prepared at a combination of A3B1C3D2 (3-60 degrees C-0.33 mol/L-1000 degrees C) has the largest SSA (28.25 m(2)/g), and high CA/Me ratios and low gelation temperatures result in big and porous particles. For nine nanocomposites, complete oxidation of methane occurs first, followed by partial oxidation of methane and then methane cracking at 950 degrees C and 1 atm in the reduction step of chemical-looping steam methane reforming. The first two reactions proceed until the lattice oxygen is depleted, but the last one takes place before the oxidation reactions are completed. As the redox cycle number increases, the first and last two reactions become insignificant. No combination can produce an oxygen carrier that exhibits high selectivity toward partial oxidation but low selectivity toward complete oxidation and methane cracking. Regarding methane conversion, syngas selectivity, and coke selectivity, the best combinations of CA/Me, gelation temperature, cation concentration, and calcination temperature are A2B1C1D1 (2-60 degrees C-0.98 mol/L-800 degrees C), A1B2C3D3 (1-80 degrees C-0.33 mol/L-1200 degrees C), and A3B3C2D3 (3-100 degrees C-0.49 mol/L-1200 degrees C), respectively. Concerning hydrogen purity in the oxidation step, the best combination is A3B3B3D3 (3-100 degrees C-0.33 mol/L-1200 degrees C).