Perovskite-type catalyst for catalytic combustion in MCFC system

Lots of developed MCFC power generation systems are combined with LNG reforming system for suppling hydrogen. In MCFC-LNG reformer combined system, some unreacted hydrogen was effluented as residue gases with appreciable amount of heat. To enhance the energy efficiency of MCFC power generation system, we will use hot residue gases which include unreacted hydrogen to heat up MCFC stack by using catalytic combustion. ABO_3- type perovskite oxides have high potential for oxidation. And substitution of the metal in position A and/or B can change catalytic property of oxides. La_1-x A' _xFeO₃ (A: Sr, Ag, Ce, X : 0.1, 0.3) perovskites were synthesized by citiric acid sol gel method using metal nitrates. The catalysts were chacterized by powder XRD and BET. The catalytic activity in hydrogen combustion were tested in a conventional flow reactor. Surface area of perovskite oxides decreased with increasing metal content up. La _0.9Ce_0.1Fe0₃ catalyst showed the highest surface area 23.0m²/g at 700°C calcined. The patterns observed for all sample correspond mainly perovskite-type structure by using JCPDS program. This means that Sr, Ce was well substituted and posed in perovskite structure. But Ag substituted perovskite was looked Ag₂O peak at 38.0 degree and the peak site was larger when X=0.3. Catalytic activity of all A-site substitutued catalyst are always higher than LaFeO₃. Especially La_0.9Sr_0.9Fe0₃ shows the highest hydrogen combustion activity. The temperatures required for 50% and 90% conversion of hydrogen in its combustion are 139°Cand 185°C, respectively for the La_0.9Sr_0.1Fe0₃, and 227 °C and 345 °C, respectively for the LaFeO₃.