CATALYTIC CARBON-MONOXIDE OXIDATION OVER STRONTIUM, CERIUM AND COPPER-SUBSTITUTED LANTHANUM MANGANATES AND COBALTATES

被引:117
作者
CHAN, KS
MA, J
JAENICKE, S
CHUAH, GK
LEE, JY
机构
[1] NATL UNIV SINGAPORE, DEPT CHEM, SINGAPORE 0511, SINGAPORE
[2] NATL UNIV SINGAPORE, DEPT CHEM ENGN, SINGAPORE 0511, SINGAPORE
关键词
CARBON MONOXIDE OXIDATION; (LA; SR)MNO3; LA(MN/CU)O3; (LA/SR)COO3 AND (LA/CE)COO3; OXYGEN MOBILITY; PEROVSKITES; STEADY-STATE MULTIPLICITY;
D O I
10.1016/0926-860X(94)85156-5
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The influence of either A or B-site substitution in perovskite-type mixed oxides on the catalytic oxidation of carbon monoxide has been studied. The following systems were investigated: (La,Sr) MnO3, La (Mn,Cu)O3, (La,Sr)CoO3 and (La,Ce)CoO3. Cobaltates are generally more active than the manganates. Substitution in the A or B-site improved the catalytic activity with oxidation starting from 75-degrees-C. A volcano plot of activity versus composition was obtained for each series with up to a 10-fold increase in catalytic activity for the substituted compounds. Lattice oxygen participates in the reaction even under stoichiometric conditions. The catalysts show a positive rate dependence on the carbon monoxide partial pressure so that under reducing conditions, the reaction is not inhibited. A bistability in the rate of catalytic oxidation at high carbon monoxide concentration was observed over La1-xSrxMnO3 and LaMn1-xCuxO3 (0 less-than-or-equal-to x less-than-or-equal-to 0.2). This bistability has been attributed to a carbon monoxide-driven reconstruction of the reduced surface, leading to pairs of Mn2 ions with a Mn-Mn distance comparable to the spacing in the metal. These pairs provide reactive sites for carbon monoxide oxidation and oxygen chemisorption. Such metal-metal pairs are not found in the perovskite lattice but are a structural feature of the closely related hexagonal 4-layered packing which is the normal crystal structure of SrMnO3. The change back to the less active state is due to reoxidation of the surface. It was confirmed that a low mobility of lattice oxygen is a necessary condition for hysteresis in these oxides.
引用
收藏
页码:201 / 227
页数:27
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