Departamento de Química, ICEx, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, 31270-901 Minas Gerais, Brazil.
Anal Bioanal Chem. 2010 Apr;396(8):2785-95. doi: 10.1007/s00216-009-3308-5. Epub 2009 Dec 3.
A series of bulk and Al(2)O(3)-supported perovskite oxides of the type LaMn(1-x-y)Fe(x)Mo(y)O(3) (x = 0.00-0.90 and y = 0.00-0.09) were synthesized by the citric acid complexation-gelation method followed by annealing in air at 800 degrees C. For all samples, the local environment and the chemical state and concentration of surface species were determined. Mössbauer spectra revealed the only presence of octahedral Fe(3+) ions dispersed in the perovskite structure, however well-crystallized together with a poorly crystalline LaFeO(3) phases were detected for larger substitutions (x = 0.90). A similar picture was obtained for Mo-loaded (y = 0.02 and 0.05) samples but a new phase most likely related to Fe(3+) ions dispersed aside from the perovskite structure was found for larger substitutions (y = 0.09). Together with these structures, supported samples showed the presence of LaFeO(3) nanoparticles. Finally, photoelectron spectroscopy indicated that the chemical state and composition of the samples in the surface region (2-3 nm) approaches that of the bulk. For the unsupported substituted samples, iron (and molybdenum) enters into the perovskite structure while manganese tends to be slightly segregated. Moreover, in supported perovskites, a fraction of Mo and La atoms interact with the alumina surface. All these oxides were active in methane combustion and best performance was recorded for the Fe-rich composition (x = 0.9) in which both Mn(3+) and Mo(3+) ions were in the same proportion (y = 0.05).
采用柠檬酸络合-凝胶法合成了一系列体相和 Al(2)O(3)负载的钙钛矿型氧化物 LaMn(1-x-y)Fe(x)Mo(y)O(3)（x = 0.00-0.90 和 y = 0.00-0.09），然后在 800°C 的空气中进行退火。对于所有样品，均确定了其局部环境以及表面物种的化学状态和浓度。Mössbauer 谱表明仅存在分散在钙钛矿结构中的八面体 Fe(3+)离子，但对于较大取代度（x = 0.90），检测到结晶良好的 LaFeO(3)相与结晶较差的 LaFeO(3)相共存。负载 Mo（y = 0.02 和 0.05）的样品也得到了类似的结果，但对于较大取代度（y = 0.09），发现了一种可能与分散在钙钛矿结构之外的 Fe(3+)离子有关的新相。除了这些结构，负载样品还显示出 LaFeO(3)纳米颗粒的存在。最后，光电子能谱表明，表面区域（2-3nm）的样品化学状态和组成与体相相近。对于未负载的取代样品，铁（和钼）进入钙钛矿结构，而锰则略有偏析。此外，在负载的钙钛矿中，一部分 Mo 和 La 原子与氧化铝表面相互作用。所有这些氧化物在甲烷燃烧中均具有活性，在富铁组成（x = 0.9）中表现出最佳性能，其中 Mn(3+)和 Mo(3+)离子的比例相同（y = 0.05）。
