摘要
采用柠檬酸络合-有机模板剂分解法制备出具有不同(n_(La)+n_(Mn))/(n_(La)+n_(Mn)+n_(Ce))比、不同温度焙烧的La-Mn-Ce-O系列多元介孔混合氧化物催化剂,并与传统共沉淀法制备的La-Mn-Ce-O催化剂进行比较.N_2吸附和脱附结果表明,采用模板剂法制得的样品具有较大的比表面积(高达103.5m^2·g^(-1))和较均匀的孔径分布(3.4-4.4nm);500℃焙烧样品的比表面积约为共沉淀法所制样品的三倍.600℃焙烧后,样品的孔径分布范围稍有加宽,但仍保持介孔结构.XRD表征结果表明,Mn物种具有高度的分散性,XRD难以检测,La-Ce和Mn-Ce可能部分形成了固溶体结构.XPS结果揭示,Mn-Ce间存在电子态的强相互作用,出现了Mn2p的震激峰,这种相互作用促进了氧物种在Ce和Mn物种间的传递,增强了样品的氧化还原性能,震激峰最明显的样品具有最佳的氧化性能.H_2-TPR结果表明,采用柠檬酸络合-有机模板剂分解法制备的催化剂中,锰氧化物更容易被还原,Mn—O键的活动度与CO氧化活性密切相关.活性评价结果表明,500℃焙烧的(n_(La)+n_(Mn))/(n_(La)+n_(Mn)+n_(Ce))为0.5的样品,起燃温度比传统共沉淀法制得的样品降低了50℃左右,并表现出较高的热稳定性.
A series of mesoporous multicomponent mixed oxide catalysts La-Mn-Ce-O with various （nLa＋nMn）/（nLa＋ nMn＋nCe） ratios were prepared by citric acid complexation-organic template decomposition （CAC-OTD） method. For comparison, the sample with the same composition was also prepared by conventional coprecipitation method. The results of N2 adsorption/desorption showed that the samples prepared by CAC-OTD method possessed relatively large specific surface area and uniform pore diameter distribution （3.4-4.4 nm）. The results of X-ray diffraction （XRD） identified the formation of La-Ce and Mn-Ce solid solution. No Mn species were detected by XRD. The results of X-ray photoelectron spectroscopy （XPS） showed that there was a strong electronic state interaction between Mn and Ce species, resulting in the formation of Mn 2p shake-up peak. Such interaction enhanced the transfer of oxygen species from Ce to Mn oxide and therefore increased the redox activity of the samples. The sample with the strongest shake-up peak showed the highest oxidation activity. The results of temperature programmed reduction （TPR） showed that the manganese species in the samples prepared by using CAC-OTD method were easier to be reduced, which was relevant to the oxidation activity of the catalysts. The results of activity evaluation showed that the light-off temperature of the LMC（0.5）-500 sample was about 50 ℃ lower than that of the sample prepared by using coprecipitation method. The samples prepared by using CAC-OTD method showed good thermal stability.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2007年第5期641-646,共6页
Acta Physico-Chimica Sinica
基金
国家高技术研究发展计划(863计划)(2006AA06Z348)
国家自然科学基金(20676097)资助项目
关键词
多元介孔催化剂
制备
柠檬酸络合
有机模板剂
结构表征
Multicomponent mesoporous catalyst
Preparation
Citric acid complexation
Organic template
Structural characterization
