Cooperative effect of Ce and Mn in MnCe/Al₂O₃ environmental catalysts

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• 作者：N. Drenchev ; I. Spassova ; E. Ivanova ; M. Khristova ; K. Hadjiivanov ; ^{kih@svr.igic.bas.bg}
• 关键词：Adsorption ; CO ; NO ; FTIR spectroscopy ; Catalysis ; NO decomposition ; Oxidation of CO ; NO  ; +  ; CO reaction
• 刊名：Applied Catalysis B: Environmental
• 出版年：2013
• 出版时间：17 July, 2013
• 年：2013
• 卷：138-139
• 期：Complete
• 页码：362-372
• 全文大小：1528 K

文摘

Three samples, Mn/Al₂O₃, Ce/Al₂O₃ and MnCe/Al₂O₃ (containing 10 wt. % metal) were prepared by impregnation and comparatively studied by means of FTIR spectroscopy, other characterization techniques and catalytic measurements. It was established that the active phase deposition led to (i) partial disappearance of all kinds of the alumina OH groups and (ii) blocking of part of the Al³⁺ Lewis acid sites. The results indicated that manganese was better dispersed on the MnCe/Al₂O₃ sample as compared to Mn/Al₂O₃. As a result, the bimetallic sample was the most active one in a series of catalytic reactions: NO decomposition, CO oxidation and CO + NO interaction.

Interaction of all samples with CO leads to formation of carbonates and hydrogencarbonates increasing in amount with the temperature of interaction and in the sequence Al₂O₃ < Ce/Al₂O₃ < Mn/Al₂O₃ ? MnCe/Al₂O₃. When the samples interacted with NO, different nitrogen oxo-compounds were formed and manganese nitrosyls appeared with the Mn-containing samples. In agreement with the higher Mn dispersion, the amount of the latter was larger with the bimetallic sample. Interaction between CO and NO results in formation of isocyanates, (hydrogen)carbonates and nitrogen oxo-compounds (nitrosyls, nitro-nitrito and nitrate species). When the interaction occurs at ambient temperature, the surfaces of the Al₂O₃, Ce/Al₂O₃ and Mn/Al₂O₃ are covered mainly by nitrates and nitro-nitrito species. With increase of the interaction temperature these species are gradually replaced by (hydrogen)carbonates. The temperature of this replacement decreases in the order Al₂O₃-Ce/Al₂O₃-Mn/Al₂O₃. With the MnCe/Al₂O₃ sample carbonates dominate even at 373 K interaction. Consequently, the NO + CO catalytic conversion occurs in two regimes. The low temperature regime (the temperature interval depends on the catalyst) is associated with NO_x precovered surface, while at higher temperatures the catalysts surfaces are precovered with (hydrogen)carbonates.