Critical influence of the amorphous silica-to-cristobalite phase transition on the performance of Mn/Na2WO4/SiO2 catalysts for the oxidative coupling of methane
Critical influence of the amorphous silica-to-cristobalite phase transition on the performance of Mn/Na2WO4/SiO2 catalysts for the oxidative coupling of methane
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DOI：
10.1006/jcat.1998.2109
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发表时间：
1998-07-25
影响因子：
7.3
通讯作者：
Lambert, RM
中科院分区：
文献类型：
--
作者：
Palermo, A;Vazquez, JPH;Lambert, RM
XRD、XPS/XAES、TPR 分析和催化测试已应用于 Na/W/Mn/SiO2 甲烷偶联催化剂以及不含 Na、Mn 和 W 中的一种或多种的相应配方。我们发现催化剂性能和最终煅烧材料中的载体结构之间存在明显的相关性。无定形二氧化硅产生活性但选择性非常低的催化剂。结晶 SiO2（α-方英石）可产生活性且高选择性的催化剂，尤其是在乙烯的形成方面。我们证明Na的存在对于异常低温二氧化硅->方石英载体相变的发生至关重要。结构、催化和光谱结果表明Na具有结构促进剂和化学促进剂的双重作用。 (C) 1998 年学术出版社。
XRD, XPS/XAES, TPR analysis and catalytic testing have been applied to Na/W/Mn/SiO2 methane coupling catalysts and to corresponding formulations without one or more of Na, Mn, and W. We find a clear correlation between catalyst performance and support structure in the final calcined material. Amorphous silica yields active but very unselective catalysts. Crystalline SiO2 (alpha-cristobalite) generates active and highly selective catalysts-especially with respect to the formation of ethylene. We demonstrate that the presence of Na is essential for the anomalous low temperature silica --> cristobalite support phase transition to occur. The structural, catalytic, and spectroscopic results indicate that Na plays a dual role as both structural and chemical promoter. (C) 1998 Academic Press.