Cu-ZSM-5 Zeolites for the Formation of Methanol from Methane and Oxygen: Probing the Active Sites and Spectator Species
Cu-ZSM-5 Zeolites for the Formation of Methanol from Methane and Oxygen: Probing the Active Sites and Spectator Species
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DOI：
10.1007/s10562-010-0380-6
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发表时间：
2010-08-01
影响因子：
2.8
通讯作者：
Bitter, Johannes H.
中科院分区：
文献类型：
--
作者：
Beznis, Nadzeya V.;Weckhuysen, Bert M.;Bitter, Johannes H.
通过改变电荷补偿阳离子、铜前体、铜负载量和pH的性质来制备一系列Cu-ZSM-5沸石。报道了在Cu-ZSM-5沸石上由甲烷和氧气产生的甲醇的量与在22，700 cm（-1）处的UV-Vis-NIR DRS电荷转移带之间的线性关系，与所使用的合成路线无关。22，700 cm（-1）波段的绝对强度总是很低，表明样品中活性位点的数量很少。在所有研究的Cu-ZSM-5沸石中，至少存在两种铜物种：（a）分散在ZSM-5外表面上的Cu-O簇和（B）高度分散在通道内的铜-氧物种，在样品中占少数。通过将催化活性与吸附的新戊腈的FT-IR数据相关联，可视化沸石外表面上的Cu-O颗粒，以及随后吸附的NO，指示沸石通道内的Cu-O物种，可以得出结论，外表面上的Cu-O物种不参与氧化反应，而通道内的铜负责甲烷向甲醇的选择性转化。
A series of Cu-ZSM-5 zeolites was prepared by varying nature of the charge compensating cation, copper precursor, copper loading, and pH. The materials were tested for the oxidation of methane to methanol using oxygen. A linear relationship between the amount of methanol produced over Cu-ZSM-5 zeolites from methane and oxygen and a UV-Vis-NIR DRS charge transfer band at 22,700 cm(-1) is reported irrespective of the synthesis route used. The absolute intensity of the 22,700 cm(-1) band is always low, indicating a low number of active sites in the samples. In all studied Cu-ZSM-5 zeolites at least two copper species were present: (a) Cu-O clusters dispersed on the outer surface of ZSM-5 and (b) highly dispersed copper-oxo species inside the channels, a minority fraction in the sample. By relating catalytic activity to FT-IR data of adsorbed pivalonitrile, visualizing Cu-O particles on the outer surface of the zeolite, and subsequently adsorbed NO, indicative of the Cu-O species inside the zeolite channel, it was concluded that Cu-O species on the outer surface are not involved in the oxidation reaction, while copper inside the channels are responsible for the selective conversion of methane to methanol.