New light on the state of active sites in CuZSM-5 for the NO decomposition reaction and N2 adsorption
New light on the state of active sites in CuZSM-5 for the NO decomposition reaction and N2 adsorption
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DOI：
10.1039/b304538m
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发表时间：
2003-07
影响因子：
3.3
通讯作者：
Y. Kuroda;Kazunori Yagi;Naoko Horiguchi;Y. Yoshikawa;R. Kumashiro;M. Nagao
中科院分区：
文献类型：
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作者：
Y. Kuroda;Kazunori Yagi;Naoko Horiguchi;Y. Yoshikawa;R. Kumashiro;M. Nagao
采用三种不同的方法对ZSM-5型分子筛进行了铜离子交换，以获得铜离子交换ZSM-5型分子筛（CuZSM-5）的NO分解有效位的状态和作用以及N2吸附活性的信息。第一种制备方法是使用双（1，1，1，5，5，5-六氟乙酰丙酮合）铜（II）[Cu（hfac）2]作为挥发性络合物的化学气相沉积（CVD），第二种方法是利用CuCl作为蒸发源。将这些与第三种方法，即使用CuCl 2水溶液的普通离子交换方法进行比较。显然，在第一种方法中，在ZSM-5上沉积的Cu 2+物质为[Cu（hfac）2]（即，通过布朗斯台德酸中心和配体的假芳环之间的氢键）在573 K下通过抽真空被还原为单价物种（Cu+），并且Cu 2+的还原性上级在水溶液中通过常规离子交换制备的样品中的还原性。对于通过使用CuCl制备的样品，通过在高于573 K的温度下处理并释放HCl，以CuCl沉积的Cu+与HZSM-5样品中的布朗斯台德酸位点上的H+交换。通过CVD方法制备的CuZSM-5样品由于吸附的CO物质而在2159 cm-1处给出单一IR带，而通过在573 K蒸发CuCl制备的样品以及在水溶液中离子交换的样品在2155 cm-1附近给出宽带（由2159和2151 cm−1处的两个谱带组成），表明在这些CuZSM-5样品中存在至少两种主要类型的可交换位点。每个样品揭示了NO分解反应性和N2吸附的不同特征，并且这种行为由铜离子所占据的各个位点的比率的差异来解释。结果表明，CuZSM-5的NO分解催化活性与同时存在的两种位置密切相关，而2151 cm−1谱带的位置是N2吸附的有效位置。
Ion-exchange of ZSM-5-type zeolites with copper ion was carried out by three different methods to obtain information on the states and roles of the effective sites for NO decomposition and N2 adsorption activity of copper-ion-exchanged ZSM-5-type zeolites (CuZSM-5). The first method of preparation is chemical vapour deposition (CVD) using bis(1,1,1,5,5,5-hexafluoroacetylacetonato)copper(II), [Cu(hfac)2], as a volatile complex, and the second one is to utilize CuCl as a vaporizing source. These were compared with the third method, that is, the ordinary ion exchange method using an aqueous solution of CuCl2. It is apparent that in the first method the Cu2+ species deposited on ZSM-5 as [Cu(hfac)2] (i.e., via the hydrogen bonding between a Bronsted acid site and a pseudo-aromatic ring of ligands) is reduced to the monovalent species (Cu+) by evacuation at 573 K, and also that the reducibility of Cu2+ is superior to that in the sample prepared by the conventional ion-exchange in an aqueous solution. As for the sample prepared by using CuCl, Cu+ deposited as CuCl was exchanged with H+ on a Bronsted acid site in the HZSM-5 sample through treatment at temperatures above 573 K with a release of HCl. The CuZSM-5 sample prepared by the CVD method gave a single IR band at 2159 cm−1 due to the adsorbed CO species, while the sample prepared by evaporation of CuCl at 573 K and also the sample ion-exchanged in an aqueous solution gave a broad band at around 2155 cm−1 (composed of two bands at 2159 and 2151 cm−1) for the adsorbed CO species, indicating the existence of at least two dominant types of exchangeable sites in these CuZSM-5 samples. Each sample reveals different features for NO decomposition reactivity and N2 adsorption, and such behaviours are explained by the difference in ratio of the respective sites occupied by copper ions. As a result, it was clearly demonstrated that the simultaneous existence of two types of sites lying close together has important implications for the catalytic activity for NO decomposition by CuZSM-5, and that the site giving the 2151 cm−1 band is the effective site for N2 adsorption.