Infrared spectroscopic studies of acid properties of NaHZSM-5 zeolites
Infrared spectroscopic studies of acid properties of NaHZSM-5 zeolites
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DOI：
10.1016/0021-9517(86)90139-9
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发表时间：
1986-11
影响因子：
7.3
通讯作者：
J. Datka;E. Tużnik
中科院分区：
文献类型：
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作者：
J. Datka;E. Tużnik
用吡啶吸附的红外定量研究了不同交换度的NaHZSM-5分子筛的酸性质。已证实吡啶可用作此类研究的吸附质。用HCl和NH 4 NO3溶液交换法制备了两个系列的NaHZSM-5分子筛.在NaHZSM-5沸石中检测到两种布朗斯台德酸中心，在3609 cm− 1处振动的OH基团是强酸中心，而其他质子中心的酸性较低。这两种布朗斯台德中心和刘易斯酸中心的浓度被确定为交换度和制备方式的函数。已经发现，引入沸石的第一个质子形成弱的布朗斯台德酸中心和少量的3609-cm− 1 OH基团。在交换30-40%的Na+离子后，弱酸中心的数量达到恒定值，接下来引入的质子形成3609-cm− 1的OH基团。引入质子的方式不影响位点形成的顺序或强酸和弱酸位点的比例。发现通过IR光谱测定的酸位点的量等于通过离子交换引入沸石中的质子的量，因此表明将质子引入沸石中不会“酸化”在离子交换之前预先存在于沸石中的较弱位点。NaHZSM-5分子筛中的质子酸中心对脱羟基反应有很强的抑制作用（刘易斯酸中心的量很低），这可能是由于所研究的分子筛具有较高的硅铝比所致。
Acid properties of NaHZSM-5 zeolites of various exchange degrees were studied by quantitative infrared (IR) studies of pyridine adsorption. It has been verified that pyridine may be used as adsorbate for such studies. Two series of NaHZSM-5 zeolites were prepared by exchange in HCl and NH 4 NO 3 solutions. Two kinds of Brønsted acid sites were detected in NaHZSM-5 zeolites, OH groups vibrating at 3609 cm− 1 being strong acid sites and other protonic sites of lower acidity. The concentrations of these two kinds of Brønsted site and also of Lewis acid sites were determined as a function of exchange degree and also of mode of preparation. It has been found that first protons introduced into zeolite form weak Brønsted acid sites and a small amount of 3609-cm− 1 OH groups. The amount of weak acid sites attains a constant value after the exchange of 30–40% of Na+ ions and the next-introduced protons form 3609-cm− 1 OH groups. The mode of introduction of protons do not influence either the sequence of sites formation or the proportion of strong and weak acid sites. The amounts of acid sites determined by IR spectroscopy were found to be equal to the amounts of protons introduced into zeolites by the ion exchange, thus indicating that the introduction of protons into the zeolite do not “acidify” weaker sites preexisting in the zeolite before ion exchange. The protonic acid sites in NaHZSM-5 zeolite are resistant to dehydroxylation (the amount of Lewis acid sites is low), which may be due to the high Si Al ratio of zeolites studied in the present research.