Adsorption of CO on NaZSM-5 zeolite under moderate temperature and pressure conditions: An FTIR investigation
Adsorption of CO on NaZSM-5 zeolite under moderate temperature and pressure conditions: An FTIR investigation
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DOI：
10.1039/a807155a
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发表时间：
1999
影响因子：
3.3
通讯作者：
B. Shete;V. S. Kamble;N. Gupta;V. Kartha
中科院分区：
文献类型：
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作者：
B. Shete;V. S. Kamble;N. Gupta;V. Kartha
在温度300-470 K和压力5-500 Torr范围内，用FTIR光谱研究了CO在NaZSM-5沸石上的吸附。评价了用质子或钙交换NaZSM-5中的电荷平衡阳离子的效果。还收集了NaY、CaY和CaX沸石的数据用于比较。我们检测到六个不同的C-O伸缩带的发展，在2111，2130，2146，2160，2176和2194 cm-1附近的最大值在室温下在NaZSM-5沸石吸附CO。这伴随着在CO2的ν3区出现了2356 cm-1的显著带和2336、2340、2370和2380 cm-1附近的弱肩带。所有的ν（CO）带和CO2的ν3区的带都表现出类似的行为，作为吸附质压力、抽空、样品温度升高和电荷平衡阳离子交换的函数。例如，所有的C-O伸缩带的强度显示出类似的增长行为与增加吸附质压力，虽然这种增长的程度是不同的个别IR带。同样，这些带在撤离时同时被移除。此外，在ν（CO）区的所有振动带都表现出一致的同位素位移，对应的频率比ν（13 C/12 C）约为1.5。13 C ~（16）O和12 C ~（18）O的吸附量分别为0.977和0.976; 13 C ~（16）O和12 C ~（18）O的吸附量分别为0.977和0.976;在本研究的条件下，CO吸附后未观察到ν（OH）带的位移。结果因此表明，单独的沸石表面位点，Al 3+位点、布朗斯台德酸位点或电荷平衡阳离子在室温或更高温度下可能不直接参与CO分子的键合。相反，沸石的笼效应起着重要作用。的数据被解释为建议形成弱键合的CO和CO2分子簇，闭塞在沸石笼和稳定的阳离子场下。
Adsorption of CO on NaZSM-5 zeolite was investigated at temperatures in the range 300–470 K and at pressures of 5–500 Torr using FTIR spectroscopy. The effect of exchanging the charge balancing cation in NaZSM-5 with a proton or calcium was evaluated. Data were also collected on NaY, CaY and CaX zeolites for comparison. We detected the development of six distinct C–O stretching bands with maxima at around 2111, 2130, 2146, 2160, 2176 and 2194 cm-1 during the adsorption of CO on NaZSM-5 zeolite at ambient temperatures. This was accompanied by the appearance of a prominent band at 2356 cm-1 and weak shoulder bands at frequencies around 2336, 2340, 2370 and 2380 cm-1 in the ν3 region of CO2. All the ν(CO) bands and also the bands in the ν3 region of CO2 exhibited similar behaviour as a function of adsorbate pressure, evacuation, rise in sample temperature, and the exchange of charge balancing cation. For instance, the intensity of all the C–O stretching bands showed a similar growth behaviour with increasing adsorbate pressure, though the extent of this growth was different for the individual IR bands. Similarly, these bands were removed simultaneously on evacuation. Furthermore, while all the vibrational bands in the ν(CO) region showed a uniform isotopic shift corresponding to a frequency ratio ν(13C/12C) of ca. 0.977 and ν(18O/16O) of 0.976 for the adsorption of 13C16O and 12C18O, respectively, the bands in the ν3(CO2) region showed a red shift ν(13C/12C) of 0.972 with 13CO and an isotopic shift corresponding to 16O12C18O on 12C18O adsorption. No shift in ν(OH) bands was observed after CO adsorption under the conditions of this study. The results thus indicate that the individual zeolitic surface sites e.g., the Al3+ sites, Bronsted acid sites or the charge balancing cations, may not participate directly in the bonding of CO molecules at room temperature or above. Instead, the cage effect of zeolites plays an important role. The data are interpreted to suggest the formation of weakly bonded clusters of CO and CO2 molecules, occluded in the zeolitic cages and stabilized under the cationic field.