Reaction-probe infrared investigation on drastic change in reactivity of mesoporous silica for acetalization of cyclohexanone with methanol; pore-size dependence
Reaction-probe infrared investigation on drastic change in reactivity of mesoporous silica for acetalization of cyclohexanone with methanol; pore-size dependence
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DOI：
10.1016/j.micromeso.2018.11.027
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发表时间：
2019-04
影响因子：
5.2
通讯作者：
Ryota Osuga;Y. Hiyoshi;T. Yokoi;J. Kondo
中科院分区：
文献类型：
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作者：
Ryota Osuga;Y. Hiyoshi;T. Yokoi;J. Kondo
对于环己酮与甲醇的缩醛化反应，小孔（<2.5 nm）介孔氧化硅的催化活性明显高于大孔（≥2.5 nm）介孔氧化硅。采用反应探针红外光谱法研究了介孔氧化硅（MCM-41和SBA-15）的孔径效应对反应活性的影响。用CO、吡啶和乙腈吸附的常规红外表征方法没有观察到明显的差异。反应物之一甲醇在小孔径（MCM-41）和大孔径（SBA-15）样品上的红外光谱基本一致。另一方面，环己酮的吸附导致不同的IR光谱：除了在SBA-15上观察到的，在少量吸附的MCM-41上在低频侧出现C双键O伸缩带。这一结果表明，环己酮与MCM-41的相互作用比与SBA-15的相互作用更强。通过原位红外观察反应的时间过程，证实了活性羰基的消耗和反应产物1，1-二甲氧基环己烷的生成。活化的环己酮的存在最可能是由于吸附在附近的两个（或多个）OH基团上，而非活化的物种占据单个OH基团。因此，反应探针红外光谱法是一种直接有效的方法来提取催化作用的微小差异。
Small-pored (<2.5 nm) mesoporous silica showed remarkably higher catalytic activity for cyclohexanone acetalization with methanol than large-pored ones (≥2.5 nm). For the clarification of the pore-size effect of mesoporous silicas (MCM-41 and SBA-15) on the reactivity, the reaction probe infrared (IR) method was applied. No evident differences were observed by conventional IR characterization methods using CO, pyridine and acetonitrile adsorption. IR spectra of methanol, one of the reactants, on small-pored (MCM-41) and large-pored (SBA-15) samples appeared the same. On the other hand, adsorption of cyclohexanone resulted in different IR spectra: a Cdouble bondO stretching band appeared at lower frequency side on MCM-41 at a small amount of adsorption in addition to that observed on SBA-15. This result indicates the presence of the stronger interaction of cyclohexanone with MCM-41 than that with SBA-15. When the time course of the reaction was observed byin-situIR observation, the consumption of activated carbonyl groups and the generation of 1,1-dimethoxycyclohexane, the reaction product, were confirmed. The presence of the activated cyclohexanone was most probably due to the adsorption on two (or more) OH groups in vicinity, while a non-activated species occupied a single OH group. The reaction probe IR method is thus, a direct and effective approach to extract the small differences in catalysis.