Post-synthesis incorporation of Al into germanosilicate ITH zeolites: the influence of treatment conditions on the acidic properties and catalytic behavior in tetrahydropyranylation
Post-synthesis incorporation of Al into germanosilicate ITH zeolites: the influence of treatment conditions on the acidic properties and catalytic behavior in tetrahydropyranylation
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DOI：
10.1039/c4cy01594k
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发表时间：
2015-04
影响因子：
5
通讯作者：
M. Shamzhy;M. Opanasenko;F. Ramos;L. Brabec;M. Horáček;Marta Navarro-Rojas;R. Morris;H. O. Pastore;J. Čejka
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文献类型：
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作者：
M. Shamzhy;M. Opanasenko;F. Ramos;L. Brabec;M. Horáček;Marta Navarro-Rojas;R. Morris;H. O. Pastore;J. Čejka
锗硅酸盐中孔ITH沸石的合成后铝化被证明是调节其酸性的有效程序。用Al（NO3）3水溶液处理不同化学组成（Si/Ge = 2.5，4.4和5.8）的ITH沸石，导致富Ge（Si/Ge = 2.5，4.4）的ITH样品中形成强的Bronsted和刘易斯酸中心，并增加了超微孔和介孔的比例。掺入骨架中的Al浓度随着母体ITH的Si/Ge比的降低而增加。铝化温度从80 ° C增加到175 °C（HT条件）导致（1）形成的布朗斯台德酸位点的浓度增加1.5-2倍，和（2）用碱探针分子（即吡啶、2，6-二叔丁基吡啶）可检测的骨架Al原子的分数降低，即“内部”酸位点的浓度增加。制备的Al取代的ITH沸石在醇的四氢吡喃化中的活性随着大体积晶体中可接近的酸位点的量的增加（例如在较低温度下的铝化）或随着微小ITH晶体内酸中心的总浓度的增加（例如在HT条件下的铝化）而增强。随着所研究的底物分子的动力学直径的增加，这种趋势变得更加突出（甲醇< 1-丙醇< 1-己醇）。
Post-synthesis alumination of germanosilicate medium-pore ITH zeolites was shown to be an effective procedure for tuning their acidity. Treatment of ITH zeolites synthesized with different chemical compositions (i.e. Si/Ge = 2.5, 4.4 and 5.8) with aqueous Al(NO3)3 solution led to the formation of strong Bronsted and Lewis acid sites and an increasing fraction of ultramicro- and meso-pores in Ge-rich ITH samples (Si/Ge = 2.5 and 4.4). The concentration of Al incorporated into the framework increases with decreasing Si/Ge ratio of the parent ITH. The increasing temperature of alumination from 80 to 175 °C (HT conditions) resulted in (1) a 1.5–2-fold increase in the concentration of Bronsted acid sites formed and (2) a decreasing fraction of framework Al atoms detectable with base probe molecules (i.e. pyridine, 2,6-di-tert-butylpyridine), i.e. an increased concentration of the “inner” acid sites. The activity of prepared Al-substituted ITH zeolites in tetrahydropyranylation of alcohols is enhanced with increasing amount of accessible acid sites in bulky crystals (e.g. alumination at lower temperature) or with increasing total concentration of acid centres within tiny ITH crystals (e.g. alumination under HT conditions). This trend became more prominent with increasing kinetic diameter of the substrate molecules under investigation (methanol < 1-propanol < 1-hexanol).