Gil Barbara, Makowski Wacław, Marszalek Bartosz, Roth Wieslaw J, Kubu Martin, Čejka Jiři, Olejniczak Zbigniew
Faculty of Chemistry, Jagiellonian University in Kraków, Poland.
Dalton Trans. 2014 Jul 21;43(27):10501-11. doi: 10.1039/c4dt00130c. Epub 2014 Mar 21.
The unilamellar form of zeolite MWW, MCM-56, which is obtained by direct hydrothermal synthesis has been studied with regard to acidity and porosity in its original and post-synthesis modified pillared and delaminated forms. The acidity measured by FTIR was found to be only slightly lower than the highly active 3-D MWW forms, MCM-22 and MCM-49. Pivalonitrile adsorption, which is a measure of spatial openness, showed 50% accessibility vs. <30% for MCM-22/49. It highlights the potential of MCM-56 as a layered material with increased access to acid sites because it does not entail laborious post-synthesis modification. Swelling, pillaring and delamination of MCM-56 are facile but result in a reduction in the number of Brønsted acid sites (BAS) while increasing accessibility to pivalonitrile. The delamination procedure involving sonication and acidification of the highly basic mother liquor produces the most visible increase in surface area and access to all BAS. The accompanying doubling of the solid yield and the decrease in absolute number of BAS suggest significant precipitation of dissolved silica generated during swelling and sonication in high pH medium. The viability of separating surfactant covered layers upon sonication with the consequence of exposing hydrophobic hydrocarbon tails to aqueous environment is addressed.
通过直接水热合成获得的MWW型沸石MCM - 56的单层形式，已针对其原始形式以及合成后改性的柱撑和脱层形式的酸度和孔隙率进行了研究。通过傅里叶变换红外光谱（FTIR）测量的酸度仅略低于高活性的三维MWW型沸石MCM - 22和MCM - 49。新戊腈吸附是空间开放性的一种度量，结果显示MCM - 56的可达性为50%，而MCM - 22/49的可达性小于30%。这突出了MCM - 56作为一种层状材料的潜力，因为它无需繁琐的合成后改性就能增加对酸性位点的可达性。MCM - 56的溶胀、柱撑和脱层操作简便，但会导致布朗斯台德酸位点（BAS）数量减少，同时增加对新戊腈的可达性。涉及对高碱性母液进行超声处理和酸化的脱层程序能使表面积和对所有BAS的可达性有最显著的增加。伴随而来的固体产率翻倍以及BAS绝对数量的减少表明，在高pH介质中溶胀和超声处理过程中产生的溶解二氧化硅有大量沉淀。文中还讨论了超声处理时分离表面活性剂覆盖层从而使疏水烃尾暴露于水环境的可行性。
