沸石表面有机金属化学──ZSM-5外表面上—Ge(n-C_4H_9)_x基团的接枝及其性质研究

Surface Organometallic Chemistry on Zeolite Grafting Reaction of Ge(n-C_4H_9)_x Fragments over ZSM-5 outer Surface and Adsorption Properties of the Resulting Materials

用气体分析及IR ,NMR和元素分析等方法研究了真空系统中 2 30和 2 80℃下四丁基锗在ZSM 5沸石表面上的接枝反应 ,并对所得沸石的热稳定性和吸附性质进行了表征 .与作者曾报道的在硅胶及丝光沸石上的反应类似 ,四丁基锗也能与ZSM 5沸石表面上的硅羟基发生缩合反应 ,在其外表面或孔口生成组成为 (≡Si—O) xGe(n C4 H9) 4-x(x =13)的表面有机锗化合物 .在 2 30℃接枝丁基锗基团不影响沸石的结构和表面积 ,仅改变它的孔口大小 .在改性后的沸石上 ,N2 的吸附性质没有改变 ,而不同分子尺寸的烃 ,如正己烷、2 甲基戊烷、2 ,3 二甲基丁烷却呈现出完全不同于起始ZSM 5沸石的择形吸附效应 .

The reaction of tetrabutylgermanium with ZSM-5 surface at 230 and 280 ℃ was studied by means of gas volumetry, infrared spectroscopy, solid-state NMR and elemental analysis. The thermal stability and the adsorption properties of the resulting solids were also determined. A condensation occurred between tetrabutylgermanium and the surface hydroxyl groups of ZSM-5, being closly analogous to what had been observed on silica and mordenite. The products in the gas phase are C1—C4 hydrocarbons formed by cracking of the evolved butane on the highly acidic ZSM-5, and in contrast to the report on silica or mordenite, a mixture of [(≡Si—O)_xGe(n-C_4H_9)_x-4)](x=1, 2, 3) species was formed. Increasing the reaction temperature resulted in much more dealkylated species. After heating at 450 ℃, no butyl ligand remained on germanium. No modification of the solid was detected by nitrogen adsorption, showing that the zeolitic structure was retained upon grafting. The modified materials show that the adsorption properties are quite different from those of the starting ZSM-5. For example, 2,3-dimethyl butane is totally excluded from the modified zeolite while the unmodified one easily adsorbs it.n-Hexane and 2-methyl pentane are also discriminated by this zeolite but, in this case, it is due to a decrease of the sorption rate at the pore entrance due to steric hindrances caused by the grafted fragments.