Preparation of New Molecular Sieve Material by Selective Leaching Method

采用一种新的合成方法制备了介孔γ-氧化铝，即在1000 ℃左右煅烧高岭土，使γ-氧化铝颗粒分散在无定形二氧化硅基体中，并用KOH溶液选择性地浸出无定形二氧化硅，使原料的假晶颗粒中形成均匀的介孔。以格鲁吉亚高岭土为原料，经1000 ℃煅烧和4 M KOH溶液在90 ℃选择性浸出1h后，可得到孔径分布很窄的孔结构，孔径分布在几个nm左右。U.S.A.as多孔γ-氧化铝具有比迄今报道的各种γ-氧化铝更均匀的孔径和更大的孔体积的特性。因此，在室温下的γ-氧化铝的水蒸气吸附-脱附等温线显示出非常陡峭的增加吸附在周围的相对湿度（RH）的80%通过毛细管冷凝和达到最大吸附约。600毫升（STP）/克在RH为90%。另一方面，从γ-氧化铝中的中孔的冷凝水的解吸在70%的RH下突然发生。由于γ-氧化铝中的水蒸气的非常快速的吸附和脱附被理解为由于均匀的介孔的毛细冷凝和蒸发，因此认为通过本选择性浸出方法制备具有分子筛性质的介孔γ-氧化铝。

Mesoporous gamma-alumina was prepared by a new synthetic method, i.e. calcining kaolin minerals at around 1000ﾟC to form fine microtexture with dispersing very fine gamma-alumina grains in amorphous silica matrix and selectively leaching amorphous silica properly using KOH solution to evolve uniform mesopores within the pseudomorph particles of the starting materials. Pore structure with very sharp pore size distribution at several nm in size was obtained by this selective leaching method when it was synthesized using kaolinite from Georgia, U.S.A.as the starting material, calcining at 1000ﾟC and selective leaching at 90ﾟC for 1h by 4M KOH solution. The porous gamma-alumina had characteristic properties to show more uniform pore size and larger pore volume than those of various gamma-alumina reported so far. Therefore, the water vapor adsorption-desorption isotherms of the gamma-alumina at room temperature showed very steep increase of adsorption at around relative humidity (RH) of 80% by capillary condensation and reached maximum adsorption of ca.600ml (STP) /g at RH of 90%. On the other hand, desorption of condensed water from mesopores in the gamma-alumina occurred suddenly at RH of 70%. Since the very quick adsorption and desorption of water vapor in the gamma-alumina was understood due to capillary condensation and evaporation owing to the uniform mesopores, mesoporous gamma-alumina with molecular sieve properties was considered to be prepared by the present selective leaching method.