超稳含硅介孔Al2O3及其催化裂化应用

利用水解正硅酸四乙酯对薄水铝石进行后修饰，通过焙烧可以得到含硅Al₂O₃。采用X射线衍射、红外、物理吸附、固体核磁共振、NH₃程序升温脱附等手段表征含硅Al₂O₃的孔道结构和酸性质。考察了含硅Al₂O₃的热稳定性和水热稳定性及其对烃类的催化裂化活性。结果表明，SiO₂主要以单层形式嫁接在γ-Al₂O₃表面Al-OH上，形成了Si-O-Al键，并大幅提高其对烃类的裂化活性。当1 nm2的γ-Al₂O₃表面含32个Si原子时，其对异丙基苯的催化裂化转化率为原料γ-Al₂O₃的27倍。在1100℃高温空气下焙烧，或在800℃高温水蒸气气氛下焙烧，含硅Al₂O₃的晶体结构和催化活性都能较好地保留。

Preparation and Characterization of Ultrastable Mesoporous Silicated Alumina and Its Application in Catalytic Cracking

The silicated alumina was synthesized by grafting of hydrolytic silicon specials on the surface of AlOOH, and a calcination step. The textural and acidity properties of the resultant materials were characterized by various techniques, i.e. powder X-ray diffraction (XRD), infrared(IR) spectroscopy, N₂ adsorption/desorption, nuclear magnetic resonance(NMR) spectroscopy, and temperature programmed desorption of ammonia(NH₃-TPD). The results show that the monolayer SiO₂ majorly grafts on the alumina surface, where the specific surface reactivity of  γ-Al₂O₃ to realize a new class of silicated alumina catalysts featuring is well defined. Because of the enhanced Lewis acid sites and new formed Si-O-Al species, the silicated alumina shows high activity in the cracking of hydrocarbon. Such as, the cumene (IPB) cracking conversion for silicated alumina sample with 32 Si atoms per square nanometer is 27 times as high as that of starting alumina. The crystal structure and cracking activities of silicated alumina are well preserved after calcination at 800℃  for 4 h in steam or at 1100℃ for 6 h in air.