梯度压力晶化法合成高水热稳定性的MCM-41介孔材料

Preparation of Highly Hydrothermally Stable MCM-41 Mesoporous Silica Crystallized under the Gradient Pressure of Ar

提出了一种利用梯度升压方式,对MCM-41材料进行水热晶化合成高水热稳定性MCM-41介孔材料的新方法.研究表明:在100℃恒温的Ar气氛下,通过分段提升Ar压力,经常压24h、1.2 MPa 24h和1.6MPa 24h三梯度过程晶化合成的样品,在保持很好初始介观结构同时,水热稳定性大幅度提升.该焙烧样品经100℃沸水回流12h后,仍能保持很好的介观结构,仍有高达822m2/g的比表面积与0.65cm3/g的孔体积;而非压力晶化的MCM-41样品,经相同100℃沸水回流12h后,其介观结构完全崩塌,比表面积只有129m2/g.IR羟基谱和29Si NMR显示:与非压力晶化样品相比,梯度压力晶化样品的表面羟基明显减少,一部分Si(OSi)2(OH)2和Si(OSi)3OH已缩聚形成了更稳定的Si(OSi)4结构,表明对MCM-41无定型孔壁施加外部高压可促使MCM-41无定形孔壁更好交联.另还分别研究了外加Ar压力大小、晶化时间、梯度升压方式对MCM-41材料水热稳定性的影响.方法操作简单、经济、高效,可在无需添加其他改良剂、保持原有介观结构和化学性质情况下,制备出高质量、高水热稳定性的MCM-41材料.

It demonstrates a new approach to prepare hydrothermally stable MCM-41 mesoporous silica via crystallizing under the gradient pressure of Ar. The sample, which crystallized at 100℃ under the gradient pressure of 0 MPa, 1.2 MPa and 1.6 MPa for 24 h, respectively, shows high hydrothermal stability, as well as mesostructure maintains. Its surface area and pore volume can retain as high as 822 m^2/g and 0.65 cm^3/g, respectively, after treated in boiling water for 12 h. In contrast, the one crystallized without pressure exhibits sharp decrease in its surface area to 129 m^2/g after the same hydrothermal test, which indicates the loss of its ordered mesoporous structure. IR spectra and ^29Si NMR spectra reveal that the sample crystallized under the gradient pressure of Ar has less hydroxyl groups. Some Si（OSi）2 （OH）2 and Si（OSi）3OH on its surface have turned into much more stable structure of Si（OSi）4, compared with the one crystallized without pressure. The result indicates that the sample has better dehydration condensation in pore walls. In addition, the influence of Ar pressure, crystallization time and the exerted model of Ar pressure on hydrothermal stability have been studied also. This approach is of high efficiency, simple and capable to prepare highly hydrothermally stable MCM-41 materials with well ordered mesostructure without needing to add other components to avoid changing its surface property.