铝改性介孔二氧化硅泡沫载体材料合成及其DBT加氢脱硫性能

介孔二氧化硅泡沫(MCFs)材料具有超大的三维球形孔结构、超大孔容(1.0–2.4 cm3/g)、高比表面(1000 m2/g)、孔径可调范围较广(24–50 nm)且球形孔道之间通过窗口(9–22 nm)联结,因此具有优良的传质性能,能够促进加氢脱硫反应.但是,与传统的微孔分子筛相比,该纯硅类介孔材料酸性较弱,不利于一些酸催化反应;因此,对纯硅材料进行金属改性以增加其酸性,从而促进催化剂的催化活性.而一般对纯硅类介孔材料采用Al,Ti,Zr等金属,铝改性主要是为纯硅载体提供酸性,而钛锆改性则是为了调变活性金属以及促进金属的分散,从而提高催化剂的加氢脱硫活性.因此,我们主要采用后改性方法,以P123为微乳液体系中的表面活性剂,TEOS为硅源,TMB为扩孔剂,异丙醇铝为铝源,成功合成了一系列Si/Al比不同的介孔二氧化硅泡沫材料.通过改变异丙醇铝的加入量,成功合成了系列Si/Al比(x)的NiMo/Al-MCFs(x)(x=10,20,30,40和50)催化剂.对所合成的载体及相应的催化剂通过SAXS,N2吸附脱附,SEM,Py-FTIR,UV-Vis,H2-TPR,NH3-TPD,HRTEM,Raman及27Al MAS NMR等表征手段进行分析,并在高压加氢微反装置上对相应的NiMo负载型催化剂进行DBT HDS活性评价,系统分析了不同硅铝比对催化剂DBT HDS反应活性的影响.SAXS和SEM表征结果表明,Al后改性并没有破坏载体材料的结构;27Al MAS NMR表征结果表明,后改性法能成功把Al掺杂进纯硅材料的骨架中.催化剂UV-Vis和Raman表征结果表明,当Si/Al比为20时,NiMo/Al-MCFs(20)催化剂Mo物种的带隙能量最大,且氧化钼的平均粒径较小,Mo物种在该催化剂中的分散度较好;H2-TPR分析结果表明,NiMo/Al-MCFs(20)催化剂还原温度较低,最易还原.Py-FTIR结果表明,随着Al加入量的增大,其酸性逐渐增大,当Si/Al比为20时酸性达到最大,继续增加Al的加入量,其酸性不再增加;此外,NiMo/Al-MCFs(20)的硫化度最高,且其MoS2的堆垛层数较低.负载活性金属后制备了NiMo/Al-MCFs(x)催化剂,将其应用于DBT加氢脱硫反应,并与传统NiMo/γ-Al2O3催化剂加氢脱硫反应活性作对比.研究发现,所制备的NiMo/Al-MCFs(x)系列催化剂由于具有较大孔径、比表面积及孔容和较强的酸性,因而其DBT HDS活性明显高于传统的工业NiMo/γ-Al2O3催化剂,且催化剂活性在硅铝比达到20时最大,最高可达96%,因此它作为加氢脱硫催化剂载体具有很大的应用前景.

Al-modified mesocellular silica foam as a superior catalyst support for dibenzothiophene hydrodesulfurization

A series of Al-containing mesostructured cellular silica foams (Al-MCFs) with different Si/Al molar ratios (x; x = 10, 20, 30, 40, or 50) were prepared by a post synthetic method using aluminum iso-propoxide as an alumina source. The corresponding NiMo catalysts supported on Al-MCFs were prepared and evaluated using dibenzothiophene (DBT) as the probe reactant. All the synthesized samples were characterized by small-angle X-ray scattering, scanning electron microscopy, nitrogen adsorption-desorption, UV-Vis diffuse reflectance spectroscopy, H2 temperature-programmed re-duction, 27Al MAS NMR, temperature-programmed desorption of ammonia, pyridine-FTIR, Raman spectroscopy, HRTEM, and X-ray photoelectron spectroscopy to analyze their physicochemical properties and to gain a deeper insight of the interrelationship between the structures and the cat-alytic performance. The synthesis mechanism was proposed to involve the formation of Br?nsted acid and Lewis acid sites through the replacement of Si4+ with Al3+. Aluminum introduced into MCFs by the post synthetic method has a negligible influence on the mesostructure of the parent MCFs but can form silicoaluminate materials with moderate Br?nsted acidity. For Al-MCFs(x) materials, the detection of tetrahedrally coordinated Al3+ cations demonstrated that the Al species had been suc-cessfully incorporated into the silicon frameworks. Furthermore, the DBT hydrodesulfurization (HDS) catalytic activity of the NiMo/Al-MCFs(x) catalysts increased with increasing Si/Al molar ratio, and reached a maximum at a Si/Al molar ratio of 20. The interaction of Ni and Mo species with the support became stronger when Al was incorporated into the MCFs supports. The high activities of the NiMo/Al-MCFs catalysts for the DBT HDS were attributed to the suitable acidity properties and good dispersions of the Ni and Mo active phases.