双酸体系下有序介孔SO42-/ZrO2-SiO2材料的合成

采用一锅合成法通过调变自组装过程中硫酸和盐酸的体积比,成功制备了系列介孔SO₄^2-/ZrO₂-SiO₂固体酸材料(Zr/Si物质的量为1.1).XRD、UV-Vis DRS、HR-TEM等表征结果表明,所得材料均具有高度有序的二维介孔结构及四方相氧化锆的晶体结构.氮吸附和FT-IR表征结果进一步发现,通过改变硫酸/盐酸体积比可有效调变材料比表面积、孔容、孔径及表面L酸与B酸的相对强度.与纯硅介孔分子筛SBA-15不同,此系列SO₄^2-/ZrO₂-SiO₂固体酸材料均在正戊烷的异构化反应中表现出较高的催化活性和稳定性.其原因在于,在合成过程中硫酸的加入不仅促使了酸基的形成,而且稳定了催化剂的晶体结构;盐酸的存在则保持了有序的介孔结构.由此可见,混酸合成体系有望制备出结构有序、酸性可调、催化性能优越的新型催化材料,并在众多酸催化反应中取得应用.

Synthesis of well-ordered SO42-/ZrO2-SiO2 materials in bi-acid system

A series of solid acid SO₄^2-/ZrO₂-SiO₂ catalysts with a fixed Zr/Si molar ratio of 1.1 were successfully synthesized in one-pot through changing the H₂SO₄/HCl volume ratio during the self-assembly process. X-ray diffraction (XRD), UV-visible DRS, and high resolution transmission electron microscopy (HRTEM) results demonstrate that all the resultant catalysts exhibit a highly ordered 2D hexagonal mesostructures with zirconia particles of homogenously distributed tetragonal nanocrystallites in mesoporous walls. N₂ adsorption and pyridine in-situ Fourier-transformed infrared spectra (FT-IR) further reveal that the surface area, pore volume, pore diameter and the relative strength of Lewis and Brønsted acidic sites of resultant catalysts can be controlled by tuning the H₂SO₄/HCl volume ratio during the synthesis. Different from pure mesoporous SBA-15 material, the mesoporous SO₄^2-/ZrO₂-SiO₂ materials prepared in this work exhibit high structural stability and catalytic activity in n-pentane isomerization, which is attributed not only to hydrochloric acid that facilitates the formation of mesoporous silica but also to sulfuric acid that helps to stabilize the structure of catalysts and produce acid sites. The methods proposed in this work provide an important approach to synthesize ordered solid acid catalysts with high stability and potential applications in various acidic-catalyzed reactions.