Synthesis of well-ordered SO₄^2-/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.