Preparation, characterization of superacid SO₄ ²⁻/ZrO₂-SiO₂ and its activity on catalytic synthesis of methyl p-nitrobenzoate

Abstract

Solid superacid SO₄ ²⁻/ZrO₂-SiO₂ was prepared by dip-impregnation method, and its catalytic activity was tested with esterification of p-nitrobenzoic acid and methanol. The optimum conditions were also found, that is, the molar ratio between silica and zirconia was 10:1, the calcination temperature was 550 °C and the soaked consistency of H₂SO₄ was 1.0 mol·L⁻¹. Under the conditions that the ratio of methanol to acid(mL/g) was 12:1, the amount of catalyst was 0.5 g, the reaction time was 5 h and the stirring speed was 800 r·min⁻¹, the yield of methyl p-nitrobenzoate could reach up to 90.5%. Then the characterizations of cataslyst, including the acidity and types of acidic centers, specific surface area and surface structure was respectively examined by Hammett indicator, in-situ pyridine IR, BET method, FT-IR(KBr), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results showed that the catalyst SO₄ ²⁻/ZrO₂-SiO₂ was superacid with high specific surface area due to H _o<-12.70. It contained acidic sites of Lewis and Brψnsted, and its surface structure changed after esterification. The zirconia crystal was mainly tetragonal and silica crystal was not found.

Keywords

solid superacid / methyl p-nitrobenzoate / in-situ pyridine IR / X-ray diffraction

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