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

Solid superacid SO42-/Zr O2-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 ℃ and the soaked consistency of H2SO4 was 1.0 mol?L-1. Under the conditions that the ratio of methanol to acid(m L/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 SO42-/Zr O2-SiO2 was superacid with high specific surface area due to Ho-12.70. It contained acidic sites of Lewis and BrΦnsted, and its surface structure changed after esterification. The zirconia crystal was mainly tetragonal and silica crystal was not found.