Preparation, characterization of superacid SO sub(4) super(2-)/ZrO sub(2)-Si O sub(2) and its activity on catalytic synthesis of methyl p-nitrobenzoate

Solid superacid SO sub(4) super(2-)/ZrO sub(2)-Si O sub(2) 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 degree C and the soaked consistency of H sub(2)SO sub(4) was 1.0 mol.L super(-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 super(-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 SO sub(4) super(2-)/ZrO sub(2)-Si O sub(2) was superacid with high specific surface area due to H sub(o)