Different solid superacid sulfated zirconium dioxide (SO₄²⁻/ZrO₂) samples were successfully prepared by conventional and ultrasonic-assisted chemical precipitation process, and then, they were characterized by X-ray diffraction, Fourier transform infrared, thermal gravimetric analyzer (TGA), nitrogen adsorption–desorption, ammonia temperature programmed desorption (NH₃-TPD) and pyridine adsorbs Fourier transform infrared. The results of characterizations indicate that the sulfonic acid group is successfully introduced, and the acidity and surface area of sulfated sample can be increased by using ultrasonic method. Furthermore, this ultrasonic-assisted catalyst was used for the chlorobenzene nitration using nitrogen dioxide (NO₂) as nitrating agent. The catalyst shows excellent catalytic activity and reusability for the nitration of chlorobenzene giving high para-selectivity. In the optimal reaction conditions, the conversion of chlorobenzene can reach 85.2% with 88.5% selectivity to para-nitrochlorobenzene (p-NCB). Furthermore, the reaction mechanism was proposed by combination of experimental results and theoretical calculations. The present work provides an easy-to-implement, mild and environmentally friendly approach for the efficient preparation of valuable p-NCB, which has extensive industrial application prospects.

Graphical abstract