Gas phase sulfation of ceria-zirconia solid solutions for generating highly efficient and SO resistant NH-SCR catalysts for NO removal.

A series of ceria-zirconia solid solutions (CeZrO) were prepared by co-precipitation method and then sulfated with SO + O at 200 °C. Subsequent testing with the selective catalytic reduction of NO by NH (NH-SCR) showed that the activity of the sulfated CeZrO catalysts oxide catalysts exhibited a volcano-type tendency with increasing Zr content. Furthermore, the sulfated CeZrO catalyst showed the most desirable NH-SCR activity at 250-300 °C, and exhibited much better SO resistance at 250 °C. Detailed characterization results demonstrated that CeZrO could adsorb more surface sulfate species and then produce more stable acid sites than pure CeO at 200 °C. After sulfation treatment, more Ce and oxygen vacancies were formed on the surface of CeZrO. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments suggested that the nitrates species deposited on the surface of as-prepared CeZrO, which showed no reactivity, could barely deposit on the same sample after sulfation. While, the sulfated CeZrO had more reactive acid sites to participate in the NH-SCR and the reaction proceeded via Eley-Rideal mechanism. This work proved that sulfation treatment could be used in designing an efficient cerium-zirconium based NH-SCR catalyst with great application prospect.