Gas phase sulfation of ceria-zirconia solid solutions for generating highly efficient and SO2 resistant NH3-SCR catalysts for NO removal

Abstract

A series of ceria-zirconia solid solutions (CexZr1-xO2) were prepared by co-precipitation method and then sulfated with SO2 + O2 at 200 °C. Subsequent testing with the selective catalytic reduction of NO by NH3 (NH3-SCR) showed that the activity of the sulfated CexZr1-xO2 catalysts oxide catalysts exhibited a volcano-type tendency with increasing Zr content. Furthermore, the sulfated Ce0.6Zr0.4O2 catalyst showed the most desirable NH3-SCR activity at 250-300 °C, and exhibited much better SO2 resistance at 250 °C. Detailed characterization results demonstrated that Ce0.6Zr0.4O2 could adsorb more surface sulfate species and then produce more stable acid sites than pure CeO2 at 200 °C. After sulfation treatment, more Ce3+ and oxygen vacancies were formed on the surface of Ce0.6Zr0.4O2. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments suggested that the nitrates species deposited on the surface of as-prepared Ce0.6Zr0.4O2, which showed no reactivity, could barely deposit on the same sample after sulfation. While, the sulfated Ce0.6Zr0.4O2 had more reactive acid sites to participate in the NH3-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 NH3-SCR catalyst with great application prospect.