DRIFT study of CuO-CeO₂-TiO₂ mixed oxides for NOx reduction with NH₃ at low temperatures.

A CuO-CeO2-TiO2 catalyst for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperatures was prepared by a sol-gel method and characterized by X-ray diffraction, Brunner-Emmett-Teller surface area, ultraviolet-visible spectroscopy, H2 temperature-programmed reduction, scanning electron microscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). The CuO-CeO2-TiO2 ternary oxide catalyst shows excellent NH3-SCR activity in a low-temperature range of 150-250 °C. Lewis acid sites generated from Cu(2+) are the main active sites for ammonia activation at low temperature, which is crucial for low temperature NH3-SCR activity. The introduction of ceria results in increased reducibility of CuO species and strong interactions between CuO particles with the matrix. The interactions between copper, cerium and titanium oxides lead to high dispersion of metal oxides with increased active oxygen and enhanced catalyst acidity. Homogeneously mixed metal oxides facilitate the "fast SCR" reaction among Cu(2+)-NO, nitrate (coordinated on cerium sites) and ammonia (on titanium sites) on the CuO-CeO2-TiO2 catalyst at low temperatures.