Promotional effects of Zr on K + -poisoning resistance of CeTiO x catalyst for selective catalytic reductionof NO x with NH 3

Insights into the co-doping effect of Fe3+ and Zr4+ on the anti-K performance of CeTiOx catalyst for NH3-SCR reaction

A novel K-resistant Fe³⁺ and Zr⁴⁺ co-doped CeTiO_x catalyst was first prepared by co-precipitation method for the ammonia-selective catalytic reduction (NH₃-SCR) of NO_x. On the premise of retaining the outstanding catalytic activity of CeTiO_x catalyst, Fe³⁺ and Zr⁴⁺ co-doping efficiently improves its K-resistance with superior NO_x conversion up to 84% after K-poisoning. Specially, the grain growth during the second calcination after K poisoning is successfully inhibited by Fe³⁺ and Zr⁴⁺ co-doping. Consequently, the large specific surface area with increased acid sites and efficiently retained reducibility over K-poisoned FeZrCeTiO_x catalyst are realized, which prompt NH₃ activation and NO oxidation, further benefit NH₃-SCR. Besides, NH₃-SCR reaction over CeTiO_x and FeZrCeTiO_x catalysts follows a possible L-H mechanism, and K-poisoning makes no change to it. Finally, a reasonable anti-K poisoning mechanism of FeZrCeTiO_x catalyst is proposed: the excellent K-resistance is attributed to part of Fe and Zr are sacrificed to form Fe-O-K and Zr-O-K species protecting the active site Ce-O-Ti from K-poisoning, as well as the additional reducibility and surface acidity brought from Fe-O species with Zr prompting its uniform distribution.

Catalytic Combustion of Diesel Soot on Ce/Zr Series Catalysts Prepared by Sol-Gel Method

Cerium-zirconium (Ce-Zr) solid solutions have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction with lower cost compared to noble metal-based systems. A series of Ce-Zr-based catalysts was prepared by the sol-gel method. The structure and morphology of these catalysts were characterized by X-ray diffraction, thermogravimetric-differential scanning calorimetry, scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. Furthermore, investigation on catalytic performance was carried out by constructing a test platform, and the result indicated that the catalysts apparently decreased the soot ignition temperature. These catalysts exhibited higher catalytic activity for soot oxidation under narrow contact conditions. The results revealed that some soot particles could react with adsorbed oxygen, and other part of diesel soot reacted with lattice oxygen. The activity of these catalysts was attributed to synergistic effect arising from the combination of K/Co/Zr and Ce-Zr solid solution, which led to the decrease in the ignition temperature to 294 °C (data from the test platform). The catalyst still keeps good stability and catalytic activity after the cycle oxidation experiment. A reaction pathway was proposed to explain catalytic combustion process of soot, i.e., combination of K/Co/Zr with Ce-Zr solid solution reduced the binding energy of Ce-Zr solid solution, which was conducive to provide more active sites to release the active oxygen (O2−) or lattice oxygen (O2−).