Abstract
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−).
Highlights
Nowadays, humanity is facing various environmental problems, such as water pollution and air pollution, and a great number of researchers have reported different ways to treat contaminants [1,2,3,4].Among them, the problem of air pollution is prominent
The results revealed that some soot particles could react with adsorbed oxygen, and other part of diesel soot could react with lattice oxygen
Ce0.75 Zr0.25 O2 ) prepared by sol–gel method make it possible to use these catalysts in diesel emission prepared method makesystem, it possible to use these catalysts in diesel emission control
Summary
Humanity is facing various environmental problems, such as water pollution and air pollution, and a great number of researchers have reported different ways to treat contaminants [1,2,3,4]. A large number of catalysts has been investigated for controlling the exhaust emissions of diesel engines, and the main objective of most of these studies is to improve the catalytic performance for soot combustion. The Ce4+ /Ce3+ redox cycle confers the ability to absorb gaseous O2 , forming active oxygen at the catalyst surface (Oads ), which can be transferred to the soot catalyst interface by superficial diffusion For this reason, properties of the Ce4+ /Ce3+ couple and the capacity of CeO2 to exchange oxygen with the gas phase make CeO2 -based materials one of the most promising catalysts for soot combustion [13,14]. A reaction pathway was proposed for comprehensive understanding of the catalytic oxidation of diesel soot using the as-fabricated catalysts
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