Abstract
A novel active Ca-Co dually-doping pyrochlore oxide La2−xCaxSn2−yCoyO7 catalyst was synthesized by the sol-gel method for catalytic oxidation of soot particulates. The microstructure, atomic valence, reduction, and adsorption performance were investigated by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), H2-TPR (temperature-programmed reduction), and in situ diffuse reflection infrared Fourier transformed (DRIFTS) techniques. Temperature programmed oxidation (TPO) tests were performed with the mixture of soot-catalyst under tight contact conditions to evaluate the catalytic activity for soot combustion. Synergetic effect between Ca and Co improved the structure and redox properties of the solids, increased the surface oxygen vacancies, and provided a suitable electropositivity for oxide, directly resulting in the decreased ignition temperature for catalyzed soot oxidation as low as 317 °C. The presence of NO in O2 further promoted soot oxidation over the catalysts with the ignition temperature decreased to about 300 °C. The DRIFTS results reveal that decomposition of less stable surface nitrites may account for NO2 formation in the ignition period of soot combustion, which thus participate in the auxiliary combustion process.
Highlights
The diesel engine has been widely used in the transport vehicle market for decades due to its inherent high thermal efficiency, low fuel consumption, and durability
This well demonstrates that A-site substitution may lead to the formation of tiny separated phases, whereas B-site doping allows the doping ions to be highly dispersed into the crystal lattice, as reported previously [14]
18.17 a 222 crystal face; b Lattice constant calculated from X-ray powder diffraction (XRD) characteristic peaks of samples; Average crystallite size calculated from the 222 crystal face by XRD; d Brunauer–Emmett–Teller (BET) specific surface area; e Total pore volume; f Average pore diameter
Summary
The diesel engine has been widely used in the transport vehicle market for decades due to its inherent high thermal efficiency, low fuel consumption, and durability. A variety of catalysts have been widely investigated and applied to soot removal, including noble metal [4,6], alkaline metal oxides [6,7], transition metal oxides [8,9], as well as mixed metal oxide [10] materials. Luca Lietti et al proposed the theory of electrodeposition of alkali and alkaline earth metals to the soot oxidation, which inspired us to study the substitution of Ca to the A site of pyrochlore in this study [7]. The in situ DRIFT technique was employed with individual catalysts in the presence of NO + O2 , to explore the intermediate species that produced by the NO2 auxiliary combustion process
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