Combined removal of diesel soot particulates and NO over CeO2–ZrO2 mixed oxides

Abstract

CeO 2 and Ce-Zr mixed oxides with different Ce:Zr ratio have been prepared, characterised by Raman spectroscopy, XRD, TEM, N 2 adsorption at -196ºC and H 2 -TPR, and tested for soot oxidation under NO x /O 2 . Among the different mixed oxides, Ce 0.76 Zr 0.24 O 2 provided the best results. Ce 0.76 Zr 0.24 O 2 presents a higher activity than pure CeO 2 for soot oxidation by NO x /O 2 when both catalysts are calcined at 500ºC (soot oxidation rates at 500ºC are 14.9 and 11.4 g soot /s, respectively), and the catalytic activity of CeO 2 decays significantly with calcination temperature (from 500 to 1000ºC) while Ceria is an important material in the framework of the three-way catalysts (TWCs) which are used in gasoline automobile catalytic converters for the treatment of exhaust gases [1,2]. One of the key functions of this material is the ability of cerium to switch between the Ce 4+ and Ce 3+ oxidation states and to incorporate more or less oxygen into their crystal structure depending on various parameters such as the gaseous atmosphere with which they are in contact, temperature and pressure [3]. Therefore, early on, ceria was given a main role as oxygen storage component in order to extend the three-way window on the lean side of stoichiometry by acting as a sink for gas-phase oxygen during rich-to- It has been established that addition of zirconium to ceria to form a mixed oxide solution greatly enhances the reducibility of Ce 4+ in the catalyst material, which has generated considerable interest in the Ce-Zr system [5][6][7][8]. The energetics of the Ce 4+ /Ce 3+ reduction step and the corresponding formation of oxygen vacancies are likely to be involved [9]. Indeed, it is clear that fundamental solid state properties such as the precise role of structural defects and dopants, the nature of redox reactions to create electronic species (both within the bulk and at the surfaces), as well as the mechanism of oxygen migration, are crucial to the greater understanding of these important materials. supplies the oxygen necessary for the redox mechanism that takes place during the reaction.The scope of this paper is to study the catalytic performance of Ce-Zr mixed oxides for the removal of soot under simulated Diesel exhaust conditions in a gas flow containing O 2 and NOx. Special attention is paid to the simultaneous removal of NOx. The catalytic activity of the Ce-Zr mixed oxides is compared with that of pure CeO 2 and the thermal stability of the pure and mixed oxides is studied in detail since the thermal stability is a key requirement for the application of these materials in a real soot trap. 2.-Experimental Catalyst preparationCe-Zr mixed oxides with different metal ratio were prepared by using a coprecipitation route. The required amounts of ZrO(NO 3 ) 2 ·6H 2 O and/or Ce(NO 3 ) 3 ·6H 2 O (supplied by Aldrich) were dissolved in water and the hydroxides were precipitated by dropping an ammonia solution to keep the pH about 9. The precipitates were dried at 90ºCin air overnight and calcined in air ...

NO Adsorption and Oxidation on Mn Doped CeO2 (111) Surfaces: A DFT+U Study

“…NO oxidation plays an increasingly significant role in NO x removal technologies (Bray and Schneider, 2015;Xie et al, 2017), including NO x storage and reduction (Lin et al, 2013;Zhang et al, 2016), selective catalytic reduction (Zahaf et al, 2015;Guo et al, 2017), dry sorbent injection (Rezaei et al, 2015) and absorption in wet flue gas desulfurization (Liu et al, 2014;Guo et al, 2015b). Cerium oxide has been widely utilized in catalysts pleased in these mobile source and stationary source applications, due to its outstanding oxygen storage capacity (OSC) (Atribak et al, 2008;Zhang et al, 2011;Hong et al, 2016).…”

Simultaneous Control of NOx-Soot by Substitutions of Ag and K on Perovskite (LaMnO3) Catalyst

“…The NOx formation by the internal combustion due the high ignition temperature is well understood but the formation soot is more complicated and difficult to examine [4,5]. It is a big challenge to control these two pollutants with the fulfillment of exhausts emission regulation without affecting the fuel economy of diesel engines [6,7].…”

Opportunities for ceria-based mixed oxides versus commercial platinum-based catalysts in the soot combustion reaction. Mechanistic implications

“…However, the NO to NO 2 oxidation capacity does not match linearly to the soot combustion rate, because there are some other factors that influence this reaction, such as lattice oxygen mobility and production and transfer of "active oxygen", as reported in the literature for ceria-based catalysts [22,35]. In a recent preliminary study [36], the rate of soot combustion under isothermal conditions at 400°C shown by a copper-doped ceria-zirconia catalyst was very high, and only a little bit lower than that of a commercial Pt-catalyst in terms of mass of catalyst, but higher if the activity was expressed in terms of price of catalyst.…”