Impact of Soot on NO_x Adsorption over Cu-Modified Hydrotalcite-Derived Lean NO_x Trap Catalyst

Abstract

The impact of soot on NO adsorption was studied over a Cu-modified hydrotalcite-derived lean NO trap catalyst in a NO + O atmosphere. Powder X-ray diffraction, scanning electron microscopy, Raman scattering spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the surface properties of the pure catalyst and the soot/catalyst mixture. The adsorbed NO species on the samples were evaluated by in situ diffuse reflectance Fourier transform spectroscopy. The soot coverage decreases the available adsorption sites on the surface of the catalyst, and a portion of active oxygen species are consumed by the soot oxidation during He pretreatment process. The NO adsorption on two catalyst samples simultaneously undergoes two routes: the "nitrite route" and the "nitrate route". The "nitrite route" is more dominant than the "nitrate route". During NO adsorption, the soot oxidation weakens the NO oxidation to NO, and the released CO competes with NO on the adsorption sites. Moreover, the temperature-programmed desorption tests indicate that the presence of soot reduces the NO storage capacity of the catalyst and shifts the NO desorption peak to the lower temperature range by 50 °C.

Ultralight and spongy La–Mn-based perovskite catalysts modified by alkali metals and Ce: facile synthesis and excellent catalytic performance for soot combustion

“…67 The vibration band at 1623 cm –1 corresponding to gaseous or weakly adsorbed NO 2 . 68,69 When the temperature is higher than 300 °C, the peaks of the nitrate species disappear in the IR spectra due to their decomposition at high temperatures.…”

“…67 The vibration band at 1623 cm -1 corresponding to gaseous or weakly adsorbed NO 2 . 68,69 When the temperature is higher than 300 °C, the peaks of the nitrate species disappear in the IR spectra due to their decomposition at high temperatures. Based on the above analysis, the possible reaction mechanism for soot combustion on the developed catalysts is proposed, and the corresponding scheme is shown in Fig.…”

Global Kinetic Model of a Three-Way-Catalyst-Coated Gasoline Particulate Filter: Catalytic Effects of Soot Accumulation

“…This is well documented in the literature. 54,55 Thus, this inhibition effect was simulated in this study over the Pd/CeZr/ Al 2 O 3 sample using the reaction expressions and kinetic parameters estimated above, with the purpose of understanding the kinetic processes taking place in the presence of soot over the whole range of operating conditions. Compared to soot-free experiments, the feed temperature was limited between 125 and 300 °C to prevent the soot oxidation, whereas λ-values were kept the same, ranging from 0.85 to 1.15.…”

Effects of Feed Gas Composition on Fresh and Aged TWC-Coated GPFs Loaded with Real Soot

“…This degradation of the TWC activity is probably related to the mass transfer resistance caused by the soot. The soot deposition limits the diffusion of species toward the active sites, resulting in a reduced performance compared to the soot-free samples. − …”

“…Their results indicated that the presence of soot considerably reduced the formation or stability of ammonium nitrates, leading to higher NO x conversion at low temperatures during fast SCR conditions. On the contrary, Li et al 16 examined the NO x adsorption on a lean NO x trap (LNT) catalyst in the absence and presence of soot. They concluded that the soot trapped physically covered the catalyst surface, causing a masking effect by reducing the number of available NO x adsorption sites.…”