NOx reduction on a transition metal-free γ-Al2O3 catalyst using dimethylether (DME)

Abstract

NO 2 and dimethylether (DME) adsorption as well as DME and NO 2 co-adsorption on a transition metal-free g-alumina catalyst were investigated via in-situ transmission Fourier transform infrared spectroscopy (in-situ FTIR), residual gas analysis (RGA) and temperature programmed desorption (TPD) techniques. NO 2 adsorption at room temperature leads to the formation of surface nitrates and nitrites. DME adsorption on the alumina surface at 300 K leads to molecularly adsorbed DME, molecularly adsorbed methanol and surface methoxides. Upon heating the DME-exposed alumina to 500-600 K the surface is dominated by methoxide groups. At higher temperatures methoxide groups are converted into formates. At T > 510 K, formate decomposition takes place to form H 2 O(g) and CO(g). DME and NO 2 co-adsorption at 423 K does not indicate a significant reaction between DME and NO 2 . However, in similar experiments at 573 K, fast reaction occurs and the methoxides present at 573 K before the NO 2 adsorption are converted into formates, simultaneously with the formation of isocyanates. Under these conditions, NCO can further be hydrolyzed into isocyanic acid or ammonia with the help of water which is generated during the formate formation, decomposition and/or NCO formation steps. #

NOx storage and reduction pathways on zirconia and titania functionalized binary and ternary oxides as NOx storage and reduction (NSR) systems

“…While the former feature has been assigned to linear (type-I) OH species, the latter one is characteristics for three-fold (type-III) hydroxyls [35][36][37][38][39][40][41][42] which disappear from the surface upon interaction/coordination with adsorbed nitrates and nitrites. Another broad and highly convoluted feature centered at 3512 cm −1 can be attributed to H-bonded surface hydroxyl species [38,39]. In Fig.…”

Fine-Tuning the Dispersion and the Mobility of BaO Domains on NOx Storage Materials via TiO2 Anchoring Sites

“…28,[34][35][36][37] The most prominent band after the first few initial NO 2 doses in Figure 3a at 1230 cm -1 and the shoulder at about 1320 cm -1 are attributed to the nitrites on the alumina surface. Concomitant with the formation of nitrites, further NO 2 doses lead to the oxidation of the surface nitrite species to nitrates.…”

“…34,35,[44][45][46][47] The high-frequency section of the IR data in Figure 4a (ν OH > 3650 cm -1 ), shows the development of several negative bands located at 3730, 3760, and 3775 cm -1 and shoulders at ∼3690 and 3795 cm -1 during the NO 2 (g) adsorption process on pure alumina. Appearance of these negative features and their relative intensity changes can be explained by a gradual consumption of the isolated hydroxyl groups on the alumina surface with increasing surface NO x coverage.…”

SO uptake and release properties of TiO2/Al2O3 and BaO/TiO2/Al2O3 mixed oxide systems as NO storage materials

“…6a compares the NO x uptake characteristics of the fresh and poisoned ␥-Al 2 O 3 surface at 323 K. After the saturation of the fresh ␥-Al 2 O 3 surface with NO 2 (g), vibrational features associated with different types of nitrate species were observed. These nitrate species adsorbed on ␥-Al 2 O 3 were in the form of bridged (1258, 1628 cm −1 ), bidentate (1300, 1604 cm −1 ) and monodentate nitrates (1300, 1564 cm −1 ) [37,72]. Additionally, the weak band located at ∼1958 cm −1 that was formed after NO x adsorption on the poisoned surface is associated with the adsorbed NO + and/or weakly adsorbed N 2 O 3 [73].…”