Mechanism of the selective catalytic reduction of NOx by C2H5OH over Ag/Al2O3

Abstract

[1] The exchange of carbonyl sulfide (COS) between lawn and the atmosphere was investigated by using a static enclosure under natural field conditions. The results indicated that the lawn acted as a sink for atmospheric COS and a source of dimethyl sulfide (DMS). The exchange fluxes of COS and DMS ranged between À3.24 pmol m À2 s À1 and À94.52 pmol m À2 s À1 , and between 0 and 3.14 pmol m À2 s À1 , respectively. The lawn was capable of continuously absorbing COS in nighttime as well as in daytime. The COS fluxes depended strongly on the ambient COS mixing ratios. The dependency of DMS emission fluxes on temperature was observed in November 2002. Soil also acted as a sink for COS during our study. However, the COS exchange fluxes of the lawn were much higher than that of the soil. The average COS and DMS fluxes were much higher in spring than in autumn and in summer. The daytime vertical profiles of COS also indicated that the lawn acted as a net sink for COS.

Environmentally-benign catalysts for the selective catalytic reduction of NOxfrom diesel engines: structure–activity relationship and reaction mechanism aspects

“…Further studies confirmed that the enolic species originating from the partial oxidation of butyl alcohol (BA), sec-butyl alcohol (SBA), and isobutyl alcohol (IBA), propyl alcohol, 160 isopropyl alcohol (IPA), 161 and acetaldehyde 162 over Ag/Al 2 O 3 also exhibited high activity toward NO + O 2 , and thus are responsible for NO x reduction by these oxygenated hydrocarbons. The characteristic IR peaks of -NCO located around 2230 and 2250-2260 cm À1 have been commonly observed on Ag/Al 2 O 3 during HC-SCR, while the assignments of their coordination sites are still controversial.…”

“…162,165,166,173,179 Two kinds of surface enolic species, adsorbed only on Al sites (CH 2 QCH-CHQCH-O-Al 6 O 5 (OH) 8 ) and bound on or close to Ag (CH 2 QCH-O-Ag, CH 2 QCH-CHQCH-O-Al-Ag) were suggested by DFT calculations over Ag/Al 2 O 3 and Al 2 O 3 , with the simulation molecular structure model and corresponding FTIR spectrum shown in Fig. 3D-F, respectively.…”

Review of Ag/Al2O3-Reductant System in the Selective Catalytic Reduction of NO x

“…In recent studies, relatively durable and inexpensive alumina-supported silver catalysts (Ag/Al 2 O 3 ) have been considered to be a promising candidate for practical usage in the HC-SCR of NO x [2][3][4][5][6][7][8]. In our research into the HC-SCR of NO x over Ag/ Al 2 O 3 , we found a novel enolic surface species on Ag/ Al 2 O 3 [9] and proposed a new mechanism to explain the high-level efficiency of the SCR of NO x by ethanol over Ag/Al 2 O 3 [7,9,10], as shown in Scheme 1. The reaction starts with the formation of nitrates adsorbed on Al 2 O 3 via NO oxidation by O 2 , and enolic species and acetate adsorbed on Ag and Al 2 O 3 via the partial oxidation of C 2 H 5 OH on Ag/Al 2 O 3 [7].…”

“…So far, researchers have agreed that the -NCO species acts as the key intermediate during the SCR of NO x , and its high reactivity with NO + O 2 results in a highly efficient reduction of NO x [7, 9-11, 15, 16, 21, 28-31]. We recently proposed a novel mechanism for the SCR of NO x by C 2 H 5 OH, as shown in Scheme 1, where the surface enolic species is related to the high surface concentration of -NCO and the high efficiency of NO x reduction by C 2 H 5 OH [7,9,10]. In order to clarify the high activity of enolic species towards NO + O 2 to form -NCO, the dynamic changes of the surface intermediates on Ag/ Al 2 O 3 as a function of time have been investigated by using in situ DRIFTS measurement [10].…”

“…We recently proposed a novel mechanism for the SCR of NO x by C 2 H 5 OH, as shown in Scheme 1, where the surface enolic species is related to the high surface concentration of -NCO and the high efficiency of NO x reduction by C 2 H 5 OH [7,9,10]. In order to clarify the high activity of enolic species towards NO + O 2 to form -NCO, the dynamic changes of the surface intermediates on Ag/ Al 2 O 3 as a function of time have been investigated by using in situ DRIFTS measurement [10]. Figure 2 shows time dependence of the integrated area of the bands for different species in the DRIFTS spectra.…”