Selective catalytic reduction of NOx over Ag/Al2O3 catalyst: from reaction mechanism to diesel engine test

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

“…13,158,191 Generally, the presence of water vapor usually suppressed the NO x reduction by hydrocarbons such as propene over Ag/Al 2 O 3 , while high NO x conversion was maintained when oxygenated hydrocarbons such as ethanol were employed as reductants. In our previous work, 16 in situ DRIFTS results showed that the presence of water vapor promoted the formation of enolic species intimately linked to Ag sites, while it suppressed the formation of acetate species. These opposite effects of water vapor on the two species may derive from their different behaviors on the adsorbed sites, identification of which may provide important implications for understanding the effect of water vapor on the HC-SCR.…”

“…[175][176][177] On a detailed mechanistic level, the role of silver species in the HC-SCR of NO x over Ag/Al 2 O 3 was mainly attributed to enhancement of the partial oxidation of reductants to form active intermediates, and their further reaction to produce N 2 . 16,158,172,178 In situ DRIFTS spectra showed that the surface species formed from the partial oxidation of ethanol over Ag/Al 2 O 3 ( Fig. 3C) were closely related to Ag loading.…”

“…3,4,7,[13][14][15][16][17][18][19] Among the catalysts proposed for HC-SCR technology, zeolitic oxide catalysts are effective for NO x reduction, while their water tolerance has been little improved. 5 Noble metal catalysts such as Pt/Al 2 O 3 exhibit high deNO x activity in the low temperature range of 200-300 1C while exhibiting a narrow operation temperature window.…”

“…20,21 Up to now, alumina-supported silver (Ag/Al 2 O 3 ) has been known as one of the most effective catalysts for the HC-SCR even in the presence of water vapor and SO 2 . 13,16,[22][23][24][25][26][27][28][29][30][31][32] The distinctive advantage of HC-SCR is that the on-board fuel can be used as the reductant for NO x conversion, thus reducing the cost involved in infrastructure development for delivering the reductant to the automotive engine exhaust system. The past several years have witnessed a growth in research in NO x reduction by fuel-component hydrocarbons over Ag/Al 2 O 3 , while the light-off temperature for NO x reduction is still too high to be used for commercial application in diesel vehicles, even though it has been reported that low temperature activity can be promoted by the addition of H 2 .…”

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].…”