Novel Enolic Surface Species Formed during Partial Oxidation of CH₃CHO, C₂H₅OH, and C₃H₆ on Ag/Al₂O₃:  An in Situ DRIFTS Study

Abstract

In situ DRIFTS was used to investigate the formation and reactivity of surface species on Ag/Al2O3 during partial oxidation of CH3CHO, C2H5OH, and C3H6. The exposure of Ag/Al2O3 to CH3CHO/C2H5OH/C3H6 + O2 in a steady state leads to the formation of two kinds of partial oxidation products: acetate and a novel enolic surface species. Peaks at 1633, 1416, and 1336 cm-1 are assigned to an adsorbed enolic species. The adsorbed enolic species is more prone to react with NO + O2 on Ag/Al2O3 than acetate is, and plays a crucial role in the formation of NCO, which is a key intermediate during selective catalytic reduction of NO.

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].…”

Conformational analysis and comparison between theoretical and experimental vibration spectra for isocyanate species on Ag/Al2O3 catalyst

“…An Ag/Al 2 O 3 catalyst (Ag loading is 5.0 wt.%) was prepared by an impregnation method as described in our earlier paper [12]. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) spectra were recorded on a Nexus 670 (Thermo Nicolet) FT-IR, equipped with an in situ diffuse reflection chamber and a high sensitivity MCT detector.…”

“…diesel and lean-burn engines) [5][6][7][8]. The mechanism of HC-SCR of NO in the presence of excess oxygen over Ag/Al 2 O 3 has been proposed as [9][10][11][12][13][14][15][16] …”

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

“…[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.…”

“…In our earlier papers, 162,172,173 the formation and dynamic performance of partial oxidation products of ethanol over Ag/Al 2 O 3 were studied by an in situ DRIFTS method, and we found a novel enolic species originating from the partial oxidation of ethanol, with the structural feature of an oxygen atom adjacent to carbon-carbon double bonds (CQC-O). As shown in Fig.…”