Effect of H2 on deNOx performance of HC-SCR over Ag/Al2O3: Morphological, chemical, and kinetic changes

Kim, Pyung Soon; Kim, Mun Kyu; Cho, Byong K.; Nam, In−Sik; Oh, Se H.

doi:10.1016/j.jcat.2013.01.026

Cited by 80 publications

(43 citation statements)

References 47 publications

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“…2b, the percentage of isolated Ag + was more than 95% on nano-Al 2 O 3 , while about 60% of Ag species existed in the Ag n δ+ state on micro-Al 2 O 3 . These UV-vis results reveal that the Ag species on nano-Al 2 O 3 are mainly the isolated Ag + ions at low Ag loading (1-2 wt%) and form the metallic Ag n clusters at relatively high Ag loading (4-8 wt%) 6,30,[32][33][34][35][36][37] , whereas even 1% Ag on micro-Al 2 O 3 tends to form Ag n δ+ clusters, consistent with the HAADF-STEM images. XAFS measurements were then conducted to study the valence and coordination condition of Ag species on the nano-Al 2 O 3 surface.…”

Section: Resultssupporting

confidence: 73%

“…A lumina-supported silver (Ag/Al 2 O 3 ) is a widely used catalyst in a variety of industrial applications, such as NO x emission control via selective catalytic reduction (SCR) with using hydrocarbons (HC-SCR) [1][2][3][4][5][6] or NH 3 (NH 3 -SCR) 7,8 , soot oxidation 9,10 , selective catalytic oxidation of ammonia (NH 3 -SCO) [11][12][13] , oxidation of volatile organic compounds 14,15 , ethylene epoxidation 16,17 , among others. The valence state, dispersion, and morphology of Ag species have been found to play important roles to the activities of Ag-based catalysts as these factors are all closely related to how Ag species are anchored on the Al 2 O 3 surface.…”

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confidence: 99%

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Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance

et al. 2020

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is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al 2 O 3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al 2 O 3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al 2 O 3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al 2 O 3 . Density-functional-theory calculations confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al 2 O 3 , but not on microsized γ-Al 2 O 3 . The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts.

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Section: Resultssupporting

confidence: 73%

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confidence: 99%

Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance

et al. 2020

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“…Since ethane is more difficult to activate compared to ethene [48], this indicates that the role of hydrogen over the In/Al 2 O 3 catalyst could be to increase the hydrocarbon activation. Enhancement of hydrocarbon activation has previously been pointed out as a possible origin of the hydrogen effect over Ag/Al 2 O 3 [4,22,30,31].…”

Section: The Non-oxygenated Hydrocarbons As Reductantsmentioning

confidence: 95%

“…In the open literature, the origin of the hydrogen effect is extensively debated. The main suggestions involve reduction of adsorbed nitrogen species [27][28][29][30], enhanced activation of the hydrocarbon [4,22,26,30,31], modification of the Ag-species [4,26,30,31], as well as direct effects on the reaction mechanism [30,32]. For In/Al 2 O 3 , a minor hydrogen effect has previously been reported during NH 3 -SCR [33].…”

Section: Introductionmentioning

confidence: 93%

Hydrogen-assisted SCR of NO over alumina-supported silver and indium catalysts using C2-hydrocarbons and oxygenates

Ström

Carlsson

Skoglundh

et al. 2016

Applied Catalysis B: Environmental

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Please cite this article as: Linda Strddotom, Per-Anders Carlsson, Magnus Skoglundh, Hanna Härelind, Hydrogen-assisted SCR of NOx over alumina-supported silver and indium catalysts using C2-hydrocarbons and oxygenates, Applied Catalysis B, Environmental http://dx. Graphical abstractHighlights  Impregnated catalysts coated onto monoliths are evaluated for lean HC-SCR.  C2-based reductant probing of active sites over Ag/Al2O3 and In/Al2O3 is performed.  The origin of the hydrogen effect is evaluated and compared between the catalyst. AbstractThis work focuses on the selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with ethane, ethene, acetic acid, dimethyl ether (DME) and ethanol, respectively, over aluminasupported silver and indium catalysts. The impact of hydrogen and the nature of the reductant on the catalyst structure and SCR activity are studied. The ability to reduce NO x differs significantly among the studied reductants, but also between the two catalysts, of which Ag/Al 2 O 3 is the overall most active catalyst. However, the In/Al 2 O 3 catalyst exhibits high SCR activity with DME as reductant in contrast to the Ag/Al 2 O 3 catalyst, which shows negligible activity. We attribute this difference to the higher number of acidic sites on the In/Al 2 O 3 catalyst and the higher degree of DME combustion over Ag/Al 2 O 3 . Moreover, the number of sites that previously have been identified to promote hydrocarbon activation, i.e. silver cluster sites (Ag n δ+ ) in Ag/Al 2 O 3 catalysts and indium cluster sites (In 3+ ) in In/Al 2 O 3 catalysts, are shown to increase upon addition of small amounts of hydrogen in the feed. We suggest that the increased SCR activity over In/Al 2 O 3 originates from an increased number of sites for activation of hydrocarbons, analogous to previous proposals for Ag-based catalysts, in combination with a direct effect on the reaction mechanism.

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“…However, recently In/Al 2 O 3 , which also has been studied for SCR applications [13][14][15][16][17][18][19], was found to exhibit a hydrogen effect, albeit to a lower extent compared to Ag/Al 2 O 3 [20]. The hydrogen effect over Ag/Al 2 O 3 has been suggested to originate from the reduction of adsorbed nitrogen species [10,21,22], changes in the type of Ag species [23][24][25], and/or enhanced activation of the reductant [9,11]. However, in contrast to other precious metal catalysts, alumina-supported silver is not active for H 2 -SCR [26].…”

Section: Introductionmentioning

confidence: 99%

Surface Species and Metal Oxidation State during H2-Assisted NH3-SCR of NOx over Alumina-Supported Silver and Indium

et al. 2018

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Alumina-supported silver and indium catalysts are investigated for the hydrogen-assisted selective catalytic reduction (SCR) of NO x with ammonia. Particularly, we focus on the active phase of the catalyst and the formation of surface species, as a function of the gas environment. Diffuse reflectance ultraviolet-visible (UV-vis) spectroscopy was used to follow the oxidation state of the silver and indium phases, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to elucidate the formation of surface species during SCR conditions. In addition, the NO x reduction efficiency of the materials was evaluated using H 2 -assisted NH 3 -SCR. The DRIFTS results show that the Ag/Al 2 O 3 sample forms NO-containing surface species during SCR conditions to a higher extent compared to the In/Al 2 O 3 sample. The silver sample also appears to be more reduced by H 2 than the indium sample, as revealed by UV-vis spectroscopic experiments. Addition of H 2 , however, may promote the formation of highly dispersed In 2 O 3 clusters, which previously have been suggested to be important for the SCR reaction. The affinity to adsorb NH 3 is confirmed by both temperature programmed desorption (NH 3 -TPD) and in situ DRIFTS to be higher for the In/Al 2 O 3 sample compared to Ag/Al 2 O 3 . The strong adsorption of NH 3 may inhibit (self-poison) the NH 3 activation, thereby hindering further reaction over this catalyst, which is also shown by the lower SCR activity compared to Ag/Al 2 O 3 .

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Effect of H2 on deNOx performance of HC-SCR over Ag/Al2O3: Morphological, chemical, and kinetic changes

Cited by 80 publications

References 47 publications

Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance

Resolving the puzzle of single-atom silver dispersion on nanosized γ-Al2O3 surface for high catalytic performance

Hydrogen-assisted SCR of NO over alumina-supported silver and indium catalysts using C2-hydrocarbons and oxygenates

Surface Species and Metal Oxidation State during H2-Assisted NH3-SCR of NOx over Alumina-Supported Silver and Indium

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