Adsorption chemistry of NOx on Ag/Al2O3 catalyst for selective catalytic reduction of NOx using hydrocarbons

Brosius, Roald; Arve, Kalle; Groothaert, Marijke H.; Martens, Johan A.

doi:10.1016/j.jcat.2005.01.034

Cited by 90 publications

(63 citation statements)

References 23 publications

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“…loading was between 5 and 7 wt % in contrast to literature, 2,8,15,17,20,21,33,34,42,43 where 2 wt % is typically reported as the standard catalyst. It is believed that these high loadings of silver can be obtained by using boehmite as the precursor for γ-alumina, as this ensures a high surface area for the final catalyst (see Table 1) and has been reported 35 to maintain a strong interaction between silver and alumina, preventing silver from sintering during calcination.…”

Section: Resultsmentioning

confidence: 83%

New Insights into the Active Surface Species of Silver Alumina Catalysts in the Selective Catalytic Reduction of NO

et al. 2010

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The performance of silver alumina catalysts and silver aluminate was studied in the selective catalytic reduction (SCR) of NO by propene. The use of boehmite during the impregnation step ensured a strong interaction between the silver species and the alumina surface in the final calcined catalyst. Thus, higher silver loadings (5-7 wt % silver) could be used without significant loss in selectivity to N 2 during SCR. The nature of the silver species and the formation of adsorbed surface species during SCR and hydrogen-assisted SCR (H 2 -SCR) was studied by activity measurements and by combined in situ IR and X-absorption spectroscopic measurements. The combination of these techniques in the same reaction cell allowed simultaneous monitoring of the state of silver and the formation of surface species under realistic reaction conditions. The active silver species on alumina support were concluded to be 2-dimensional oxidic Ag n δ+ species. Silver aluminate was ruled out as a possibility for an active phase for the SCR reaction. The oxidic Ag n δ+ species were present under both SCR and H 2 -SCR reaction conditions and even on a prereduced catalyst under the SCR reaction conditions. Hydrogen is proposed to enhance the formation of adsorbed surface species, especially nitrites, but not to change the nature of the active silver sites.

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Section: Resultsmentioning

confidence: 83%

New Insights into the Active Surface Species of Silver Alumina Catalysts in the Selective Catalytic Reduction of NO

et al. 2010

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“…Mn +3 to Mn +4 ) or creates some oxygen vacancies to maintain the electrical neutrality [33][34][35][36][37]. The higher oxidation state ions are usually known to possess higher catalytic activity whereas the oxygen vacancies enhance the surface oxygen and oxygen mobility in the lattice and both of these factors lead to increase in the catalytic activity [38][39][40][41].…”

Section: Alkali Metal Substitutionmentioning

confidence: 99%

Simultaneous Control of NOx-Soot by Substitutions of Ag and K on Perovskite (LaMnO3) Catalyst

Dhal

Dey

Прасад

2017

Bull. Chem. React. Eng. Catal.

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The different Ag and K substituted perovskite catalysts including base catalyst were LaMnO3 by the solid state method and the diesel soot was prepared in the laboratory. Their structures and physicochemical properties were characterized by X-ray diffraction (XRD), BET, SEM, H2-TPR, and XPS techniques. The Ag Substituted at A-site perovskite structured catalysts are more active than other type of catalysts for the simultaneous soot-NOx reaction, When Ag and K are simultaneously introduced into LaMnO3 catalyst, soot combustion is largely accelerated, with the temperature (Tm) for maximal soot conversion lowered by at least 50 °C, moreover, NOx reduction by soot is also facilitated. The high activity of La0.65Ag0.35MnO3 perovskite catalyst is attributed to presence of metallic silver in the catalyst. The activity order of Ag doped LaMnO3 is as follows La0.65Ag0.35MnO3 > La0.65Ag0.2MnO3 > La0.65Ag0.4MnO3 > La0.65Ag0.1MnO3. The dual substitution of silver and potassium in place of La in LaMnO3 gives better activity than only silver doped catalyst. In a series of La0.65AgxK1-xMnO3, the optimum substitution amount of K is for x=0.25. The single and doubled substituted perovskite catalyst proved to be effective in the simultaneous removal of NOx and soot particulate, the two prevalent pollutants in diesel exhaust gases in the temperature range 350-480 °C.

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“…ii) the initiation of radical reactions [5,6]; iii) the formation of intermediate surface species like cyanides or nitrites and nitrates [5,7]. Satokawa et al [1,2,4] have concluded on the basis of in situ UV/vis studies that H 2 facilitates the formation of moderately agglomerated Ag n δ+ clusters, which are responsible for activation of hydrocarbons [3,8] or also promote dissociation of NO or O 2 [9,10].…”

Section: Introductionmentioning

confidence: 99%

“…Shimizu [5], earlier shown to be a relevant reaction step of NO x -SCR by in situ FTIR studies of NO reduction with ethanol in the presence of oxygen [12]. Additionally, hydrogen reduces the concentration of surface nitrates [7], which block active sites for the SCR reaction over Ag/Al 2 O 3 below 523 K. The suggested mechanistic concepts are still controversial and in some aspects partial. For example, the reaction pathways leading to N 2 O, a possible undesired sideproduct of this reaction, are scarcely investigated.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic aspects of N2O and N2 formation in NO reduction by NH3 over Ag/Al2O3: The effect of O2 and H2

Kondratenko

Bentrup

Richter

et al. 2008

Applied Catalysis B: Environmental

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A mechanistic scheme of N 2 O and N 2 formation in the selective catalytic reduction of NO with NH 3 (NH 3 -SCR) over a Ag/Al 2 O 3 catalyst in the presence and absence of H 2 and O 2 was developed by applying a combination of different techniques: transient experiments with isotopic tracers in the temporal analysis of products (TAP) reactor, HRTEM, in situ UV/vis and in situ FTIR spectroscopy. Based on the results of transient isotopic analysis and in situ IR experiments, it is suggested that N 2 and N 2 O are formed via direct or oxygen-induced decomposition of surface NH 2 NO species. These intermediates originate from NO and surface NH 2 fragments. The latter NH 2 species are formed upon stripping of hydrogen from ammonia by adsorbed oxygen species, which are produced over reduced silver species from NO, N 2 O and O 2 . The latter is the dominant supplier of active oxygen species. Lattice oxygen in oxidized AgO x particles is less active than adsorbed oxygen species particularly below 623 K. The previously reported significant diminishing of N 2 O production in the presence of H 2 is ascribed to hydrogen-induced generation of metallic silver sites, which are responsible for N 2 O decomposition.

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Adsorption chemistry of NOx on Ag/Al2O3 catalyst for selective catalytic reduction of NOx using hydrocarbons

Cited by 90 publications

References 23 publications

New Insights into the Active Surface Species of Silver Alumina Catalysts in the Selective Catalytic Reduction of NO

New Insights into the Active Surface Species of Silver Alumina Catalysts in the Selective Catalytic Reduction of NO

Simultaneous Control of NOx-Soot by Substitutions of Ag and K on Perovskite (LaMnO3) Catalyst

Mechanistic aspects of N2O and N2 formation in NO reduction by NH3 over Ag/Al2O3: The effect of O2 and H2

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