Ag–Al2O3 catalysts for lean NOx reduction—Influence of preparation method and reductant

Kannisto, Hannes; Ingelsten, Hanna Härelind; Skoglundh, Magnus

doi:10.1016/j.molcata.2008.12.003

Cited by 77 publications

(95 citation statements)

References 46 publications

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“…To better understand issues as varied as the mechanism of selective reduction of NOx or the hydrocarbon adsorption process of silver based catalysts, it is necessary to determine the chemical state and the location of silver nanoparticles in the zeolitic framework. 3,13,18,19 Recently, a considerable number of studies have explored the catalytic properties of silver-zeolite catalysts for the SCR of NOx by hydrocarbons [20][21][22] or alcohols. [23][24][25] Our research group reported that silver-exchanged Na-mordenite catalysts were active and selective in the removal of nitrogen oxides using butane or toluene as reducing agents.…”

Section: Introductionmentioning

confidence: 99%

Study of the Nature and Location of Silver in Ag-Exchanged Mordenite Catalysts. Characterization by Spectroscopic Techniques

et al. 2013

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Catalysts based on Na-mordenite (symbolized as 'M') exchanged with 5, 10 and 15 wt. % of Ag were characterized by XPS, EXAFS, XANES and UV-Vis DRS spectroscopic techniques in order to investigate the effect of different treatments on the chemical state and surface concentration of silver species. The Ag x M catalysts were analyzed in oxidizing (O 2 ) or reducing (H 2 /Ar) atmospheres and also after being used in the selective catalytic reduction of NOx or in successive cycles of toluene adsorption/desorption.In calcined samples, EXAFS profiles showed two types of Ag-O spheres of coordination, one due to a dispersed phase of silver oxide and the other, to Ag + ions in interaction with the oxygen of the zeolite framework. The UV-Vis DRS spectra showed the coexistence of isolated Ag + , Ag n δ+ (n < 10) cationic clusters and Ag x O particles. In addition, through the modified Auger parameter (α'), calculated from XPS measurements, it was possible to identify Ag + ions at exchange sites (α'~722 eV) and Ag x O (α'~725 eV) highly dispersed on the surface. Both species constitute stable active centers for the SCR of NOx under severe reaction conditions. However, during the adsorption-desorption of toluene, the reduction of silver oxides produces Ag(0) due to thermal hydrocarbon decomposition.

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Section: Introductionmentioning

confidence: 99%

Study of the Nature and Location of Silver in Ag-Exchanged Mordenite Catalysts. Characterization by Spectroscopic Techniques

et al. 2013

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“…The proportion of small silver clusters and metallic silver depends much on the silver loading and preparation technique. With impregnation methods, high silver loading tends to produce more metallic silver while low silver loading gives a higher proportion of small clusters of silver [15]. Sol-gel methods produce catalysts containing small silver clusters and oxidized silver which are more finely distributed in the alumina matrix [16,17].…”

Section: Introductionmentioning

confidence: 99%

Studies on H2-Assisted Liquefied Petroleum Gas Reduction of NO over Ag/Al2O3 Catalyst

Yadav

Thakur

et al. 2017

Bull. Chem. React. Eng. Catal.

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Hydrocarbon-Selective catalytic reduction (HC-SCR) is one of the potential methods to remove NOx emissions from diesel engine, lean burn petrol engines and natural gas engines exhaust. Ag/Al2O3 is a good catalyst for HC-SCR of NOx under lean-burn conditions. Further, addition of small amount of H2 is effective for enhancing HC-SCR activity. This effect is unique to silver and to specific Ag/support combinations, namely, Ag/γ-Al2O3. Various HC reductants, such as: octane, decane, dodecane and propane, have been reported in the literatures. Only a single study on LPG as a reductant over Cu-ZSM catalyst was reported. There was no work reported on H2 assisted LPG over Ag/Al2O3 catalyst. Thus, this gap in the literature is filled with the present investigation of NO reduction over 2 wt.% Ag/Al2O3 catalyst using LPG reductant. The fresh and used catalyst was characterized by various techniques like low temperature N2-adsorption, XRD, XPS and SEM. There was practically no change in the characteristics of the fresh and used catalyst. Two different reductants of CO and LPG were compared for SCR of NO over the catalyst without and with H2-assisted. The experiments were performed in a fixed bed tubular flow reactor under the following conditions: 100mg catalyst; 0.13% NO, 2.5% LPG/CO, 1% H2, 10% O2, rest Ar; total flow rate 60 mL/min; temperature ambient 400 o C and pressure 1 atm. Around 100% conversion of NO was achieved using LPG reductant. Light off temperature of NO reduction significantly reduced by H2assisted LPG reductant. The maximum conversion of NO with CO was limited to 35.15% at temperature of 224 o C and above. Whereas, 97.79 % NO conversion was achieved at 365 o C with LPG reductant. While, the maximum conversions with H2-LPG and H2-CO reductants were 100 and 99.46% at 117 and 220 o C, respectively. Therefore, H2-LPG-SCR of NOx over 2 wt.% Ag/Al2O3 catalyst system can be used to get 100% reduction at low temperature.

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“…From the literatures (Jackson et al 1995;Chen and Zhang 2003;Kwon et al 2005), it can be found that the thermal decomposition products of AgNO 3 are Ag 0 , NO 2 and O 2 following the equation 2AgNO 3 = 2Ag + 2NO 2 + O 2 . But the sliver exits in three forms of Ag 0 , Ag 2 O and Ag-O-Al species after loaded on the γ -Al 2 O 3 support (Kannisto et al 2009), their binding energy are 368.1 eV, 367.7 eV and 367.4 eV respectively (Schön 1973). Figure 3 shows the XPS spectrum of the core level of Ag 3d 5/2 region recorded with S15AgU sorbent.…”

Section: Resultsmentioning

confidence: 99%

Preparation of γ-Al2O3 sorbents loaded with metal components and removal of thiophene from coking benzene

et al. 2012

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Series sorbents of Cu, Zn, Ni, Ce and Ag metal components supported on γ -Al 2 O 3 carrier for removing thiophene from benzene were prepared by conventional and ultrasound-assisted incipient-wetness impregnation method. The static adsorption experiments were carried out in the thiophene-benzene solution with thiophene concentration of 500 mg/L. The results show that the desulfurization activity of all γ -Al 2 O 3 sorbents modified by different metal components obviously increase, among which the sorbent modified by silver nitrate has the best performance. The active components of sorbents from Cu, Zn, Ni, Ce nitrates loaded on γ -Al 2 O 3 carrier are their oxides. Besides Ag 2 O, the products of silver nitrate thermal decomposition in sorbent prepared still have Ag 0 and Ag-O-Al species. The assistant ultrasound in the process of sorbent preparation can not only shorten the impregnation time, but also enrich the pore structure of sorbent and improve the size and distribution of the Ag species, which is favorable to the removal of thiophene from benzene. The desulfurization capacity of sorbent changes with the Ag content loaded. The sorbent with 15 % quality content of Ag prepared by ultrasoundassisted impregnation method has the highest desulfurization efficiency. It could reduce the thiophene concentration to 1.7 mg/L from 500 mg/L at room temperature and ambient pressure, with the desulfurization efficiency of more than 99 %, when the ratio of sorbent to solution was 1:4 (g/mL).

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Ag–Al2O3 catalysts for lean NOx reduction—Influence of preparation method and reductant

Cited by 77 publications

References 46 publications

Study of the Nature and Location of Silver in Ag-Exchanged Mordenite Catalysts. Characterization by Spectroscopic Techniques

Study of the Nature and Location of Silver in Ag-Exchanged Mordenite Catalysts. Characterization by Spectroscopic Techniques

Studies on H2-Assisted Liquefied Petroleum Gas Reduction of NO over Ag/Al2O3 Catalyst

Preparation of γ-Al2O3 sorbents loaded with metal components and removal of thiophene from coking benzene

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