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The catalytic activity of cobalt-exchanged mordenites for the abatement of NO with CH4 in the presence of excess O2 (Articolo in rivista)

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The catalytic activity of cobalt-exchanged mordenites for the abatement of NO with CH4 in the presence of excess O2 (Articolo in rivista) (literal)

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Maria Cristina Campa; Igor Luisetto; Daniela Pietrogiacomi; Valerio Indovina (2003)
The catalytic activity of cobalt-exchanged mordenites for the abatement of NO with CH4 in the presence of excess O2
in Applied catalysis. B, Environmental (Print); ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS, AMSTERDAM (Paesi Bassi)
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Maria Cristina Campa; Igor Luisetto; Daniela Pietrogiacomi; Valerio Indovina (literal)

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The results of this research allow to conclude that Co-MOR are far more active than Na-MOR and H-MOR. Co-Na-MOR and Co-H-MOR with the same cobalt content and markedly different Brønsted acid site content have the same activity. These facts reinforce the point that acid protons play a negligible role when Co is present. Irrespective of the commercial MOR used for the catalyst preparation, Co-MOR catalysts with the same Co content are equally active and selective. The activity of Co-MOR-9.2-(T) is somewhat higher than that of other Co-MOR samples and approaches that of Co-MFI. Both the catalytic activity and the amount of CoII-carbonyls in the alpha-sites are higher in Co-MOR-9.2-(T) than in all other Co-MOR samples. CoII in the main channels are the active sites for the CH4+NO+O2 reaction. Although we cannot rule out a role of CoII in the beta-sites of MOR, we can rule out the possibility that this species alone is active, otherwise all Co-MOR would have been equally active. (literal)

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The use of methane as reducing agent for the NO abatement in the presence of O2 has attracted particular attention both on fundamental and applicative view-point (NO abatement in fixed plants). At the present, the only catalysts active in the NO abatement with methane are zeolite systems exchanged with transition metal ions, particularly MFI. Within this framework, we have studied the abatement of NO with methane in the presence of oxygen on various commercial MOR in the Na-form (Na-MOR) and H-form (H-MOR), or exchanged to various extents with cobalt (Co-MOR). To gain more information about the dependence of catalytic activity on cobalt and Brønsted acid site content, we investigated the catalytic activity for CH4+NO+O2 and CH4+NO2 on MOR samples with Si/Al ratios ranging from 6.5 to 25, and the corresponding Co-exchanged samples. Samples were characterized by chemical analyses of sodium and cobalt content, FTIR and volumetric measurements of CO adsorption. The aim was to clarify some fundamental aspects of environmental catalysis. (literal)

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Sezione \"Materiali Inorganici e Catalisi Eterogenea\" dell'Istituto IMIP (CNR), Dipartimento di Chimica, Università degli Studi di Roma \"La Sapienza\", Piazzale Aldo Moro 5, 00185 Rome, Italy (literal)

Titolo

The catalytic activity of cobalt-exchanged mordenites for the abatement of NO with CH4 in the presence of excess O2 (literal)

Abstract

The abatement of NO with methane in the presence of oxygen was studied on various commercial MOR in the Na-form (Na-MOR) and H-form (H-MOR), or exchanged to various extents with cobalt (Co-MOR). The sodium and cobalt contents were determined by atomic absorption. Samples were characterized by FTIR and volumetric measurements of CO adsorption. Chemical analysis indicated that one cobalt species replaced two Brønsted acid sites in H-MOR and two Na+ ions in Na-MOR. The IR analysis of the OH stretching region, evidencing an unexpected presence of Brønsted acid sites (band at 3610 cm-1) in Co-MOR, indicated that the exchange process had a more complex stoichiometry. The adsorption of CO at RT on Co-MOR, in addition to the bands of the corresponding H-MOR and Na-MOR matrices, yielded two types of CoII-carbonyls, the first type occupied the mordenite main channels, and the second one the mordenite smaller channels. Brønsted acid sites in mordenites were active for the selective catalytic reduction of NO with CH4. Co-MOR samples were far more active than Na-MOR and H-MOR samples, showing that acid protons play a negligible role when Co is present. Co-MOR catalysts showing the highest activity had the largest amount of CoII-carbonyls in the main channels. This result strongly suggests that CoII in the main channels of MOR are the active sites for the CH4+NO+O2 reaction. (literal)

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