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The application of modified layered double hydroxides in selective catalytic reduction of nitrogen oxides by ammonia (NH3-SCR)

Szymaszek Agnieszka, Motak Monika, Samojeden Bogdan

Polish Journal of Chemical Technology

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2020

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Vol. 22, nr 1

61--67

EN

Selective catalytic reduction with ammonia (NH3-SCR) is very efficient DeNOx technique. According to some problems with the commercial catalyst, novel one should be prepared. Hydrotalcites are potential precursors of the new catalysts of NH3-SCR. In this paper, several attempts to apply these materials in NH3-SCR are presented.

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Modified bentonite-derived materials as catalystsfor selective catalytic reduction of nitrogen oxides

Szymaszek Agnieszka, Kubeł Maciej, Samojeden Bogdan, Motak Monika

Chemical and Process Engineering

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2020

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Vol. 41, nr 1

13–-24

EN

In the last few years, cationic layered clays, including bentonites have been investigated as potentialcatalysts for SCR DeNOxsystems. In this work, bentonite as the representative of layered clays wasmodified in order to obtain an alternative, low-cost NH3–SCR catalyst. Samples of raw clay wereactivated with HCl or HNO3, treated with C2H2O4and subsequently pillared with alumina by the ion-exchange. Afterwards, the modified materials were impregnated with iron and copper. The obtainedcatalysts were characterized by XRD and FT-IR. SCR catalytic tests carried out over analyzed samplesindicated the conversion of NO of approximately 90% for the most active sample. The type of acidused for modification and the type of active phase strongly influenced the catalytic properties of theanalyzed materials.

3

The influence of holmium on catalytic properties of Fe or Cu-modified vermiculites

Samojeden Bogdan, Grzybek Teresa, Kowal Joanna, Szymaszek Agnieszka, Jabłońska Magdalena, Gläser Roger, Motak Monika

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 6

1484--1495

EN

Natural layered clay, vermiculite, was modified and tested as catalyst for the selective catalytic reduction of NOx with ammonia (NH3-SCR). Its modification included the application of the blowing agent (azodicarbonamide), acid treatment and pillaring with Al2O3. Active phase (transition metals: Cu or Fe) was introduced via impregnation. The obtained materials were characterized by N2 sorption (texture), XRD (structure), DR-UV-Vis (oxidation state and aggregation of the active phase), H2-TPR (reducibility of the active phase), in situ DRIFTS (types of adsorbed species due to contact of the sample NH3) and NH3-TPD (type/strength of the acidic sites). The initial modification procedures (treatment with azodicarboamide) resulted in the increase of specific surface area of vermiculite. The introduction of transition metal ions provided a significant amount of acidic sites. The promoting impact of holmium was confirmed by the increased strength of the sites. The highest catalytic activity was exhibited by the sample Fe-containing vermiculite and doped with Ho.

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Selective catalytic reduction of NOX with ammonia NH3-SCR over transition metal-based catalysts -influence of the catalysts support

Szymaszek Agnieszka, Samojeden Bogdan, Motak Monika

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 6

1429-1441

EN

Natural layered clays (bentonite and vermiculite) and natural zeolite (clinoptilolite) were tested and compared as the supports of the catalysts forselective catalytic reduction withammonia (NH3-SCR). The raw materials were modified in order to improve their catalytic properties. Layered clays were treated with HNO3 and intercalated with Al2O3 pillars to enhance their acidity, porosity and specific surface area. Clinoptilolite was ion-exchanged with NH4NO3 in order to increase the content of Brönsted acid sites, indispensablefor NH3 adsorptionduring the reaction. Subsequently, iron as an active phase was deposited on the modified supports by various methods, including incipient wetness impregnation, ion-exchange and co-precipitation. The efficiency of these methods was compared as NOx conversionobtained for each material. XRD analysis indicated that the initial modifications affected the structure of the raw aluminosilicates. FT-IR measurement confirmed the presence of characteristic Si-O and Al-O bonds and H2O molecules that occurnaturally in the materials. UV-Vis spectroscopy results indicated that different types of Fe species were deposited on the catalysts surface and theirform strongly depends on the type of the support. NH3-SCR catalytic tests showedthat all of the analyzed materials exhibitsatisfactory level of NO conversion and negligible concentration of by-product (N2O) in the exhaust gas. The highest catalytic activity (ca. 50% at 170°C and over 95% above 250°C) was obtained for Fe-Bent. The lowest concentration of N2O in the flue gas (less than 5 ppm in the whole temperature range) was observed for Fe-Clin.