Usuwanie tlenków azotu metodą SCR : praca przeglądowa

W pracy omówiono źródła powstawania tlenków azotu, wpływ NOx na środowisko i życie człowieka, jak również katalityczne reakcje ich usuwania. W szczególności omówiono technologię procesu selektywnej katalitycznej redukcji NO amoniakiem (proces NH3-SCR), w tym stosowane w procesie komercyjne katalizatory oparte na tlenku tytanu oraz mieszane tlenki pochodzenia hydrotalkitowego. Uzyskane wyniki jednoznacznie wskazują na duży potencjał materiałów hydrotalkitowych jako katalizatorów technologii SCR.Nowadays, NOx reduction has become one of the major issues in environmental protection. Looking for an active and selective catalyst is one of the challenges. Up to now, tungsten and molybdenum promoted V2O5/TiO2 catalysts exhibit the best performance in the NOx reduction process, and these catalysts have already been industrialized. For the vehicle applications there is a trend for considering other catalysts due to some drawbacks of titania-supported catalysts. Application of Cu-containing mixed metal oxides obtained from hydrotalcite-like materials as catalysts for this process could be a potential solution; however, further research in real operating conditions is needed

Total oxidation of methanol low temperatures on (Cu, Mn)-Mg-Al mixed metal oxides derived from hydrotalcites

A series of (Cu, Mn)-Mg-Al hydrotalcite-like layered double hydroxides (HTs) was synthesized by a co-precipitation method.The incorporation of Mn into the Mg-Al and Cu-Mg- Al HTs structure was investigated by employing powder X-ray diffraction. Calcination of the precursors resulted in destruc- tion of the layered structure and led to low-crystalline MgO. Ob- tained mixed metal oxides were tested as catalysts for the process of total oxidation of methanol.The catalytic performance of the Cu-containing samples was better comparing to the Mn-based catalysts and decreased in the following order: Cu-Mg-Al > Cu- Mn-Mg-Al > Mn-Mg-Al > Mg-Al. Quantitative total oxidation of methanol was achieved at 325 C with Cu-Mg-Al mixed oxides

MCM-41-type mesoporous silicas modified with alumina in the role of catalysts for methanol to dimethyl ether dehydration

MCM-41-type mesoporous silicas were modified with alumina by the impregnation, co-condensation, and template ion-exchange (TIE) methods. The obtained materials were characterized with respect to their chemical composition (ICP-OES), textural parameters (low-temperature N2 sorption), structure (XRD), and surface acidity (NH3-TPD) and tested as catalysts of methanol to dimethyl ether (DME) dehydration in a flow microreactor system. The catalytic performance of the studied materials was analyzed with respect to their porous structure, as well as their density and the strength of their acid sites. It was shown that the performance of the studied catalysts depends on the contribution of the surface exposed aluminum species, as well as their aggregation. For the most active catalyst, the study of its catalytic stability under rection conditions was performed. It was shown that the catalyst can be effectively regenerated by the incineration of carbon deposits under air flow at 550 °C for 1 h

Rozkład N2ON_2O przy użyciu nowoczesnych mikro-mezoporowatych materiałów o właściwościach zeolitów

In the presented studies two modern approaches of synthesis of hierarchical micro-mesoporous materials with zeolitic properties are shown. In the first synthesis the protozeolitic particles were aggregated (under specified conditions) with simultaneous creation of mesopores between the zeolite seeds. In the second synthesis the zeolite nanoseeds were impregnated on the surface of mesoporous, amorphous SBA-15 material. Both used synthesis routs resulted in formation of combined micro-mesoporous materials with zeolitic properties, what was proven by nitrogen sorption, XRD, TGA and IRDRIFT measurements. The combination of zeolitic properties with mesopores (preferable diffusion rate) increased the accessibility of ion-exchange positions allowing the introduction of iron species nearly exclusively in the form of isolated cations. The prepared micro-mesoporous materials were tested as catalysts in low-temperature N_{2}O decomposition in the presence of oxygen

Spherical Al-MCM-41 doped with copper by modified TIE method as effective catalyst for low-temperature NH3_{3}-SCR

Aluminum containing silica spherical MCM-41 was synthesized and modified with copper by the template ion-exchange method (TIE) and its modified version, including treatment of the samples with ammonia solution directly after template ion-exchange (TIE-NH3). The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low temperature N2 sorption), morphology (SEM-EDS), form and aggregation of deposited copper species (UV-vis DRS), reducibility of copper species (H2-TPR), and surface acidity (NH3-TPD). The deposition of copper by the TIE-NH3 method resulted in much better dispersion of this metal on the MCM-41 surface comparing to copper introduced by TIE method. It was shown that such highly dispersed copper species, mainly monomeric Cu2+ cations, deposited on aluminum containing silica spheres of MCM-41, are significantly more catalytically effective in the NH3-SCR process than analogous catalysts containing aggregated copper oxide species. The catalysts obtained by the TIE-NH3 method effectively operated in much broader temperature and were less active in the side process of direct ammonia oxidation by oxygen

Selective catalytic oxidation (SCO) of ammonia to nitrogen over hydrotalcite originated Mg-Cu-Fe mixed metal oxides

Mg-Cu-Fe oxide systems, obtained from hydrotalcite-like precursors, were tested as catalysts for the selective catalytic oxidation (SCO) of ammonia. Copper containing catalysts were active in low-temperature SCO processes; however, their selectivity to nitrogen significantly decreased at higher temperatures. The optimum composition of the catalyst to guarantee high activity and selectivity to N2 was proposed. Temperature-programmed experiments, SCO catalytic tests performed with various contact times and additional tests on the samples in the selective catalytic reduction of NO with ammonia showed that the SCO process over the studied calcined hydrotalcites proceeds according to the internal SCR mechanism and oxidation of ammonia to NO is a rate-determining step in the low-temperature range

Catalytic performance of bimetallic systems (Cu-Fe, Cu-Mn, Fe-Mn) based on spherical MCM-41 modified by template ion-exchange in NH3−SCRNH_{3}-SCR process

Mesoporous silica of MCM-41 type with spherical morphology was modified with copper, iron, or manganese as well as pairs of these metals by template ion-exchange (TIE) method. The obtained samples were characterized with respect to their structure (XRD), morphology (SEM-EDS), textural parameters (low-temperature N2 sorption), surface acidity (NH3-TPD), transition metal loadings (ICP-OES), their deposited forms (UV-vis DRS) and reducibility (H2-TPR). The catalytic performance of monometallic and bimetallic samples in the selective catalytic reduction of NO with ammonia (NH3-SCR) was tested. The best catalytic results presented a bimetallic copper-manganese sample, which was significantly more active than the mechanical mixture of monometallic copper and manganese catalysts. The synergistic cooperation of manganese and copper species is possibly related to charge relocation between them, resulting in activation of the catalyst in oxidation of NO to NO2, which is necessary for the fast NH3-SCR reaction

A short review about NOx storage/reduction catalysts based on metal oxides and hydrotalcite-type anionic clays

[EN] The increasing problem of atmospheric pollution by NOx has resulted in stricter regulations on their emissions. NOx storage/reduction (NSR) is considered as efficient catalytic technology to abate lean-burn NOx. A wide variety of catalysts have been extensively examined for this purpose. The use of metal oxides, hydrotalcites and their derivatives as NOx storage/reduction catalysts has been reviewed. Suitable combination particularly the catalytic redox component and the storage component can lead to improved activity in NOx decomposition and capturing under the lean-rich conditionsJablonska, M.; Palomares Gimeno, AE.; Wegrzyn, A.; Chmielarz, L. (2014). A short review about NOx storage/reduction catalysts based on metal oxides and hydrotalcite-type anionic clays. Acta Geodynamica et Geomaterialia. 11(2):175-186. doi:10.13168/AGG.2013.0063S17518611