TY - JOUR A1 - Richter, M. A1 - Trunschke, A. A1 - Bentrup, U. A1 - Brzezinka, Klaus-Werner A1 - Schreier, E. A1 - Schneider, M. A1 - Pohl, M.-M. A1 - Fricke, R. T1 - Selective Catalytic Reduction of Nitric Oxide by Ammonia over Egg-Shell MnOx/NaY Composite Catalysts N2 - A novel composite catalyst system for the selective catalytic reduction (SCR) of NOx by NH3 is described operating at temperatures lower than 470 K in the presence of water with NO conversions of 80–100% at space velocities of 30,000–50,000 h-1. The catalyst is prepared by egg-shell precipitation of MnO2 on the external surface of zeolite NaY. Structural and thermal stability of precipitated MnO2 as well as of the MnO2/NaY composite catalyst were characterized by N2 adsorption, X-ray diffraction, laser Raman spectroscopy, temperature-programmed reduction, and electron microscopy. MnO2 precipitated on zeolite NaY (15 wt% loading) retained its amorphous state up to calcination temperatures of 775 K. The zeolite component remained structurally intact. Calcination at higher temperatures destroyed the zeolite structure and transformed MnO2 into Mn3O4. DRIFT spectroscopic investigations revealed the presence of symmetric O=N—O—N=O species formally corresponding to N2O3 on the composite catalyst after contact with NO. Catalytic measurements under integral flow conditions showed that the catalyst performance is associated with a close coupling of nitrite formation and its drain off from equilibria with NO/NO2 and nitrate by ammonia. Several results are in line with the “diazotation” mechanism, including NH3 protonation to NH4+, whereas prevailing Lewis acid sites should enable NH3 activation via amide species, thus leading to a parallel “amide/nitrosamide” SCR reaction route. The activity-temperature profile fulfills the requirements of a low-temperature NOx reduction catalyst for mobile diesel engines if an ammonia supply is implemented “on board,” e.g., by urea decomposition. PY - 2002 DO - https://doi.org/10.1006/jcat.2001.3468 SN - 0021-9517 SN - 1090-2694 VL - 206 SP - 98 EP - 113 PB - Acad. Press CY - San Diego, Calif. AN - OPUS4-1638 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mehner, Hartmut A1 - Pitsch, I. A1 - Geßner, W. A1 - Brückner, A. A1 - Möhmel, St. A1 - Uecker, D.-Ch. A1 - Pohl, M.-M. T1 - Synthesis and characterization of Fe2O3 containing aluminas by thermal decomposition of modified ammonium dawsonite N2 - Aluminas with Fe2O3 particles finely divided in the Al2O3 matrix were prepared via a crystalline precursor derived from ammonium dawsonite and its calcination. The precursors with Fe content between 1 and 10 wt% were synthesized by reaction of ammonium hydrogen carbonate with mixtures containing aluminium ammonium sulfate and ferric ammonium sulfate. The characterization of the as-synthesized and calcined products by chemical analysis, XRD, EPR, Mössbauer, TEM and adsorption measurements shows that all the Fe3+ ions are incorporated into the structure of dawsonite when the Fe content is low and that the calcined materials with micropores and mesopores (maximum 30–40 Å) also contain very small Fe2O3 particles (<10 nm) at higher Fe contents. PY - 2001 DO - https://doi.org/10.1039/b101466h SN - 0959-9428 SN - 1364-5501 IS - 11 SP - 2498 EP - 2503 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-1206 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kosslick, H. A1 - Pitsch, I. A1 - Deutsch, J. A1 - Pohl, M.-M. A1 - Schulz, A. A1 - Vu, A.T. A1 - Nguyen, D.T. A1 - Frunza, L. A1 - Jäger, Christian T1 - Improved large mesoporous ordered molecular sieves - Stabilization and acid/base functionalization N2 - The preparation of nanoporous materials with enhanced stability using an improved synthesis route using reactive inorganic silica and alumina species is reported. This way improved mesoporous molecular sieves were obtained. The synthesized aluminum substituted mesoporous molecular materials (Al-MMS) contain very large pores of 50–200 Å size combined with an improved pore wall thickness. Increased wall thickness and Al substitution lead to an improved chemical stability against alkaline solution. The textural, structural and acid properties are investigated by physico-chemical methods. The catalytic performance acidic materials was tested in the benzoylation reaction; amino functionalized materials were studied in the base catalyzed Michael addition. KW - Nanoporous molecular sieve KW - Al substitution KW - Stability KW - Synthesis KW - Acidity KW - Catalysis PY - 2010 DO - https://doi.org/10.1016/j.cattod.2010.03.005 SN - 0920-5861 VL - 152 IS - 1-4 SP - 54 EP - 60 PB - Elsevier CY - Amsterdam AN - OPUS4-23960 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tidjani, Adams A1 - Wald, Oliver A1 - Pohl, M.-M. A1 - Hentschel, Manfred P. A1 - Schartel, Bernhard T1 - Polypropylene-graft-maleic anhydride-nanocomposites: I-Characterization and thermal stability of nanocomposites produced under nitrogen and in air N2 - The morphology and thermal behaviour of polypropylene–graft–maleic anhydride (PP–g–MA) layered silicate (montmorillonite) nanocomposites were investigated using X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and thermogravimetry. The study focuses on the influence of the presence of oxygen during the preparation of PP–g–MA–nanocomposite using two different modified clays. The nanocomposites show tactoid, intercalated and exfoliated structures side by side with different dominant states depending on the clay used and on the processing conditions. The systems are described as multi-component blends rather than binary blends since the organic ions do not only change the mixing behaviour, but also influence material properties. Beside the physical barrier property of the clay layers also chemical processes were found to play an important role. KW - Polypropylene-graft-maleic anhydride KW - Montmorillonites KW - Nanocomposites KW - X-ray KW - Thermal stability PY - 2003 DO - https://doi.org/10.1016/S0141-3910(03)00174-5 SN - 0141-3910 SN - 1873-2321 VL - 82 IS - 1 SP - 133 EP - 140 PB - Applied Science Publ. CY - London AN - OPUS4-2773 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gatla, S. A1 - Mathon, O. A1 - Rogalev, A. A1 - Pascarelli, S. A1 - Radnik, Jörg A1 - Pohl, M.-M. A1 - Brückner, A. T1 - Influence of Sb on the structure and performance of Pd-based catalysts: An X-ray spectroscopic study N2 - Combined X-ray photoelectron and absorption fine spectroscopy (XAFS) investigations on 10 wt % Pd–16 wt % Sb/TiO2 catalyst allow new insight into the impact of the co-component Sb on the active Pd species, which catalyzes the gas-phase acetoxylation of toluene to benzyl acetate. Ex situ Pd 3d XPS and Pd L-edge XANES studies indicate the presence of an excess electron charge on metallic Pd species (more 4d electrons than in Pd metal) formed after several hours of stream. This observation was explained by the electron transfer from metallic Sb incorporated into the Pd bulk to the neighboring Pd atoms. TEM-EDX analysis confirms the presence of intermixed Pd–Sb particles with an atomic ratio of between 5 and 6 in the most active catalysts and of 3 in deactivated samples. In situ Sb-K-edge XAFS investigations provide evidence that the Pd–Sb interaction is more pronounced under reaction feed than in the ex situ samples. KW - X-ray spectroscopy KW - Catalysis KW - Alloying / Intermixing PY - 2017 DO - https://doi.org/10.1021/acs.jpcc.6b10932 SN - 1932-7447 VL - 121 IS - 7 SP - 3854 EP - 3861 PB - American Chemical Society AN - OPUS4-39231 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kreft, S. A1 - Radnik, Jörg A1 - Agostini, G. A1 - Pohl, M.-M. A1 - Gericke, E. A1 - Hoell, Armin A1 - Beller, M. A1 - Junge, H. A1 - Wohlrab, S. T1 - Dye activation of heterogeneous Copper(II)-Species for visible light driven hydrogen generation N2 - Heterogeneous Cu catalysts are widely used in photocatalytic hydrogen generation. The typical working mode includes the transfer of photo-induced charges from a semiconductor to CuO which itself is reduced to Cu2O to initiate the catalytic cycle. In this contribution a photosensitizer (dye), excited by visible light absorption, was used to transfer an electron to the CuO which after reduction catalyzes the water reduction to hydrogen. Several copper(II)-catalysts on high surface silica were prepared by impregnation or precipitation and applied in photocatalytic water reduction. The best catalyst CuO(Cl0.1)/SiO2, synthesized via incipient wetness impregnation of CuCl2 in MCM-41 and a following precipitation with NaOH, achieved a 6 times higher activity (1702 mmol h-1 g-1) compared to a previously investigated copper system (280 mmol h-1 g-1 for CuI) under the same reaction conditions. All materials were fully characterized by XRD, TEM and N2 sorption and further by magnetic resonance and X-ray methods EPR, ASAXS and XAS. In situ measurements evidenced a reduction of the initial Cu(II)-species, which confirms the (proposed) photocatalytic mechanism. KW - Hydrogen generation KW - CuO nanoparticles KW - Molecular sieves PY - 2019 DO - https://doi.org/10.1016/j.ijhydene.2019.04.006 VL - 44 IS - 53 SP - 28409 EP - 28420 PB - Elsevier Ltd. AN - OPUS4-49350 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -