Frank Girgsdies

The Active Site of Methanol Synthesis over Cu/ZnO/Al2O3 Industrial Catalysts

Mechanisms in Methanol Catalysis The industrial production of methanol from hydrogen and carbon monoxide depends on the use of copper and zinc oxide nanoparticles on alumina oxide supports. This catalyst is “structure sensitive”; its activity can vary by orders of magnitude, depending on how it is prepared. Behrens et al. (p. 893, published online 19 April; see the Perspective by Greeley) used a combination of bulk and surface-sensitive analysis and imaging methods—along with insights from density functional theory calculations—to study several catalysts, including the one similar to that used industrially. High activity depended on the presence of steps on the copper nanoparticles stabilized by defects such as stacking faults. Partial coverage of the copper nanoparticles with zinc oxide was critical for stabilizing surface intermediates such as HCO and lowering energetic barriers to the methanol product. Catalysis is favored by stepped copper nanoparticles decorated with zinc oxide, which promotes stronger intermediate binding. One of the main stumbling blocks in developing rational design strategies for heterogeneous catalysis is that the complexity of the catalysts impairs efforts to characterize their active sites. We show how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al2O3 methanol synthesis catalyst by using a combination of experimental evidence from bulk, surface-sensitive, and imaging methods collected on real high-performance catalytic systems in combination with density functional theory calculations. The active site consists of Cu steps decorated with Zn atoms, all stabilized by a series of well-defined bulk defects and surface species that need to be present jointly for the system to work.

Al13Fe4 as a low-cost alternative for palladium in heterogeneous hydrogenation

Replacing noble metals in heterogeneous catalysts by low-cost substitutes has driven scientific and industrial research for more than 100 years. Cheap and ubiquitous iron is especially desirable, because it does not bear potential health risks like, for example, nickel. To purify the ethylene feed for the production of polyethylene, the semi-hydrogenation of acetylene is applied (80 × 10(6) tons per annum; refs 1-3). The presence of small and separated transition-metal atom ensembles (so-called site-isolation), and the suppression of hydride formation are beneficial for the catalytic performance. Iron catalysts necessitate at least 50 bar and 100 °C for the hydrogenation of unsaturated C-C bonds, showing only limited selectivity towards semi-hydrogenation. Recent innovation in catalytic semi-hydrogenation is based on computational screening of substitutional alloys to identify promising metal combinations using scaling functions and the experimental realization of the site-isolation concept employing structurally well-ordered and in situ stable intermetallic compounds of Ga with Pd (refs 15-19). The stability enables a knowledge-based development by assigning the observed catalytic properties to the crystal and electronic structures of the intermetallic compounds. Following this approach, we identified the low-cost and environmentally benign intermetallic compound Al(13)Fe(4) as an active and selective semi-hydrogenation catalyst. This knowledge-based development might prove applicable to a wide range of heterogeneously catalysed reactions.

Dissolved Carbon Controls the Initial Stages of Nanocarbon Growth

Carbon is a versatile material that, depending on its hybrid-ization and assembly in one-, two-, or three-dimensionalnetworks, exhibits important electronic and chemical proper-ties with countless practical applications. For example, it isfound in printer inks, pencils, water purification systems,thermal isolation, and antistatic materials.

Nanosizing Intermetallic Compounds Onto Carbon Nanotubes: Active and Selective Hydrogenation Catalysts**

Therefore, nanosizing andsupporting the annealed metal products remain challenges.Another difficulty is in directly preparing supportedcatalysts while simultaneously obtaining good crystallite sizecontrol. A good catalyst support should be capable ofinhibiting sintering and loss of the catalyst during reaction.Fabrication of supported intermetallics catalysts in nanoscaledimensionsrequiresareliablemethodthatfacilitatesnotonlysize control but a thermally stable phase under reactionconditions. Since the work of Iijima in 1991,

Pore structure and surface area of silica SBA-15: influence of washing and scale-up

Summary The removal of the surfactant (EO20PO70EO20) by washing before final calcination is a critical step in the synthesis of silica SBA-15. In contrast to washing with pure water or ethanol, washing with water and ethanol may, depending on the quantity of solvent used, alter the homogeneity and order of the pores, but also lead to an increase of the surface area of SBA-15. A reduction of solvent volume and a controlled washing protocol allow the synthesis of high surface area SBA-15 materials with a narrow monomodal pore size distribution. For larger batch sizes the influence of the quantity of solvent on the quality of the SBA-15 is reduced.

Chemically Induced Fast Solid-State Transitions of ω-VOPO4 in Vanadium Phosphate Catalysts

Vanadium phosphates are important catalysts for the oxidation of alkanes, and commercial catalysts comprise a complex range of V4+ and V5+ phosphates. We used three complementary in situ characterization methodologies—powder x-ray diffraction and laser Raman and electron paramagnetic resonance spectroscopies—to show that the metastable phase ω-VOPO4 is very sensitive to many of the reactants and products of butane oxidation. A rapid transformation from ω-VOPO4 to δ-VOPO4 occurs on exposure to butane at the reaction temperature, and hence the metastable ω-VOPO4 may play a role in the formation of commercial catalysts.

Intramolecularly stabilized organoaluminium and organogallium compounds: synthesis and X-ray crystal structures of some dimethylaluminium and -gallium alkoxides Me2MOROR′ and amides Me2MNHROR′

Abstract The intramolecularly stabilized dimeric organoaluminium and organogallium alkoxide complexes [(CH 3 ) 2 Al(μ-OROR′)] 2 (R/R′ = CH 2 CH 2 /C 6 H 5 ( 1a ) CH(CH 3 )CH 2 /CH 3 ( 2a ), CH 2 CH 2 C(CH 3 ) 2 /CH 3 3a ), CH 2 C 6 H 4 -2/CH 3 ( 4a ), C 6 H 4 -2/CH 3 ( 5a ), C 6 H 4 -2/C 2 H 5 ( 6a ), C 6 H 3 -4-CH 3 -2/CH 3 ( 7a ), [(CH 3 ) 2 Ga(μ-OROR′)] 2 (R/R′ = CH(CH 3 )CH 2 /CH 3 ( 2b ), CH 2 CH 2 C(CH 3 ) 2 /CH 3 ( 3b ), CH 2 C 6 H 4 -2/CH 3 ( 4b ), C 6 H 4 -2/CH 3 ( 5b ), C 6 H 4 -2/C 2 H 5 ( 6b ), CH 2 CH 2 /CH 3 ( 8b ),, [(CH 3 ) 2 Al(μ-NHROR′)] 2 (R/R′ = CH 2 CH 2 /CH 3 ( 9a ) and CH 2 CH 2 CH 2 /CH 3 ( 10a )) have been synthesized from trimethylaluminium or trimethylgallium and the corresponding alkoxy alcohols. Trimethylgallium reacts with CH 3 OCH 2 CH 2 NH 2 and CH 3 OCH 2 CH 2 CH 2 NH 2 with formation of the 1:1 adducts 11b and 12b , which decompose above 110 °C to yield CH 4 as well as [(CH 3 ) 2 Ga(μ-NH(CH 2 ) 2 OCH 3 )] 2 ( 9b ) and [(CH 3 ) 2 Ga(μ-NH(CH 2 ) 3 OCH 3 )] 2 ( 10b ) respectively. The 1 H-, 13 C-NMR and mass spectra of the new compounds, as well as the X-ray crystal structure analyses of 2b, 4a, 5a, 5b, 8b , and 12b , are reported and discussed.

Spinel-Type Cobalt–Manganese-Based Mixed Oxide as Sacrificial Catalyst for the High-Yield Production of Homogeneous Carbon Nanotubes

Potential applications of carbon nanotubes (CNTs) in very different fields such as electronics, medicine, or catalysis have been widely demonstrated on a laboratory scale. The development of CNT-based commercial products now mainly relies on CNTs’ ability to also fulfill the expectations on an industrial scale and on our ability to produce them at a reasonable cost. In the past, several attractive materials, such as fullerenes or nanodiamonds, lost some of their appeal because their synthesis is difficult to scale up for technical and economical reasons. For multiwalled carbon nanotubes (MWCNTs), their integration in commercial products depends on the availability of highpurity nanotubes with high homogeneity in size and in structure at a relatively low price. To date, high-quality MWCNTs are produced by catalytic chemical vapor deposition (CCVD) using transition metal heterogeneous catalysts. Despite many efforts, the yields remain relatively low, at best a few tens of grams MWCNTs per gram of catalyst. Purification using strong acids is therefore necessary to remove the remaining catalyst, which significantly increases the complexity of the production process. Herein, we demonstrate that spinel-type cobalt– manganese-based mixed oxide is a unique catalyst to produce MWCNTs. The yield is typically 2–9 times higher than that obtained with conventional catalysts, so that the purification step is no longer needed. In addition, the MWCNTs are exceptionally homogeneous in diameter, the standard deviation being only 4 nm. The high quality and high yield obtained allow for, to our knowledge, the first time MWCNTs to become a commodity chemical. Co, Mn, Al, and Mg in their nitrate forms were coprecipitated at pH 10 by using sodium hydroxide (see the Supporting Information). The precipitate was then filtered and thoroughly washed with distilled water to eliminate sodium and nitrate ions until the conductivity of the washing solution matched that of the freshly distilled water. The filtrate was subsequently dried in air at 180 8C for 5 h and calcined at 400 8C for 4 h to decompose it into the corresponding spinel-type mixed oxide. Finally, its efficiency in growing MWCNTs was tested by reducing it in diluted hydrogen (50 %) and exposing it to an ethylene/hydrogen feed at 650 8C for 2 h (see the Supporting Information for additional details). The yield was 179 gCNT g 1 catalyst (17 900 wt %), which is 2–9 times higher than the best yields previously obtained under similar conditions (Figure 1). Furthermore, residual catalyst impurities in the synthesized material were scarce and the purity was close to 99.5 % carbon, which is sufficient for most applications. Therefore, the traditional purification step with strong mineral acids is no longer required, thus rendering the overall process safer, greener and cheaper. In addition, the diameter distribution calculated from high-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (HRTEM) images was centered at 14 nm with a standard deviation of 4 nm, which is remarkably narrow. The produced MWCNTs were fully character-

Homoleptische Amide von Zink, Cadmium und Quecksilber

ZnCl2, CdCl2 und HgCl2 reagieren mit den Lithiumsalzen (1 a–5 a) der sterisch anspruchsvollen sekundaren Amine HN(SiMe3)Ph (1), HN(SiMe3)C6H3Me2-2,6 (2), HN(SiMe3)C6H3iPr2-2,6 (3), HN(SiMe3)C6H3tBu2-2,5 (4) und HN(SiMe2NMe2)C6H3iPr2-2,6 (5) unter Bildung der entsprechenden homoleptischen Metallamide Zn[N(SiMe2R′)R]2 (1 b–5 b), Cd[N(SiMe2R′)R]2 (1 c, 5 c) und Hg[N(SiMe2R′)R]2 (1 d–5 d). Mit Ausnahme des dimeren {Zn[N(SiMe3)Ph]2}2 (1 b) sind alle Verbindungen monomer. Die Charakterisierung der Verbindungen erfolgte durch Elementaranalysen, Molekulargewichtsbestimmungen, NMR- und Massenspektren. Die daruberhinaus durch Einkristall-Rontgenstrukturanalysen charakterisierten Zink- (1 b–5 b) und Quecksilberverbindungen (1 d–3 d und 5 d) zeigen mit Ausnahme von 1 b und 5 b eine lineare N–M–N Anordnung. Homoleptic Amides of Zinc, Cadmium, and Mercury ZnCl2, CdCl2 and HgCl2 react with the lithium salts (1 a–5 a) of the sterically demanding secundary amines HN(SiMe3)Ph (1), HN(SiMe3)C6H3Me2-2,6 (2), HN(SiMe3)C6H3iPr2-2,6 (3), HN(SiMe3)C6H3tBu2-2,5 (4), and HN(SiMe2NMe2)C6H3iPr2-2,6 (5) yielding the corresponding homoleptic metal amides Zn[N(SiMe2R′)R]2 (1 b–5 b), Cd[N(SiMe2R′)R]2 (1 c, 5 c), and Hg[N(SiMe2R′)R]2 (1 d–5 d), respectively. Except the dimeric {Zn[N(SiMe3)Ph]2}2 (1 b), all complexes are monomeric. The compounds were characterized by elemental analyses, molecular weight determinations, NMR and mass spectra. Furthermore, the zinc amides (1 b–5 b) and the mercury amides 1 d–3 d and 5 d were characterized by single crystal X-ray structure analysis. Except 1 b and 5 b, they show a linear N–M–N arrangement.

Sulfated zirconia with ordered mesopores as an active catalyst for n-butane isomerization

Zirconia/surfactant composites were hydrothermally synthesized in aqueous sulfuric acid at 373 K using Zr(O-nPr)4 as oxide precursor and hexadecyl-trimethyl-ammonium bromide as template. Mesostructural features similar to those of MCM-41 were detected by X-ray diffractometry, with d=4.6 nm. A sample obtained from a starting mixture with Zr:S:CTAB = 2:2:1 was stable enough for removal of occluded organics. After calcination at 813 K, the d-value was 3.6 nm, the surface area 200 m2/g, and the mean pore diameter estimated by the BJH method 2.2 nm. Extended X-ray absorption fine structure analysis suggests Zr to be in a short-range structure (<4 Å) similar to that of Zr in monoclinic ZrO2. Scanning electron microscopy including energy dispersive X-ray analysis showed 1-5 μm sulfur-containing ZrO2 spheres. The material catalyzes the isomerization of n-butane to i-butane at 378 K with a steady activity in the order of magnitude of commercial sulfated ZrO2.