Manfred Schwickardi

Ti-doped alkali metal aluminium hydrides as potential novel reversible hydrogen storage materials

Abstract New reversible hydrogen storage systems are proposed, based on catalyzed reactions (Eqs. 4–6). The catalytic acceleration of the reactions in both directions is achieved by doping alkali metal aluminium hydrides with a few mol% of selected Ti compounds. The PCI diagrams of the Ti catalyzed systems show an absence of hysteresis and nearly horizontal pressure plateaus. The PCI of the NaAlH4 system reveals two temperature-dependent pressure plateaus, corresponding to the two-step reversible dissociation of NaAlH4. The PCI of the Na3AlH6 system shows only one pressure plateau; the latter can be lowered by partial substitution of Na by Li. In cyclic tests, reversible H2 capacities of 4.2–3.1 and 2.7–2.1 wt% H have been achieved.

Metal-doped sodium aluminium hydrides as potential new hydrogen storage materials

Abstract Thermodynamics and kinetics of the reversible dissociation of metal-doped NaAlH 4 as a hydrogen (or heat) storage system have been investigated in some detail. The experimentally determined enthalpies for the first (3.7 wt% of H) and the second dissociation step of Ti-doped NaAlH 4 (3.0 wt% H) of 37 and 47 kJ/mol are in accordance with low and medium temperature reversible metal hydride systems, respectively. Through variation of NaAlH 4 particle sizes, catalysts (dopants) and doping procedures, kinetics as well as the cyclization stability within cycle tests have been substantially improved with respect to the previous status [B. Bogdanovic, M. Schwickardi, J. Alloys Comp. 253–254 (1997) 1]. In particular, using combinations of Ti and Fe compounds as dopants, a cooperative (synergistic) catalytic effect of the metals Ti and Fe in enhancing rates of both de- and rehydrogenation of Ti/Fe-doped NaAlH 4 within cycle tests, reaching a constant storage capacity of ∼4 wt% H 2 , has been demonstrated. By means of 57 Fe Mossbauer spectroscopy of the Ti/Fe-doped NaAlH 4 before and throughout a cycle test, it has been ascertained that (1) during the doping procedure, nanosize metallic Fe particles are formed from the doping agent Fe(OEt) 2 and (2) already after the first dehydrogenation, the nanosize Fe particles with NaAlH 4 present are probably transformed into an Fe–Al-alloy which throughout the cycle test remains practically unchanged.

Co3O4-SiO2 nanocomposite: a very active catalyst for CO oxidation with unusual catalytic behavior

A high surface area Co(3)O(4)-SiO(2) nanocomposite catalyst has been prepared by use of activated carbon as template. The Co(3)O(4)-SiO(2) composite, the surface of which is rich in silica and Co(II) species compared with normal Co(3)O(4), exhibited very high activity for CO oxidation even at a temperature as low as -76 °C. A rather unusual temperature-dependent activity curve, with the lowest conversion at about 80 °C, was observed with a normal feed gas (H(2)O content ~3 ppm). The U-shape of the activity curve indicates a negative apparent activation energy over a certain temperature range, which has rarely been observed for the heterogeneously catalyzed oxidation of CO. Careful investigation of the catalytic behavior of Co(3)O(4)-SiO(2) catalyst led to the conclusion that adsorption of H(2)O molecules on the surface of the catalyst caused the unusual behavior. This conclusion was supported by in situ diffuse reflectance Fourier transform infrared (DRIFT) spectroscopic experiments under both normal and dry conditions.

Listening to catalysis - a real time parallel method for high throughput product analysis

In this paper, we describe the development of two parallel real time detection systems for the analysis of the products of a heterogeneously catalyzed gas phase reaction based on the photoacoustic effect. We developed a process addressing the problem of automated catalyst preparation and prepared bulk metal oxides with high surface areas by an automated, parallelized synthesis based on activated carbon. To evaluate analytical systems and catalytic activity of our materials we performed catalytical tests in CO oxidation and ODH of ethane.

Direct Synthesis of Supported Noble Metal Catalysts via the Activated Carbon Route

Abstract Simultaneous impregnation of activated carbon with a base metal oxide precursor and a noble metal precursor with subsequent combustion of the activated carbon leads in one step to supported metal particles on very high surface area support oxides having specific surface areas of several hundred square metres per gram. For some of the noble metals (Rh, Pt) it is possible to synthesize supported particles in the size range of one to a few nanometers via this route.

Magnesiumorganische Innerkomplexe, Teil I [1] Bis(dialkylaminoalkyl)- und Bis(alkoxybutyl)magnesium-Verbindungen / Organomagnesium Inner Com plexes, Part I [1] Bis(dialkylaminoalkyl)- and Bis(alkoxybutyl)magnesium Compounds

A series of magnesium inner complexes has been prepared by reacting MgH2 (prepared by homogeneous catalysis) with dialkylallyl- and -3-butenylamines and -3-butenylethers in the presence of catalytic amounts of ZrCl4. The monomeric nature of bis(4-methoxybutyl)magnesium has been confirmed by X-ray diffraction. The analogous syntheses of bis(3-alkoxypropyl)magnesium compounds failed: cleavage of the allyl ether with elimination of propene occurred. This cleavage reaction is accelerated by catalytic amounts of NiCl2 or ZrCl4