High-Temperature Hall Measurements on BaSnO3Ceramics

Simultaneous Hall and conductivity measurements were performed in situ between 650° and 1050°C on n-type semiconducting BaSnO₃ceramics. The variation of the Hall mobility and the Hall carrier density as a function of oxygen partial pressure between 10² and 10⁵ Pa and of temperature was investigated. At temperatures below 900°C the conductivity exhibits a dependence on temperature and oxygen partial pressure which is mainly determined by variations of the Hall mobility. Above 900°C most of the significant dependence is due to a variation in carrier density. Furthermore, a simple defect model assuming doubly ionized oxygen vacancies and acceptor impurities is discussed for BaSnO₃.     

New Aromatic Azapentalenes: 3H‐ and 2H‐Imidazo[1,2‐d]tetrazoles

A number of title compounds ( 3a,c,4a—c ) were prepared by cyclization of 5‐aminotetrazolium salts having ketonic substituents ( 1,2 ). The following procedures were applied: a) for 3a, 4a,b : heating of 1a, 2a,b with acetic anhydride‐ base; b) for 3c,4c : heating of 1b,2b in a buffer solution of pH 6.5 (Tschitschibabin reaction). The proclivity for ring closure was more pronounced with the salts 2 . The 6‐unsubstituted representatives 3c and 4c underwent S_E‐reactions, the 2H‐isomer 4c being slightly more reactive; this was confirmed by AM1 calculations. The nitroso product 4g exists predominantly as the valence‐isomeric nitrile oxide 6 .     

Verlustfreie Katalysatorrezirkulation durch ein neuartiges Verfahrensprinzip bei der Hydroformylierung höhermolekularer Olefine

Free-of-loss Catalyst Recycling in the Hydroformylation of Higher Molecular Olefins by a Novel Process Technology In this paper a novel homogenous-heterogeneous procedure for the hydroformylation reaction of higher molecular olefins is presented, at which the reaction itself is homogeneously catalyzed and only after the reaction the catalyst complex is heterogenized only for separation. This procedure is achieved by using the lithium salt of triphenylphosphine monosulfonic acid (Li-TPPMS) as complex ligand for the hydroformylation catalyst and methanol as solubilizer. Li-TPPMS and its complexes with metal carbonyls are highly soluble in water and methanol, but completely insoluble in almost all other organic solvents. After the reaction the methanol is distilled off. The catalyst system becomes insoluble and can be separated from the reaction product by filtration or by extraction with water. The aqueous catalyst solution is evaporated to dryness and the catalyst system dissolved in methanol for a new reaction.     

Infrared characterization of the surface intermediates in the oxidation of toluene on vanadyl pyrophosphate catalysts

The adsorption and reaction of toluene on vanadyl pyrophosphate catalysts was studied by in situ infrared spectroscopy. Strongly adsorbed benzaldehyde and physically adsorbed cyclic anhydride species were observed at temperatures above 523 K. Water formed during reaction generates acid hydroxyl groups which cause a stronger adsorption of benzaldehyde and consecutive oxidation reactions. By co-adsorption of pyridine the acid sites are blocked and the deeper oxidation is suppressed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydroformylierung einfach und mehrfach ungesättigter Fettstoffe mit heterogenisierten Cobaltcarbonyl- und R

Hydroformylation of mono and multiple unsaturated fatty substances with heterogenized cobaltcarbonyl and rhodiumcarbonyl catalysts. Heterogenized cobalt and rhodiumcarbonyl catalyst systems can be used for the hydroformylation of mono and polyunsatured fatty substances in a technically simple and satisfying manner to useful chemical intermediates. The used solid tert. phosphane complex ligands have a silicate matrix and therefore they are also suitable for the cobalt catalyzed hydroformylation which is best performed at temperatures of 160–180^oC. The cobalt catalyzed reaction gives with polyunsaturated fatty substances almost only products with monofunctionalized fatty acid chains. Whereas, the rhodium catalyzed reaction gives with linolic acid compounds inhomogeneous mixtures of mono- and diformyl derivatives of these fatty substances. The heterogenized rhodium carbonyl catalyst systems therefore seem to be more suitable for the hydroformylation of monounsaturated compounds. This is also true for rhodiumcarbonylsupported aqueous phase-catalysts which give likewise mixtures of mono and diformyl derivatives in the hydroformylation of polyunsaturated fatty substances. In batch process after the complete conversion of the olefin and reduction of the CO/H₂-pressure the loss of catalyst metal from the support is negligible and in most cases below the detection limit (<1 ppm).     

Development of organosilicone–polyurethanes as stone preservation and consolidation materials

Two organosilicone-modified polyurethanes are investigated as potential materials for the conservation and consolidation of natural stones. The materials are low molecular weight oligomers at the application stage and react with the humidity of the air to give polymers, forming continuous microlayers. The two differ in the length of the organosilicone chain, resulting in pronounced differences in their physical state: one forms a brittle glassy material (T_g ≈ 70°C). and the other, a soft rubbery material (T_g ≈ −100°C). The rate of the polymerization of the prepolymers was investigated at different conditions, showing a strong dependence on the presence of a catalyst and air humidity. Both these favorable conditions exist probably in the natural stone pores, enhancing the formation of the protective hydrophobic internal microlayer. © 1996 John Wiley & Sons, Inc.