Adsorption and interaction of ethylene on RuO2(110) surfaces

Ethylene (C2H4) adsorbed on the stoichiometric and oxygen-rich RuO2(110) surfaces, exposing coordinatively unsaturated Ru-cus and O-cus atoms, is investigated by applying high-resolution electron energy-loss spectroscopy and thermal desorption spectroscopy in combination with isotope labeling experiments. On the stoichiometric RuO2(110) surface C2H4 adsorbs and desorbs molecularly. In contrast, on the oxygen-rich RuO2(110) surface ethylene adsorbs molecularly at 85 K and is completely oxidized through interaction with O-cus and O-bridge upon annealing to 500 K. The first couple of reactions are observed at 200 K taking place on Ru-cus: A change from pi- to sigma-bonding, formation of -C=O and -C-O groups, and dehydrogenation giving rise to H2O adsorbed at Ru-cus. Maximum reaction rate is reached for C2H4 chemisorbed at Ru-cus with O-cus neighbors on each side. A model for the first couple of reactions is sketched. For the final combustion, C2H4 reacts both with O-cus and O-bridge. Ethylene oxide is not detected under any circumstance.     

Strukturuntersuchungen an Derivaten des Nickelkomplexes Ni(ONO) (ONO2− = Dianion einer dreizähnigen Schiffschen Base)

Structure Studies on Derivatives of the Nickel Complex Ni(ONO) (ONO^2? = Dianion of a Tridentate Schiff Base) The thermodynamically stable form of the solvent free, formally tri-coordinate complex Ni(ONO) (ONO^2? = dianion of N-(2-hydroxyphenyl)-2-ethoxycarbonyl-3-ox(o-butene(1) amine(1)) as well as the mono adducts Ni(ONO)X with X = ammonia and X = diphenyl thiourea (DPT) have been characterized by X-ray structure analysis. In all cases the central atom is coordinated in a square-planar fashion, only for the adduct Ni(ONO)(DPT) a pyramidal distortion is observed which is due to the formation of hydrogen bonds. The solvent free form is a dimer [Ni(ONO)]₂, and represents one of the few examples of dinuclear nickel complexes with a planar [NO₃] coordination. The phenolic O-atoms act as bridging ligands. Due to their reduced π-donor strength the bond lengths Ni? O trans to the bridges are significantly shortened. In contrast to the analogous complex with an aliphatic bridge, “NiEIA”, both halves of the dimeric molecules are coplanar with a Ni? Ni distance of 3.29 Å.     

Inhibition of CO oxidation on RuO2(110) by adsorbed H2O molecules

Catalytic CO oxidation on the RuO(2)(110) surface was studied at 300 K by scanning tunneling microscopy (STM), high-resolution electron-energy-loss spectroscopy (HREELS), and thermal desorption spectroscopy (TDS). Upon repeatedly exposing the surface to several 10 L of CO and O(2) at 300 K, STM shows that unreactive features accumulate with each CO and O(2) titration run. HREELS and TDS show formation of increasing amounts of H(2)O, retarded formation of O-cus atoms and incomplete removal of CO-bridge molecules during O(2) dosing, and a changing ratio of single- and double-bonded CO-bridge molecules. It is concluded that H(2)O (presumably from the residual gas) is accumulating at the Ru-cus sites thus blocking them, so that the dissociative adsorption of oxygen is prevented and the CO oxidation reaction is suppressed. Some 10% CO- bridge remains on the surface even during oxygen exposure. Consistent with this interpretation, deactivation of the surface is suppressed at 350 K, at the onset of H(2)O desorption.     

Surfactant polymer interactions between strongly interacting cationic surfactants and anionic polyelectrolytes from conductivity and turbidity measurements

The interactions between oppositely charged surfactant/polymer mixtures have been studied using conductivity and turbidity measurements. The dependence of aggregation phenomenon on the chain length and head group modifications of conventional cationic surfactants, i.e., hexadecyl- (HTAB), tetradecyl- (TTAB), and dodecyltrimethylammonium bromides (DTAB) and dimeric cationic surfactants, i.e., decyl- (DeDGB) and dodecyldimethylgemini bromides (DDGB), is investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolytes at critical aggregation concentration (cac). The cac values are considerably lower than the critical micelle concentration (cmc) values for the same surfactant. After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in aqueous polyelectrolyte than in pure water. Among the conventional and dimeric cationic surfactants, DTAB and DeDGB, respectively, have been found to have least interactions with oppositely charged polyelectrolytes.     

Mixed micelle behavior of Pluronic L64 and Triton X-100 with conventional and dimeric cationic surfactants

The mixed micellar properties of a triblock copolymer, Pluronic L64, (EO)13(PO)30(EO)13, and a nonionic surfactant, Triton X-100, in aqueous solution with conventional alkyl ammonium bromides and their dimeric homologues were investigated with the help of fluorescence and cloud point measurements. The composition of mixed micelles and the interaction parameter, beta, evaluated from the critical micelle concentration (cmc) data for different mixtures using Rubingh's and Motomura's theories are discussed. It has been observed that the mixed micelle formation between monomeric/dimeric alkyl ammonium bromides and L64 was due to synergistic interactions which increase with the increase in hydrophobicity of the cationic component. On the other hand, synergistic mixing was observed in the mixed micelles of Triton X-100 and monomeric cationic surfactants, the magnitude of which decreases slightly with the increase in hydrophobicity of the cationic component. Antagonistic interactions were observed in the case of Triton X-100 and dimeric cationic surfactants.     

Investigation of Al diffusion in different oxide thin-film layers by SNMS/HFM method

Depth profiles of Ga₂O₃/a-SiO₂/Al₂O₃- substrate, Ga₂O₃/a-Si₃N₄/Al₂O₃- substrate, and Ga₂O₃/Al₂O₃ substrate thin layers were determined by the SNMS/HFM method. Al diffusion from the Al₂O₃ substrate was investigated after 50, and in some cases after 600 hours of heat treatment time at different temperatures (600 °C,850 °C,950 °C,1050 °C and 1150 °C). The diffusion coefficient of Al at 850 °C was found to be D _Al=8.7 * 10^–18 cm²/s in amorphous SiO₂; D _Al=1.5*10^–17 cm²/s in amorphous Si₃N₄ and D _Al=5.5* 10^–16 cm²/s in Ga₂O₃ at 600 °C, respectively. The possible diffusion mechanism is explained in terms of the metal-oxygen bond-strengths. Although the studied materials have high resistivity at room temperature, the applied SNMS/HFM method has proven to be an efficient surface analytical tool even in these cases.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Zur deprotonierung von chloromethyleniminiumchloriden

Deprotonation of chloromethyleniminium chlorides ($\text{1}$, $\text{13}$) leads to cis-trans-isomeres 1,2-diamino-1,2-dichloro-ethenes ($\text{3a}$, $\text{3b}$ resp. $\text{14a}$, $\text{14b}$); their reactivity is described.