Interaction of water, hydrogen and their mixtures with SnO2 based materials: the role of surface hydroxyl groups in detection mechanisms

DRIFTS, TGA and resistance measurements have been used to study the mechanism of water and hydrogen interaction accompanied by a resistance change (sensor signal) of blank and Pd doped SnO2. It was found that a highly hydroxylated surface of blank SnO2 reacts with gases through bridging hydroxyl groups, whereas the Pd doped materials interact with hydrogen and water through bridging oxygen. In the case of blank SnO2 the sensor signal maximum towards H-2 in dry air (R-0/R-g) is observed at similar to 345 degrees C, and towards water, at similar to 180 degrees C, which results in high selectivity to hydrogen in the presence of water vapors (minor humidity effect). In contrast, on doping with Pd the response to hydrogen in dry air and to water occurred in the same temperature region (ca. 140 degrees C) leading to low selectivity with a high effect of humidity. An increase in water concentration in the gas phase changes the hydrogen interaction mechanism of Pd doped materials, while that of blank SnO2 is unchanged. The interaction of hydrogen with the catalyst doped SnO2 occurs predominantly through hydroxyl groups when the volumetric concentration of water in the gas phase is higher than that of H-2 by a factor of 1000.

Bridging the Gap between Ionic Liquids and Molten Salts: Group 1 Metal Salts of the Bistriflamide Anion in the Gas Phase

Fourier transform ion cyclotron resonance mass spectrometry experiments showed that liquid Group 1 metal salts of the bistriflamide anion undergoing reduced-pressure distillation exhibit a remarkable behavior that is in transition between that of the vapor-liquid equilibrium characteristics of aprotic ionic liquids and that of the Group 1 metal halides: the unperturbed vapors resemble those of aprotic ionic liquids, in the sense that they are essentially composed of discrete ion pairs. However, the formation of large aggregates through a succession of ion-molecule reactions is closer to what might be expected for Group I metal halides. Similar experiments were also carried out with bis{(trifluoromethyl)sulfonyl}amine to investigate the effect of H+, which despite being the smallest Group 1 cation, is generally regarded as a nonmetal species. In this case, instead of the complex ion-molecule reaction pattern found for the vapors of Group I metal salts, an equilibrium similar to those observed for aprotic ionic liquids was observed.