No abstract

Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N2O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N2O, temperature programmed desorption of H2, and kinetic experiments. The presence of ZnO dramatically influences the N2O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu-ZnO interface and can be used to easily quantify the intensity of Cu-Zn interaction. N2O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H2.

No abstract

Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N₂O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N₂O, temperature programmed desorption of H₂, and kinetic experiments. The presence of ZnO dramatically influences the N₂O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu-ZnO interface and can be used to easily quantify the intensity of Cu-Zn interaction. N₂O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H₂

By reaction of the tetrafluorides MF4 or the ternary silver fluorides Ag3M2F14 (M = Zr, Hf) with dry liquid ammonia at –40 °C, the pentaammoniates [M(NH3)4F4]·NH3 (1, M = Zr; 2, M = Hf) were obtained, and these compounds represent hitherto unknown molecular inorganic Zr and Hf compounds that simultaneously bear nitrogen and fluorine ligands. The compounds crystallize isotypically in the shape of colorless needles in the tetragonal space group P4/ncc. As a further product [NH4(NH3)]F (3) was isolated in the form of colorless cubes in the orthorhombic space group Pca21. It is the first ammoniate of ammonium fluoride. Ag(NH3)2F·2NH3 (4) can be synthesized either from AgF or AgF2 in liquid ammonia. The compound crystallizes merohedrally twinned in the orthorhombic space group Pnna and represents the first crystallographically characterized diamine silver(I) halide complex. In the latter two structures, free fluoride anions are encountered. The ammoniates are highly temperature‐sensitive and decompose at temperatures above –30 °C due to their ammonia pressure.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)