Über Oberflächenverbindungen von Übergangsmetallen VI. Die Umsetzung von Oberflächen—Chrom(II) mit Ammoniak

Abstract

Die Komplexbildung von koordinativ ungesättigtem Oberflächen‐Chrom(II) mit NH3 wurde mittels Reflexionsspektroskopie und Thermogravimetrie untersucht. Bei Temperaturen ≦100°C wird NH3 unter Bildung eines violetten Komplexes der Stöchiometrie Cr(II)/H3 = 1:2 gebunden. Bei Temperaturen ≦50°C und 1 atm. NH3 bildet sich eine NH3‐reichere, tiefblaue Verbindung, der die Stöchiometrie 1:4 zugeordnet wird. Die thermogravimetrischen Messungen können hier nicht ohne zusätzliche Annahmen (Adsorptionsmodell!) ausgewertet werden, wodurch eine größere Unsicherheit des Resultats verursacht wird.

Nature and Estimation of Functional Groups on Solid Surfaces

“…Adsorption of other Lewis bases has also been studied. Ammonia [508], water [509], alcohol [509], ethers [509] and trimethylsilanol [509] form quite stable, purle-colored complexes with a ratio of Cr: ligand equal to 1: 2. When the adsorptive are offered in excess, additional molecules are adsorbed much more weakly.…”

Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

“…With ethylene, CO and H 2 , Cr 2+ is the dominant species on silica, while on alumina Cr 3+ is preferentially formed . The obtained reduced Cr n + species (with n = 2, 3, or 5) can be either saturated or unsaturated, and the latter will readily chemisorb different molecules, like ammonia, water, olefins, alcohols, ethers, CO, and NO. − ,− ,,,, The interaction between Cr 5+ and ammonia, ethylene, and water has been extensively investigated by ESR. , Upon adsorption of small water doses on Cr/SiO 2 , pseudotetrahedral Cr 5+ (coordination number of 4) is converted to a square-planar Cr 5+ (coordination number of 5) and octahedral Cr 5+ (coordination number of 6). The same results are obtained with ethylene instead of water …”

“…36 Detailed DRS studies on the interaction between water, alcohol, and ether molecules and silica-supported Cr 2+ ions were carried out by Krauss and co-workers. [52][53][151][152][153][154][155] They show that a coordinative unsaturated Cr 2+ ion can be easily converted to its coordinative saturated counterpart by introducing various molecules. Finally, CO and NO can chemisorb on reduced Cr sites and IR spectroscopy may be used to discriminate between the different coordination geometries, as outlined in the characterization In addition, the interaction between supported Cr 2+ and ethylene can be followed by IR spectroscopy.…”

Mechanistic aspects of the olefin polymerization by Phillips catalysts via C1 species

“…The experimental apparatus consists of a gas-handling system, a reactor, and an on-line product analysis by gas chromatography, quadrupole mass spectroscopy (QMG 101-Balzers), and IR spectroscopy. The catalyst preparation and the chromium analysis were described earlier (Hierl and Krauss, 1973;Krauss et al, 1975). The metal concentrations of the catalysts were chosen to be 0.3-0.9% * Kraftwerk Union AG, DeNOx-, DeSOx-Department, Postfach 3220, D-8520 Erlangen, FRG.…”