Oberflächenverbindungen von Übergangsmetallen. XVIII. Der Einfluß der Cr-Konzentration auf Oxydationszahl und „Qualität”︁ von Cr-Oberflächenverbindungen auf Silicagel

Surface Compounds of Transition Metals. XVIII. The Influence of Cr Concentration on Oxidation Number and “Quality” of Cr Surface Compounds on Silicagel Mean oxidation number (OZ ) and mean unsaturated character (q ) of reduced Cr surface compounds on silicagel depend on the concentration of Cr in the product. The first effect is caused by the decrease of thermally stable surface Cr^VI with increasing Cr concentration in the activated product, since surface Cr^VI is the only precursor of surface Cr^II (constant yield of reduction～90%); consequently OZ _red shifts to higher values with increasing concentration. — The measured decrease of q with increasing Cr content cannot be correlated with a possible coordination of neighbouring SiOH groups, as it was suggested for the influence of T_act and T_red; other explanations are proposed. For the analyzed product, the results support the postulated model of an ensemble of topologically different individual surface species of typical reactivity.     

Über Oberflächenverbindungen von Übergangsmetallen. VIII. Die Komplexbildung von koordinativ ungesättigtem Oberflächen-Chrom (II) mit Oxiden des Stickstoffs

On Surface Compounds of Transition Metals. VIII. Complex Formation of a Coordinatively Unsaturated Cr^II Surface Compound with Nitrogen Oxides N₂O forms with surface-Cr(II) a relatively unstable light blue compound of the stoichiometry 1:1, while addition of NO results in formation of a very stable dark brown, diamagnetic surface complex . By reaction with O₂ this complex undergoes — depending on reaction temperature — either replacement of NO unter reoxidation of the metal (→Cr(VI)) or/and reaction of the ligand (→NO₂). Direct reaction of NO₂ with results in the same products as stepwise addition of NO and 1/2 O₂. reacts with HCl/ROH under formation of the soluble, paramagnetic kation [Cr(NO)(ROH)_n]²⁺, which is formulated as [Cr(II)(NO)]²⁺ ? [Cr(I)(NO⁺)]²⁺ accordingly to the e.s.r. spectra.     

Über Oberflächenverbindungen von Übergangsmetallen. X [1]. Zum Stöchiometrie-Problem der Bindung von Oberflächen-Chrom(II) an Silicagel

On Surface Compounds of Transition Metals. X. The stoichiometry Problem of Fixation of Surface Chromium (II) on Silicagel. Thermogravimetric analysis of a reduced Philips catalyst (support: silicagel “Merck 7733”) shows that the metal is bound prediminantly (if not only) in chromate-like units up to a concentration of 2,8% Cr^II. At higher Cr^II contents. up to the maximum of 3.5%, the additionally fixed chromium does not consume further OH^s, within the scope of the thermogravimetric method formation of polychromatelike structures and/or use of not-neighbouring OH groups. The analysis further demonstrates that not all the Si? Oh groups comprised by the method are able to accommodate surface chromium. The fixation of the metal seems to proceed most likely by reaction with the vicinal pairs of Si? OH, as a correlation of our data with silica models shows.     

Oberflächenverbindungen von Übergangsmetallen. XXX. Fischer-Tropsch-analoge Umsetzung von CO/H2 bzw. CO2/H2 an Oberflächen-Chrom(II)

Surface Compounds of Transition Metals. XXX. Fischer-Tropsch Analogous Reactions of CO/H₂ and CO₂/H₂ on Surface Chromium(II) Surface chromium(II)/silicagel catalyzes the reduction of CO and CO₂ by hydrogen to CH₄, C₂H₆ and C₃H₈. The catalyst is partially desactivated by this reaction, but a permanent activity of ca. 30% remains. – The reaction can be formulated via the sequence formaldehyde complex → <CH₂>-complex → alkane. If cycloalkenes or chlorobenzene are added simultaneously, these scavenger molecules are methylated by <CH₂>.     

Über Oberflächenverbindungen von Übergangsmetallen. V. Oligomere Reaktionsprodukte bei der Polyäthylen- Synthese mit Chrom-Oberflächenverbindungen

On surface compounds of transition metals. V. Oligomeric reaction products by the polymerization of ethylene with chromium surface compounds Short time polymerization of ethylene with Cr(II) and Cr(VI) surface species on oxide carriers produces oligomeric reaction products, when followed by protonolysis, that originate, at least in part, from the decomposition of a soluble organochromium complex. Different homologous series result according to the type of heterogeneous catalyst employed: with Cr(II) contact α-olefines are obtained (in presence of O₂ the corresponding n-aldehydes are formed), Cr(VI) contacts give straightchain methylketones. Whereas the aldehyde formation occurs in secondary reactions the CH₃CO endgroup is produced evidently through the primary oxidation of C₂H₄ with surface Cr(VI). A polymerization sequence is then discussed in terms of protonolysis products wherein the alkene and acetyl endgroups are attached at that chain end which is not bound to chromium.     

„Die Kristallstruktur von Molybdännitridchlorid,MoNCl3”︁

The thermal decomposition of CoCO₃ Co(OH)₂ (H₂O)_0,5 in the temperature range from 20 to 600°C, in air as well as in a dynamic nitrogen atmosphere, employing TGA, DTA, chemical analysis, and X-ray analysis, has been investigated. The course of the process in N₂ differs completely from that in air, passing through a number of stages. The most probable mechanism of decomposition is proposed and an interpretation of the phenomena is given.