With two examples, the oxidation of H, and CO on Pt carrier catalysts, it is shown that special states of chemisorption and kinetics of surface processes can create periodicity and bistable behaviour of catalytic reactions. The (nonisothermal) oscillations of the HZ oxidation can be traced back to the superposition of a slow oxidation-reduction process under participation of an active and an inactive (blocking) chemisorption species of oxygen, in agreement with TDS measurements. By means of a stability analysis, based on the linearized balance equations, the main features of the oscillatory behaviour can be explained. -With the CO oxidation oscillations under isothermal conditions have been studied that appear as precursors to a quenching of the reaction. A periodic change of the CO coierage (blocking) of the catalyst surface was demonstrated. For the formation of the CO coverage via CO clusters on the surface, in the sense of dissipative structures, a mechanism with co-operation of the chemisorption process and the LH-reaction is shown up. The periodic reactivation of the surface is attributed to the increase of desorption probability (decrease of desorption energy) with increasing packing density of the CO. A quantitative treatment, however, is not yet possible at present, because relationships for the kinetics of non-random distributions on surface sites are rnissinp.
The present work is devoted to the study of spontaneous periodic potential oscillations under corrosion of ductile chromium with admixtures of 0.1 to 0.4 wt-% Ru, Os, Ir, Pt, or Pd in still aerated 40 to 55% solutions of H2S04 at temperatures between 40 and 120°C. -A mechanism has been suggested to describe the formation of potential oscillations on chromium alloys. It is assumed that oscillations appear, when the alloy is in a passive-active state, as a result of the change in the value of pH in the near-electrode layer. -It has been established that cathodic additives (Ru, Os, Ir, Pt, Pd) differ in their effect upon the appearance of oscillations of potential on chromium alloys.
Aus Eiweißstoffen wurden nach den von Troensegaard angegebenen Methoden mehrere basische Stoffe in Form krystallisierter Salze isoliert. 1 ) Die Summenformel dieser Stoffe wies darauf hin, daß es sich um ringförmige Verbindungen handelte. Die weitere Frage war nun, ob diese Einge -entsprechend der von Troensegaard aufgestellten Theorie -als solche im Eiweißmolekül vorhanden waren, oder ob sie sich erst sekundär aus aliphatischen Spaltprodukten des Proteins oder aus Seitenketten solcher Spaltprodukte durch die erwähnte Behandlungsmethode gebildet hatten.Für die Basen C 5 H 12 N 2 und C 7 H 16 N 2 wurde vor kurzem der Konstitutionsbeweis erbracht 2 ); in ihnen liegen substituierte Piperazine vor, die aus Diketopiperazinen bei der Keduktion nach Troensegaard entstanden sind. -Die vorliegende Arbeit bringt den Konstitutionsbeweis und die Entstehungsweise zweier weiterer Basen. Die eine -C 5 H 11 NO -wurde nach dem "Eeduktionsverfahren", die andere -O^nNgO -nach dem "Acetolyseverfahren" gewonnen. Ihre Isolierung und Beschreibung erfolgte in früheren Arbeiten. 3 ) Die Base C 5 H 1]L NO war aus Gliadin durch Acetylierung, anschließende Eeduktion mit metallischem Natrium in Amylx ) Troensegaard,, Wrede u. Mygind,
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