Die entscheidende Mitwirkung der Metall- und Sauerstoffionen von Nickeloxid beim Ablauf der Oxidation von o-Xylol

The Decisive Cooperation of Metal and Oxygen Ions of Nickel Oxide During the Oxidation of o-Xylene As can be concluded from the experimental results at 450°C in the reaction mixtures consisting of N₂ O₂-o-Xylene, both nickel oxide pure and doped with Li₂O or In₂O₃ is unsuited as catalyst for the oxidation of o-xylene to phthalic anhydride. In contrast to NiO which ionosorbs both oxygen and o-xylene, NiO Li₂O, a strong ionosorbent for o-xylene, prevents the ionosorption of oxygen because of the large concentration of holes. Since gaseous oxygen does not react with ionosorbed o-xylene but a reduction of nickel oxide to metallic nickel has been observed in spite of the fact of enough oxygen in the gas phase it can be assumed that o-xylene is forced to remove oxygen ions from the NiO lattice under generation of oxygen-ion vacanxies and nickel atoms. The predominant portions of the reaction products are H₂O and CO₂. With undoped nickel oxide and NiO In₂O₃ which were not reduced under the same experimental conditions, the reaction products had roughly the same composition. The reduction of NiO Li₂O however will be prevented in a gas mixture with a high oxygen pressure which oxidizes the formed nickel atoms on the surface of NiO Li₂O to nickel oxide making possible the entrance of oxygen from the gas phase and, therefore, the oxidation of o-xylene. A turbulent motion of a 2-component catalyst powder from NiO-1mole% Li₂O covered with ionosorbed o-xylene and ZnO-1mole% In₂O₃ covered with ionosorbed oxygen in the same gas mixture resulted in the same reaction products as in the presence of sole NiO Li₂O under simultaneous reduction of nickel oxide. From that we can conclude that the oxidation of o-xylene by oxygen ions of NiO occurs more easily than the reaction with ionosorbed oxygen on ZnO In₂O₃ which obviously seems to be bounded too strongly. This result is also confirmed by the prevention of the oxidation of gaseous o-xylene in the presence of only ZnO In₂O₃. Finally, the operation of the carrier catalyst V₂O₅/TiO₂ which is employed for the oxidation of o-xylene to phthalic anhydride will be prevented to a large extent in simultaneous presence of nickel oxide either pure or doped with Li₂O and In₂O₃ in roughly the same amount. This result can be mentioned as a proof for the interaction of a 2-component catalyst the mechanism of which is at present not satisfactorily understood.