Journal fur Praktische Chemie - Chemiker-Zeitung p. 109 - 112 (1995)
Update date:2022-08-30
Topics:
Hauffe, K.
Buss, D. H.
Glemser, O.
As can be concluded from the experimental results at 450 deg 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 t he 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-LiO2 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-1molepercent Li2O covered with ionosorbed 0-xylene and ZnO-1molpercent 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.
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