Phase Transformation On Ni-catalyst Surface In Co Catalytic Oxidation

Category: Ukrainean-polish sympozium

PHASE TRANSFORMATION ON Ni-CATALYST SURFACE IN CO CATALYTIC OXIDATION

V. K. Yatsimirsky, V. L. Budarin, V. Y. Diyuk

Shevchenko University, Chemistry departement,

Volodimirska 64, Kyiv, 01017, UKRAINE

E-mail: yats@chem.univ.kiev.ua

It is known that there are two mechanisms of catalytic oxidation of CO on NiO. The shift from one mechanism to the other occurs at 623-673K. The nickel Curie point (633K) is occurs in the same temperature range.

The reaction of CO catalytic oxidation on NiO and the reaction of NiO reduction by CO were studied in a closed apparatus with circulating argon flow. Pulse method of gas injection was realised. Product concentration (CO2) was determined in an IR-cell by means of an IR-spectrometer (SPECORD 71). The sensitivity of this method is 10-7 mol/l.

It has been found that in the reaction of CO catalytic oxidation on NiO at the Curie temperature of Ni (Tc=633K) occurs a mechanism change. The mechanism change is characterised not only by the change of kinetic parameters at T=633K, but also by modification of the catalyst structure which exists in equilibrium with reaction mixture.

At high temperature (T>633K) occurs the formation of Ni clusters on NiO surface. These clusters according to magnetic measurement data (the magnetic susceptibility via temperature) are ferromagnetic. Ni clusters dimensions exceed 10-30 Å. So as a result of catalysis at temperatures more then 633K the partial NiO reducing with formation of new phase (Ni) in subsurface catalyst layer takes place.

The samples of catalyst at T

In order to explain mechanism change of nickel oxide (NiO) catalysis at 633K, the kinetics of the reactions of nickel oxidation with molecular oxygen

at 473-973K and reduction of nickel oxide with CO at 423-703K are being studied in detail.

There are no critical phenomena at 633K for Ni oxidation with O2.

The reaction of NiO reduction with CO occurs only at T>633K. At 633K the mechanism of NiO reduction changes. It is shown that at T



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