TAP studies on the reoxidation of some partially reduced vanadia-based catalysts

The interaction of oxygen with partially reduced vanadia-based catalysts was investigated by Temporal Analysis of Products (TAP) transient technique in order to determine the degree of reduction and its effect on the reoxidation process. The well-defined Eurocat catalyst EL10V1 was chosen as reference catalyst and, based on the results obtained by oxygen titration (oxygen adsorption capacity), its degree of reduction was determined at different reaction temperatures. The values were in good agreement with those obtained by propane titration. The reducibility increases by increasing the temperature. The degree of reduction of a new class of vanadium oxide catalysts, obtained by magnetron sputter deposition, was also determined and the values were compared with those obtained on EL10V1, when a number of propane molecules equivalent of a degree of reduction of 21% for EL10V1 was pulsed over all samples. For the sputtered catalysts, the oxygen uptake at 773 K decreased from 0.94 to 0.68 μmol O2/m2 with increasing deposition time from 1 to 5.5 h. The degree of reduction of another well-defined Eurocat catalyst, EL10V8, was also determined. At the same temperature the oxygen uptake increased from 0.18 μmol O2/m2 on EL10V8 to 1.17 μmol O2/m2 on EL10V1. Reversible molecular adsorption of oxygen, followed by irreversible dissociation, allows to describe the single-response TAP data for EL10V1 and EL10V8. For the sputtered catalysts a one-stage irreversible dissociative adsorption of oxygen provides the best description of such single-response TAP data.