Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Decomposition of hydrogen peroxide in aqueous solution was studied on nickel oxide-molybdenum trioxide two-component catalysts with various proportions of the constituents covering the entire region of 0-100% of one component. The systems were found to comprise the two oxides and, in the region of 18-92 mol.% MoO₃, a small quantity of nickel molybdate, which, however, does not affect appreciably their catalytic activity. A change in the kinetics of the reaction was found in its initial stage, which is probably associated with surface reduction of Mo⁶⁺ ions (major catalytic centres) to ions in lower oxidation state (minor centres) whose surface concentration determines the catalytic activity. The nickel oxide present probably accelerates this process, obviously occuring also during the ageing of the catalysts. In the regions of very low contents of one component the catalytic activity is determined by that of the major constituent, but is appreciably affected by the admixture oxide. In the range of 15 mol.% MoO₃ both oxides contribute significantly to the catalytic activity; the activity is rather high, which is explained in terms of the concept of bivalent catalytic centres. In addition to the minor centres constituted by Ni³⁺ and probably also Mo⁵⁺ ions, determining the catalytic activity of the system, catalytic centres of another kind also take part in the reaction; these may be associated with structure defects on the catalyst surface. The greatest part play these centres in catalysts with roughly equal proportions of the two constituents. Neither the mutual influencing of the two components of the system nor the mechanism of the testing reaction alters on prior irradiation of the system by gamma radiation or by neutrons. The irradiation, however has a negative effect on the catalytic activity of the sample with 2.7 mol.% MoO₃, both kinds of catalytic centres (of charge and structure nature, respectively) being probably affected. In the case of catalyst with 76.2 mol.% MoO₃, radiation of both kinds induces increase in the catalytic activity; this is probably due to the establishment of a new equilibrium of the charge defects acting as catalytic centres in the reaction in question.