Influence of Conditions of Synthesis of Cobalt and Manganese Oxides on Their Ability to Catalytic Decomposition of Hydrogen Peroxide

Abstract

Cobalt and manganese oxides and their complex oxide compositions were obtained by the sol-gel method using various precipitators(ammonia solution and HMTA). It was determined by X-ray diffraction method that both individual and co-precipitated hydroxo compounds after calcination at 400 °С form oxide phases of Co3O4 and Mn3O4 composition. Samples obtained by sedimentation with ammonia solution have a larger specific surface area than synthesized in HMTA solution. When calcined at 400 °C, the specific surface area for cobalt-containing samples sedimentated with ammonia solution decreases, and for samples sedimentated from HMTA solution - increases. The pore volume depends on the precipitator and changes little during calcination. For co-sedimentated and calcined at 400 °C samples, the specific surface area plays a significant role: the higher it is, the greater the catalytic ability of the sample to decompose hydrogen peroxide. On the SEM image of samples driedat 100 °C, sedimentated with ammonia solution, agglomeration of flat particles of gitrated oxides of cobalt and/or manganese of globular form is observed. For samples deposited in HMTA solution, SEM images are represented by agglomeration of particles in the form of planar layers. Calcination at 400 °C partially destroys the structure. Kinetic studies of the decomposition of hydrogen peroxide with theparticipation of the obtained samples indicate the first order of the reaction. Samples of cobalt hydroxide and co-sedimentated cobalt and manganese hydroxy compounds synthesized in HMTA solution showed the best ability to catalyze. The highest productivity (dm3 H2O2 of decomposed 1 g of catalyst) is inherent in samples of cobalt hydroxy compounds and its composition with manganese compounds synthesized by HMTA, after heat treatment at 100 °C. The ability of such samples to catalytic decomposition of hydrogen peroxide is estimated to be not less than 2.4 dm3 H2O2 (14 days). Compared to compounds synthesizedwith ammonia solution, they retain their activity for a longer time.