II — kinetics of the catalytic decomposition of hydrogen peroxide solution by manganese dioxide samples

✍ Scribed by M.W. Rophael; N.S. Petro; L.B. Khalil

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 721 KB
• Volume: 22
• Category: Article
• ISSN: 0378-7753
• DOI: 10.1016/0378-7753(88)87004-6

✦ Synopsis

The catalytic decomposition rates of hydrogen peroxide solution by twelve MnO, samples have been shown to follow a similar order to those of the reduction rates by hydrazine. This suggests a correlation between the catalytic and battery activities of MnOz. Doping MnO, with Ga"' and MoV' increased the catalytic decomposition of H,Oz compared with the undoped sample, an effect which may be due to lattice distortion. In general, the catalytic decomposition rate of H,O, was found to increase with the BET surface area. Acid-washing increased the rate of decomposition. This is believed to remove Mn" ions, which probably inhibit, rather than participate in the catalytic decomposition, from the surface. The initial decomposition rates of H,O, at pH 7.2 and 25 "C followed first order kinetics with respect to the peroxide. At pH values between 3 and 10, however, the decomposition rate was constant but at a pH of 12 it increased sharply. At even higher pH values the decomposition rate decreased. This last effect was attributed to the intrinsic instability of H,O, in alkaline solutions, possibly enhanced by OH-catalysis.

The difference in the catalytic decomposition rates of H,O, over the various crystalline manganese dioxides may, in view of the proton diffusion rates, be explained by differences in the crystallographic structure. The catalytic decomposition rate increased as the particle size decreased, emphasising the importance of the real rather than the BET surface area. The low catalytic decomposition rates observed with partially reduced samples, compared with the rates for the unreduced samples, may be explained by the formation of surface Mn"' ions on reduction.