Reduction of Mn(IV) oxide by (NH4)(2)SO3 in the presence of metal ions in ammoniacal medium

The reduction of manganese dioxide with ammonium sulphite in the presence o f Cu(II), Ni(II) and Co(II) has been studied. It was observed that the cata lytic activity is in the order Cu(II)> Co(II)> Ni(II). The activation energ ies were estimated to be approximately 41, 70 and 74 kJ mol(-1) in the pres ence of Cu(II), Co(II) and Ni(TI), respectively. The catalytic reduction fo llows the shrinking core model. The interactive effects of metal ions were studied using 2(3) full factorial design of experiments. The linear coeffic ients for the three metals were positive whereas Cu(II)-Co(II) showed a neg ative correlation and Ni(II) did not have any synergistic effect. (C) 1999 Published by Elsevier Science B.V. All rights reserved.