Synthesis of manganese oxide octahedral molecular sieves containing cobalt, nickel, or magnesium, and the catalytic properties for hydration of acrylonitrile Original Research Article

An octahedral molecular sieve known as OMS-1 has todorokite structure composed of magnesium and manganese oxides, which was named as Mg-todorokite here. Octahedral molecular sieves containing cobalt (Co-todorokite) or nickel (Ni-todorokite) without magnesium were prepared by a sequential method under optimum conditions and compared with the Mg-todorokite by powder XRD, ICP, FESEM, and catalytic reactions. The compositions of Co-todorokite, Ni-todorokite, and Mg-todorokite are Co0.37MnO2.3(H2O)2.1, Ni0.24MnO2.0(H2O)2.1, and Mg0.22MnO2.0(H2O)2.2, respectively. The Co-todorokite and Ni-todorokite are comparable in crystallinity with the highly crystalline Mg-todorokite. The catalytic properties were examined for the hydration of acrylonitrile. The apparent activation energies depend on the foreign metals. The order is Co-todorokite < Ni-todorokite < Mg-todorokite. The four products of the Mg-todorokite catalysis are 3-hydroxy-propionitrile, and bis-2-cyano-ethylether, succinonitrile, and acrylamide. The acid treatments for Mg-todorokite suppress the formations of 3-hydroxy-propionitrile and bis-2-cyano-ethylether, which would be due to the weakening of the basicity with the removal of magnesium ions. The only product of the Co-todorokite and the Ni-todorokite catalysis is acrylamide because of not containing magnesium.