Cu Containing Octahedral Molecular Sieves and Octahedral Layered Materials

Abstract

Manganese oxide octahedral molecular sieves (OMS) with Cu2+in the tunnel (Cu-OMS-1) and octahedral layer (OL) manganese oxides with Cu2+in the interlayer of buserite-like materials (Cu-OL-1) were prepared and characterized by X-ray diffraction, scanning electron microscopy/energy dispersive X-ray analysis, temperature programmed reduction, thiosulfate titrations, and volumetric adsorption of carbon monoxide (CO). The materials were tested as CO oxidation catalysts. Results show that autoclave treatment of Cu-OL-1 suspensions induces complete removal of chlorine as well as a change of the Cu/Mn ratio and average manganese oxidation state. Such changes depend on the initial MnO−4/Mn2+ratio. At a ratio of 0.34–0.40, autoclave treatment increases the manganese oxidation state and the Cu/Mn ratio. At a ratio of 0.44, however, treatment decreases manganese oxidation state and the Cu/Mn ratio. A possible mechanism is proposed for the hydrothermal transformation of Cu-OL-1 to Cu-OMS-1. CO oxidation data show that Cu-OMS-1 has a CO conversion of 89–99% at 60–100°C, while Cu-OL-1 has almost no activity in the same temperature region. This dramatic difference is due to the fact that Cu-OMS-1 has more surface oxygen and a larger CO adsorption capacity, as compared to Cu-OL-1. Different structural properties may also contribute to the difference in catalytic activity, since the todorokite tunnel structure of OMS-1 is correlated with CO conversion. Blockage of the tunnels by water and tunnel collapse cause a significant decrease in CO oxidation. Kinetic studies of CO oxidation show that water vapor in the feed stream induces a small and reversible inhibition and that a positive reaction order is found with respect to CO partial pressure under these experimental conditions.