STRUCTURE FUNCTION RELATIONSHIPS IN ND2O3-DOPED MGO CATALYSTS FOR THEMETHANE COUPLING REACTION/

MgO doped with Nd2O3 has been evaluated as a catalyst for the oxidativ e coupling of methane (OCM) reaction, It is demonstrated that signific ant improvements in methane conversion efficiency and selectivity to C -2 products (as compared to pure MgO) can be achieved. The level of ca talytic improvement is shown to be dependent on the Nd2O3 concentratio n and the precise catalyst preparation method. Detailed transmission e lectron microscopy studies have been performed on the Nd2O3/MgO cataly sts prepared by an impregnation route and by a number of coprecipitati on methods. Six distinct neodymia morphologies on the MgO support have been identified. These are (i) crystalline thin films, (ii) Nd2O3 cry stallites attached to the MgO support, (iii) isolated Nd2O3 needles, ( iv) epitaxial microclusters, (v) disordered thin films, and (vi) isola ted clusters. The relative proportions of these Nd2O3 morphologies in the catalysts are also shown to depend upon the neodymia loading and t he preparation route. Cross-correlation between microstructural observ ations and catalytic performance data for these materials enable us to deduce that the disordered neodymia films, which probably contain som e dissolved Mg2+ ions, are largely responsible for the improvement in OCM performance. (C) 1997 Academic Press.