Surface morphology and reactivity towards CO of MgO particles: FTIR and HRTEM studies

The morphology and adsorptive behaviours of two different MgO samples are compared. High resolution transmission electron micrographs indicate that MgO powders produced by decomposition of the hydroxide contain extremely rough particles, whereas nicely shaped and smooth cubelets are present in the MgO smoke sample. The proportion of surface sites exposed on (001) planes (five-coordinated) as compared with sites exposed on edges (four-coordinated) and corners (three-coordinated) is much larger on MgO smoke than on MgO ex-hydroxide. CO adsorption shows that at 300 K various families of polymeric anionic species are formed by interaction with basic sites in the lowest coordination (O2−3C) in corner positions. The relative population of the different species depends on the morphology of the particles. CO adsorption at 77 K produces bands due to CO adsorbed on acidic Mg2+5C, Mg2+4C and Mg2+3C sites, whose relative intensities also depend on the morphology of the particles.