Surface morphology and reactivity of microcrystalline MgO - Single and multiple acid-base pairs in low coordination revealed by FTIR spectroscopy of adsorbed CO, CD3CN and D-2

The surface morphology of two types of high specific surface area MgO powde rs (an ex-hydroxide MgO and a smoke one, eroded by H2O and CO2 attack) was studied by high resolution transmission electron microscopy (HRTEM) and inf rared spectroscopy of adsorbed probe molecules. HRTEM images show that sign ificant morphological defects are present on the surface of MgO microcrysta ls in both cases. Insights at a molecular level provided by the IR spectra of adsorbed probe molecules (CO, CD3 CN, D-2) indicate that Mg2+ ions on co rners, edges and (1 0 0) faces are exposed in comparable amount on the surf ace of the microcrystals of both kind of powders. By contrast, relevant dif ferences were found for multiple cationic sites and reactive Mg2+O2- pairs located in region with enhanced irregularity, constituted by steep successi ons of steps of one unit-cell dimension. This suggests that, besides the pr esence of different types of single morphological defects, the presence of ensembles of such sites must be taken into account when adsorption properti es and surface reactivity of different type of microcrystalline MgO materia ls are compared. (C) 2001 Elsevier Science B.V. All rights reserved.