CHARACTERIZATION OF MG-AL MIXED OXIDES BY TEMPERATURE-PROGRAMMED REACTION OF 2-PROPANOL

In this work, temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) of several probe molecules were used to investigate the surface structure of magnesia, magnesium-aluminum mixed oxides, and alumina. Results from TPD of CO2 and 2-aminopropane and TPR of a-propanol indicate that the mixed oxides derived from hydrotalcites have surface adsorption capacities and reactivities similar to those of MgO. However, these characteristics are signifcantly influenced by the hydrotalcite synthesis method. The adsorption capacities of these materials for CO2, 2-aminopropane, and 2-propanol suggest that the surfaces of calcined hydrotalcites (mixed oxides) are oxygen-terminated (111) planes with surface defects that expose metal-oxygen pairs. These defects are the likely sites for adsorption and reaction. We speculate that, as the amount of aluminum incorporated into the mixed oxide increases, more of these surface defects are formed, thus increasing the adsorption capacity of the materials.