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 inve stigate the surface structure of magnesia, magnesium-aluminum mixed ox ides, and alumina. Results from TPD of CO2 and 2-aminopropane and TPR of a-propanol indicate that the mixed oxides derived from hydrotalcite s 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 su rfaces of calcined hydrotalcites (mixed oxides) are oxygen-terminated (111) planes with surface defects that expose metal-oxygen pairs. Thes e defects are the likely sites for adsorption and reaction. We specula te that, as the amount of aluminum incorporated into the mixed oxide i ncreases, more of these surface defects are formed, thus increasing th e adsorption capacity of the materials.