Simultaneous Characterization of Solid Acidity and Basicity of Metal Oxide Catalysts via the Solid-State NMR Technique

A novel characterization method for simultaneous determination of acidity and basicity of metal oxide catalysts has been developed by using the solid-state NMR technique. Three typical oxides, namely ZrO2, Al2O3, and MgO, were characterized by the 13C and 31P MAS NMR using 13CO2 and trimethylphosphine as the acidic and basic probe molecules, respectively. The results reveal that simultaneous characterization of acidity and basicity is different from the sole one because the acidic and basic sites coexist on the surface of metal oxides and both of them influenced each other through interaction between probe molecules and acid or base centers. To validate the simultaneous characterization method, the reaction of acetone self-condensation was further investigated by an in situ NMR technique. The reaction results are well in accordance with the acidic and basic properties characterized by the coadsorption method with acidic and basic probe molecules. The present work provides an efficient method for simultaneous characterization of acidity and basicity of a catalyst.