'H MAS NMR Studies of Alumina-Supported Metal Oxide Catalysts

The interactions of two-dimensional vanadium oxide and molybdenum oxide overlayers with the surface hydroxyls of an alumina support were examined with 'H MAS NMR spectroscopy. The measurements demonstrated that these surface metal oxide overlayers are homogeneously distributed over the alumina surface and essentially titrate all the accessible surface hydroxyls at monolayer coverage. The investigation also revealed that there are a small number of protons formed near monolayer coverage, suspected of being Bronsted acid sites, which are not titrated by these metal oxide overlayers and are capable of undergoing H/D exchange. In addition, there are protons in blocked pores of the alumina support that neither are accessible to the metal oxide overlayers nor are capable of undergoing H/D exchange. The present 'H MAS NMR results are in excellent agreement with corresponding IR spectroscopy results on the same catalysts.