AN INFRARED-SPECTROSCOPY AND TEMPERATURE-PROGRAMMED DESORPTION STUDY OF CO ON MOO3/AL2O3 CATALYSTS - QUANTITATION OF THE MOLYBDENA OVERLAYER

The adsorption of CO on pure gamma-Al2O3 and a series Of MoO3/Al2O3 catalysts with different Mo loading has been investigated using infrared (IR) spectroscopy and temperature-programmed desorption (TPD). Carbon monoxide adsorbs selectively on Al3+ sites on the uncovered, free alumina portion of the surface; these sites are created by dehydroxylation of the alumina. As the Mo loading is increased, the CO adsorption capacity of the catalysts decreases in a linear fashion as the MoO3 overlayer covers an increasing fraction of the alumina support. Overlayer growth saturates at a loading of (42 +/- 3) x 10(13) Mo atoms/cm2 and corresponds to less than a complete monolayer as 14 +/- 5% of the alumina support remains uncovered. Extrapolation of the overlayer growth curve to ''monolayer'' coverage allows calculation of a MoO3 cross-sectional area of approximately 22 angstrom2, in good agreement with values predicted by theoretical models.