Carbon Monoxide Adsorption on Molybdenum Phosphides: Fourier Transform Infrared Spectroscopic and Density Functional Theory Studies

Molybdenum phosphide (MoP) and supported molybdenum phosphide (MoP/g-Al2O3) have been prepd. by the temp.-programmed redn. method. The surface sites of the MoP/g-Al2O3 catalyst were characterized by carbon monoxide (CO) adsorption with in situ Fourier transform IR (FT-IR) spectroscopy. A characteristic IR band at 2037 cm-1 was obsd. on the MoP/g-Al2O3 that was reduced at 973 K. This band is attributed to linearly adsorbed CO on Mo atoms of the MoP surface and is similar to IR bands at 2040-2060 cm-1, which correspond to CO that has been adsorbed on some noble metals, such as platinum, palladium, and rhodium. D. functional calcns. of the structure of molybdenum phosphides, as well as CO chemisorption on the MoP(001) surface, have also been studied on periodic surface models, using the generalized gradient approxn. (GGA) for the exchange-correlation functional. The results show that the chemisorption of CO on MoP occurred mainly on top of molybdenum, because the bonding of CO requires a localized min. potential energy. The adsorption energy obtained is DHads ~ -2.18 eV, and the vibrational frequency of CO is 2047 cm-1, which is in good agreement with the IR result of CO chemisorption on MoP/g-Al2O3.