Characterization and Fourier transform infrared studies of the effects of TiO 2 crystal phases during CO oxidation on [formula omitted] catalysts

Abstract

The catalytic oxidation of CO was investigated on Pt TiO 2 catalysts in an infrared cell reactor to study the influence of strong metal-support interaction effects on oxidation reactions and of using different crystal forms of TiO 2. Catalysts were prepared using rutile and anatase TiO 2 and were characterized by chemisorption, X-ray diffraction, and X-ray photoelectron spectroscopy. Hydrogen reduction at 500 °C suppresses CO and H 2 chemisorption and leads to changes in Pt 4f 7 2 electron binding energies for both phases of TiO 2. The anatase catalysts show an infrared absorption band around 2091 cm −1 which is assigned to linear-bonded CO; whereas, the rutile catalysts show an absorption doublet for adsorbed CO around 2094 and 2075 cm −1 and bands around 1840 cm −1 assigned to bridge-bonded CO. Both catalysts show the adsorption of CO 2 as a carbonate-like species which is demonstrated to be adsorbed onto the support. The effects of reduction temperature and of support material on CO oxidation activity were compared through temperature-programmed reaction experiments. The catalysts reduced at 200 °C show slightly higher activity and lower ignition temperatures than those reduced at 500 °C. The rutile-supported catalysts show much higher CO oxidation activity with lower ignition temperatures; the increased activity is speculated to result from a lower activation energy for oxygen desorption. A morphological model of metalsupport interactions involving oxygen transfer from the rutile support is proposed to coexist with the Langmuir-Hinshelwood reaction mechanism.