ADSORPTION OF NO AND CO ON RH/ZRO2(100)

The structure and adsorption properties of Rh films supported on a ZrO2(100) crystal have been examined using Auger electron spectroscopy (AES), transmission electron microscopy (TEM), and temperature programmed desorption (TPD) of NO and CO. For Rh vapor deposition at 300 K, film growth is close to two dimensional; however, metal particles are formed by heating above ≈500 K or exposure to air. Transmission electron diffraction (TED) indicates that the particles are preferentially oriented with respect to the substrate, which implies that interactions exist between the support and the Rh. TPD curves for CO are essentially independent of particle size and are similar to curves obtained on bulk Rh crystals. However, TPD curves for NO are strongly affected by particle size and film annealing. For particles between 3 and 10 nm formed by annealing, more than 98% of the NO dissociated during TPD from a saturation exposure. For the 10-nm particles, the TPD results were similar to curves on bulk metals in that N2 left the surface from two separate features: a sharp peak at 440 K due to NOad + Nad = N2 + Oad and a broad feature between 450 and 700 K due to Nad recombination. For smaller particles, only the recombination feature was observed at approximately the same temperature. The implications of these results to understanding support and particle size effects for NO reduction by CO are discussed. The results do not indicate strong electronic interactions between Rh and ZrO2, but do suggest that Rh particle morphologies may be altered by ZrO2, which could, in turn, affect catalytic properties. © 1991.