NO adsorption and reaction on single crystal rutile TiO₂(110) surfaces studied using UHV–FTIRS

Abstract

The adsorption and reaction of NO on both the oxidized and reduced single crystal rutile TiO2(110) surfaces were studied in a UHV-FTIRS system at low temperature. The monodentate adsorption configuration of the cis-(NO)2 dimer at bridge oxygen vacancy (Vo) sites was detected for the first time on reduced TiO2(110) surfaces. With the aid of (NO)2 dimer adsorption anisotropy, the bidentate configuration of the cis-(NO)2 dimer on fivefold coordinated Ti5c(4+) cation sites was clearly confirmed. The (NO)2 dimer converts to N2O on Ti5c(4+) cation sites at higher NO dosage on both oxidized and reduced surfaces, rather than at Vo sites. The (NO)2 → N2O conversion is independent of the presence of Vo on TiO2(110) surfaces. To explain the signs of absorption bands of the dimer monodentate configuration, the local optical constant at Vo sites was introduced.

Nitric Oxide Reaction Pathways on Rutile TiO2(110): The Influence of Surface Defects and Reconstructions

“…According to the selection rule and the polarization/azimuth-resolved anisotropic IRRAS results, we can exactly clarify the vibration modes and the corresponding configurations of (NO) 2 dimers on oxidized TiO 2 (110) surfaces from the incident geometries of the IR beam in Figure , parts e and f: the negative 1875 cm –1 band in Figure , parts a and b, corresponds to the out-of-plane vibration; the 1748 cm –1 band with opposite signs in Figure , parts b and c, corresponds to the in-plane vibration along the [001] direction. These results confirm the presence of the cis -(NO) 2 dimer, , which adsorbs on the oxidized TiO 2 (110) surface in bidentate configuration along the [001] direction. In other words, two NO molecules adsorbing on adjacent Ti 5c sites couple though the N–N bond, as shown in Figure , parts g and h, denoted as cis -(NO) 2 /Ti&Ti dimer.…”

Temperature-programmed desorption study of NO reactions on rutile TiO2(110)-1 × 1

“…A stronger binding energy of 35 kcal/mol on oxygen vacancy sites has been also predicted by theory. Further, other bonding configurations such as (NO) 2 dimers have been theoretically [12,15] predicted and recently observed experimentally [15,16].…”

“…NO dimers of various forms (e.g., cis and trans) have been proposed to have binding energies of 10 -15 kcal/mol theoretically [12,41] [15,16]. Theoretical studies [15,44] on NO 2 /TiO 2 indicate that NO 2 is more strongly bound to TiO 2 than NO when NO 2 is bound to the Ti sites with its two oxygen atoms (η 2 -bonding configuration).…”

“…A great deal of insight has been obtained from studies performed on model rutile TiO 2 (110) surfaces [12][13][14][15][16]. It has been shown that NO adsorbs molecularly below ~ 100 K and desorbs at 120 K [17].…”

Temperature-Controlled CO Adsorption Configurations on (2 × 1)Ni–O/Ni(110) Surfaces

“…The experiments were carried out in a UHV−FTIRS system, 24 which combines a vacuum FTIR spectrometer (Bruker, Vertex 80v) and a multichamber UHV system (the base pressure better than 5 × 10 −11 mbar) equipped with a low energy electron diffraction (LEED)/Auger electron spectroscopy (AES) (with a gain power of microchannel plates BDL 600IR-MCP) and a quadrupole mass spectrometer for TDS measurements. The optical path inside the IR spectrometer and the space between the UHV chamber and the spectrometer were evacuated in order to avoid any unwanted IR absorption from gas phase species.…”