Insights into Acetone Photochemistry on Rutile TiO₂(110). 1. Off-Normal CH₃Ejection from Acetone Diolate

Abstract

Thermal-and photon-stimulated reactions of acetone coadsorbed with oxygen on rutile TiO 2 (110) surface are studied with infrared reflection−absorption spectroscopy (IRAS) combined with temperature-programmed desorption and angle-resolved photon stimulated desorption. IRAS results show that η 2 -acetone diolate ((CH 3 ) 2 COO) is produced via thermally activated reactions between the chemisorbed oxygen and coadsorbed acetone. Formation of acetone diolate is also consistent with 18 O/ 16 O isotopic exchange experiments. During UV irradiation at 30 K, CH 3 radicals are ejected from the acetone diolate with a distribution that is peaked at ∼±66°from the surface normal along the [11̅ 0] azimuth (i.e., perpendicular to the rows of bridging oxygen and Ti 5c ions). This distribution is also consistent with the orientation of the C−CH 3 bonds in the η 2 -acetone diolate on TiO 2 (110). The acetone diolate peaks disappear from the IRAS spectra after UV irradiation, and new peaks are observed and associated with η 2 -acetate. The data presented here demonstrate direct signatures of the previously-proposed two-step mechanism for acetone photooxidation on TiO 2 (110).

WO3-Based Gas Sensors: Identifying Inherent Qualities and Understanding the Sensing Mechanism

“…This indicates that the methyl group is not strongly affected by the adsorption of acetone to the surface. As a result of thermal activation, Petrik et al found the formation of acetone diolates through the reaction of adsorbed acetone with adsorbed surface oxygen . Based on theoretical calculations, Würger et al attribute a splitting of the band attributed to the carbonyl (two bands at 1700 and 1679 cm –1 ) to the formation of these diolates.…”

“…As a result of thermal activation, Petrik et al found the formation of acetone diolates through the reaction of adsorbed acetone with adsorbed surface oxygen. 65 Based on theoretical calculations, Wurger et al attribute a splitting of the band attributed to the carbonyl (two bands at 1700 and 1679 cm −1 ) to the formation of these diolates. This splitting is clearly visible in the DRIFT spectra of the ME sample at 200 °C.…”

Photoconversion of 2-Propanol on Rutile Titania: A Combined Liquid-Phase and Surface Science Study

“…Interestingly, the peak at 1700 cm –1 corresponding to the CO stretching vibration is very small in comparison to the other band. Usually, in Fourier transform infrared (FT-IR) spectroscopy, this band is the most prominent for carbonyl-containing compounds. , One reason may be that we started with irradiating the multilayer before heating and the ACE formation is dependent on the IPA concentration. A second interpretation is that the ACE precursor does not contain a carbonyl bond and thus ACE may be formed during desorption.…”

Adsorption and reactions of C6 compounds with CC, COH, and/or CO groups on TiO2

“…[ 12 ] Recently, adsorption of acetone and acetaldehyde on the single crystal surface of rutile TiO 2 (110) has been investigated using infrared spectroscopy. [ 28,29 ] In addition to the physisorption forms, with infrared absorptions similar to those of gas molecules, acetone and acetaldehyde can be adsorbed in the forms of η 2 ‐acetone diolate ((OC(CH 3 ) 2 O), with 1,013, 1,178, and 1,195 cm −1 for the vibrational modes of ρ(CH) 3 , ν(CCC) and/or ν(OCO), and of dioxymethylene ((OCH 2 O), with 1,065 and 1,075 cm −1 for ν(CO)), respectively. [ 28,29 ] In Figure 1a, the small, broad peak approximately at 1,590 cm −1 could be due to MO, the condensation product of acetone.…”