Time-resolved FT-IR spectra of ethylene hydrogenation over alumina-supported Pt catalyst were recorded at 25 ms resolution in the temperature range 323 to 473 K using various H 2 flow rates (1 atm total gas pressure). Surface ethyl species (2870 and 1200 cm

New sulfoximine- and phenanthrene-based photochemical precursors to oxynitrenes have been developed. These precursors have been used to examine the chemistry and spectroscopy of oxynitrenes. The first EPR spectra of oxynitrenes are reported and are consistent with their triplet ground states. Additional support for the triplet ground state of oxynitrenes is provided by trapping and reactivity studies, nanosecond time-resolved IR investigations, and computational studies.

The aqueous photochemistry of the sodium salt of 1-(N,N-diethylamino)-diazen-1-ium-1,2-diolate (3) has been investigated by both experimental and computational methods. Photolysis results in the formation of the N-nitrosodiethylamine radical anion (5) and nitric oxide (NO) via a triplet excited state. The nitrosamine radical anion either undergoes electron transfer with NO before cage escape to form triplet NO(-) and nitrosamine (minor process) or rapidly dissociates to form an additional molecule of NO and ultimately amine (major process). The production of nitrosamine radical anion 5 upon photolysis of diazeniumdiolate 3 is confirmed by low-temperature EPR spectroscopy. The calculated energetics for the ground and excited states of the parent diazeniumdiolate ion at the CIS and B3LYP levels of theory as well as B3LYP calculations on the fragmentation processes were very effective in rationalizing the observed photodissociation processes.

Time-resolved FT-IR spectra of carbon monoxide hydrogenation over aluminasupported ruthenium particles were recorded on the millisecond time scale at 700 K using pulsed release of CO and a continuous flow of H 2 /N 2 (ratio 0.067 or 0.15, 1 atm total pressure). Adsorbed carbon monoxide was detected along with gas phase products methane (3016 and 1306 cm -1 ), water (1900 -1300 cm -1 ), and carbon dioxide (2348 cm -1 ). Aside from adsorbed CO, no other surface species were observed. The rate of formation of methane is 2.5 ± 0.4 s -1 and coincides with the rate of carbon dioxide growth (3.4 ± 0.6 s -1 ), thus indicating that CH 4 and CO 2 originate from a common intermediate.The broad band of adsorbed carbon monoxide has a maximum at 2010 cm -1 at early times (36 ms) that shifts gradually to 1960 cm -1 over a period of 3 s as a result of the decreasing surface concentration of CO. Kinetic analysis of the adsorbed carbon monoxide reveals that surface sites absorbing at the high frequency end of the infrared band are temporally linked to gas phase product growth. Specifically, a (linear) CO site at 2026 cm -1 decays with a rate constant of 2.9 + 0.1 s -1 , which coincides with the rise constant of CH 4 . This demonstrates that the linear CO site at 2026 cm -1 is the kinetically most relevant one for the rate-determining CO dissociation step under reaction conditions at 700 K.

Vanadia was incorporated in the 3-dimensional mesoporous material TUD-1 with a loading of 2% w/w vanadia. The performance in the selective photo-oxidation of liquid cyclohexene was investigated using ATR-FT-IR spectroscopy. Under continuous illumination at 458 nm a significant amount of product, i.e. cyclohexenone, was identified. This demonstrates for the first time that hydroxylated vanadia centers in mesoporous materials can be activated by visible light to induce oxidation reactions. Using the rapid scan method, a strong perturbation of the vanadyl environment could be observed in the selective oxidation process induced by a 458 nm laser pulse of 480 ms duration. This is proposed to be caused by interaction of the catalytic centre with a cyclohexenyl hydroperoxide intermediate. The restoration of the vanadyl environment could be kinetically correlated to the rate of formation of cyclohexenone, and is explained by molecular rearrangement and dissociation of the peroxide to ketone and water. The ketone diffuses away from the active center and ATR infrared probing zone, resulting in a decreasing ketone signal on the tens of seconds time scale after initiation of the photoreaction. This study demonstrates the high potential of time resolved ATR FT-IR spectroscopy for mechanistic studies of liquid phase reactions by monitoring not only intermediates and products, but by correlating the temporal behavior of these species to molecular changes of the vanadyl catalytic site.