Time-Resolved Study of Acetyl Radical in Zeolite NaY by Step-Scan FT-IR Spectroscopy

Abstract

Step-scan FT-infrared spectroscopy of 1-naphthyl acetate and pinacolone photodissociation in zeolite NaY revealed a transient at 2125 cm -1 assigned to acetyl radical. Comparison of the intensities of transient and final product absorptions, 2-acetyl-1-naphthol in the case of naphthyl acetate and acetaldehyde for pinacolone, indicates that the acetyl radical represents the main, and probably only, reaction channel. The decay of the radical at room temperature is best described by a single-exponential law with a lifetime of 71 ( 15 µs (1-naphthyl acetate) and 315 ( 30 µs (pinacolone). This constitutes the first detection and kinetic study of a small transient radical in a zeolite. The kinetic result is interpreted in terms of complete separation of the photogenerated pairs from the parent supercage, followed by random walks in subspaces of the zeolite lattice imposed by the much less mobile precursor molecules. These force the geminate radicals to react and thereby contribute to the high selectivity of these photoreactions.

Probing zeolites by vibrational spectroscopies

“…in the ns range. There have been only a few reports on the use of step-scan FTIR to characterize homogeneous 851 and heterogeneous [852][853][854] catalytic systems in general and zeolites [855][856][857][858][859][860][861][862] in particular. Under these conditions, the data are signals S x j (t i ) as a function of time t i for each position x j .…”

“…855 To the best of our knowledge, this result represented the first time-resolved IR spectrum of a transient molecule in a zeolite. 855 Subsequently, the same group used the step-scan FTIR method to monitor short-lived radicals (formyl and acetyl radicals) in zeolites 857,858,860 and Fe-AlPOs 859 molecular sieves. The observed Dñ(CO) = À100 cm À1 of this band, relative to the n(CO) of the ground state, confirms the pp* character of the lowest triplet state of duroquinone, as expected due to the highly polar environment of the Na-Y zeolite cage.…”

Probing the Reactivity of Photoinitiators for Free Radical Polymerization: Time-Resolved Infrared Spectroscopic Study of Benzoyl Radicals

“…It has been demonstrated that time-resolved infrared (TRIR) spectroscopy is a powerful technique for the direct detection of benzoyl and aliphatic acyl radicals. [19][20][21][22] This is due to the fact that these radicals generally have strong ν CO absorptions, in the range 1780-1880 cm -1 , with high extinction coefficients; e.g., for the unsubstituted benzoyl radical with ν CO ) 1828 cm -1 in n-hexane, ≈ 1300 M -1 cm -1 . 22 In this paper we report a systematic TRIR study of the reactivity of benzoyl radicals 1b-6b toward the acrylic monomer n-butylacrylate and toward oxygen addition.…”

Acid-Free Nitration of Benzene and Toluene in Zeolite NaZSM-5

“…Testova et al [15] have reported bands at 2345 and 2140 cm −1 in HZSM-5 while Chao and Lundsford report peaks at 2000 and 2100 cm −1 in NaY [24]. Comparison with the acetyl radical [25,26] suggests that it may be more appropriate to designate these species as zeolite⋅ ⋅ ⋅ Na (1− )+ ⋅ ⋅ ⋅ NO 2 + (abbreviated from here on as NO 2 + for brevity) resulting from donation of electron density from the NO 2 HOMO to the Na + when the complex forms. As increases, the peak of the symmetric stretch will shift to a higher frequency (see Figure 5) 1677 cm −1 originate from NO 2 that interacts only weakly with the zeolite's environment because they are close to the gasphase frequency [29].…”