The formation of H adducts during radiolysis of zeolites containing olefinic and aromatic hydrocarbon guests was demonstrated to occur by H atom transfer from the zeolite to the adsorbed molecules. The H adducts and other paramagnetic radiolysis products (radical cations and H-loss radicals) were detected by EPR spectroscopy. The mechanism of H adduct formation was confirmed by, inter alia, H/D isotopic labeling and comparison of results in HZSM5 and H−Mordenite to results in their Na+-exchanged counterparts. The effects of charge transfer among radiolysis products and zeolite−adsorbate interactions on the relative yields of trapped species is discussed. It is proposed that molecules smaller that a critical size adsorb inhomogeneously in ZSM5, forming aggregates in which ion−molecule reactions occur. Interpretation of the experimental results was aided by quantum chemical calculations of the molecular properties of the intermediates and their reaction energetics. This included evaluation of electron-transfer exothermicities, activation energies for H addition, and the relative acidities of the radical cations.

The reactions of •OH, O•- and SO4 •- with 2-, 3-, and 4-cresols were studied by pulse radiolysis, laser flash photolysis, and product analysis techniques. The rates of OH reaction with cresols are very high (k ≈ 1 × 1010 M-1 s-1), whereas O•- was found to be less reactive (k ≈ 2.4 × 109 M-1 s-1). The second-order rate constants for SO4 •- reaction with cresols are in the range (3−6) × 109 M-1 s-1. The transient absorption spectra measured in OH reaction exhibited peaks in the range 295−325 nm with a red shift for the meta isomer. The absorption spectra obtained for O•- reaction with 2-cresol has a peak at 360 nm, which is different from those measured with the m and p isomers (λ max = 310 and 380 nm). The absorption spectra of the transient species in SO4 •- reaction obtained by pulse radiolysis and flash photolysis techniques are similar, with absorption maxima centered around 290 and 390 nm in all three isomers. The intermediates formed in •OH, O•-, and SO4 •- reactions are assigned to OH adducts, substituted benzyl radicals, and radical cations, respectively. The rates for oxygen addition to OH adducts of 2-, 3-, and 4-chlorotoluenes and cresols are high, with k f values lying in the range (1−2.7) × 108 M-1 s-1. The relatively higher stability constants of peroxyl radicals formed with cresols (K = k f/k r = (2−5) × 104 M-1) than with chlorotoluenes suggest that the product-forming reaction competes effectively with the reverse reaction in cresols. Dihydroxytoluenes with OH groups ortho to each other were only formed in oxygenated solutions of cresols, and the mechanism involves the addition of oxygen to 1,3-type OH adducts at the carbon carrying the hydroxyl function.

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