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Room-temperature oxidation of methane to methanol by α-oxygen is of great mechanistic interest for both conventional and biomimetic oxidation catalysis. This work was carried out using new-generation FeZSM-5 samples that have the Oα concentration of 100 μmol/g. This value exceeds 3−15 times the Oα concentration on the earlier studied samples, thus providing more precise quantitative measurements related to the reaction mechanism. Fourier transform infrared spectroscopy data confirmed an earlier conclusion that CH4 + Oα surface reaction proceeds by the hydrogen abstraction mechanism. This mechanism leads to hydroxy and methoxy groups residing on α-sites. The methanol formation takes place by hydrolysis of (Fe-OCH3)α groups at the step of extraction. For the first time dimethyl ether (DME) was identified in the reaction products, its amount comprising 6−7% of the methane reacted. In distinction to methanol, DME is readily extracted both by dry solvents (acetonitrile, tetrahydrofuran, ethanol) and their mixtures with water. A reliable extraction procedure was developed, which provides a 75% recovery of the methane oxidation products (methanol + DME). The missing products are shown to remain on the catalyst surface and can be quantitatively recovered in the form of CO x at heating the sample. A mechanism involving CH3 • radicals formed in the H-abstraction step is suggested to explain the reaction stoichiometry CH4:Oα = 1:1.75 and a deficit of the carbon balance at extraction.

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In spite of a long investigation history, the low-temperature isotopic exchange in dioxygen taking place without involvement of the catalyst oxygen (R0 exchange) is still an exotic and poorly understood phenomenon in heterogeneous catalysis. Although very strong bonds are to be cleft in O2 molecules (118 kcal/mol), over some metal oxides R0 can be observed even at the temperature of liquid nitrogen. In this work, we studied the R0 exchange over a FeZSM-5 zeolite at 233 K and discovered for the first time a linear dependence of the R0 rate on the concentration of O•– radicals (α-oxygen), which identifies a catalytic role of these species. Upon transition to cryogenic temperatures, O•– species lose the ability to exchange themselves with dioxygen, but start functioning as a principal part of unique active sites capable of catalyzing a very smooth redistribution of the oxygen–oxygen bonds in adsorbed O2 molecules. Running by a highly concerted mechanism, this remarkable process leads to the R0 exchange with almost zero activation energy (0.2 kcal/mol). The catalytic role of O•– radicals well explains all previous results obtained for the R0 exchange in the literature. Possible models of active sites comprising O•– species are discussed.

The present study focuses on a new method for obtaining C2−C3 carbonyl compounds (ketones and aldehydes) by the gas-phase selective oxidation of a propane−propylene mixture using nitrous oxide (N 2 O). The oxidation is carried out without catalyst in the temperature range of 623−773 K at elevated pressure. The obtained results reveal that only propylene in the propane− propylene mixture reacts with nitrous oxide. The reaction proceeds by the nonradical mechanism involving the 1,3-dipolar cycloaddition of N 2 O to the CC double bond of olefin. The main reaction products are acetone, propanal, and acetaldehyde. At 723 K and a pressure of 0.7 MPa, the total selectivity to these products amounts to 74.6%, the N 2 O conversion attains 74.5%, and the propylene conversion is 12.5%. An important feature of the reaction is the additional formation of methylcyclopropane with a selectivity of ca. 6%.

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The experimental Brønsted-Evans-Polanyi (BEP) correlations in the field of oxidation catalysis, describing both the liquid-phase reactions on metal complexes and especially the gas-phase oxidations on metal oxides including the O 2 isotopic exchange, were analyzed. It was shown that the rate of deep oxidations on metal oxides is determined by two thermodynamic parameters of a catalytic system: the heat of oxygen adsorption, Q O2 , and the heat of reaction, Q r , which constitute a unified BEP descriptive parameter Q uni = (Q r -Q O2 ). The correlations based on the energy of chemical bonds that are cleaved or formed in the course of reaction are more limited and less predictive.Special attention was paid to the numerical value of the Brønsted coefficient β. It was found that for all oxidations, in both the liquid and gas phases, β ≈ 0.5. Using the unified BEP descriptor Q uni with β = 0.5, a universal correlation was plotted describing the rates of all reactions over all catalysts under consideration.An idea of considering the kinetic compensation effect as a part of an extended BEP correlation is suggested. One may think that this long-debated phenomenon may relate primarily to mechanistic features of the reaction rather than to the nature of catalyst.In conclusion, difficult questions arising from analysis of the BEP correlations are summarized.