Gennady I. Panov

Generation of active oxygen species on solid surfaces. Opportunity for novel oxidation technologies over zeolites

Generation of surface oxygen species and their role in partial oxidation reactions catalyzed by metal oxides are discussed. Main attention is paid to a new concept related to a recent discovery of remarkable ability of Fe complexes stabilized in a ZSM-5 matrix to generate a new form of surface oxygen (α-oxygen) from N2O. At room temperature, α-oxygen exhibits a high reactivity typical for the active oxygen of monooxygenases, and mimics its unique ability to perform selective oxidation of hydrocarbons. This opens new opportunity for creating novel technologies based on biomimetic strategy. A process of direct oxidation of benzene to phenol, recently demonstrated by Solutia on a pilot plant scale, is evidence of great potential of this approach.

Iron complexes in zeolites as a new model of methane monooxygenase

Iron complexes in the ZSM-5 zeolite matrix (α-centers) are shown to perform single-turnover cycles of methane oxidation to methanol at room temperature when nitrous oxide is used as a source of oxygen. The origin of carbon and oxygen in the product methanol was traced using13C and18O isotopes. Probable structure of α-sites as well as mechanistic features of the reaction allow to consider this system as a first successful model of methane monooxygenase.

Selective oxidation of methane to methanol on a FeZSM-5 surface

Abstract Methane is selectively oxidized to methanol at room temperature over the interaction with α-form of the surface oxygen produced on FeZSM-5 zeolite by N2O decomposition.

Direct hydroxylation of benzene to phenol by nitrous oxide

Publisher Summary In the early 1990s it was reported that N 2 O emissions from adipic acid producers could contribute to atmospheric ozone depletion and global warming. It was estimated that adipic acid production may account for up to 10% of the annual increase in the atmospheric N 2 O. The ketone-alcohol (KA) to adipic acid yields are near 94% of the theory. Glutaric and succinic acids are the major byproducts and account for most of the yield loss. Monsanto and some other adipic acid producers recover or upgrade these to salable byproducts, resulting in an overall KA utilization efficiency that approaches 99%. Two general areas of utilization were considered: oxidation of N 2 O to NO and subsequent conversion to nitric acid and the use of N 2 O as a selective oxidant. The latter had the potential of satisfying the criterion of value addition. Benzene can be reacted with nitrous oxide in the vapor phase at elevated temperatures over ZSM-5 or similar catalysts to give phenol and nitrogen. The reaction has very high selectivity of benzene conversion to phenol (>99%). A further step was taken to incorporate the phenol scheme into an overall adipic acid process. The process would use N 2 O to hydroxylate benzene to phenol. The phenol would be hydrogenated to cyclohexanone using available technology. The final step is the currently practiced nitric acid oxidation of cyclohexanol and cyclohexanone that returns N 2 O for use in the front end of the process. The successful commercialization of the overall process concept depended on the viability of the first step that is a breakthrough technology.

NON-CATALYTIC LIQUID PHASE OXIDATION OF ALKENES WITH NITROUS OXIDE. 1. OXIDATION OF CYCLOHEXENE TO CYCLOHEXANONE

A very efficient way of alkenes oxidation to carbonyl compounds is discovered. It is based on remarkable ability of nitrous oxide to interact directly with the double C=C bonds of liquid alkene and to transfer its oxygen, without catalyst aid, to unsaturated carbon atom with nearly 100% selectivity. This oxidation method can be applied to a wide range of organic compounds including aliphatic, cyclic, heterocyclic alkenes and their numerous derivatives.

Biomimetic oxidation on Fe complexes in zeolites

One-step hydroxylation of aromatic nucleus with nitrous oxide (N 2 O) is among recently discovered organic reactions. A high efficiency of FeZSM-5 zeolites in this reaction relates to a pronounced biomimetic-type activity of iron complexes stabilized in ZSM-5 matrix. N 2 O decomposition on these complexes produces particular atomic oxygen form (α-oxygen), whose chemistry is similar to that performed by the active oxygen of enzyme monooxygenases. Room temperature oxidation reactions of α-oxygen as well as the data on the kinetic isotope effect and Moessbauer spectroscopy show FeZSM-5 zeolite to be a successful biomimetic model.

New Way of Hydroquinone and Catechol Synthesis using Nitrous Oxide as Oxidant

The synthesis of dihydroxybenzenes (DHB) via the gas-phase oxidation of phenol with nitrous oxide in the presence of benzene was studied. Addition of benzene to the feed mixture greatly improves the selectivity and catalytic stability of the Fe-containing ZSM-5 zeolite, that was previously considered to be a main obstacle to the development of a new process. Reaction conditions strongly affect the distribution of the DHB isomers: the ratio of hydroquinone to catechol may vary from 1.4 to 10, with the resorcinol fraction being nearly constant and comprising 3 ± 5%. Some 40h experiments on the oxidation of a phenol-benzene mixture demonstrated the high efficiency of the formed FeZSM-5 catalyst. With a good stability, the catalyst provides 97% phenol selectivity referred to DHB and 85 ± 90% N2O selectivity referred to the sum of DHBs and phenol. A new process for hydroquinone and catechol synthesis based on the neat oxidation of benzene with recycling of the phenol as an intermediate product is suggested.

Rate of14N2 desorption from the surfaces of nitrides in the presence and absence of15N2 in the gas phase

The rates of14N2 desorption from the surfaces of nitrides have been measured in the presence and absence of15N2 in the gas phase. Whatever the adsorption heat and the form of surface species, the adsorption of15N2 molecules does not affect the rate of14N2 desorption.AbstractПроведены измерения скоростей десорбции азота14N2 с поверхности нитридов в присутствии и отсутствии молекул15N2 в газовой фазе. Показано, что независимо от теплоты адсорбции и атомности поверхностных частиц адсорбция молекул15N2 не влияет на скорость десорбции14N2.

The Brønsted−Evans−Polanyi Correlations in Oxidation Catalysis

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 O2 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, QO2, and the heat of reaction, Qr, which constitute a unified BEP descriptive parameter Quni = (Qr – QO2). 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 Quni 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.

Identification of Active Oxygen Species over Fe Complexes in Zeolites

In the framework of identification problem of active oxygen species involved in the oxidation catalysis a possible role of M=O, O2- and O- species is analyzed. Particular attention is paid to a recently discovered oxygen species Oα formed upon N2O decomposition over Fe complexes in zeolites. High reactivity of α-oxygen coupled with the high concentration allow to reliably identify its participation in the oxidation of methane to methanol and benzene to phenol on the FeZSM-5 surface.