G. I. Panov

Mechanism of Coke Influence on the Catalytic Activity of FeZSM-5 in the Reaction of Benzene Oxidation into Phenol

The influence of coke formation in the reaction of benzene oxidation by nitrous oxide into phenol on the catalytic activity and concentration of iron-containing active sites (α-sites), which are stabilized in the microporous structure of FeZSM-5 zeolite, is studied. The deactivation by coke is explained by the poisoning of α-sites, whose concentration decreases linearly with an increase in the coke content, rather than by the blocking of zeolite pores. The activity per one α-site remains unchanged. This fact indicates the absence of diffusion limitations associated with coke formation. The toxicity of coke for the α-sites is determined. The coke amount equivalent to 100–120 benzene molecules is shown to result in the deactivation of one active site.

Stoichiometry of oxidation reactions involving α-oxygen on FeZSM-5 zeolite

The stoichiometry of the low-temperature reaction between surface α-oxygen formed by decomposing N2O over Fe-containing ZSM-5 zeolite and methane, hydrogen (deuterium), and carbon monoxide is studied. Methane and hydrogen react with α-oxygen in stoichiometric ratios of 1 : 1.8 and 1 : 1.6, respectively. The observed stoichiometry is due to the mechanisms of the corresponding reactions. According to a mechanism proposed for the interaction of α-oxygen with methane and hydrogen, this reaction is accompanied by the dissociation of CH4and H2molecules. For hydrogen, such a mechanism is supported by IR spectroscopic studies of resulting surface compounds, namely, of new hydroxyl groups that were formed on the zeolite surface in the course of the reaction. α-Oxygen reacts with CO in the ratio of 1 : 1 to form CO2in amounts equal to those of α-oxygen on the surface.

Role of α-Sites in the selective catalytic reduction of NO x with ammonia over Fe-ZSM-5 catalysts

The catalytic properties of Fe-ZSM-5 zeolites with different iron contents have been investigated in the selective catalytic reduction (SCR) of NOx with ammonia. The observed catalytic properties the zeolites are correlated with the concentration of the iron-containing sites that are stabilized in the zeolite and effect N2O decomposition (α-sites). The catalysts activated at a high temperature to increase the α-site concentration (by a factor of 5–10) are more active in NOx SCR with ammonia than the unactivated samples. However, the difference between the activities of the activated and unactivated catalysts is well below the difference between the α-site concentrations in these catalysts. The nonlinear relationship between these parameters is evidence that the α-sites in Fe-ZSM-5 is not the only factor determining the activity of Fe-ZSM-5 in NOx SCR with ammonia. The activated catalysts show a low activity in nonselective ammonia oxidation and, accordingly, a high selectivity in the target process at high temperatures.

Liquid-phase noncatalytic oxidation of monoterpenoids with nitrous oxide

A series of monoterpenoids differing in the number of double bonds and the pattern of their substitution were tested in the liquid-phase noncatalytic oxidation with nitrous oxide (N2O). The structure of olefins has a significant effect on the oxidation route. In the case of terpenoids containing 1,1-disubstituted double bond, nor-carbonyl compounds are formed with high selectivity.

High-temperature carboxidation of cyclopentene with nitrous oxide

It is demonstrated by the example of cyclopentene that the noncatalytic oxidation of alkenes with nitrous oxide to carbonyl compounds (carboxidation), which is known to occur in the liquid phase at 150–250°C, can also take place in the gas phase at higher temperatures (300–475°C). Like liquid-phase carboxidation, the gas-phase reaction likely proceeds via a dipolar 1,3-addition mechanism. However, 4-pentenal is formed along with cyclopentanone in the gas phase. The 4-pentenal selectivity increases from 2.5 to 23% as the reaction temperature is raised. High-temperature cyclopentene carboxidation can be carried out in a paraffin melt (bp ∼ 400°C). Filling the reactor with paraffin accelerates the reaction and reduces its activation energy.