Catalytic activity iron/zeolite catalysts

Large amounts of styrene are commercially produced by dehydrogenation of ethylbenzene (EB) in the presence of steam using iron oxide-based catalysts. Carbon dioxide, small amounts of which are formed as a by-product in the ethylbenzene dehydrogenation, was known to depress the catalytic activity of commercial catalyst [7,8]. However, it has been recently reported that several examples show the positive effect of carbon dioxide in this catalytic reaction [5,9,10]. In this study, we investigated the effect of carbon dioxide in dehydrogenation of ethylbenzene over ZSM-5 zeolite-supported iron oxide catalyst. 

Iron-modified zeolites (Fe/ZSM-5) are highly efficient catalysts for a wide range of important processes than include the selective oxidation of benzene with N O (the Panov reaction) [37], catalytic decomposition of N O [38], selective catalytic reduction (SCR) of NOx [39], and many others. These unique properties stem from the presence of specific extra-framework iron-containing cationic species in the micropores of ZSM-5 zeolite [40]. Because of a very heterogeneous iron speciation in the zeolite catalyst, the direct determination of the catalytically active iron species and the mechanism of the catalytic reaction by experimental methods was not possible. The exact speciation will obviously depend on such parameters as the Fe loading, the method of iron introduction, and the history of the sample (calcination, reduction, etc.). Many studies have indicated that the reactivity of Fe/ZSM-5 for the selective benzene oxidation is mainly associated with the presence of highly dispersed Fe + extraframework cations [41]. On the contrary, the high catalytic activity in the N O decomposition... 

Catalytic oxidative dehydrogenation of propane by N20 (ODHP) over Fe-zeolite catalysts represents a potential process for simultaneous functionalization of propane and utilization of N20 waste as an environmentally harmful gas. The assumed structure of highly active Fe-species is presented by iron ions balanced by negative framework charge, mostly populated at low Fe loadings. These isolated Fe sites are able to stabilize the atomic oxygen and prevent its recombination to a molecular form, and facilitate its transfer to a paraffin molecule [1], A major drawback of iron zeolites in ODHP with N20 is their deactivation by accumulated coke, leading to a rapid decrease of the propylene yield. 

In the direct ammoxidation of propane over Fe-zeolite catalysts the product mixture consisted of propene, acrylonitrile (AN), acetonitrile (AcN), and carbon oxides. Traces of methane, ethane, ethene and HCN were also detected with selectivity not exceeding 3%. The catalytic performances of the investigated catalysts are summarized in the Table 1. It must be noted that catalytic activity of MTW and silicalite matrix without iron (Fe concentration is lower than 50 ppm) was negligible. The propane conversion was below 1.5 % and no nitriles were detected. It is clearly seen from the Table 1 that the activity and selectivity of catalysts are influenced not only by the content of iron, but also by the zeolite framework structure. Typically, the Fe-MTW zeolites exhibit higher selectivity to propene (even at higher propane conversion than in the case of Fe-silicalite) and substantially lower selectivity to nitriles (both acrylonitrile and acetonitrile). The Fe-silicalite catalyst exhibits acrylonitrile selectivity 31.5 %, whereas the Fe-MTW catalysts with Fe concentration 1400 and 18900 ppm exhibit, at similar propane conversion, the AN selectivity 19.2 and 15.2 %, respectively. On the other hand, Fe-MTW zeolites exhibit higher AN/AcN ratio in comparison with Fe-silicalite catalyst (see Table 1). Fe-MTW-11500 catalyst reveals rather rare behavior. The concentration of Fe ions in the sample is comparable to Fe-sil-12900 catalyst, as well as... 

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

As described above, it was found that physicochemical properties of the iron cluster supported on zeolite and the catalytic activity for toluene disproportionation were significantly affected by the preparation conditions. The catalyst which was prepared by modifying NH Y with 0.25M Fe(N03)3 solution at 323K showed the highest activity among the samples obtained. 

The reduced iron atoms of complex C, being inert to dioxygen, are readily oxidized by nitrous oxide into complex D to give adsorbed species of a-oxygen, Oa. As Figure 7.3 shows, the reversible redox transition Fc" <-> Fe provides the catalytic activity of FeZSM-5 both the oxidation cycle due to the oxygen transfer from N20 to a substrate and the decomposition cycle of N20 into N2 and 02 due to recombination of a-oxygen into the gas phase. The decomposition is an environmentally important process, and FeZSM-5 zeolites are considered to be the best catalysts for this reaction (see review [117] and references therein). 

The efficiency and selectivity of a supported metal catalyst is closely related to the dispersion and particle size of the metal component and to the nature of the interaction between the metal and the support. For a particular metal, catalytic activity may be varied by changing the metal dispersion and the support thus, the method of synthesis and any pre-treatment of the catalyst is important in the overall process of catalyst evaluation. Supported metal catalysts have traditionally been prepared by impregnation techniques that involve treatment of a support with an aqueous solution of a metal salt followed by calcination (4). In the Fe/ZSM-5 system, the decomposition of the iron nitrate during calcination produces a-Fe2(>3 of relatively large crystallite size (>100 X). This study was initiated in an attempt to produce highly-dispersed, thermally stable supported metal catalysts that are effective for synthesis gas conversion. The carbonyl Fe3(CO) was used as the source of iron the supports used were the acidic zeolites ZSM-5 and mordenite and the non-acidic, larger pore zeolite, 13X. 

We have prepared the Fe Pc/ zeolite catalyst and used in the aerobic oxidation of 1-octene and cyclohexene. Zeohte-encapsulated iron phthalocyanine proved to be an active and stable catalyst in the oxidation of hydroquinone and in the triple catdytic oxidation of 1-octene and cyclohexene. Product distribution, selectivity and yield were similar to those obtained with free iron phthalocyanine. No decrease in catalytic activity was observed during the catalytic reaction. The zeohte-encapsulated complex is easier to handle than the non-supported one, it can be removed from the reaction mixture by simple filtration and it can be reused in several subsequent catalytic runs with similar catalytic activity. 

The Fe-ZnO catalyst shows two kinds of catalytic sites, that is, iron species effective for F-T reaction formed from a -Fc203(Fe304) and Fe promoted ZnFe204 effective for methanol synthesis. In the absence of zeolite, the F-T reaction sites are very active to produce hydrocarbons with the Schulz-Anderson-Flory distribution. On the other hand, the sites for F-T reaction are deactivated and the sites for methanol synthesis ZnFe204 exhibit the catalytic activity in the case of the composite catalyst. Therefore, hydrocarbons were obtained by MTG reaction with a non-Schulz-Anderson-Florv distribution over Fe-ZnO/HY (Figure 4). 

Among zeolite-supported iron oxide catalysts the highest catalytic activity was obtained in the case of 5.0 wt.% loading of iron oxide... 

We presented a facile route for the modification of zeolites and for the preparation of bifunctional catalysts possessing both acidic and hydrogenation functions via solid-solid reaction. Branched and higher hydrocarbons were obtained over such modified composite catalysts. Sodium migration from the surface of the iron-based catalyst to the zeolite during the solid-solid reaction accounts for the change of catalytic activity. XRD measurements exhibited evidence for Na migration. 

Source of Activity in other Siliceous Catalysts.—Although various oxides can be combined with silica to give amorphous, acidic catalysts, the replacement of aluminium in zeolites (specially non-faujasitic zeolites) has proved to be very difficult with any element other than gallium. Materials of ZSM-5 structure with iron or boron in place of aluminium have been claimed recently, but it is not yet certain that either iron or boron is part of the zeolite lattice or that the catalytic activity observed is not due to residual lattice aluminium. 

The catalyst is an iron-containing ZSM-5 zeolite. Its half-life is three to four days so that, periodically, catalytic activity must be restored by passing air through the deactivated catalyst at high temperature no performance deterioration has been reported after more than 100 regeneration cycles. 

In Parton et al., a new type of heterogeneous catalyst was proposed consisting of a solid catalyst (iron phthalocyanine zeolite Y) dispersed in a dense PDMS (polydimethylsiloxane) polymer matrix.[l] The system resulted in strongly increased catalytic activities in the oxidation of cyclohexane.[2] Other systems, such as Mn(bipy)2-Y (mangtuiese bipyridine zeolite Y) were also proven to benefit from such incorporation.[3,4] The results presented here using Ti-MCM-41 confirm this for the epoxidation of olefins, an important route for the production of fine chemicals.[5] The influence of the polymer on the reaction activity and selectivity is shown by using different oxidants and solvent conditions in the epoxidation of 1-octene. It will enable the deduction of the advantages and limitations of the reported membrane occluded catalyst system. 

The iron vapor-toluene reaction has evoked interest because of the lability of the proposed bis(arene)iron complex to ligand subsitu-tion and to loss of both toluene molecules to free the metal atom. In the latter case the toluene molecules may be usefully regarded as metal atom carriers which can be used to direct the latent reactivity of the atom in subsequent solution phase chemistry. In this way the metal atom experiment can benefit from the convenience and additional versatility afforded by bench-top chemical manipulations. These results are relevant to a reported preparation of a dehydroxy-lated silica-supported Fischer-Tropsch catalyst from a static reactor codeposition of Fe and toluene.(46) In the liquid phase, iron atoms "bottled" in this way have also been utilized in an exceedingly mild method for making minute catalytically active superparamagnetic clusters on the surface and within the cavities of a dehydrated sodium zeolite Y.(38) Using the rotary reactor, preformed solutions of solvated iron atoms (as the toluene complex) are cannulated below their decomposition temperature out of the flask to a cold slurry of the support in toluene. Diffusion of intact... 

Fe-FER, Fe-BEA, and Fe-MFI catalysts prepared by the proposed method provide for high catalytic activity in all three test reactions, i.e. NO oxidation (see Fig. 4), SCR of NO by propane (see Fig. 5), and N2O decomposition, showing 50 % conversion of N2O at 350 °C for all three iron-zeolite samples with Fe/Al value of about 0.05. For the same iron content activity of the Fe-MFI sample in NO oxidation is lower in comparison with Fe-FER and Fe-BEA samples, both reaching the equilibrium NO2/NO composition for temperature above 300°C. In the SCR reaction the picture is more complex, with Fe-MFI showing higher activity at lower temperatures and then decreasing at temperatures above 350°C. Significantly, the selectivity of the process, i.e. the... 

The zeolite-encapsulated iron phthalocyanine catalyst was also active in this reaction and the catalytic activity was similar to that of the free complex. After the injection of a new portion of hydroquinone, the catalyst showed almost the same activity as in the first run, indicating that there was no catalyst deactivation during the reaction. The supported catalyst can be filtered off and used in new experiments. 

The zeolite-encapsulated iron phthalocyanine catalyst exhibited a similar behavior. When the oxygen uptake in the first run had ceased, 1-decene was injected into the reactor (second run), and the oxygen uptake was measured again. A similar rate was measured in the second run as in the first one, i.e. the catalytic activity did not decrease during the oxidation reaction, in spite of the presence of the strong acid HCIO4 in the reaction mixture. 

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