Oxygen zeolite catalyst

The process which was developed hy DOW involves cyclodimerization of hutadiene over a proprietary copper-loaded zeolite catalyst at moderate temperature and pressure (100°C and 250 psig). To increase the yield, the cyclodimerization step takes place in a liquid phase process over the catalyst. Selectivity for vinylcyclohexene (VCH) was over 99%. In the second step VCH is oxidized with oxygen over a proprietary oxide catalyst in presence of steam. Conversion over 90% and selectivity to styrene of 92% could he achieved. ... 

For this purpose we studied a temperature-programmed interaction of CH with a-oxygen. Experiments were carried out in a static setup with FeZSM-5 zeolite catalyst containing 0.80 wt % Fe203. The setup was equipped with an on-line mass-spectrometer and a microreactor which can be easily isolated from the rest part of the reaction volume. The sample pretreatment procedure was as follows. After heating in dioxygen at 823 K FeZSM-5 cooled down to 523 K. At this temperature, N2O decomposition was performed at 108 Pa to provide the a-oxygen deposition on the surface. After evacuation, the reactor was cooled down to the room temperature, and CH4 was fed into the reaction volume at 108 Pa. 

There are a few examples of 02 oxidations catalyzed by zeolite-encapsulated complexes. Encapsulated CoPc was active in the oxidation of propene to aldehyde, whereas the free complex was inactive.76 A triple catalytic system, Pd(OAc)2, benzoquinone, and a metal macrocycle, was used to oxidize alk-enes with molecular oxygen at room temperature.77,78 Zeolite-encapsulated FePc79-81 and CoSalophen80,82 complexes were used as oxygen-activating catalysts. 

The highly oxygenated bio oil can be de-oxygenated, and thereby upgraded, over acidic zeolite catalysts through the formation of mainly water at low temperatures and C02 and CO at higher temperatures [1-3], Successful catalytic pyrolysis of woody biomass over Beta zeolites has been performed in a fluidized bed reactor in [4]. A drawback in the use of pure zeolitic materials has been the mechanical strength of the pelletized zeolite particles in the fluidized bed. 

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. 

Figure 1. DR UV-vis spectra of hydrated Fe-zeolite catalysts pretreated by calcination in flow of dry oxygen at 540 °C (black curves) and steam-treated in the flow of water vapor at 540 °C (gray curves). A) Fe-sil-12900, B) Fe-MTW-11500, C) Fe-MTW-14700, Fe-MTW-18900.

Butane isomerization is usually carried out to have a source of isobutane which is often reacted with C3-C5 olefins to produce alkylate, a high octane blending gasoline [13]. An additional use for isobutane was to feed dehydrogenation units to make isobutene for methyl tert-butyl ether (MTBE) production, but since the phaseout of MTBE as an oxygenate additive for gasoline, this process has decHned in importance. Zeolitic catalysts have not yet been used industriaUy for this transformation though they have been heavily studied (Table 12.1). 

From the previous paragraphes it follows that a substantial amount of experimental data exist that illustrate the oxygenation properties of zeolite catalysts. In very general terms zeolites are used to heterogenize transition metal ions in ion exchange or lattice positions, to stabilize transition metal oxide dispersions and to prepare ship-in-bottle complexes. 

NOx reduction conversions met in the DOC are quite low. Excess of air in burned lean fuel mixture results in excess of oxygen in the exhaust. Under such conditions, the reducing components naturally present in diesel exhaust (CO, H2 and HC) are readily oxidized by the excessive oxygen and NOx remains unreduced. However, the unburned hydrocarbons still exhibit a certain activity for NO reduction on NM/y-Al203 and NM/zeolites catalysts under lean conditions (HC-SCR). Many efforts have been put into the investigation of different NM-based or alternative catalysts tailored for the HC-SCR reaction and the development of reliable reaction mechanisms—cf., e.g., Joubert et al. 

According to Sachtler and coworkers, the role of MnO applied for a Rh on zeolite NaY zeolite catalyst is to promote the formation and stabilization of CxHvOj. intermediates, including surface acetate groups.523 These undergo hydrogenation to form the final oxygenate products if they are located in immediate proximity to a Rh particle, that is, at the Rh-MnO interface. 

Tracer studies with 13C showed that the carbon of methoxy species formed in CO hydrogenation appeared as the central C atom of isobutylene.531 Methoxy was shown to be reduced to surface methyl species that was transformed to surface acetyl group via insertion of CO into the methyl-metal bond. Aldol condensation of C2 oxygenates with formaldehyde affords iso-C4 products.532 Earlier results of a different approach for isosynthesis using metal-zeolite catalyst systems are summarized in a 1998 review.533... 

Exclusive ring-nitration occurs with alkylbenzenes. The nitration of toluene in the presence of H-ZSM-5 and molecular oxygen shows a remarkable enhancement of para selectivity (ortho para ratio = 0.08).268 A review is available for the nitration of aromatics by nitrogen oxides on zeolite catalysts.269... 

Molecular sieve effects and their influence on catalytic selectivity offer important possibilities. Chen (48) showed that for a given reaction synthetic offretite, with its 12-membered rings of oxygen ions, exhibited no selectivity where the presence of small amounts of erionite (3%) resulted in an effective blocking of the large openings and the creation of selectivity. This emphasizes the possible influence of impurities on the practical uses of zeolite catalysts. 

In this paper, the results of the isomerization of hexane, heptane and octane over a Mo2C-oxygen-modified-catalyst, a Mo03-carbon-modified catalyst and a Pt//l-zeolite catalyst, at atmospheric pressure, are presented. Also, the results for a conventional Pt/Al203 catalyst are presented for the isomerization of hexane. Then, the effect of pressure on the isomerization of heptane and octane over the molybdenum catalysts and the Pt//l-zeolite catalyst is shown. Finally, the ability of the molybdenum catalysts to catalyse the isomerization reaction at high conversion with high selectivity even with hydrocarbons larger than hexane is demonstrated this is not possible over the Pt catalysts. The differences between the catalysts are discussed in terms of the reaction mechanisms. 

Although the epoxidation by nitrous oxide proceeds over non-zeolite catalysts, they also include iron as an active element One may think that in all these cases a special oxygen species generated by N20 plays an important role, similar to the a-oxygen on FeZSM-5. 

Acetaldehyde decomposition, reaction pathway control, 14-15 Acetylene, continuous catalytic conversion over metal-modified shape-selective zeolite catalyst, 355-370 Acid-catalyzed shape selectivity in zeolites primary shape selectivity, 209-211 secondary shape selectivity, 211-213 Acid molecular sieves, reactions of m-diisopropylbenzene, 222-230 Activation of C-H, C-C, and C-0 bonds of oxygenates on Rh(l 11) bond-activation sequences, 350-353 divergence of alcohol and aldehyde decarbonylation pathways, 347-351 experimental procedure, 347 Additives, selectivity, 7,8r Adsorption of benzene on NaX and NaY zeolites, homogeneous, See Homogeneous adsorption of benzene on NaX and NaY zeolites... 

The reductive/oxidative properties of transitional metal elements in these zeolite catalysts were also examined by TPR and TPO, and it is shown that metallic species in certain cation locations may migrate under calcination, reduction, and reaction conditions [7], The different treatment, e g, coking or even the oxidative regeneration, will produce metallic species of varied oxidation states with different distributions in the molecular sieve structures as exemplified by the above XPS data. The redox properties of these metallic cations exhibit the influence of hydrogen and/or coke molecules, and it is further postulated that the electron transfer with oxygen species are considered responsible for their catalyzed performance in the TPO regeneration processes, as shown in Figure 2. 

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