Oxidation Over Zeolites

Oxidation over zeolites The results of Iwamoto et al. on the oxidation of benzene to phenol [58] stimulated further efforts in the search for new and more efficient catalytic systems. As a result, in 1988, ZSM-5 zeolites were shown to be the best catalysts for this reaction [59-61]. Over zeolites, the reaction proceeded at much lower temperature and, which was even more important, with a very high selectivity, approaching 100%. Further studies involving many other groups [62-80] contributed much to the improvement of ZSM-5 catalysts. Some other type zeolites and FeP04 were shown to be also active [69, 70, 73, 80, 81], although their efficiency was inferior to that of ZSM-5. 

In several recent studies an assumption is made concerning the homogeneous-heterogeneous mechanisms of oxidation reactions as a reason for critical effects, in particular in the oxidation of cyclohexane over zeolites [131] and of CO over Pd [132-134] and V [135] catalysts. Berman and Elinek [131] have established in their experiments that cyclohexane oxidation over zeolites follows a mixed homogeneous-heterogeneous mechanism. Studies of the mathematical reaction model written down in accordance with the law of mass action showed that the system can have from one to three steady states. When the steady state is unique, there exists a region of parameters... 

The oxidation of intracrystalline ammonium cations has been reported 3, 65), but most oxidations over zeolites featuring molecular oxygen-hydrocarbon systems have featured transition metal zeolites. The oxidative dehydrogenation of ethylbenzene to styrene and selective oxidation of benzyl alcohol to benzaldehyde over MnY at 250°-370°C were reported earlier 62). Propylene has been oxidized to formaldehyde, COo, and minor quantities or acrolein and acetaldehyde over Cu( II)-exchanged Y-type zeolite (39). 

Hydration of Ethylene Oxide over Zeolite Catalyete ... 

The transition states leading to the cis and trans alcohols differ substantially in size and the way in which they can be accommodated in the pores of zeolite Beta. That for the cis isomer is more or less linearly aligned with the pore axis and can easily be accommodated within the straight channels of the zeolite. The transition state for the formation of the trans isomer is more or less perpendicular to the channel wall and cannot be well accommodated within the micropores (Scheme 5). As required by this mechanism, the cis alcohol was found to undergo Oppenauer oxidation over zeolite Beta whereas activity for the trans isomer being negligible. 

A linear polycyclic compound, 4,4 -dimethylbiphenyl (4,4 -DMBP), is an intermediate for making monomer of some advanced polymer materials, but the selective synthesis of 4,4 -DMBP is difficult. In this work, modifications were made on a ZSM-5 zeolite for selective methylation of 4-methybiphenyl (4-MBP) to form 4,4 -DMBP. The use of binder, deposition of basic oxide such as calcium oxide over zeolite internal and external surface can effectively improve the product selectivity. An isomorphous substitution of ZSM-5 framework A1 with Fe by a post-synthetic treatment, coupled with modification of external and internal surface by P or Ca leads to high-performance catalyst with stable activity and superior selectivity for synthesis of 4,4 -DMBP by 4-MBP methylation. 

Zhidomirov GM, Larin AV, Trubnikov DN, Vercauteren DP (2009) Ion-exchanged binuclear clusters as active sites of selective oxidation over zeolites. J Phys Chem C 113 8258... 

The addition of water during Cl-VOC oxidation over zeolites considerably reduces the amount of coke deposited due to the steam gasification reaction. However, the preferential adsorption of water molecules over acid sites resulted in a higher deactivation of the catalysts. Thus, the effect of competitive adsorption on acid sites between H2O and Cl-VOC is stronger than the effect of lower coke formation. 

Marie Rose, S., Belin, T., Mijoin, J., et al. (2009). Destruction of PAH and dioxin precursors using selective oxidation over zeolite catalysts. Influence of the presence of ammonia in the flue gas, Appl. Catal. B Environ., 93, pp. 106-111. 

The purpose of this work was to increase the A3 selectivity at low conversion through a catalyst modification. Previous studies of phenol alkylation with methanol (the analogue reaction) over oxides and zeolites showed that the reaction is sensitive to acidic and basic properties of the catalysts [3-5]. It is the aim of this study to understand the dependence of catalyst structure and acidity on activity and selectivity in gas phase methylation of catechol. Different cations such as Li, K, Mg, Ca, B, incorporated into y-Al203 can markedly modify the polarisation of the lattice and consequently influence the acidic and basic properties of the surface [5-8] which control the mechanism of this reaction. 

Reactivity of racemic hutan-2-ol over zeolite Y modified hy homochiral dithiane oxides. 

This discovery was quite unexpected, since iron oxide has been never reported as an active catalyst in either partial or full oxidation. The studies of two simplest reactions, i.e. O2 isotopic exchange and N2O decomposition, revealed a dramatic change of Fe properties in the ZSM-5 matrix compared to Fe203 [4]. Fe atoms lose their ability to activate O2 but gain remarkably in their ability to activate N2O. It gives rise to a great effect of the oxidant nature in the reaction of benzene oxidation over the FeZSM-5 zeolite (Table 1). Thus, in the presence of N2O benzene conversion is 27% at 623 K, while in the presence of O2 it is only 0.3% at 773 K. And what is more, there is a perfect change of the reaction route. Instead of selective phenol formation with... 

Pentene oxidation over TS-1 catalyst is a fast reaction and hence fulfils a basic requirement for being suited to micro-channel processing [30]. Thus, it can serve as a model reaction to demonstrate the benefits of micro chemical engineering, particularly for zeolite-catalyzed reactions. Apart from this, epoxidations are an important class of organic reactions, also of industrial importance. 

Hensen EJM, Zhu Q, van Santen RA. 2005. Selective oxidation of benzene to phenol with nitrous oxide over MFI zeolites. 2. On the effect of the iron and aluminum content and the preparation route. J Catal 233 136-146. 

Iwamoto, M., Yokoo, S., Sakai, K. el al. (1981) Catalytic decomposition of nitric oxide over copper(II)-exchanged Y-type zeolites, J. Chem. Soc. Faraday Trans., 77, 1629. 

It is well known that Rh(I) complexes can catalyze the carbonylation of methanol. A heterogenized catalyst was prepared by ion exchange of zeolite X or Y with Rh cations.126 The same catalytic cycle takes place in zeolites and in solution because the activation energy is nearly the same. The specific activity in zeolites, however, is less by an order of magnitude, suggesting that the Rh sites in the zeolite are not uniformly accessible. The oxidation of camphene was performed over zeolites exchanged with different metals (Mn, Co, Cu, Ni, and Zn).127 Cu-loaded zeolites have attracted considerable attention because of their unique properties applied in catalytic redox reactions.128-130 Four different Cu sites with defined coordinations have been found.131 It was found that the zeolitic media affects strongly the catalytic activity of the Cd2+ ion sites in Cd zeolites used to catalyze the hydration of acetylene.132... 

Figure 2. Energy versus reaction coordinate for the dissociation of the first nitrous oxide over i) Z " Fe, (p-t))(p-OI I)Fe211 and ii) Z " Qh [Fe1( t-0)( t-0H)Fe2]+. For clarity sake, the clusters representing part of the zeolite were omitted in these figures. N20 molecule is represented by a red ball (O) and two bleu balls (N).

G. I. Panov, A. S. Kharitonov, and V. I. Sobolev, Oxidative hydroxylation using dinitrogen monoxide a possible route for organic synthesis over zeolites, Appl. Catal. A 98, 1 (1992). 

C. R. Jacob, S. R. Varkey, and R. Ratnasamy, Selective oxidation over copper and manganese salens encapsulated in zeolites, Microporous Mesoporous Mater. 22, 465 74 (1998). 

Shen, Q Zhu, X., and Dong, J. (2009) Hydrodealkylation of C9-t aromatics to BTX over zeolite-supported nickel oxide and molybdenum oxide catalysts. Catal. Lett., 129, 170-180. 

The third and last part of the book (Chapters 12-16) deals with zeolite catalysis. Chapter 12 gives an overview of the various reactions which have been catalyzed by zeolites, serving to set the reader up for in-depth discussions on individual topics in Chapters 13-16. The main focus is on reactions of hydrocarbons catalyzed by zeolites, with some sections on oxidation catalysis. The literature review is drawn from both the patent and open literature and is presented primarily in table format. Brief notes about commonly used zeolites are provided prior to each table for each reaction type. Zeolite catalysis mechanisms are postulated in Chapter 13. The discussion includes the governing principles of performance parameters like adsorption, diffusion, acidity and how these parameters fundamentally influence zeolite catalysis. Brief descriptions of the elementary steps of hydrocarbon conversion over zeolites are also given. The intent is not to have an extensive review of the field of zeolite catalysis, but to select a sufficiently large subset of published literature through which key points can be made about reaction mechanisms and zeolitic requirements. 

Mochida et al. studied the oxidation of propylene by molecular oxygen over zeolite Y exchanged with Cu2+ [12-15]. The oxidation products obtained at different feed gas compositions are listed in Table 1. 

Zeolites may be used in purely inorganic catalysis, however. One reaction that may be used to reduce air pollution from mixed nitrogen oxides, NO, in the industrial production or nitric acid is catalytic reduction by ammonia over zeolitic catalysts ... 

To manufacture aniline from chlorobenzene and ammonia, cuprous oxide or diamino cuprous chloride has been used as the catalyst and the reaction is usually carried out in the liquid phase under pressure (7). There are few reports on the reaction in gas phase. Jones (8) found that CuX was active for aniline formation while ZnX led to the formation of dichlorobenzenes. The reaction of benzaldehyde with ammonia over zeolite has never been reported. 

A specificity of N20 oxidant compared to 02 is one of the most interesting points arising from benzene oxidation over FeZSM-5 zeolites. The specificity is clearly seen from the results presented in Table 7.6 [ 118]. With nitrous oxide, benzene conversion is 27% at 623 K, whereas with dioxygen it is only 0.3% at 773 K. Moreover, the reaction route changes totally N20 leads to selective formation of phenol, while 02 leads only to the products of complete oxidation. 

The work described in the previous section was essentially concerned with the physical rather than chemical adsorption of some highly polarizable molecules on zeolites. With pyridine, such information can sometimes be obtained as easily using infrared spectroscopy. However, transmission IR spectroscopy cannot so easily be used to study chemisorption on oxides if it is essential to obtain low frequency spectral data (e.g., adsorbent-adsorbate stretching modes) because of the opacity of most oxides over much of the low frequency spectral region. Recent work has shown that the Raman technique can be extremely useful in this context (4). 

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