HZSM-5 support

A novel HZSM-5-supported N-interstitial Reio cluster catalyst has now exhibited the highest phenol selectivity (93.9%) using O2 as the sole oxidant at a good benzene conversion of 9.9% [107]. Although rhenium with various valences possesses oxophilic and redox properties similar to molybdenum and vanadium, it has not been widely used as catalyst for selective oxidation because of the easy sublimation of Re207. However, rhenium acts as a good component of oxidation catalysts under reductive atmosphere, for example, coexisting with methanol [108-110] and ammonia [111-114]. 

Pt-Zn/Al203 Pt-Ga A1203 and HZSM-5 supports Dodecane and Isobutane dehydrog. 480°, 0.1 MPa, H2/RH=8/1) Aromatization of C3/C4 hydrocarbons. 

In recent years, a lot of research effort has been directed towards dehydroaromatisation of methane in which methane is converted to aromatic products such as benzene and naphthalene in addition to hydrogen. Perhaps the most well studied system has been that employing Mo/ZSM-5 based catalysts, where the bifunctional interaction between the zeolite Bronsted acidity and molybdenum species is well recognised. Under reaction conditions, the active molybdenum species are known to be in the form of carbides or oxycarbides, and recently it has been proposed that the a-MoCi-x phase is the most active form. Deactivation, primarily due to coke formation, is well precedented in this reaction and represents a major obstacle to be overcome in the successful application of these catalysts. In this respect, it is interesting to note that Ichikawa and co-workers have published studies indicating that the inclusion of low levels of CO or CO2 in the feed can promote the reaction via the suppression of coke formation in the case of both Mo/HZSM-5 and Re/HZSM-5 catalysts. Other approaches adopted towards this aim have been the inclusion of second metal components and a reduction of the acid strength of the HZSM-5 support. ... 

The Pd-ZSM-5 catalysts are prepared by impregnation and by solid exchange methods on the carrier of HZSM-5 and NaZSM-5 (Si/Al = 26) with variable palladium loading and different pre-treatment gas (He and O2). N2-physisorption, DRX and CH4-TPR are the main techniques used to characterise these catalysts. Furthermore, total methane oxidation is used to test their catalytic activity. Among the preparative variables, the solid exchange method, the NaZSM-5 support and the increase of the palladium loading improve considerably the activity of the Pd-ZSM-5 catalysts in methane oxidation. 

Furthermore, no significant differences are observed on the methane conversion or on the ignition temperatures of the Pd2HZSHe and the Pd2HZS02 catalysts. This result presumes that the catalyst pre-treatment with oxidant or with inert gas has the same effect on the activity of the Pd-HZSM-5 catalysts prepared by the solid-exchange method. Moreover, a noticeable methane conversion increase is observed when the NaZSM-5 support is used instead of the HZSM-5 zeolite. The ignition temperatures... 

A ground mixture of iron(III) nitrate and HZSM-5 zeolite, termed zeofen , has also been used both, in dichloromethane solution and in solid state under MW irradiation conditions [101]. It has been suggested that the zeolite aids the reproducibility of the reaction but any other aluminosilicate support would probably be equally effective. Recent studies point out attractive alternatives that do not employ any of the solid supports in such oxidations with nitrate salts [102]. 

S. (2008) liquid phase oxidation of benzene to phenol by molecular oxygen over La catalysts supported on HZSM-5. Top. Catal, 47, 98-100. 

Scheme 10.4 (a) Structural changes in the Re-CVD/HZSM-5 (19) catalyst during direct phenol synthesis from benzene and O2 and treatment with NH3 (b) proposed model structure of the N-interstitial Reio-cluster catalyst supported in the pore of HZSM-5 (calculated by DFT). 

In recent years, modification of zeolites, such as HZSM-5, by phosphoric compounds or metal oxides has been extensively studied, but little information is available on the modification of zeolites by diazomethane, which is an excellent methylating agent for protonic acidic sites. It is capable of entering into the small pores of zeolites because of its small molecular size and linear molecular structure. Yin and Peng (1,2) reported that the acidity and specific surface area of the inorganic oxide supports (AljOs, SiOj) and zeolite catalysts... 

Materials 2M2B 2-methyl-2-butene HZSM-5 zeolite with MFI framework (lUPAC nomenclature) NaCaA zeolite with LTA framework (lUPAC nomenclature) NaX zeolites with FAU framework (lUPAC nomenclature) Pd/A Os alumina supported palladium catalyst TAME tert-amyl methyl ether or 2-methoxy-2-methylbutane TAOH tert-amyl alcohol or 2-methyl-butan-2-ol... 

In early 1993, Haw and co-workers (107) reported in situ studies of allyl alcohol-/-13C on HZSM-5 and CsHX. No persistent carbenium ions were observed, but 1,3 label exchange was observed for the alcohol on the weakly acidic zeolite. We interpreted this as support for a transient allyl cation. The low stability of this cation was invoked to explain the failure to observe this species as a persistent species. Downfield signals observed in that study were attributed to the formation of propanal. Later in 1993, Biaglow, Gorte, and White (BGW) (108) reported similar studies conducted at different loadings and assigned a downfield resonance (variously reported at 216 and 218 ppm by BGW) to the allyl cation in HZSM-5. 

The occurrence of carbenium ions as reaction intermediates is strongly supported by the observation that the isotopic exchange can be totally suppressed in the presence of carbon monoxide.68 Furthermore, trapping of the intermediate carbenium ions by CO and water has been observed by insitu NMR spectroscopy when isobutane, water, and CO reacted on HZSM-5 zeolite to form pivalic acid.69,70 Regarding the small conversion, only a limited number of acid sites are suggested to be strong enough for the initial protolytic activation to take place. 

A HZSM-5 zeolite-supported novel N-interstitial Re10 cluster was found to be active for the direct phenol synthesis from benzene and 02 in the presence of NH3 [169, 170]. The acidity and pore structure of HZSM-5 led to the self-limited formation of the novel N-interstitial Re10 cluster in the pore, which cannot be produced on other oxide surfaces or in solutions, and direct phenol synthesis using 02 as a sole oxidant was achieved with impressive results (10% conversion and 94% selectivity) for the first time [169-171]. 

Zeolite-supported Re catalysts have been synthesized by chemical vapor deposition (CVD) ofMTO (CH3Re03) (3) on various zeolites such as HZSM-5, H-Beta, H-USY and H-Mordenite. HZSM-5 samples with different A1 contents were prepared by a hydrothermal synthesis method. For comparison, conventional impregnated catalysts were also prepared by an impregnation method using an aqueous solution of NH4Re04. All catalysts were pretreated at 673 K in a flow of He before use as catalyst. 

Thus, HZSM-5 (Si02/Al203 = 19) among the zeolites employed was the most favorable support for the Re species. The results also suggest that Al-OH in the HZSM-5 framework is a coordination site for active Re species (Table 2.4). 

Molecular oxygen was the active oxidant for the phenol synthesis and the maximum phenol selectivity (93.9%) was achieved on the N-interstitial Re cluster supported on HZSM-5. Molecular oxygen was activated in the space between the two Re6 octahedral cores of the Re10 cluster and benzene concertedly reacted on the activated 02 with the very low activation energy of 24 kj mol-1. The pore size of HZSM-5 is 5.5 A, which is similar to the size of the Re6-octahedral cluster framework,... 

Nitration of o-xylene with N02 has been performed in the gas phase over several zeolites (HBeta, HY, HZSM-5 and HMordenite), as well as on sulfuric acid supported on silica and sulfated zirconia at temperatures between 50 and 130°C.[72] HBeta was found the most active and selective catalyst for the production of 4-o-NX giving ratios of 4-o-NX 3-o-NX as high as 6 1, whereas no dinitro-o-xylene compounds were detected. 

Sophisticated catalysts, such as ZSM-5 or HZSM-5 [22] and other zeolites are also suggested in numerous papers, e.g. KEY [23], HY and H-mordenite [24], Re-zeolite-based Engelhardt FCC commercial catalyst [25], and steamed commercial zeolite catalyst [26]. These investigations are mainly devoted to fundamental studies and the correlation between feed composition, catalyst properties, process parameters and efficiency connected with prodnct distribution. Iron supported on silica-alumina, mesoporous silica and active carbons serves as the next example of materials applied in the waste plastics cracking [27, 28]. On the other hand, according to some results [29] application of cracking catalysts such as Zn-13X, Fe-5A and CoMo-HY are ineffective in waste plastics cracking. 

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