Vanadium-containing molecular sieve

Recently the large pore vanadium containing molecular sieve, V-NCL-1 with a pore size of 7 A, has been shown to be an active catalyst for the oxidation of larger molecules, such as napthalenes, 1,4-napthoquinones and phthalic anhydride (Scheme 22)[187]. The as synthesised form of V-NCL-1 contains atomically dispersed V4+ ions located in fiamework postions although not neccessarily in tetrahedral coordination. The vandium ions can be oxidised to the pentavalent state by calcination, as evidenced by ESR [157], with some... 

The oxidation of aniline was carried out in the liquid phase over a series of transition metal - substituted molecular sieves. For low oxidant/aniline ratios, azoxybenzene (AZY) was the major product formed over Ti-containing catalysts, the reaction was limited by diffusion for medium pore zeolites like TS-l and mesoporous silicas were preferred as they permitted the use of both H2O2 and tert-butyl hydroperoxide as oxidants. Higher oxidant/aniline ratios (>2) led to the formation of nitrobenzene (NB), whose selectivity was proportional to the catalyst concentration. In contrast, vanadium containing molecular sieves were only active with TBHP and aniline was converted very selectively into nitrobenzene for all oxidant concentrations. 

High selectivity was also reported for the ammoxidation of 4-methylpyridine, e. g. over vanadium-molybdenum oxides [90] highly dispersed vanadia on sili-cated alumina [91] or on vanadium-containing molecular sieves (VSAPO, VAPO [92], also used for the ammoxidation of 3-methylpyridine [93,94]). The ammoxidation of 2-methylpyridine leads to the formation of large amounts of pyridine, by total oxidation of the methyl group and subsequent decarboxylation, in addition to the desired nitrile [95]. Yields in excess of 90% can, nevertheless, be achieved, e. g. over vanadium-tin oxide at ca 670 K [23] or over molybdenum phosphates [96]. When the ammoxidation of 2-, 3- and 4-methylpyridine over vanadium phosphates was compared catalyst activity and the nitrile selectivity reflected the reactivity order 4- > 3- > 2-methylpyridine, probably as a result of different sterie hindranee [41]. 

Table 4. ESR parameters of in vanadium containing molecular sieves ...

Vanadium-Containing Molecular Sieves by Secondary Synthesis. . 208... 

Similar to Ti-containing molecular sieves, an IR band at ca. 960 cm was also reported for [Si,V]MFI structures (cf., e.g., [340] and Volume 1, Chapter 7, pages 208-209, of the present series and references therein). Thus, Hongbin Du et al. [341] observed by the FTIR/KBr technique in synthesized large pore V-contain-ing zeolite Beta a band at 960 cm" and took the appearance of this signal as an indication of vanadium incorporation into the framework to produce H-[Si,Al,V]Beta. 

The subsequent Chapter 7 is devoted to the synthesis and characterization of molecular sieve materials containing transition metals in the framework. Authored by G. Perego, R. Millini and G. Bdlussi, this Chapter focuses on titanium-silicalite-1 which has recently been found to be a unique catalyst for selective oxidations with hydrogen peroxide. Also covered in this Chapter is the synthesis of vanadium- and iron-containing molecular sieves. 

Further interesting developments in this field are the discovery of the large pore titanium silicate molecular sieve ETS-10 [77] and the synthesis of mesoporous materids containing titanium and vanadium [78-81], Much systematic work will be required to elucidate how useful these new materials are as catalysts in selective oxidation reactions. 

Similarly, 2,3,5-trimethylphenol (239) was converted into the quinone 240 ca 80%) using H3PMoi204o"" or titanium substituted aluminophosphate (TiAPO-5) molecular sieves" . Efficient oxidation of phenols to the corresponding quinones has also been effected with H2O2-V-HMS (vanadium-containing mesoporous molecular sieves)" . 

The potential of NIR FT-Raman spectroscopy for the investigation of zeolites (vanadyl-containing MFI, TS-1) as well as alumophosphate-based molecular sieves (AEI, CHA, CEO) are described. In Raman spectra of template containing samples bands of the organic species dominate. By dispersive Raman microscopy a spatial distribution in a CoAPO-34 crystal is observed. The Raman spectra allow a very rapid and sensitive detection of anatase formed during thermal treatment of as-synthesised titanium-containing zeolites. Different vanadium species are detected in vanadium-containing ZSM-5. 

Doubly substituted analogues of TS-1 have also been reported. Trong et al. (130) synthesized bifunctional molecular sieves with titanium and various trivalent ions, for example, Ti-MFI that also contained, Al, or Ga. Tin and vanadium have also been incorporated into the titanium silicalite structure (33,131) by a primary synthesis method. The incorporation of a second metal changes the redox properties of the materials as well as their morphology. Incorporation of tin into titanium silicalite improved the epoxidation selectivity of the catalyst compared with that of (mono-substituted) TS-1. 

Copper hydroxyphosphate also allows the direct hydroxylation of 2,3,6-TMP, leading to selectivities for TMHQ (1) of >80%. The main by-product is TMQ (5). Heterogeneous catalysts which have been used for the oxidation of 3 include zeolites, mesoporous materials and molecular sieves contaiiung transition metals. Molecular sieves containing transition metals such as vanadium or copper in the framework can simply be mixed with 2,3,6-TMP and H2O2 in acetoiutrile for the oxidation. ... 

Vanadium-cobalt substituted aluminophosphate molecular sieve of AEI structure (VCoAPO-18) was found to be active and selective in the ODH of ethane. Its catalytic behavior can be related to the presence of redox (probably related to and Co " ") and acid sites (related to Co + cations) in addition to its unique structural properties. The conversion and ethene selectivity decreases in the order VCoAPO-18 >VO c/CoAPO-18 > CoAPO-18 [38]. At 873 K, the VCoAPO-18 catalyst showed a 50% ethene selectivity at 60% ethane conversion for an ethane/oxygen molar ratio of 4 8. Acid SAPO-34-based microporous catalysts with chabasite structure have been tested for the ODH of ethane in the temperature range of 823 to 973 K. Pure acid and La/Na containing SAPO-34 were catalytically active and a 75 ethene selectivity for 5% ethane conversion and a 60% ethane selectivity for 30% ethane conversion was observed [39]. 

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