Fe-TON

Nature of active sites in the Fe-TON Zeolites Mossbauer and IR studies... 

Keywords Fe-TON, acidity, extraframework iron, Mossbauer, FTIR... 

Fe-TON (Fe-ZSM-22) zeolites of different Si/Fe ratios (27, 36, 50, and 150) were synthesized hydrothermally using 1-ethylpirydinium bromide (EtPBr) as template. The syntheses were carried out following the procedure reported in Ref [7]. The molar composition of gels used for the syntheses was ... 

XL30). Mossbauer spectroscopy (KFKIj was applied to follow the state of Fe species in the zeolites. Carbon monoxide and ammonia adsorption (monitored with FTIR) (EQUINOX 55) was used to determine the nature, concentration and acid strength of the active sites in the Fe-TON zeolites. 

Irrespectively of the iron content, the applied synthesis procedure yielded highly crystalline microporous products i.e. the Fe-ZSM-22 zeolite. No contamination with other microporous phases or unreacted amorphous material was detected. The SEM analysis revealed that size and morphology of the crystals depended on the Si/Fe ratio. The ZSM-22 samples poor in Fe (Si/Fe=150) consisted of rice-like isolated crystals up to 5 p. On the other hand the preparation with a high iron content (Fe=27, 36) consisted of agglomerates of very small (<0.5 p) poorly defined crystals. The incorporation of Fe3+ into the framework positions was confirmed by XRD - an increase of the unit cell parameters with the increase in the number of the Fe atoms introduced into the framework was observed, and by IR - the Si-OH-Fe band at 3620 cm 1 appeared in the spectra of activated Fe-TON samples. 

Low temperature CO sorption experiments monitored with the IR spectroscopy were used to determine the nature of active (acid) sites present in the Fe-TON zeolites. It is well known that CO is a useful probe molecule for Lewis acid sites. Narrow and well resolved bands appear in the region 2135 - 2150 cm"1. The IR spectra of CO sorbed in amount sufficient to cover all Lewis sites in the Fe-TON of different Si/Fe ratios are presented in Figure 2A. The samples of a high iron content (Si/Fe=27, 36) showed a significantly lower thermal stability. The activation of the NFL form of these Fe-TON... 

Figure 2. (A) IR spectra of CO adsorbed on the Fe-TON zeolites of different Si/Fe ratio at very low CO coverage required for the detection of the Lewis sites., (B) Difference spectra of CO adsorbed on Fe-TON of different Si/Fe ratio recorded upon the saturation of all Bronsted sites.

Polyferose. Jefron. An iron carbohydrate chelate contg approx 45% iron in which the metallic (Fe) ton is sequestered within a polymerized carbohydrate derived from sucrose. 

In the last years a great interest was paid to the catalytic properties of iron-containing zeolites that show interesting activities in different industrial reactions. The Fe-BEA zeolite is reported to be a good catalyst in the vapour phase alkylation processes [1], the Fe-TON zeolite shows very high activity and selectivity in the olefin isomerization [2, 3]. Finally, new applications of zeolitic catalysts in the partial oxidation catalysis, such as the Solatia Inc. processes for benzene hydroxylation to phenol using Fe-MFI, open a novel route for the use of zeolites in oxidation processes [4, 5]. On the other hand, the catalytic properties of the metal-modified MOR type zeolite in the isomerization process are well known. 

The performance was further improved by the addition of a third cocatalyst, often unpredictable. For instance, the addition of Fe (TON = 9 for single metal) to the Pb/Ti system increased the TON from 1068 to 1631 but reduced it for another active Cu/Ti system [12]. By examining the frequency of cocatalysts that appear in the best ternary system after testing over 10 000 unique catalyst combinations, it can be seen that the top three metals are Pb, Ti, and Mn. Despite the success of the ternary systems, the use of three metal cocatalysts in addition to palladium made the economics of metal separation of recovery unfavorable. Therefore, the R8dD was focused on optimization of the best binary systems. 

Figure 2.21 - Current-potential curve of a platinum electrode dipped in an acidic aqueous solution containing Fe tons...

Ilmenite is more abundant than mtile. Ilmenite world suppHes are estimated to meet the requirements of the Ti02 industry into the twenty-second century. The largest sources of ilmenite are in AustraHa, Canada, South Africa, Russia, and the United States. Large, unexplored sources also exist in China. About 9 million metric tons of ilmenite are mined aimuaHy. Long-term atmospheric effects weather ilmenite into leucoxene [1358-95-8], which contains most of its iron as Fe " . The majority of the world s supply of mtile comes from the beach sands of AustraHa, Florida, India, Bra2H, and South Africa. The total worldwide supply is estimated to be about 50 million metric tons. About 0.5 million tons are mined a year. The supply should last at least until the end of the twenty-first century. 

A mononuclear diastereopure high-spin Fe alkylperoxo complex with a pen-tadentate N,N,N,0,0-ligand 33 (Scheme 17) was reported by Klein Gebbink and coworkers [109, 110]. The complex is characterized by unusual seven-coordinate geometry. However, in the oxidation of ethylbenzene the iron complex with 33 and TBHP yielded with large excess of substrate only low TON s (4) and low ee (6.5%) of 1-phenylethanol. 

Under microwave irradiation and applying MCM-41-immobilized nano-iron oxide higher activity is observed [148]. In this case also, primary aliphatic alcohols could be oxidized. The TON for the selective oxidation of 1-octanol to 1-octanal reached to 46 with 99% selectivity. Hou and coworkers reported in 2006 an iron coordination polymer [Fe(fcz)2Cl2]-2CH30H with fez = l-(2,4-difluorophenyl)-l,l-bis[(l//-l,2,4-triazol-l-yl)methyl]ethanol which catalyzed the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as oxidant in 87% yield and up to 100% selectivity [149]. An alternative approach is based on the use of heteropoly acids, whereby the incorporation of vanadium and iron into a molybdo-phosphoric acid catalyst led to high yields for the oxidation of various alcohols (up to 94%) with molecular oxygen [150]. 

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