V-silicalite

Characterization Data. A complete characterization of V- containing silicalite samples has been reported in a previous paper (7), but the main relevant aspects useful for a better understanding of the nature of vanadium species in V- silicalite samples and for the correlation with the catalytic behavior will be briefly summarized. 

The constrained environment in which electrophilic oxidation occurs has a strong influence on the exclusion of bulky product formation, but it is also important that the oxidation potential of titanium peroxo compounds is adequate, as demonstrated by the fact that the same reactions carried out in the presence of V-silicalite, which has the same pore structure, give rise to imine and nitro compounds as major reaction products (Reddy, J. S. et al., 1994). 

V has been incorporated in the framework of molecular sieves, for example, V-A1PO-5 and V-silicalites. With V-A1PO-5, epoxidation of allylic alcohols proceeds with excellent selectivity (41) ... 

Redox silicalites with elements other than titanium have found catalytic applications in various organic oxidations. V-ZSM-11 is reported to catalyze alkane oxidation and is found to oxidize even primary C-H bonds [98]. Detailed studies indicate that V silicalites are better than Ti silicalites for alkane oxidation, as it is found that molecular oxygen can act as the oxidant in the former case [99]. V-ZSM-5 shows selectivity toward alcohol oxidation in allyl and methallyl alcohols... 

Table 3 compares our results on the oxidation of toluene over the Sn-silicalite samples. The Sn-samples are active in this reaction (39.4, 36.4 and 34.2 mol % H2O2 efficiency in 24 h for samples with Si/Sn ratios of 70). Both the hydroxylation of the aromatic nucleus to give cresols and the oxidation of the methyl substitutent to give benzyl alcohol and benzaldehyde take place simultaneously on the Sn-silicalites. Based on the product distribution, it can be seen that the rate of the oxidation of the methyl substituent is about 6 times faster than the rate of aromatic hydroxylation on all the samples. After 24 h, the concentration of benzaldehyde is the highest in the product. In this respect, the Sn-silicalite molecular sieves are more similar to the V-silicalites, VS-2 than the Ti-silicalites, TS-1 or TS-2 [16]. 

The production of propylene from the oxydehydrogenation of propane is an exothermic process and thermodynamically limited. For this reason, a large number of catal tic systems have been studied for increasing propylene production. The majority of the catalysts investigated in the literature are based on vanadium compounds. They show propylene yield between 5% on vanadium-magnesium-oxide [1] and almost 30% on V-silicalite [2]. 

V-Silicalite was synthesized with Si/V = 50, according to the method given in... 

Recently, it has been shown that intra-framework V in V-silicalite can be discriminated from intra-zeoUte vanadiiun oxide clusters and even from ions exchanged into Na-ZSM-5 by its particularly high V 2p3,2 BE [106, 141]. Prerequisite for such analysis of weak V signals is a careful treatment of the X-ray sateUites at the O Is hne, which mask the weak V 2p doublet. Problems with this superposition maybe the reason for earUer reports of low V 2p BE for intra-zeohte vanadium [149]. 

Benzene O2/H2/N2O Phenol Noble metal on Ti02 or V-silicalite, Pd/TS-1 20-100 10-300 Batch reactor Y = 0.11 % 144... 

The liquid-phase oxidation of hexane on Ti- and V-silicalites resulted in a mixture of alcohols, aldehydes, and ketones Cg [128]. The same V-MFI compositions demonstrate the activity in phenol hydroxylation comparable to that of TS-1 and TS-2. 

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