Introduction of Vanadium

In order to introduce vanadium into hydrogen forms of zeolites (H,Na-MOR,H-MOR with nsi/nAi = 5 and H,Na-ZSM-5, H-ZSM-5 with nsi/nAi = 35), mixtures of V2O5 and the zeolites were subjected to heat-treatment at 1073 K in air [92,190, 191 ]. Electron spin resonance spectroscopy (ESR) yielded a spectrum (as shown for the example of H-ZSM-5 in Fig. 52) exhibiting a well-resolved hyperfine (HF) signal ofvanadyl cations with g = 193,gj = 2.02,A = 19.8 mT,and Aj = 8.3 mT. These parameters are typical of isolated cations in an almost square-planar coordination. 

In the case of H-MOR with an nsi/n i ratio of 5, which is considerably lower than in H-ZSM-5 and, thus, gives rise to a much smaller distance between the cation sites, the ESR signals were broadened due to dipole-dipole interaction of the V +-containing species. 

As mentioned above, admission of dry oxygen to V,H-ZSM-5 prepared through SSIE led to a line broadening because of dipole-dipole interaction of VO(OH)+ and the paramagnetic O2 molecules. Adsorption of ammonia or pyridine significantly changed the ESR parameters and made the SHF-splitting completely disappear. Kucherov and Slinkin [190] ascribed this to an effect of 

An attempt was made to co-introduce Cu into the above-characterized VO(OH),H-ZSM-5 via SSIE by calcining a mixture of Cu compounds and the V-containing zeolite [93]. This, however, led to a decrease in the VO(OH)+ concentration as was indicated by a decrease in the intensity of the signals related to vanadyl species (cf. Fig. 54) and to the appearance of the ESR signal of isolated Cu+ in ZSM-5 (vide supra. Sect. 5.3.2.1). Obviously, Cu + is more strongly held in the zeolite structure than VO(OH)+ and is able to easily replace the vanadyl cation. 

In a similar way as that used by Kucherov and Slinkin [92,1911, Huang et al. [192-194] prepared vanadium-containing ZSM-5 and mordenite via SSIE between V2O5 and the zeolites mentioned above. The products were characterized by XRD, XPS, and determination of their surface areas. At variance with the interpretation given by Kucherov and Slinkin, Huang et al. [192] and Shan et al. [193] claimed from their ESR results that the vanadyl species existed in two different coordination structures both in ZSM-5 and mordenite, viz., in a compressed hexacoordinated octahedral and a pentacoordinated pyramidal symmetry. Furthermore, the authors studied the acidity of the zeolites after SSIE with V2O5 by FTIR of adsorbed pyridine and titration with butylamine in apro-tic solution. In addition, the capacities for adsorption as well as the activities and selectivities for oxidation of toluene to benzaldehyde were investigated. The authors showed that the differences in adsorptive and catalytic behavior were related to the differences in acidity of the materials produced by SSIE [193]. 

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Pilling-Bedworth ratio of 1 96, anatase phase films can show cracks and fissures with, consequendy, a loss of mechanical stability, however a hydrogen reduction treatment above 600°C leads to phase transition from anatase (101) to rutile (110) [43] with XRD detecting TiH2 upon prolonged hydrogen treatment of titania. As shown in Fig. 4.4, introduction of vanadium increases the intensity of the anatase Ti02 peak above 700°C disappearance of the vanadium (001) peak and the simultaneous appearance of the rutile (110) peak are observed, but anatase continues to dominate even after heat treatment at 800° C. A sharp vanadium (001) peak is observed for heat treatments carried out in air, while no vanadium peak has been seen in the case of heat treatment at 600°C in presence of Ar/H2. 

Procedures leading to preparation of vanadium-doped alumina- and/or titania-pillared montmorillonites are described and physicochemical characterization (chemical analysis, XRD, BET, ESR) of the products is provided. Results show that introduction of vanadium into the pillared montmorillonites leads to a rigid association of the dopant with pillars, irrespective of the method of preparation. The mode of vanadyl attachment in alumina-pillared samples does not depend on the mode of preparation, while in titania-pillared montmorillonite it does. Certain degree of delocalization of the unpaired electron into ligands and increased in-plane 7t-covalent bonding is observed for vanadyl ions present in the co-pillared (V-Ti)-PILC samples which also show particularly high activity in catalytic ammoxidation of m-xylene to nitrile product, as monitored by IR. A hypothesis is advanced that this effect is due to the unique character of vanadyl species present in these catalysts. 

Following the introduction of vanadium pentoxide by De Haen it was discovered empirically by Slama and Wolf that alkalis improved catalyst activity and these have been used in all the catalysts produced ever since. They were specified as important for stability by both BASF and the General Chenucal Comparty. Vanadimn pentoxide catalysts had been used for more than 20 years before Frazer and Kirl atrick showed that the addition of alkali led to the for-... 

Introduction of vanadium into microporous materials is also discussed in Sect. 6.3.1. 

Fixed-Bed Vapor-Phase Oxidation of Naphthalene. A sihca gel or sihcon carbide support is used for catalyst involved in the oxidation of naphthalene. The typical naphthalene oxidation catalyst is a mixture of vanadium oxide and alkali metal sulfate on the siUca support. Some changes, such as the introduction of feed vaporizers, are needed to handle a naphthalene feed (14), but otherwise the equipment is the same. 

The introduction of microwave pr ents an excellent new option for the synthesis of VOPc from vanadium oxide, dicyanobenzene, and ethylene glycol. In the present study, the effectiveness of synthesizing crude VOPc liom vanadium oxide and dicyanobenzene rmder the two synthetic methods was investigate by comparing reaction temperatures. Also, the preparation of fine crystal VOPc was investigated from the crude VOPc synthesized at... 

Nitrogen adsorption/desorption isotherms on Zeolite and V-Mo-zeolite are very similar and close to a type I characteristic of microporous materials, although the V-Mo-catalysts show small hysterisis loop at higher partial pressures, which reveals some intergranular mesoporosity. Table 1 shows that BET surface area, microporous and porous volumes, decrease after the introduction of Molybdenum and vanadium in zeolite indicating a textural alteration probably because of pore blocking by vanadium or molybdenum species either dispersed in the channels or deposited at the outer surface of the zeolite. The effect is far less important for the catalysts issued from ZSM-5. 

The evaluation of carriers and catalyst compositions showed that significantly higher SO2 oxidation activity could be achieved with Cs as a promoter under the operating conditions downstream the intermediate absorption tower as demonstrated by the results in Table 1, where the activity compared to the standard product is increased by more than a factor 2. This was clearly sufficient for the introduction of VK69 to the market as a new sulphuric acid catalyst. The activity results for different melt compositions were used to optimise the vanadium content and the molar ratios of K/V, Na/V. and Cs/V. However, the choice of Cs/V was not only a question of maximum activity, because of the significant influence of the Cs content on the raw material costs (the price of caesium is 50-100 times the price of potassium on a molar basis). Here, the economic benefits obtained by the sulphuric acid producer by the marginal activity improvement at high Cs content also had to be taken into account. 

Allan Walsh, in 1955, was the pioneer for the introduction of atomic absorption spectroscopy (AAS), which eventually proved to be one of the best-known-instrumental-techniques in the analytical armamentarium, that has since been exploited both intensively and extensively in carrying out the quantitative determination of trace metals in liquids of completely diversified nature, for instance blood serum-for Ca2+, Mg2+, Na+ and K+ edible oils-Ni2+ beer samples-Cu+ gasoline (petrol)-Pb2+ urine-Se4+ tap-water-Mg2+ Ca2+ lubricating oil-Vanadium (V). 

Introduction.—Texts describing the high-temperature electrochemistry and physical chemistry of vanadium and oxygen compounds of this element have been published, and the compilation of the chemistry of organovanadium compounds has been revised. ... 

Vanadium finds application to a limited extent in the manufacture of non-ferrous alloys. The introduction of the metal up to about 0-5 per cent, into brasses which contain from 60 to 70 per cent, of copper and 80 to 40 per cent, of zinc is stated to increase the maximum stress and elongation.8 Copper-vanadium and aluminium-vanadium alloys... 

As mentioned in the introduction, the literature dealing with OMCVD of vanadium carbide is scarce.16 19 As one patent16 reported that cyclo-... 

Introduction.—The structural339 and organometallic chemistry340 of vanadium has been reviewed and the compilation of the inorganic chemistry of vanadium has been revised.341... 

Figure 3.166 shows the reactivity and potential of these early transition metal pincer carbene complexes taking vanadium as an example. The broad range of compounds becomes possible owing to the rich redox chemistry of vanadium that makes different oxidation states easily accessible. Here, examples for vanadium(ll), vanadium(III) and vanadium(IV) are shown. Abstraction of halogen is facile making the introduction of different TT-donor ligands possible, even weak ones like acetonitrile. 

Freshly prepared mixed hydroxide contains vanadium(II) clusters reactive towards dinitrogen. Some indirect evidence indicates that the number of vanadium ions in the clusters activating dinitrogen approaches four or six. For example, introduction of other ions, such as V + inhibits N2 reduction and quantitative analysis of the inhibition effect leads to the conclusion that tetramers are the likely species tetramers are also suggested by analysis of ethane and ethylene formation in the reduction of acetylene. 

In syndiospecific polymerization using soluble vanadium catalysts, defects of the chemical addition are noticeable, their number being consistent with the Markoff first — order distribution 59-6i.63> jjj jjjjg regioselectivity as well as stereospecificity are greatly influenced by the possibility of the secondary insertion of monomer The chiratity of the last monomeric unit of the growing polymer determines the stereocontrol of syndiotactic polymerization. The introduction of an achiral (ethylene) unit results in the loss of stereocontrol As active center of syndio-... 

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