Vanadium selective dehydrogenation

A V-ZSM-5 sample with a Si/V o 42 was synthetized outgoing from V0(C00)2 and Q-brand sodium silicate using TPA-Br as template. ESR spectroscopy proved that vanadium(IV) ions in the zeolitic framework exhibit a distorted square planar symmetry. Upon heat treatment a part of the framework vanadium ions migrate to extra-framework positions. After dehydration no Bronsted acidity was found. Treatment in oxygen and hydrogen above 570 K revealed the redox character of the V-ZSM-5 sample. In oxidation of n-bu-tane (as catalytic test reaction) the V-ZSM-5 zeolite exhibits selective dehydrogenation and aromatization activity. 

It has been shown that the activity of niobia for the oxidative dehydrogenation of propane can be increased by adding vanadium or chromium, while maintaining a high selectivity towards propylene. 

This paper summarized our current understanding of the factors that determine selectivity for dehydrogenation versus formation of oxygen-containing products in the oxidation of light alkanes. From the patterns of product distribution in the oxidation of C2 to C6 alkanes obtained with supported vanadium oxide, orthovanadates of cations of different reduction potentials, and vanadates of different bonding units of VO in the active sites, it was shown that the selectivities can be explained by the probability of the surface alkyl species (or the... 

The catalysts based on vanadium oxide are one of the better studied systems. A V-Mg oxide in which Mg orthovanadate (Mg2(V04)2) and MgO were the only identifiable phases was a rather selective catalyst (27). Since MgO was relatively inactive in alkane activation, Mg orthovanadate was assumed to be the active component. Indeed, Mg orthovanadate prepared as a stoichiometric compound showed high selectivities for the oxidative dehydrogenation of propane (29). In this latter study, it was shown interestingly that Mg orthovanadate was the only alkali or alkali earth orthovanadate that... 

The difference between propane and 2-methy]propane on Mg2V207 cannot be explained by the size of the C3 chain. It is then proposed that although with difficulties, a C3 species still has a finite probability to interact with both vanadium ions in a V207 unit in the catalyst to lead to the formation of combustion products. This probability is twice as large for 2-methylpropene (or 2-methylpropyl) than propene (or propyl), which may account for the lower selectivity for dehydrogenation for 2-methylpropane on this catalyst. 

In this paper, we will report the electronic and catalytic reactivities of the model VC/V(110) surface, and our attempt to extend them to VC powder catalysts. By using high-resolution electron energy loss spectroscopy (HREELS) and NEXAFS techniques, we observed that the surface properties of V(110) could be significantly modified by the formation of vanadium carbide some of the experimental results on these model surfaces were published previously.3-5 We will discuss the selective activation of the C-H bond of isobutane and the C=C bond of isobutene on V(110) and on VC/V(110) model systems. These results will be compared to the catalytic performances of vanadium and vanadium carbide powder materials in the dehydrogenation of isobutane. 

Irreversible deactivation can have a similar effect on the hydrothermal deactivation by deteriorating coke selectivity (for instance for nickel poisoning). The hydrothermal deactivation on its turn will now also have an effect on the catalyst poisons, as for instance on the mobility of vanadium and on the deactivation of vanadium and nickel as dehydrogenation catalysts [2]. 

Vanadium phosphate materials have found use as catalysts for a number of reactions beyond the widely practiced partial oxidation of butane. These applications are mainly in selective oxidation 3,73,87,90-94, 96-102,154,195,208,237,251-269), ammoxidation (88-90,270), dehydrogenation (232,271-276), and dehydration (277,278). 

Nickel and vanadium are contained within the crude oil as their respective porphyrins and napthenates (2). As these large molecules are cracked, the metals are deposited on the catalyst. Nickel which possesses a high intrinsic dehydrogenation and hydrogenolysis activity drastically increases the production of coke and dry gas (particularly H2) at the expense of gasoline. Vanadium on the other hand interacts with the zeolitic component of a cracking catalyst and leads to destruction of its crystallinity. This results in reduced activity as well as an increase in non-selective amorphous silica-alumina type cracking. Supported vanadium also has an intrinsic... 

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