Vanadium magnesium oxide

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]. 

The efficiency of zinc-chromium and vanadium-magnesium oxide catalysts in the reaction of butanediol dehydrogenation has been established. The optimum reaction conditions in butadione synthesis providing high yields and selectivity have been found. Experimental substantiation of principles for the purposeful synthesis of the catalytic systems mentioned above is considered. The catalysts were prepared based on these principles. 

We have investigated a series of the dehydrogenating catalysts for this reaction. Our attention was focused on two of them. Further study of 2,3-butanediol dehydrogenation and oxidative dehydrogenation to butadione was performed using zinc-chromium oxide catalysts and vanadium-magnesium oxide catalysts as well. 

Table 1 presents the properties of vanadium-magnesium oxide catalysts subjected to the heat treatment. The temperature of the heat treatment determines both the textural and the catalytic properties of the catalyst. Similar to the dehydrogenation of ethylbenzene into styrene [10,11], the most active catalysts occurred to be those... 

Kung, H. and Kung, M. (1997). Oxidative Dehydrogenation of Alkanes over Vanadium-Magnesium-Oxides, AjPjpZ. Catal. A Gen., 157, pp. 105-116. 

Bhattacharya, D., Bej, S.K., and Rao, M.S. Oxidative dehydrogenation of n-butane to butadiene effect of different promoters on the performance of vanadium-magnesium oxide catalysts. Appl Catal A Gen. 1992,87, 29. 

Kung, H.H. and Kung, M.C. Oxidative dehydrogenation of alkanes over vanadium-magnesium-oxides catalysts., 4pp/. Catal A Gen. 1997,157,105. 

Aluminium oxide, arsenic trioxide, bismuth trioxide, calcium oxide, chromic oxide, lanthanum oxide, lead dioxide, magnesium oxide, manganese dioxide, molybdenum trioxide, phosphorus pentoxide, stannic oxide, sulfur dioxide (explodes), tantalum pentoxide, tungsten trioxide, vanadium pentoxide. 

At very low surface areas (about 5 m /g) and constant conversion (70%), the contaminant selectivities are dominated by the matrix composition (Table I). Rare earth and magnesium-containing microspheres were prepared to examine the effects of these metal oxides on catalyst selectivities in the presence of nickel and vanadium. These oxides were chosen because the literature (3,5,10-15) has shown them to be effective at reducing the deleterious effects of vanadium in cracking catalysts. 

It has been found that compounds of the alkaline earth metals as well as rare earths are suitable for vanadium trapping. Patents relating to the use of titanates of calcium (22), barium (23), and strontium (24) have been issued. Equivalent stannates of calcium and strontium have also been recommended (24,25). Rare earths as separate particles (26) and in the same catalyst particle (27) have been proposed. Naturally occurring minerals such as Sepiolite and Dolomite which are rich in magnesium oxide and calcium oxide have been suggested (28). 

In the second process the alkaline solution is mixed with acid and the carbon dioxide liberated driven of by boiling. The resulting acidic solution is then neutralized with ammonia or magnesium oxide, whereupon uranium precipitates together with molybdenum and vanadium. The process is therefore only used if uranium ores have low concentrations of molybdenum and vanadium. 

E3.37 As noted in Section 3.17(a), nonstochiometry is common in the solid-state compounds of d-, f-, and later p-block elements. We would therefore expect vanadium carbide and manganese oxide to exhibit nonstoichiometry (two d-block metal compounds) but not magnesium oxide (an s-b ock metal oxide). 

Previously we have studied such catalysts in hydrocarbon dehydrogenation and oxidative dehydrogenation reactions [6,7]. Instrumental methods such as XRD, X-ray, photoelectron spectroscopy, DTA, UV-spectroscopy, EM were used. It has been found that activity of the Zn-Cr catalysts is determined by the stoichiometric spinel ZnCr204 [8]. In the case of the vanadium-magnesium system the activity and selectivity depend upon the presence of ions V and V grouped on the catalyst surface into clusters of 2-3 vanadium ions [9]. This was taken as a principal for the purposeful synthesis of the catalytic systems mentioned. In this work an attempt was made to spread the obtained experience on the dehydrogenation of alcohol groups. 

Oxidative dehydrogenation of butanediol on the selected vanadium-magnesium catalysts allowed to reduce the reaction temperature of butadion synthesis by about 100°C. The reaction was studied in the temperature range of 160 - 350°C at LHSV-equal to 1 h" and butanediol oxygen molar ratio equal to 1 1 (Table 2). Already at 250°C more than 85% of butanediol was converted. 

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