VMgO catalysts

Magnesium vanadates, also known as VMgO catalysts, are known to be efficient catalysts for the ODH of light alkanes. Corma and coworkers [137] suggested that the incorporahon of small amounts of V on a MgO surface notably modified not only the redox properhes of the system but also the acid-base character of the oxygen species present on the catalyst surface. These acid-base properhes were related to the nucleophiUc character of the lathee oxygen anions. 

It follows that one may conclude that basic properties as well as atomic arrangements at molecular level play an important role in alkane oxidative dehydrogenation reactions. Such a conclusion could also be reached from the study of VMgO catalysts [42] for oxidative dehydrogenation of several alkanes as ethane, propane and butane under similar conditions (see e g. fig. 5 in ref 42). 

Lemonidou, A.A. Oxidative dehydrogenation of C4 hydrocarbons over VMgO catalyst — kinetic investigations. Appl. Catal. A Gen. 2001, 216, 277. 

Pantazidis, A., Auroux, A., Herrmann, J.-M., and Mirodatos, C. Role of add-base, redox and stractural properties of VMgO catalysts in the oxidative dehydrogenation of propane. Catal. Today 1996, 32, 81. 

The behavior of ethane is different from the other alkanes. It is the only alkane that undergoes significant dehydrogenation on the VPO catalyst, as well as the only one for which combustion is the predominant reaction on VMgO. However, an ethyl species is too small to interact with two V ions simultaneously on any of the three catalysts. A phenomenological explanation of this behavior of ethane has been suggested [10]. In this explanation, the possible reactions of ethyl, propyl, and 2-methylpropyl species were compared by statistically counting the number of various types of bonds in each species ... 

A large variety of oxide catalysts have been claimed as beeing effective in the oxidative dehydrogenation (ODH) of propane [5-18]. Mainly vanadium based catalysts such as VPO, VMgO solids have been developed and some of them have been extensively studied in order to identify the active vanadate phases [7, 9-14], Recently, a vanadia on precipitated silica catalyst has been found to exhibit high yield in the ODH of propane [17], However, utilization of rare earth catalysts in oxidation reactions seems also to be attractive [18], because solids composed of oxides of Ce, Sm, Nd or Y and CeFs are able to preserve high selectivity at high conversion [16]. 

Table 28.3. Oxidative dehydrogenation of propane over different catalysts (Pt/10%Rh gauze, VMgO and Pt/monolith catalysts) at few milliseconds contact time. Adapted from Ref. 56.

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