Abstract
The catalytic activity of various Keggin polyoxometalate catalysts has been investigated in the gas-phase partial oxidation of toluene to produce benzyl alcohol and benzaldehyde. The catalyst systems HPMo12O40, HPMo11VO40, FePMo12O40, and PMo11FeO39 were prepared and characterized by FT-IR, UV-visible, SEM, XRD, TGA, and cyclic voltammetry. The acid/base properties were evaluated using the decomposition of isopropanol. Catalytic studies were carried under atmospheric pressure and over the temperature range 200°C–350°C, using carbon dioxide as a mild oxidant. Toluene conversion and product distribution depend mainly on the catalyst composition and operating conditions. In addition to benzaldehyde, benzyl alcohol is obtained with a high selectivity on the PMo11FeO39 catalyst. The kinetic data show that the reoxidation of the reduced catalyst is the rate-limiting step for the partial oxidation reaction of toluene.
Highlights
Aromatic aldehydes such as benzaldehyde are very valuable industrial organic intermediates, and their uses include the manufacture of flavors, fragrances, pharmaceutical precursors, and plastic additives
Supported vanadium oxide catalysts are used in gas-phase catalytic partial oxidation of toluene [12,13,14]. e supported vanadium-based catalysts were reported to show high benzaldehyde selectivity, but the toluene conversion was below 10% at the low temperature (
There is a large number of catalysts described in the literature and in the patent literature composed of the vanadium oxides systems modified by various promoters, supported on carriers Al2O3, SiO2, TiO2, and transition metal oxides and favorable for the catalytic gas-phase toluene oxidation to benzaldehyde [17,18,19,20,21,22,23,24], but the toluene conversion is very poor at low temperature. is catalyst system favors the formation of benzoic acid and degradation of carbon dioxide and benzaldehyde selectivity is not very satisfactory. erefore, a suitable catalyst for the selective production of benzaldehyde from toluene is strongly desired
Summary
Aromatic aldehydes such as benzaldehyde are very valuable industrial organic intermediates, and their uses include the manufacture of flavors, fragrances, pharmaceutical precursors, and plastic additives. Supported vanadium oxide catalysts are used in gas-phase catalytic partial oxidation of toluene [12,13,14]. E supported vanadium-based catalysts were reported to show high benzaldehyde selectivity, but the toluene conversion was below 10% at the low temperature (
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