Preparation of La-Mo-V mixed-oxide systems and their application in the direct synthesis of acetic acid

Abstract

In this study, mixed metal oxides developed with a perovskite-type structure that show great potential for use in catalysis. Perovskite oxide catalysts with the composition LaMo x V 1 − x O n ( x = 0.1, 0.3, 0.5, 0.7, and 0.9) have been synthesized by the sol-gel method and then used in the ethane dry reforming reaction for the direct synthesis of acetic acid. The influence of the nature of the metallic source (metal, nitrate, acetylacetonate, and ammonium) on gel formation has been studied by Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA-DTA). After calcination, the obtained perovskites were characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS) coupled with scanning electron microscopy (SEM). The catalysts were then subjected to thermo-programmed reduction (TPR). The surface area (BET) was found to increase from 2.6 m 2/g ( x = 0.1) to 5.1 m 2/g ( x = 1.0) with increasing molybdenum content following calcinations at 750°C, and pure LaMo x V 1 − x O n perovskite was obtained with good homogeneity. The catalysts have been characterized by XRD, SEM, EDS, and carbon analysis (CA). The results indicate that through this synthesis it is possible to obtain highly crystalline, homogeneous and pure solids, with well-defined structures. The direct synthesis of acetic acid from ethane over the perovskite catalysts was studied at temperatures between 450 and 850 °C and elevated pressures between 1 and 8 bar. It was found that the yield of acetic acid and the selectivity of its formation could be increased by incorporating more molybdenum into the perovskite structure. The experimental studies have shown that the calcination temperature and the molybdenum content have a significant influence on the catalytic activity. Amongst the catalysts tested, LaMo 0.7V 0.3O 4.2 exhibited the best activity and stability.