MoO <3> Catalyst And Its Selective Oxidation Of Methanol To Formaldehyde

MoO3 was considered a promising material for various industrial applications such as sensors, display materials, photochromic, electrochromic and catalysts due to its unique structure, physical and chemical properties. The MoO3 catalysts play an important role for methanol selective oxidation to formaldehyde. Compared with orthorhombic MoO3, few literatures reported the catalytic performances of the metastable MoO3. Therefore, it is important to probe the synthsis of the metastable MoO3 catalysts and their catalytic performances. The metastable h-MoO3 and β-MoO3 were successfully synthesized using molybdic acid as precursor via a facile hydrothermal treatment followed by calcination. The Fe-Mo-O、Fe-Mo-Ce-O and Fe-Mo-Co-O were synthesized by co-precipitation method. The catalytic performances of the catalysts were studied by selective oxidation of methanol to formaldehyde.1. Synthesis and catalytic performaces of bulk h-MoO3 catalystMetastable hexagonal molybdenum trioxide was successfully synthesized using molybdic acid as precursor via a facile hydrothermal treatment followed by calcination. The effect of the hydrothermal treatment temperature and calcination temperature on morphologies and phases of the catalysts were studied. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results show that the pure hexagonal MoO3 catalysts can be obtained at a hydrothermal treatment temperature of 60～120℃ and a calcination temperature of 150～350℃, respectively, and the h-MoO3 presents a morphology of hexagonal with a diameter from 1 to 10 micrometer. The synthesized h-MoO3 catalysts exhibited reactivity for methanol oxidation to formaldehyde. The conversion of methanol was 2.07%, and the selectivity of formaldehyde was 65.7%.2. Synthesis and catalytic activity research of the bulk P-MoO3 catalystMetastable monoclinic molybdenum trioxide was successfully synthesized using molybdic acid as precursor by a hydrothermal synthesis followed by calcination. The nitric acid has an important effect on the phases of the catalyst. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and Raman Spectroscopy, X-ray photoelectron spectroscopy (XPS), NH3-TPD and DSC. The results show that the pure β-MoO3 catalysts can be obtained with a HNO3/MO atomic ratio was 1.8 and a calcination temperature of 310℃. The β-MoO3 can be transformed to orthorhombic MoO3 by a thermal treatment in nitrogen at 428℃. A conversion of methanol and a selectivity of formaldehyde were up to 33% and 98%.3. Synthesis and catalytic perofrmances of the Fe-Mo-O、Fe-Mo-Ce-O and Fe-Mo-Co-O catalystsThe Fe-Mo、Fe-Mo-Ce and Fe-Mo-Co were synthesized by co-precipitation method with ammonium molybdate、ferric nitrate、cerous nitrate and cobalt nitrate as precursors. Mo:Fe:Ce and Mo:Fe:Co atomic ratio were 2.2:1:0.1. The synthesized catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), H2-TPR and NH3-TPD. The results showed that the Fe-Mo-O catalysts were composed of MoO3 and Fe2(MoO4)3 when the Mo/Fe atomic ratio between 1.5-3. The Ce and Co were added to Fe-Mo catalysts and the resulting catalysts exhibited enhanced textural properties and catalytic performaces. Fe-Mo-Co-O catalytic activity gave a methanol conversion of 55% and a formaldehyde selectivity of 98%.This paper investigated synthesis methods and physicochemical properties of metastable MoO3 for selective oxidation of methanol to formaldehyde, which offered theoretical support for the synthesis methods and structure-activity relation of metastable MoO3.