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This work aims at developing a customized ammoxidation catalyst through optimizing the metal oxide content in CrVO4/SiO2 catalysts. Various amounts of Cr–V–O with 1:1 molar ratio of Cr/V were successfully loaded on SiO2 via spray-drying method with colloidal silica as the binder. Polarized light microscope illustrated that the CrVO4/SiO2 particles presented as well dispersed microspheres in the microsize (20–80 μm). X-ray diffraction spectra confirmed the formation of monoclinic CrVO4 phase wherein the metal oxide content was ranged from 30 to 70 weight percent. FT-IR spectra indicated that the introduction of metal oxide had no obvious effects on the skeletal structure of SiO2. X-ray photoelectron spectroscopy analysis revealed that the valence state of V and Cr was hardly affected with increasing the metal oxide content. Performances of the obtained CrVO4/SiO2 catalysts with different metal oxide contents were investigated via the ammoxidation of a model compound, namely para-chlorotoluene (PCT) to para-chlorobenzonitrile (PCBN). A maximum conversion of 99.6% of PCT and 86.5% yield and 86.8% selectivity to PCBN have been obtained over the CrVO4/SiO2 catalyst with 60% weight of metal oxides at a temperature of 410 °C, n(PCT):n(NH3):n(air) = 1:3:15 and reaction load = 0.13 g/gCat·h. In addition, this catalyst was efficient and selective toward ammoxidation reactions of toluene, ortho- and meta-chlorotoluenes. [ABSTRACT FROM AUTHOR]

Vanadium-chromium composite oxides have held much interest due to their distinctive catalytic properties, which depend on their morphology and crystal structure. During the hydrothermal synthesis, reducing agents play an important role in controlling the morphology and the crystal structure of vanadium-chromium oxides. In this work, nanocrystalline chromium vanadate (CrVO4) were prepared by a simple one-pot hydrothermal method based on the reaction between V2O5 and CrO3. Three different CrVO4 crystal structures, including orthorhombic CrVO4, monoclinic CrVO4, and mixed-phased-CrVO4 were obtained by using different reducing agents. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed that nanocrystalline monoclinic CrVO4 was obtained using tartaric acid as the reducing agent. Catalytic properties of nanostructured CrVO4 were investigated for the vapor phase ammoxidation of 2-chlorotoluene to 2-chlorobenzonitrile. The monoclinic CrVO4 nanostructures exhibited excellent catalytic performance due to the proper distribution of V-O-Cr bond. It was one of the most efficient binary catalysts for such vapor phase ammoxidation processes to the best of our knowledge, and may have great potential for the ammoxidation of halogen-substituted toluenes. Monoclinic CrVO4 nanostructures are controllably prepared by hydrothermal process using tartaric acid as reductant and exhibit excellent catalytic performance for ammoxidation of 2-chlorotoluene. [ABSTRACT FROM AUTHOR]

Formulation and shaping of heterogeneous catalysts are vital in the successful industrial application. Here micro-sized vanadium chromium composite oxides catalysts with the spherical shape were prepared via spray drying with colloidal silica as a binder material. The physicochemical properties of catalysts with different Cr/V molar ratios were characterized by XRD, XPS, FT-IR, TPR, and particle size distribution analysis. It was revealed that the addition of Cr inhibited the formation of the crystalline phase V2O5 and decreased the reduction temperature of pentavalent vanadium species, and also resulted in the formation of monoclinic CrVO4 and a highly dispersed state of vanadia species. VCrO/SiO2 particles with various Cr/V atomic ratio were studied as catalysts for p-chlorotoluene ammoxidation to p-chlorobenzonitrile, in which the catalyst with Cr/V ratio of 1 exhibited the best catalytic performance. When the Cr/V ratio was less than 1, mixed phases of orthorhombic CrVO4 and monoclinic Cr2V4O13 were formed and resulted in a low catalytic activity. With the increase of Cr/V ratio, the content of monoclinic CrVO4 in the catalysts increased, resulting in the catalytic activity of the catalysts improved. However, too large an amount of Cr led to the formation of highly oxidizing hexagonal-Cr2O3 phase, which reduced the selectivity of the catalytic reaction. [ABSTRACT FROM AUTHOR]

The Nylon 6 (PA6)/the functionalized multiwalled carbon nanotubes (F-MWNTs) fibrous membranes were fabricated by electrospinning, and then incorporated into an epoxy matrix. Their morphology, thermal stability, mechanical properties, thermal conductivities, and electrical resistivity were investigated. The electrospun PA6/F-MWNTs fibers performed as a skeleton in the epoxy matrix, and the well interfacial adhesion between the epoxy matrix and the PA6/F-MWNTs fibers leads to high mechanical properties of composites. The PA6 serves as an intermediate layer and alleviates the modulus mismatch between the stiff MWNTs and the soft epoxy matrix. The thermal conductivities of the epoxy composites increase by 27.3, 35.0, and 36.1%, respectively, with 0.5, 1 and 1.5 wt% F-MWNTs loading in the PA6/F-MWNTs fibers. At the same time, the PA6 simultaneously retains the high electrical resistivity of these epoxy composites., INTRODUCTION Epoxy (EP) resin is generally used in various industrial fields owing to their low volumetric shrinkage, good chemical resistance, and superior electrical and mechanical properties [1-3]. However, its low [...]