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Abstract: Nano-structured iron molybdate materials, comprising Fe2(MoO4)3 nano-particles anchored onto MoO3 nano-rods, have been synthesised and evaluated as catalysts for the selective oxidation of methanol to formaldehyde. The catalysts were benchmarked against a standard iron molybdate catalyst prepared by co-precipitation and were found to have comparable performance under the test reaction conditions. The materials have been characterised using a combination of electron microscopy, powder X-ray diffraction and Raman spectroscopy. The synthesised MoO3 nano-rods were found to have a uniform structure, 8–10μm in length with a rectangular cross-section of 50–100nm×100–200nm. Fe was impregnated onto the MoO3 nano-rods via incipient wetness with an aqueous solution of Fe(NO3)3·9H2O. Calcination of these precursors formed 20–200nm Fe2(MoO4)3 islands on the surface of the nano-rods via a solid-state diffusion mechanism, and the size of the Fe2(MoO4)3 islands could be controlled by varying the Fe loading. The effect of the temperature and duration of calcination were investigated, and it was found that the optimum conditions were 450–500°C for 2h. At 350°C, the temperature was too low for the solid-state reaction between the MoO3 nano-rod and the surface Fe to occur, and no Fe2(MoO4)3 was formed. At higher temperatures, the nano-rod morphology was compromised, and irregular, partially coalesced particles of Fe2(MoO4)3 were generated, which had a lower catalytic performance than the nano-structured Fe2(MoO4)3/MoO3 materials. At 400°C, the solid-state reaction occurred sufficiently slowly for mechanistic aspects of the Fe2(MoO4)3 island formation to be elucidated by transmission electron microscopy. [Copyright &y& Elsevier]

Abstract: Vanadium phosphate catalysts have been widely studied for the selective oxidation of alkanes to a variety of products including maleic and phthalic anhydride. The synthesis of the precursor is a crucial factor in determining the performance of the final catalyst. Changes in the preparation procedure can alter the morphology, surface area, crystallinity and crucially, the exact vanadium phosphate phases present in the final catalyst which can all affect the selectivity and/or activity of the catalyst. In this study, the use of diblock copolymers in the preparation of phosphate oxidation catalysts has been shown to influence the crystallinity and morphology of the catalyst precursor. By adding a diblock copolymer, poly(styrene-alt-maleic acid) (PSMA), into the preparation uniform, highly crystalline VOHPO4·0.5H2O precursors are obtained, leading to a faster, more efficient, activation to the active catalyst. [ABSTRACT FROM AUTHOR]