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Three kinds of bulk iron phosphates were prepared via different methods and employed as model catalysts in the oxy-bromination of methane (OBM). NaFe(PO) was obtained via a fluoride route for the first time that showed even superior catalytic performance than FePO. Phase evolution from NaFe(PO) to NaFe(PO) after the OBM was confirmed both by X-ray diffraction and Fe Mössbauer spectroscopy. Temperature-programmed reduction of hydrogen and desorption of CHBr revealed that the redox capacity of iron phosphates were responsible for the generation of bromine radicals on catalyst surfaces while CHBr-involved reactions likely belonged to gas-phase reactions. Graphical Abstract: Model iron phosphate catalysts were synthesized by three different methods. It was found that the NaFe(PO) catalyst prepared by a fluoride route showed superior OBM performance than the other two catalysts both with the phase of FePO, especially for producing higher CHBr selectivity.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: FePO4-SBA-15 (OP) was directly synthesized via a one-pot hydrothermal technique, using Fe(NO3)3 and H3PO4 as the precursors. FePO4/SBA-15 (IMP) was also prepared as a reference, using an impregnation method and commercially available SBA-15 as the support. The yielding samples were employed to catalyze the harsh oxy-bromination of methane (OBM) reaction, showing similar initial catalytic performances. The fresh and spent samples after catalytic reaction were thoroughly characterized by N2-physisoption, inductively coupled plasma, wide- and small-angle X-ray diffraction, transmission electron microscopy, diffuse reflectance UV–vis spectroscopy, temperature-programmed oxidation, and room temperature 57Fe Mössbauer spectroscopy. It was found that the FePO4 was in good crystalline in the OP sample while it was in amorphous for the IMP catalyst. Despite this difference, both FePO4 phases in the fresh samples were transformed into Fe7(PO4)6 and Fe2P2O7 in the spent ones. Furthermore, the OP catalyst showed excellent stability in a period of 1000h time-on-stream performance without apparent deposition of cokes. The losses of P and Fe after the catalytic evaluation were only 9.5% and 15.5%, respectively, while the ratio of P/Fe remained close to 1.0. N2-adsorption and TEM observations confirmed that the mesoporous pores were extremely stable under the harsh reaction ambience, which might play a crucial role in the stability test. [Copyright &y& Elsevier]