Structure and phase analysis of one-pot hydrothermally synthesized FePO4-SBA-15 as an extremely stable catalyst for harsh oxy-bromination of methane

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.