Heteropolyacid generated on the surface of iron phosphate nanotubes: structure and catalytic activity studies

Abstract

Structural and catalytic properties of a Mo based heteropolyacid generated after impregnation of MoO_x on the surface of porous iron phosphate nanotubes (FeP) were studied. Nano sized MoO_x–FeP composites with different Mo molar loadings (1–5%) have been prepared under acidic conditions. Synthesized composites were characterised by elemental analysis, X-ray diffraction, transmission electron microscopy, Raman spectroscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy, acidity measurements using FTIR, N₂-physisorption and H₂-temperature programmed reduction methods. Spectroscopic characterization results suggest that Keggin-type FeMoP species were formed on the surface of the iron phosphate nanotubes in the case of catalysts with higher (4 and 5 mol%) Mo loadings. Pure iron phosphate nanotubes, Fe₂O₃, MoO₃ and bulk FeMoP HPA samples are less active than MoO_x–FeP composite samples for the benzylation of benzene with benzyl chloride, particularly the 5 mol% Mo loaded catalyst showed high activity. The enhanced catalytic activity of this catalyst is attributed to the presence of easily reducible, acidic and porous FeMoP heteropolyacid species. These materials can be readily separated from the reaction system for reuse. They are resistant to leaching of the active heteropolyacid species.