Green and rapid synthesis of iron molybdate catalyst by mechanochemistry and their catalytic performance for the oxidation of methanol to formaldehyde

Abstract

Iron molybdenum catalyst was successfully prepared by mechanochemistry method under ball grinding mill. The physico-chemical properties of iron molybdenum catalyst synthesized with different mechanochemical experiment conditions including the number ratio of large balls to small balls, the quality ratio of agate balls to raw materials and ball milling time, have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, N2 physical absorption, X-ray photoelectron spectroscopy (XPS), etc. The catalytic performance of iron molybdenum samples in the oxidation of methanol to formaldehyde also has been evaluated in a self-built fixed-bed micro-reactor. Results demonstrate that iron molybdenum catalyst prepared by small balls shows the highest formaldehyde yield (95.2%) than the rest samples. With the increasing quality ratio of balls to materials, the phase composition of MoO3/Fe2(MoO4)3 from iron molybdenum catalyst firstly goes down and then goes up, which has close correlation with the formaldehyde selectivity. The catalyst samples prepared under ball grinding time of 30–120 min, show the typical iron molybdenum catalyst diffraction peaks, and the further extension of ball grinding time has no obvious influence on the crystal structure of iron molybdenum catalyst. The samples prepared with ball grinding time of 120 min, has the highest formaldehyde selectivity (97.56%), which could be due to the increasing content of Fe2(MoO4)3 and the improved uniformity of particles with the increasing ball grinding time.