An iron molybdate catalyst for methanol to formaldehyde conversion prepared by a hydrothermal method and its characterization

Abstract

A one-step, low-temperature hydrothermal method has been successfully employed to prepare iron molybdate catalysts with Mo:Fe ratios ranging from 1.5:1 to 3.0:1. The resulting materials were characterized using a number of techniques including: XRD, Raman, N2 adsorption, SEM/EDX, DTA, EDXRD and combined XRD/XAS. The catalytic oxidative dehydrogenation of methanol to formaldehyde has been used as a test reaction. For Mo:Fe 1.5, phase-pure Fe2(MoO4)3 resulted from syntheses performed at temperatures as low as 100 °C in under 4 h. For samples with a Mo:Fe 3 detailed analysis of XRD, Raman and EXAFS data revealed the formation of a high surface area possessing, mixed phase material consisting of a poorly crystalline Mo5O14 and an amorphous Fe2(MoO4)3 type precursor. Both phases proved to be thermally unstable above a calcination temperature of 300 °C, going on to form high surface area mixed Fe2(MoO4)3/MoO3. Continued heating of this mixed oxide material resulted in sintering and to a decrease in the surface area. When both mildly (200 °C) and then more severely calcined (300 °C), this mixed phase sample showed a higher selectivity for formaldehyde production than a conventionally prepared (via co-precipitation) iron molybdate catalyst.