Selective Oxidation of Methanol to Formaldehyde Over Active Molybdenum Oxide Supported on Hydroxyapatite Catalysts

Abstract

Hydroxyapatite (HAP) was synthesized by sol–gel method. Different ratios of molybdenum oxide (1–15 % w/w) supported on HAP were prepared by the impregnation method and calcined at 400 °C in a static air atmosphere. The catalysts were characterized by thermogravimetry, differential thermal analysis, X-ray diffraction, FTIR spectroscopy and nitrogen sorption measurements. The surface acidity of the catalysts was investigated by the dehydration of isopropyl alcohol and the adsorption of pyridine (PY) and 2,6-dimethyl pyridine (DMPY). The gas–phase oxidation of methanol to formaldehyde was carried out in a conventional fixed-bed flow type reactor using N2 as a carrier gas. The obtained results clearly revealed that HAP–MoO3 systems were active and selective towards the formation of formaldehyde. The maximum yield of formaldehyde (97 %) was achieved on the catalyst containing 5 wt% MoO3/HAP. The generation of Mo6+as Lewis together with Bronsted acid sites play the main role in the formation of formaldehyde. Catalytic oxidation of methanol over MoO3/HAP calcined at 400 °C for 4 h.