Controlling Selectivity in Direct Conversion of Methane into Formaldehyde/Methanol over Iron Molybdate via Periodic Operation Conditions

The partial oxidation of methane over a Fe 2 (MoO 3 )4 powder catalyst was studied under transient inlet gas conditions. The preparation of the Fe 2 (MoO 4 ) 3 catalyst was performed using a hydrothermal synthesis route. Analytical-grade Fe(NO 3 ) 3 .9H 2 O and (NH 4 ) 6 Mo 7 O 24 .7H 2 O were dissolved separately in distilled water. The molybdate solution was then added dropwise to the iron nitrate solution under continuous stirring to form a homogeneous solution, which was pH-adjusted to 3 by adding NH 3 .H 2 O and HNO 3 . The solution was transferred to a Teflon lined autoclave, sealed, and kept at 140°C for 12 h. The formed precipitate was then washed several times with distilled water and ethanol. At the lowest temperature, only CO can be observed, while at the higher temperatures, also HCHO and CO 2 are formed.