Mechanistic aspects of methanol partial oxidation over supported iron oxide aerogels

Partial oxidation of methanol over Fe2O3-supported (SiO2 or MoO3) aerogels was investigated between 225 to 300 degreesC. Wide product selectivity was observed dependent on percentage of iron oxide present, support used, and temperature. The reaction evaluations were done using 1:1.6 methanol to oxygen mole ratio in supercritical carbon dioxide (pressure of 90 bar). Dimethyl ether was favored for higher iron oxide loadings (20 and 100%) and lower temperatures (225 to 250 degreesC). This is related to the Lewis acidity of the iron oxide surface sites. Formaldehyde was favored if the support was changed to molybdenum oxide (20% iron oxide). This is related to the formation of iron molybdate as an active site. Methyl formate was favored for the low percentage iron oxide on silica (250-275 degreesC). This is related to the formation of surface formates that probably react with fluid phase methanol. FT-IR probe molecule characterization studies revealed that methanol adsorbs as methoxy as the first step in all reaction processes. The work provides further insight into the mechanistic nature of the partial oxidation of methanol over iron oxide based materials. (C) 2001 Academic Press.