The formation of oxygen-containing organic molecules by the hydrogenation of carbon monoxide using a lanthanum rhodate catalyst

Abstract

A LaRhO 3 catalyst was used for the hydrogenation of carbon monoxide at 6 atm pressure and between 225 and 375 °C. The oxide is stable to reduction to the metal, but X-ray photoelectron and Auger spectroscopy studies show that the active catalyst contains a reactive carbonaceous layer with most of the rhodium in the 1+ oxidation state and with some metal present. The presence of large amounts of oxidized rhodium species correlates with the production of large quantities of oxygenated hydrocarbons up to 80+ wt%. The selectivity to different oxygenated products varies with temperature; yields of acetaldehyde and ethanol in excess of 50 wt% are found at temperatures around 300 °C. The activation energies for the formation of all the products except methanol are similar at 28 ± 2 kcal/mole indicating that they are likely to form from a common CH x precursor, obtained by dissociative adsorption of CO. Methanol is probably formed from molecular CO with an activation energy of 16 ± 3 kcal/mole. The changes in selectivity with temperature can be explained by competing carbonylation and hydrogenation reactions coupled with changing concentrations of molecular and dissociated CO on the surface.