Promoting effect of active carbons on methanol dehydrogenation on sodium carbonate - hydrogen spillover

Methanol dehydrogenation to formaldehyde was conducted in a fixed-bed flow reactor with sodium carbonate catalyst mixed with active carbons or transition metals. The additives promoted the reaction rate at 880-970 K without modifying formaldehyde selectivity. This effect increases with increasing carbon content in the carbon-carbonate mixture. Activation energy of methanol conversion is the same for the mixture and the carbonate alone. Temperature-programmed desorption experiments showed that hydrogen adsorption resulting from dissociative methanol chemisorption was enhanced by adding active carbon to the carbonate. Also, the carbon facilitates hydrogen desorption in comparison to the carbonate. It is suggested that atomic hydrogen produced on sodium carbonate during methanol dehydrogenation spills over onto active carbons (or metals) and recombines to form hydrogen gas. Hydrogen desorption from sodium carbonate, the rate-determining step, is thus accelerated.