The Impact of Sulfur on Ethanol Steam Reforming

Abstract

The effect of sulfur on the activity and selectivity of a bimetallic Rh–Pt catalyst was studied in the steam reforming of 85 % ethanol, 15 % gasoline (E85) with a sulfur concentration of 5 ppm. Tests with packed bed and monolith catalyst configurations were performed at low space velocities (22,000 h−1) and a steam to carbon ratio of 1.8. At these conditions the catalyst could achieve full conversion of the fuel to equilibrium concentrations of the main reforming products (H2, CO, CO2, and CH4), however the introduction of sulfur-containing fuel incited immediate deactivation and a drastic increase in the amount of ethylene detected. Upon removal of sulfur from the stream, selectivity shifted from ethylene to acetaldehyde, indicating that ethylene production is most impacted by the presence of sulfur. Post-reforming characterization of the catalyst indicated large deposits of increasingly graphitic coke on the surface of the catalyst. Regeneration in air resulted in a decrease in precious metal dispersion from 22 to 3 % while the surface area of the catalyst remained unaffected. The adsorption of sulfur on catalytically active sites was found to be reversible by thermogravimetric analysis. This finding was supported through reactor studies. Despite this reversibility, the sulfur-induced coke had lasting effects on catalyst performance after regeneration.