Syngas production by means of biogas catalytic partial oxidation and dry reforming using Rh-based catalysts

Abstract

The catalytic oxy-CO2 reforming of biogas (a combination of partial oxidation and dry reforming reactions) was studied with various Rh-based catalysts prepared in the laboratory using different supports: γ-Al2O3, SiO2 and CeO2. Their performance was compared to a commercial Rh/Al2O3 catalyst serving as reference. Different O2/CH4 ratios were studied: 0 (dry reforming), 0.10, 0.20 and 0.45. In all cases, both laboratory-prepared and commercial Rh/Al2O3 catalysts clearly outperformed the others, including a Pt commercial catalyst tested under dry reforming conditions. It could be established that the catalytic performance of the Rh-based catalysts prepared by impregnation on different supports had the following decreasing order: Rh/Al2O3>Rh/SiO2>Rh/CeO2. Equilibrium conditions could be achieved through 2h of dry reforming of biogas at 700°C using the Rh commercial catalyst at gas hourly space velocities (GHSV) of 30N L CH4/(gcat·h). Higher GHSV values (150 and 300N L CH4/(gcat·h)) resulted in a slow decay of the activity over time, more accentuated at the most severe space velocity condition. However, the decrease in methane conversion and H2 yield was milder when oxy-CO2 reforming conditions were used. Adding O2 to the reactor feed was proven beneficial, enhancing initial and overall CH4 conversions as well as hydrogen yields, which followed an increasing trend with increasing O2/CH4 ratios in all cases. The characterization of the spent samples under dry reforming conditions revealed the presence of carbon deposits of predominantly polymeric nature, though co-existing with other types of coke. These promising results pave the path for developing highly active and stable catalytic formulations for producing syngas by means of oxy-CO2 reforming of biogas with Rh-based catalysts.