Carbon dioxide reforming of methane to syngas over SiO₂-supported rhodium catalysts

The decomposition of CH₄ and CO₂ as well as the reaction between CH₄ and CO₂ over SiO₂-supported rhodium catalysts has been investigated in the temperature range of 600-800°C over a pulse reactor. The initial activities for methane decomposition and CO₂ decomposition increased with the increase of rhodium loading; whereas the activity for CO formation in the CH₄+CO₂ reaction was almost unaffected by the rhodium loading over catalysts with rhodium loading >0,05%. Different reaction behaviors of methane reforming with CO₂ were observed at 700°C and 800°C. At 700°C, CO₂ conversion was higher than CH₄ conversion; whereas at 800°C, CH₄ conversion was higher than CO₂ conversion. The bond order conservation-Morse potential (BOC-MP) calculations indicate that the oxygen at on-top site can promote the dissociation of methane on the Rh(111) surface. Normal deuterium isotope effect was observed to be more noticeable on the methane conversion reaction than on the CO formation reaction, while no such effect was observed on the CO₂ conversion reaction. The mechanism for CO and H₂ formation in the reforming of methane with CO₂ is discussed based on the results of the present work.