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 degrees 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 degrees C and 800 degrees C. At 700 degrees C, CO2 conversion was higher than CH4 conversion; whereas at 800 degrees 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 H-2 formation in the reforming of methane with CO2 is discussed based on the results of the present work.