Reaction mechanisms of carbon dioxide reforming of methane with Ru-loaded lanthanum oxide catalyst

摘要

A pulsed reaction technique was applied to discuss the effect of support on the activities and mechanisms in the CO_2 reforming of methane over Ru catalyst. The reaction was carried out using a fixed bed reactor equipped with an on-line mass spectrometer. Four supports:La_2O_3, Y_2O_3 and ZrO_2 which showed high activity and Al_2O_3, commonly used one in the reforming reaction, were compared when loaded with Ru. After feeding CO_2 at 600 deg C, we introduced a pulse of CH_4 over Ru/La_2O_3 catalyst under Ar steady flow. We observed the response of CO which was generated from the reaction with CH_x on the ruthenium and the Ru-O_x formed during CO_2 treatment or during the reaction of Ru-CH_x with adsorbed CO_2 onto the La_2O_3. Over Ru/Al_2O_3 catalyst, however, very small response of CO was observed. A pulse of ~13CO_2 was introduced under CH_4 steady flow over Ru/La_2O_3,Ru/Y_2O_3 and Ru/ZrO_2 catalysts. Symmetrical ~13CO response were observed, but a small response of ~12CO from ~12CH_x continued to evolve after generation of ~13CO from ~13CO_2 ceased. The following reaction cycle is believed to occur in the CO_2 reforming of methane on active supports: A part of metallic ruthenium reacted with CH_4 to vive Ru-CH_x; simultaneously ruthenium metal could be oxidized with CO_2 to give Ru-O_x and CO; and then, oxygen transfer from Ru-O_x to Ru-CH_x took place to give CO and metallic ruthenium. Distinct temperature increases in the catalyst bed for La_2O_3, Y_2O_3 and ZrO_2 supports were observed with the introduction of CO_2 pulses under Ar flow. On the other hand, a very small increase in the temperature of the catalyst bed was observed on Al_2O_3. These results indicate that CO_2 reforming of CH_4 with ruthenium loaded catalysts was strongly assisted by the activation of CO_2 adsorbed on the basic sites