Abstract
The interaction between Rh and CeO 2 over the Rh–CeO 2/Al 2O 3 catalyst was investigated for the reaction of methane reforming with CO 2. It was shown that the activity and coke resistance of Rh/Al 2O 3 were enhanced by the addition of CeO 2, which greatly depend on the interaction between rhodium and ceria under the reaction atmosphere. In situ electrical conductivity results showed that the reducing agents (CH 4, H 2) in the reaction system could be activated and dissociated on Rh 0, releasing electrons to CeO 2 in close contact with Rh 0 and generating the Ce 4+/Ce 3+ redox couple. Meanwhile, it was found from XPS measurements that the electron transfer could also happen from Rh 0 to CeO 2, creating the Rh 0/Rh δ+ couple. Thus, the very coexistence of Ce 4+/Ce 3+ and Rh 0/Rh δ+ redox couples facilitated the activation of CH 4 and CO 2 and further enhanced the catalytic activity and coke resistance of Rh/Al 2O 3. For CH 4 activation, the electron-deficient state of Rh δ+ had higher ability to accept σ electrons of CH 4 to promote CH 4 adsorption and C–H bond cleavage, while CO 2 activation was mainly facilitated by accepting free electrons of Ce 3+ species, which resulted in the enhancement of carbon elimination to yield CO. Finally, a cycle mechanism of redox couples over Rh–CeO 2/Al 2O 3 in CH 4/CO 2 reforming was proposed.
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